Title of Invention	SERIES MOTOR AND METHOD FOR CONTROLLING THE SAME.
Abstract	A circuit for a series motor is specified,wherein reliable switching is achieved by means of two electronic switches,without the use of a mechanically disconnecting switch.To this end ,two electronic switches(triacs)(14,16)are preferably connected in series to each other,the voltage drop across the triac(14)being continuously monitored by a monitoring circuit(20).A check for faults can be carried out before switching on the power tool.Alternatively,a fusible cutout can be tripped by means of a circuit breaker(triac)(16)connected in parallel thereto.

Title of Invention

SERIES MOTOR AND METHOD FOR CONTROLLING THE SAME.

Abstract

A circuit for a series motor is specified,wherein reliable switching is achieved by means of two electronic switches,without the use of a mechanically disconnecting switch.To this end ,two electronic switches(triacs)(14,16)are preferably connected in series to each other,the voltage drop across the triac(14)being continuously monitored by a monitoring circuit(20).A check for faults can be carried out before switching on the power tool.Alternatively,a fusible cutout can be tripped by means of a circuit breaker(triac)(16)connected in parallel thereto.

Full Text	Series motor and method for controlling the same The invention relates to a series motor comprising contactless switching elements for interrupting operation, said elements being embodied in the form of electronic switches. Power tools are generally driven by electric motors that are configured as series motors (universal motors) and controlled by means of mechanical switches. Although electronics are becoming more and more widespread in power tools as well, controlling power tools solely by means of power semiconductors that also serve to switch the power tool on and off is considered to be insufficiently reliable. The 2 reason for this is that semiconductors can break down (internal short circuit) and then can no longer be controlled. In the case of purely electronic switches having only a single switch path, what can occur is that a permanent connection is created between the voltage supply and the motor, i.e. that the motor can no longer be switched off, or immediately starts to turn. In order to achieve sufficiently reliable control of power tools using only electronic switches and no mechanical switches, it is known in the prior art to arrange a circuit breaker parallel to the control switch with which the motor is switched on and off, said circuit breaker tripping a fuse if there is any malfunction of the control switch (cf. DE 3 119 794 C2, DE 3 432 845 Al, DE 4 021 559 Cl). However, circuits of this kind operate reliably only when erratic behavior on the part of the machine and the electronic switching element is detected and the appliance can be brought to a defined OFF state, and any defect in the protection circuit can also be detected in order to put the appliance into a defined OFF state. In the prior art, only DE 3 119 794 C2 addresses the problem of a defect occurring in the protection circuit, but said invention requires the operator to test the protection circuit occasionally by pressing a pushbutton. The object of the present invention is therefore to provide a series motor and a method for controlling a series motor that enable the motor to be switched on and off reliably using only electronic switches, despite dispensing with mechanical switching elements. This object is achieved with a series motor, in particular for a power tool, comprising a first electronic switch (control switch) for switching the motor on and off, a second electronic switch (circuit breaker) connected in series to the control switch, a monitoring circuit that monitors the function of the switches and analyzes the voltage potential at the connection point of the control switch and the circuit breaker, and 3 further comprising an electronic controller, preferably a microprocessor, that is coupled to the two switches and the monitoring circuit and forces at least one of the switches into a blocked state when the monitoring circuit registers a malfunction in one of the switches. The technical problem of the invention is completely solved in this manner. According to the invention, the motor can be switched on and off reliably even when one of the two switches malfunctions, by virtue of the fact that two electronic switches, one control switch and one circuit breaker, are connected in series. A monitoring circuit ensures that malfunctions of the control switch and/or the circuit breaker can be detected, and that the motor can be forced into a safe OFF state. This means that manual monitoring of the system is no longer required. Instead, a test for faults is automatically conducted when switching on the motor, and only on condition that no fault has been detected is switching on enabled. In an advantageous development of the invention, a means is provided for bridging the switch path of the circuit breaker with a high impedance in order to allow a functional test of the control switch to be carried out without having to start the motor. This prevents the motor from briefly starting up in the event that the circuit breaker is energized during the initial functional test, if the control switch has broken down. By means of this high-impedance bridge across the switch path of the circuit breaker, the latter can be safely tested without the risk arising of the motor starting up if the control switch is defective. The means for high-impedance bridging across the switch path of the circuit breaker can comprise an optocoupler, for example, which preferably includes an optotriac, and which is connected in parallel to the main terminals of the circuit breaker via a resistor. 4 Another way of preventing the motor from briefly starting up if the control switch is defective when the circuit breaker is being tested is to provide a means for monitoring the rotation of the motor, said means being coupled to the controller in order to force at least one of the two switches into a blocked state in the event that the motor starts when the circuit breaker is energized without the control switch being energized. This likewise avoids the risk of the motor briefly starting up if the control switch malfunctions while the circuit breaker is being tested. The means for monitoring the rotation of the motor can be embodied in the form of a rotational speed sensor, or it can monitor the motor current. In the latter case, a shunt resistor is connected in series to the armature, and the voltage drop across the resistor is monitored. There are various options for configuring the monitoring circuit to monitor the voltage potential across the control switch. Whereas a circuit comprising a transistor, a diode and two resistors is known from the prior art, for example US 6,236,177 Bl, the invention prefers a much simpler circuit. In a preferred development of the invention, the monitoring circuit includes a voltage divider with two resistors connected in series, the first resistor being connected to a first pole of an auxiliary voltage supply and the second resistor being connected to one of the main terminals of the control switch and to the second pole of the auxiliary voltage, the connection point between the two resistors being connected via a third resistor to the other main terminal of the control switch and supplied as the output of the monitoring circuit to an input terminal of the controller. 5 Reliable monitoring can thus be achieved using only three resistors and the supply voltage, which is required anyway for the electronics. According to an alternative embodiment of the invention, the object is achieved by means of a series motor, in particular for an power tool, comprising a fuse via which the armature is connected via a first electronic switch (control switch) to the supply voltage in order to switch the motor on and off, a second electronic switch (circuit breaker) connected in parallel to the armature and to the control switch in order to trip the fuse in the event of a fault, an electronic controller, preferably a microprocessor, coupled to the switches, a means for blocking the circuit breaker and for testing the function of the circuit breaker in the blocked state, and a monitoring circuit that analyzes the voltage drop at the control switch and whose output signal is supplied to the electronic controller to force the circuit breaker to trip the fuse if the monitoring circuit registers a malfunction of the control switch. In this manner, too, the technical problem of the invention is completely solved. Whereas it was not possible in the prior art to test the function of the circuit breaker in the event of a fault, given a parallel arrangement of the circuit breaker for tripping the fuse, according to the present invention the circuit breaker is now initially blocked and can then be safely tested without tripping the fuse. To this end, in a preferred development of the invention, a transistor having an emitter and collector and which can be made conductive in order to test the circuit breaker by measuring its control current is connected between the control terminal and a main terminal of the circuit breaker in order to prevent the fuse from tripping when the circuit breaker is being tested. According to another advantageous embodiment of the invention, the electronic switches are embodied as triacs. 6 This has the advantage that high loads can therefore be switched largely without power loss, even with alternating current, and simultaneously that the control switch can also be used to regulate the power and control the speed of the motor. With regard to method, the object of the invention is further achieved with a method for controlling a series motor, preferably a series motor for a power tool, and comprising the following steps: (a) connecting the motor to a supply voltage via a first electronic switch (control switch) for switching the motor on and off, and a second electronic switch (circuit breaker), (b) monitoring the voltage potential across the control switch, (c) blocking the switches if the voltage potential across the control switch takes on values outside a predefined threshold range when both switches are in the switched-off state, (d) first switching on the circuit breaker if the voltage potential across the control switch is within the threshold range when both switches are in the switched- off state, (e) switching on the control switch if the voltage potential across the control switch takes on values outside the threshold range and (f) blocking both switches if the voltage potential across the control switch does not take on values outside the threshold range. According to the invention, a functional test is firstly performed before the control switch is switched on, in order to determine whether the circuit breaker is working 7 properly. If this is the case, the control switch is subsequently tested before it can be switched on to make the motor operational. Faults in the circuit breaker and/or the control switch can be reliably detected in this way. Disconnecting the circuit breaker or the control switch does not pose a risk, because the motor is unable to start in such a case. Due to the fact that, during the tests, opposite input signals are required at the input terminals of the electronic controller for determining whether the control switch and the circuit breaker are working correctly, any short circuit or disconnection of discrete parts of the monitoring circuit will result in a safe OFF state. Faults in the driver circuits are also detected. This is because permanent energization produces the same faults as a short circuited control switch or circuit breaker. If there is no energization, this leads to the same behavior as when the control switch or circuit breaker is disconnected. In such a case, it is not possible for the motor to start. In one advantageous development of the invention, the circuit breaker is immediately switched off again if the voltage potential does not increase when switching on the circuit breaker with the control switch switched off. In this case, there is a fault in the control switch. By switching off the circuit breaker immediately, the motor is prevented from starting. To this end, according to a further development of the method of the invention, the rotation of the motor is monitored in order to switch off the motor again immediately if any rotation of the motor is registered when switching on the circuit breaker with the control switch switched off. In an alternative embodiment, the circuit breaker can firstly be bridged by a high impedance in order to test the control switch, and a test carried out to determine whether the voltage potential across the control switch increases to the predefined threshold value. 8 In this way, the motor can be safely prevented from starting when the control switch is being tested, even if there is a defect. Alternatively, the object of the invention is achieved with a method for controlling a series motor, preferably a series motor for a power tool, comprising the following steps: (a) connecting the motor to a supply voltage via a fuse and a first electronic switch (control switch) for switching the motor on and off, and connecting a second electronic switch (circuit breaker) to the supply voltage via the fuse, (b) before switching on the control switch, first blocking the circuit breaker and testing whether the circuit breaker works by energizing the circuit breaker and testing the control current, (c) removing the block on the circuit breaker if energization of the circuit breaker is found to be working properly, and switching on the control switch in order to switch on the motor, (d) blocking energization of the control switch if a malfunction is detected in the course of step (b), (e) monitoring the voltage drop at the control switch and triggering the circuit breaker in order to trip the fuse if the voltage drop when switching off the control switch does not increase beyond a predefined threshold value. In this way, by connecting the circuit breaker in parallel, it is possible to test for any malfunction in the driver circuit for the circuit breaker prior to switching on the control switch, and for deactivation to be effected should the control switch fail. 9 It is self-evident that the features of the invention as mentioned above and to be explained below can be applied not only in the combination specified in each case, but also in other combinations or in isolation, without departing from the scope of the invention. Further advantages and features of the invention derive from the following description of preferred embodiments, in which reference is made to the drawings, in which Fig. 1 shows, in a simplified circuit diagram, a first embodiment of a series motor according to the invention; Fig. 2 shows a preferred embodiment of a monitoring circuit suitable for the motor of Fig. 1; Fig. 2a shows a graph of the input voltage across resistor R3 of the monitoring circuit in Fig. 2, and the associated output voltage at PIN 1; Fig. 3 shows an alternative embodiment of the monitoring circuit for the motor in Fig. 1; Fig. 4 shows a modified version of the circuit in Fig. 1; Fig. 5 shows a further modification of the circuit in Fig. 1 and Fig. 6 shows another embodiment of the invention, comprising a parallel circuit breaker for tripping a fuse. Fig. 1 shows an electric motor according to the invention, in the form of a series motor circuit and labeled in its entirety with reference numeral 10. 10 The motor 10 is supplied with 230 V from the two poles 24 and 26 of an alternating voltage source. Motor 10 has an armature 12, the field windings of which (not shown) are wound in series and connected to the one pole 24 of the supply voltage. The other pole of the armature 12 is connected to the other pole 26 of the supply voltage via two triacs in series, namely a circuit breaker 16 and a control switch 14. Control terminals 28 and 30 of control switch 14 and circuit breaker 16 are connected to the terminals of an electronic controller 18 in the form of a microprocessor. Electronic controller 18 is likewise connected to the two poles 24 and 26 of the supply voltage source, and is supplied in addition with a DC supply (unless this voltage supply is not already integrated in electronic controller 18). A monitoring circuit 20 is also connected between control switch 14 and circuit breaker 16, on the one hand, and the second pole 26 of the supply voltage source, on the other hand, wherein said monitoring circuit monitors the voltage potential between control switch 14 and circuit breaker 16, on the one hand, and the second pole 26 of the supply voltage source, on the other hand, and the output of which is coupled via a line 32 to an input terminal 22 (Pin 1) of electronic controller 18. By phase control of control switch 14, electronic controller 18 also performs, in an essentially known manner, the functions of a soft starter when switching on the motor and those of a speed and/or power control during motor operation. By means of monitoring circuit 20, it is now possible to perform a functional check before switching on electric motor 10, in order to ensure that both control switch 14 and circuit breaker 16 are working faultlessly. Fig. 2 shows a preferred embodiment of monitoring circuit 20. An auxiliary voltage, which may be the supply voltage VCc for the electronic controller 18, is supplied via a voltage divider to the one main terminal of control switch 14, which is connected to the second pole 26 of the AC source. The voltage divider consists of resistors Ri and R2. The tap of the voltage divider is connected to input terminal 22 (Pin 1) of controller 18. The tap of the voltage divider is also coupled via a third resistor R3 to the point of connection between control switch 14 and circuit breaker 16. 11 Such a monitoring circuit provides a very simple way of monitoring the voltage potential across control switch 14 using only three components. In alternative embodiments of the invention it is also possible to use other monitoring circuits, such as the monitoring circuit known from US 6,236,177 Bl. Such a circuit is shown in Fig. 3, where it is labeled with the reference numeral 20'. However, a monitoring circuit as shown in Fig. 2 is preferred due to its simpler construction. A modified embodiment of the electric motor according to the invention is shown in Fig. 4, where it is referenced in its entirety with numeral 10a. In this and in further modifications to be explained later, corresponding reference numerals are used for corresponding parts. The only difference between the circuit of electric motor 10a and the embodiment of electric motor 10 in Fig. 1 is that a means 36 for high-impedance bridging of circuit breaker 16 is additionally provided. Said means 36 for high-impedance bridging of circuit breaker 16 consists of an optotriac 38 which is connected in parallel to the main terminals of circuit breaker 16 via a resistor R4. Optotriac 38 is energized by an LED 40. Fig. 4 also indicates one of the two field windings, labeled with reference numeral 13, that are in series with armature 12. The manner of operation of series motor 10 or 10a shall now be described. In the circuit shown in Fig. 1 and 2, an initial test is firstly conducted, before electric motor 10 is first switched on, to determine whether the output voltage of monitoring circuit 20, which is fed to input terminal 22 (Pin 1) of microprocessor 18 via line 32, is inside the predefined threshold range. This can be seen in greater detail in Fig. 2a. While supply voltage VCc is applied across Ri and the potential across R2 is zero, the 12 AC voltage at the point of connection between control switch 14 and circuit breaker 16 is supplied via R3 to PIN 1. When control switch 14 and circuit breaker 16 are in the switched-off state, no alternating voltage is allowed across R3, with the result that the voltage at PIN 1 depends exclusively on voltage divider Ri and R2, and on Vcc. For example, if Vcc = 5V and R1=R2, there is a threshold range of 2.5V±0.5V within which the voltage at PIN 1 must lie if control switch 14 and circuit breaker 16 are not being driven. If this is the case, this first test has been passed. This test ensures that the blocking effect is tested for both the positive half-wave and the negative half-wave. Otherwise there is a fault in the circuit. Either circuit breaker 16 is defective, i.e. is short-circuited, or the driver circuit for circuit breaker 16 is defective, or monitoring circuit 20 is defective. In this case, control switch 14 is not energized and microprocessor 18 changes over to a safe fault state (OFF state). If the first test is passed, then circuit breaker 16 is energized via line 30 when switching on, as shown in Fig. 1. In this case, if the voltage at Pin 1 oscillates such that the threshold limits shown in Fig. 2a are exceeded, then the circuit is functioning properly. If not, it is malfunctioning. Either there is a defect in control switch 14 (short circuit), or the driver circuit for the control switch 14 is defective, or monitoring circuit 20 is defective. In there is a defect, circuit breaker 16 is switched off again as fast as possible and microprocessor 18 changes over to a safe fault state (OFF state). If a defect (short circuit) in either control switch 14 or circuit breaker 16 is detected, the motor cannot be switched on. If control switch 14 or circuit breaker 16 is disconnected, it is likewise not possible for the motor to start, so this does not pose a risk. By means of the circuit for motor 10 as described above, faults in the monitoring circuit as well as faults in the driver circuits can be detected. Due to the fact that, 13 during the tests, opposite input signals are required at input terminal 22 (Pin 1) of microprocessor 18 for the "Passed" function, any short circuit or disconnection of discrete parts of the monitoring circuit will result in a safe OFF state. Permanent energization either of control switch 14 or circuit breaker 16 leads to the same fault as short-circuiting the control switch or the circuit breaker. If microprocessor 18 fails to output a control signal on line 28 and line 30 to energize control switch 14 and circuit breaker 16, then this produces the same result as disconnecting control switch 14 or circuit breaker 16. It is not possible to start the motor in this case, either. In the circuits according to Fig. 1, it is essential that circuit breaker 16 be switched off again immediately if a malfunction is detected during the second test, when circuit breaker 16 is energized while control switch 14 is not energized. If there is any delay in switching off circuit breaker 16 on detection of a fault during the second test, this may result in the motor being started, which could be disadvantageous in certain circumstances. To eliminate this possibility, motor 10a in Fig. 4 is also provided with means 36 for high-impedance bridging of circuit breaker 16. When test 1 has been completed (voltage at Pin 1 is within the threshold range when the circuit breaker and the monitoring circuit are not energized), circuit breaker 16 is merely bridged with a high impedance with the aid of circuit 36, instead of being energized. It is possible in this way to perform a functional test of control switch 16 without any risk arising of the motor immediately starting up if control switch 16 is short circuited. As an alternative to circuit 36 for high-impedance bridging of control switch 16, a means for monitoring the speed of rotation of the motor is shown as a further modification in Fig. 5, where it is labeled in its entirety with reference numeral 10b. 14 To this end, a shunt resistor R5 can be provided in series with field windings 13. If, during the second test, i.e. when switching on circuit breaker 16 in order to check control switch 14, a voltage drop across shunt resistor R5 between pole 26 of the alternating voltage and line 52 is registered, energization of circuit breaker 16 is immediately interrupted to prevent the motor from starting up. Alternatively (or additionally), a rotational speed sensor 54 that monitors the rotor speed of the motor could be provided, as indicated by the broken line in Fig. 5. If rotational speed sensor 54 receives a signal during test 2, i.e. when circuit breaker 16 is energized in order to check control switch 14, then energization of circuit breaker 16 is immediately interrupted to stop the electric motor from running. The circuit of motor 10b is otherwise identical to the circuit of motor 10a. Another embodiment of an electric motor according to the invention is shown in Fig. 6, where it is referenced in its entirety with numeral 10c. In this case, a fusible cutout 56 is provided that can be tripped by a circuit breaker 16 in the event of a fault in control switch 14. For this purpose, circuit breaker 16 is connected in parallel, immediately behind fuse 56, to the two poles 24 and 26 of the supply voltage source. The drop in voltage potential across control switch 14 is monitored, in turn, by a protection circuit 20, as explained above. The output from monitoring circuit 20 is supplied, in turn, to Pin 1 of microprocessor 18. Although a complete functional test is not possible with the circuit in Fig. 6, because fuse 56 would immediately respond, the driver circuit for circuit breaker 16 can nevertheless be tested by preventing the circuit breaker or triac 16 from triggering. To this end, the gate 28 of triac 16 is connected via two series resistors R6 and R7 to an output terminal (Pin 3) of microprocessor 18. The point of connection between the two resistors R6, R7 is connected via a line 62 to a measurement input (Pin 4) of microprocessor 18. A transistor 60, the base of which can be driven via an output 15 terminal (Pin 2) of microprocessor 18, is disposed between the gate 28 of circuit breaker 16 and pole 26 of the supply voltage. For testing purposes, the monitoring circuit 20 is firstly assessed. The test is performed in the manner as described in conjunction with Figs. 2 and 2a. If a fault is detected during said test, circuit breaker 16 is triggered in order to trip fuse 56. If no fault is detected in the prior test, the driver circuit for circuit breaker 16 is then tested in the following manner: In a first step, transistor 60 is powered at its base 64 via Pin 2 of microprocessor 18. This prevents triac 16 from triggering. Gating pulses are now outputted via Pin 3, whereby transistor 60 prevents any triggering. The voltage between resistors R6, R7 can now be detected at Pin 4 of microprocessor 18. The output voltage at Pin 3 corresponds approximately to the supply voltage VCc- If no voltage is now applied at Pin 4, then either resistors R6, R7 have been disconnected or no gating pulse is out-putted, which means that a fault is present. Assuming that resistors R6, R7 are identical, approximately half the supply voltage Vz VCc must be applied to Pin 4 while the gate trigger current is flowing. In this case, the driver circuit for triac 16 is working properly. If the full supply voltage Vcc is applied to Pin 4 when gating pulses are being outputted at Pin 3, then resistor R6 is disconnected, which again means there is a fault. If no fault is detected, powering of transistor 60 via Pin 2 is cancelled in order that the circuit breaker or triac 16 can work during operation to enable control switch 14 to trip fuse 56 in the event of a fault. Control switch 14 can then be switched on in order to switch on the motor. If control switch 14 is not longer energized, i.e. no gating pulses are being outputted via line 30, then the voltage drop across control switch 14 must rise above a predefined threshold value. Otherwise, control switch 14 is defective. If a defect in control switch 14 is detected when switching it off, circuit breaker 16 is triggered via Pin 3 of control circuit 18 in order to trip fuse 56. 16 Claims 1. A series motor, in particular for a power tool, comprising a first electronic switch (control switch) (14) for switching the motor on and off (10, 10a, 10b), a second electronic switch (circuit breaker) (16) connected in series to the con trol switch (14), a monitoring circuit (20, 20') that monitors the function of the switches (14, 16) and analyzes the voltage potential at the connection point of the control switch (14) and the circuit breaker (16), and further com prising an electronic controller (18), preferably a microprocessor, that is cou pled to the two switches (14, 16) and the monitoring circuit (20, 20') and forces at least one of the switches (14, 16) into an OFF state when the moni toring circuit (20, 20') registers a malfunction in one of the switches (14, 16). 2. The series motor according to claim 1, comprising a means (36) for bridging the switch path of the circuit breaker (16) with a high impedance in order to allow a functional test of the control switch (14) without having to start the motor (10, 10a, 10b). 3. The series motor according to claim 2, in which the means (36) for high- impedance bridging includes an optocoupler, preferably an optotriac (38), that is connected in parallel via a resistor (R4) to the main terminals (42, 44) of the circuit breaker (16). 4. The series motor according to one of the preceding claims, comprising a means for monitoring the rotation of the motor (10, 10a, 10b), said means be ing coupled to the controller (18) in order to force at least one of the two switches (14, 16) into an OFF state in the event that the motor (10, 10a, 10b) starts when the circuit breaker (16) is energized without the control switch (14) being energized. 17 5. The series motor according to claim 4, wherein the means for monitoring the rotation of the motor is embodied as a rotational speed sensor (54). 6. The series motor according to claim 4, wherein the means for monitoring the rotation of the motor monitors the motor current. 7. The series motor according to claim 6, wherein the means for monitoring the rotation of the motor is a shunt resistor (R5) that is connected in series to the armature (12) and whose voltage drop is monitored. 8. The series motor according to one of the preceding claims, wherein the monitoring circuit (20) includes a voltage divider with two resistors (Ri, R2) connected in series, the first resistor (Ri) being connected to a first pole of an auxiliary voltage supply (Vcc) and the second resistor (R2) being connected to one of the main terminals of the control switch (14) and to the second pole of the auxiliary voltage, the connection point between the two resistors (Ri, R2) being connected via a third resistor (R3) to the other main terminal of the con trol switch (14) and supplied as the output of the monitoring circuit to an in put terminal (22) of the controller (18). 9. A series motor, in particular for an power tool, comprising a fuse (56) via which the armature (12) is connected via a first electronic switch (control switch) (14) to the supply voltage in order to switch the motor on and off (10c), a second electronic switch (circuit breaker) (16) connected in parallel to the armature (12) and to the control switch (14) in order to trip the fuse (56) in the event of a fault, an electronic controller (18), preferably a microproces sor coupled to the switches (14, 16), a means (16) for blocking the circuit breaker (16) and for testing the function of the circuit breaker (16) in the blocked state, and a monitoring circuit (20) that analyzes the voltage drop at the control switch (14) and whose output signal is supplied to the electronic 18 controller (18) to force the circuit breaker (16) to trip the fuse (56) if the monitoring circuit (16) registers a malfunction of the control switch (14). 10. The series motor according to claim 9, wherein a transistor (60) which can be made conductive in order to test the circuit breaker (16) by measuring its con trol current is connected with its emitter and collector between the control terminal (28) and a main terminal (44) of the circuit breaker (16) in order to prevent the fuse (56) from tripping when the circuit breaker (16) is being tested. 11. The series motor according to one of the preceding claims, wherein the switches (14, 16) are embodied as triacs. 12. A method for controlling a series motor, preferably for a power tool, compris ing the following steps: (a) connecting the motor (12) to a supply voltage via a first electronic switch (control switch) (14) for switching the motor on and off, and a second electronic switch (circuit breaker) (16), (b) monitoring the voltage potential across the control switch (14), (c) blocking the switches (14, 16) if the voltage potential across the control switch (14) takes on values outside a predefined threshold range when both switches (14, 16) are in the switched-off state, (d) first switching on the circuit breaker (16) if the voltage potential across the control switch (14) is within the threshold range when both switches (14, 16) are in the switched-off state, (e) switching on the control switch (14) if the voltage potential across the control switch (14) takes on values outside the threshold range and (f) blocking both switches (14, 16) if the voltage potential across the con trol switch (14) does not take on values outside the threshold range. 19 13. The method according to claim 12, wherein the circuit breaker (16) is imme diately switched off again if the voltage potential does not increase when switching on the circuit breaker (16) with the control switch (14) switched off. 14. The method according to claim 12 or 13, wherein rotation of the motor is monitored in order to switch off the motor again immediately if rotation of the motor is registered when switching on the circuit breaker (16) with the control switch (14) switched off. 15. The method according to one of claims 12 to 14, wherein the circuit breaker (16) is first bridged by a high impedance in order to test the control switch (14), and a test is carried out to determine whether the voltage potential across the control switch (14) increases to the predefined threshold value. 16. A method for controlling a series motor, preferably for a power tool, compris ing the following steps: (a) connecting the armature (12) to a supply voltage via a fuse (56) and a first electronic switch (control switch) (14) for switching the motor on and off, and connecting a second electronic switch (circuit breaker) (16) to the supply voltage via the fuse (56), (b) before switching on the control switch (14), first blocking the circuit breaker (16) and testing whether the circuit breaker (16) works by ener gizing the circuit breaker (16) and testing the control current, (c) removing the block on the circuit breaker (16) if the circuit breaker (16) is found to be working properly, and switching on the control switch (14) in order to switch on the motor, (d) forcing the switch (14, 16) into an OFF state if a malfunction is de tected in the course of step (b), (e) monitoring the voltage drop at the control switch (14) and triggering the circuit breaker (16) in order to trip the fuse (56) if the voltage drop when switching off the control switch (14) does not increase beyond a predefined threshold value.

Full Text

Series motor and method for controlling the same
The invention relates to a series motor comprising contactless switching elements for interrupting operation, said elements being embodied in the form of electronic switches.
Power tools are generally driven by electric motors that are configured as series motors (universal motors) and controlled by means of mechanical switches. Although electronics are becoming more and more widespread in power tools as well, controlling power tools solely by means of power semiconductors that also serve to switch the power tool on and off is considered to be insufficiently reliable. The

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reason for this is that semiconductors can break down (internal short circuit) and then can no longer be controlled. In the case of purely electronic switches having only a single switch path, what can occur is that a permanent connection is created between the voltage supply and the motor, i.e. that the motor can no longer be switched off, or immediately starts to turn.
In order to achieve sufficiently reliable control of power tools using only electronic switches and no mechanical switches, it is known in the prior art to arrange a circuit breaker parallel to the control switch with which the motor is switched on and off, said circuit breaker tripping a fuse if there is any malfunction of the control switch (cf. DE 3 119 794 C2, DE 3 432 845 Al, DE 4 021 559 Cl).
However, circuits of this kind operate reliably only when erratic behavior on the part of the machine and the electronic switching element is detected and the appliance can be brought to a defined OFF state, and any defect in the protection circuit can also be detected in order to put the appliance into a defined OFF state.
In the prior art, only DE 3 119 794 C2 addresses the problem of a defect occurring in the protection circuit, but said invention requires the operator to test the protection circuit occasionally by pressing a pushbutton.
The object of the present invention is therefore to provide a series motor and a method for controlling a series motor that enable the motor to be switched on and off reliably using only electronic switches, despite dispensing with mechanical switching elements.
This object is achieved with a series motor, in particular for a power tool, comprising a first electronic switch (control switch) for switching the motor on and off, a second electronic switch (circuit breaker) connected in series to the control switch, a monitoring circuit that monitors the function of the switches and analyzes the voltage potential at the connection point of the control switch and the circuit breaker, and

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further comprising an electronic controller, preferably a microprocessor, that is coupled to the two switches and the monitoring circuit and forces at least one of the switches into a blocked state when the monitoring circuit registers a malfunction in one of the switches.
The technical problem of the invention is completely solved in this manner.
According to the invention, the motor can be switched on and off reliably even when one of the two switches malfunctions, by virtue of the fact that two electronic switches, one control switch and one circuit breaker, are connected in series. A monitoring circuit ensures that malfunctions of the control switch and/or the circuit breaker can be detected, and that the motor can be forced into a safe OFF state. This means that manual monitoring of the system is no longer required. Instead, a test for faults is automatically conducted when switching on the motor, and only on condition that no fault has been detected is switching on enabled.
In an advantageous development of the invention, a means is provided for bridging the switch path of the circuit breaker with a high impedance in order to allow a functional test of the control switch to be carried out without having to start the motor.
This prevents the motor from briefly starting up in the event that the circuit breaker is energized during the initial functional test, if the control switch has broken down. By means of this high-impedance bridge across the switch path of the circuit breaker, the latter can be safely tested without the risk arising of the motor starting up if the control switch is defective.
The means for high-impedance bridging across the switch path of the circuit breaker can comprise an optocoupler, for example, which preferably includes an optotriac, and which is connected in parallel to the main terminals of the circuit breaker via a resistor.

4
Another way of preventing the motor from briefly starting up if the control switch is defective when the circuit breaker is being tested is to provide a means for monitoring the rotation of the motor, said means being coupled to the controller in order to force at least one of the two switches into a blocked state in the event that the motor starts when the circuit breaker is energized without the control switch being energized.
This likewise avoids the risk of the motor briefly starting up if the control switch malfunctions while the circuit breaker is being tested.
The means for monitoring the rotation of the motor can be embodied in the form of a rotational speed sensor, or it can monitor the motor current. In the latter case, a shunt resistor is connected in series to the armature, and the voltage drop across the resistor is monitored.
There are various options for configuring the monitoring circuit to monitor the voltage potential across the control switch.
Whereas a circuit comprising a transistor, a diode and two resistors is known from the prior art, for example US 6,236,177 Bl, the invention prefers a much simpler circuit.
In a preferred development of the invention, the monitoring circuit includes a voltage divider with two resistors connected in series, the first resistor being connected to a first pole of an auxiliary voltage supply and the second resistor being connected to one of the main terminals of the control switch and to the second pole of the auxiliary voltage, the connection point between the two resistors being connected via a third resistor to the other main terminal of the control switch and supplied as the output of the monitoring circuit to an input terminal of the controller.

5
Reliable monitoring can thus be achieved using only three resistors and the supply voltage, which is required anyway for the electronics.
According to an alternative embodiment of the invention, the object is achieved by means of a series motor, in particular for an power tool, comprising a fuse via which the armature is connected via a first electronic switch (control switch) to the supply voltage in order to switch the motor on and off, a second electronic switch (circuit breaker) connected in parallel to the armature and to the control switch in order to trip the fuse in the event of a fault, an electronic controller, preferably a microprocessor, coupled to the switches, a means for blocking the circuit breaker and for testing the function of the circuit breaker in the blocked state, and a monitoring circuit that analyzes the voltage drop at the control switch and whose output signal is supplied to the electronic controller to force the circuit breaker to trip the fuse if the monitoring circuit registers a malfunction of the control switch.
In this manner, too, the technical problem of the invention is completely solved.
Whereas it was not possible in the prior art to test the function of the circuit breaker in the event of a fault, given a parallel arrangement of the circuit breaker for tripping the fuse, according to the present invention the circuit breaker is now initially blocked and can then be safely tested without tripping the fuse.
To this end, in a preferred development of the invention, a transistor having an emitter and collector and which can be made conductive in order to test the circuit breaker by measuring its control current is connected between the control terminal and a main terminal of the circuit breaker in order to prevent the fuse from tripping when the circuit breaker is being tested.
According to another advantageous embodiment of the invention, the electronic switches are embodied as triacs.

6
This has the advantage that high loads can therefore be switched largely without power loss, even with alternating current, and simultaneously that the control switch can also be used to regulate the power and control the speed of the motor.
With regard to method, the object of the invention is further achieved with a method for controlling a series motor, preferably a series motor for a power tool, and comprising the following steps:
(a) connecting the motor to a supply voltage via a first electronic switch (control
switch) for switching the motor on and off, and a second electronic switch
(circuit breaker),
(b) monitoring the voltage potential across the control switch,
(c) blocking the switches if the voltage potential across the control switch takes
on values outside a predefined threshold range when both switches are in the
switched-off state,
(d) first switching on the circuit breaker if the voltage potential across the control
switch is within the threshold range when both switches are in the switched-
off state,
(e) switching on the control switch if the voltage potential across the control
switch takes on values outside the threshold range and
(f) blocking both switches if the voltage potential across the control switch does
not take on values outside the threshold range.
According to the invention, a functional test is firstly performed before the control switch is switched on, in order to determine whether the circuit breaker is working

7
properly. If this is the case, the control switch is subsequently tested before it can be switched on to make the motor operational.
Faults in the circuit breaker and/or the control switch can be reliably detected in this way. Disconnecting the circuit breaker or the control switch does not pose a risk, because the motor is unable to start in such a case. Due to the fact that, during the tests, opposite input signals are required at the input terminals of the electronic controller for determining whether the control switch and the circuit breaker are working correctly, any short circuit or disconnection of discrete parts of the monitoring circuit will result in a safe OFF state. Faults in the driver circuits are also detected. This is because permanent energization produces the same faults as a short circuited control switch or circuit breaker. If there is no energization, this leads to the same behavior as when the control switch or circuit breaker is disconnected. In such a case, it is not possible for the motor to start.
In one advantageous development of the invention, the circuit breaker is immediately switched off again if the voltage potential does not increase when switching on the circuit breaker with the control switch switched off.
In this case, there is a fault in the control switch. By switching off the circuit breaker immediately, the motor is prevented from starting.
To this end, according to a further development of the method of the invention, the rotation of the motor is monitored in order to switch off the motor again immediately if any rotation of the motor is registered when switching on the circuit breaker with the control switch switched off.
In an alternative embodiment, the circuit breaker can firstly be bridged by a high impedance in order to test the control switch, and a test carried out to determine whether the voltage potential across the control switch increases to the predefined threshold value.

8
In this way, the motor can be safely prevented from starting when the control switch is being tested, even if there is a defect.
Alternatively, the object of the invention is achieved with a method for controlling a series motor, preferably a series motor for a power tool, comprising the following steps:
(a) connecting the motor to a supply voltage via a fuse and a first electronic
switch (control switch) for switching the motor on and off, and connecting a
second electronic switch (circuit breaker) to the supply voltage via the fuse,
(b) before switching on the control switch, first blocking the circuit breaker and
testing whether the circuit breaker works by energizing the circuit breaker and
testing the control current,
(c) removing the block on the circuit breaker if energization of the circuit breaker
is found to be working properly, and switching on the control switch in order
to switch on the motor,
(d) blocking energization of the control switch if a malfunction is detected in the
course of step (b),
(e) monitoring the voltage drop at the control switch and triggering the circuit
breaker in order to trip the fuse if the voltage drop when switching off the
control switch does not increase beyond a predefined threshold value.
In this way, by connecting the circuit breaker in parallel, it is possible to test for any malfunction in the driver circuit for the circuit breaker prior to switching on the control switch, and for deactivation to be effected should the control switch fail.

9
It is self-evident that the features of the invention as mentioned above and to be explained below can be applied not only in the combination specified in each case, but also in other combinations or in isolation, without departing from the scope of the invention.
Further advantages and features of the invention derive from the following description of preferred embodiments, in which reference is made to the drawings, in which
Fig. 1 shows, in a simplified circuit diagram, a first embodiment of a series motor according to the invention;
Fig. 2 shows a preferred embodiment of a monitoring circuit suitable for the motor of Fig. 1;
Fig. 2a shows a graph of the input voltage across resistor R3 of the monitoring circuit in Fig. 2, and the associated output voltage at PIN 1;
Fig. 3 shows an alternative embodiment of the monitoring circuit for the motor in Fig. 1;
Fig. 4 shows a modified version of the circuit in Fig. 1;
Fig. 5 shows a further modification of the circuit in Fig. 1 and
Fig. 6 shows another embodiment of the invention, comprising a parallel circuit breaker for tripping a fuse.
Fig. 1 shows an electric motor according to the invention, in the form of a series motor circuit and labeled in its entirety with reference numeral 10.

10
The motor 10 is supplied with 230 V from the two poles 24 and 26 of an alternating voltage source. Motor 10 has an armature 12, the field windings of which (not shown) are wound in series and connected to the one pole 24 of the supply voltage. The other pole of the armature 12 is connected to the other pole 26 of the supply voltage via two triacs in series, namely a circuit breaker 16 and a control switch 14. Control terminals 28 and 30 of control switch 14 and circuit breaker 16 are connected to the terminals of an electronic controller 18 in the form of a microprocessor. Electronic controller 18 is likewise connected to the two poles 24 and 26 of the supply voltage source, and is supplied in addition with a DC supply (unless this voltage supply is not already integrated in electronic controller 18). A monitoring circuit 20 is also connected between control switch 14 and circuit breaker 16, on the one hand, and the second pole 26 of the supply voltage source, on the other hand, wherein said monitoring circuit monitors the voltage potential between control switch 14 and circuit breaker 16, on the one hand, and the second pole 26 of the supply voltage source, on the other hand, and the output of which is coupled via a line 32 to an input terminal 22 (Pin 1) of electronic controller 18.
By phase control of control switch 14, electronic controller 18 also performs, in an essentially known manner, the functions of a soft starter when switching on the motor and those of a speed and/or power control during motor operation.
By means of monitoring circuit 20, it is now possible to perform a functional check before switching on electric motor 10, in order to ensure that both control switch 14 and circuit breaker 16 are working faultlessly.
Fig. 2 shows a preferred embodiment of monitoring circuit 20. An auxiliary voltage, which may be the supply voltage VCc for the electronic controller 18, is supplied via a voltage divider to the one main terminal of control switch 14, which is connected to the second pole 26 of the AC source. The voltage divider consists of resistors Ri and R2. The tap of the voltage divider is connected to input terminal 22 (Pin 1) of controller 18. The tap of the voltage divider is also coupled via a third resistor R3 to the point of connection between control switch 14 and circuit breaker 16.

11
Such a monitoring circuit provides a very simple way of monitoring the voltage potential across control switch 14 using only three components.
In alternative embodiments of the invention it is also possible to use other monitoring circuits, such as the monitoring circuit known from US 6,236,177 Bl. Such a circuit is shown in Fig. 3, where it is labeled with the reference numeral 20'. However, a monitoring circuit as shown in Fig. 2 is preferred due to its simpler construction.
A modified embodiment of the electric motor according to the invention is shown in Fig. 4, where it is referenced in its entirety with numeral 10a. In this and in further modifications to be explained later, corresponding reference numerals are used for corresponding parts.
The only difference between the circuit of electric motor 10a and the embodiment of electric motor 10 in Fig. 1 is that a means 36 for high-impedance bridging of circuit breaker 16 is additionally provided. Said means 36 for high-impedance bridging of circuit breaker 16 consists of an optotriac 38 which is connected in parallel to the main terminals of circuit breaker 16 via a resistor R4. Optotriac 38 is energized by an LED 40.
Fig. 4 also indicates one of the two field windings, labeled with reference numeral 13, that are in series with armature 12.
The manner of operation of series motor 10 or 10a shall now be described.
In the circuit shown in Fig. 1 and 2, an initial test is firstly conducted, before electric motor 10 is first switched on, to determine whether the output voltage of monitoring circuit 20, which is fed to input terminal 22 (Pin 1) of microprocessor 18 via line 32, is inside the predefined threshold range. This can be seen in greater detail in Fig. 2a. While supply voltage VCc is applied across Ri and the potential across R2 is zero, the

12
AC voltage at the point of connection between control switch 14 and circuit breaker 16 is supplied via R3 to PIN 1. When control switch 14 and circuit breaker 16 are in the switched-off state, no alternating voltage is allowed across R3, with the result that the voltage at PIN 1 depends exclusively on voltage divider Ri and R2, and on Vcc. For example, if Vcc = 5V and R1=R2, there is a threshold range of 2.5V±0.5V within which the voltage at PIN 1 must lie if control switch 14 and circuit breaker 16 are not being driven.
If this is the case, this first test has been passed. This test ensures that the blocking effect is tested for both the positive half-wave and the negative half-wave.
Otherwise there is a fault in the circuit. Either circuit breaker 16 is defective, i.e. is short-circuited, or the driver circuit for circuit breaker 16 is defective, or monitoring circuit 20 is defective. In this case, control switch 14 is not energized and microprocessor 18 changes over to a safe fault state (OFF state).
If the first test is passed, then circuit breaker 16 is energized via line 30 when switching on, as shown in Fig. 1. In this case, if the voltage at Pin 1 oscillates such that the threshold limits shown in Fig. 2a are exceeded, then the circuit is functioning properly. If not, it is malfunctioning. Either there is a defect in control switch 14 (short circuit), or the driver circuit for the control switch 14 is defective, or monitoring circuit 20 is defective.
In there is a defect, circuit breaker 16 is switched off again as fast as possible and microprocessor 18 changes over to a safe fault state (OFF state).
If a defect (short circuit) in either control switch 14 or circuit breaker 16 is detected, the motor cannot be switched on. If control switch 14 or circuit breaker 16 is disconnected, it is likewise not possible for the motor to start, so this does not pose a risk. By means of the circuit for motor 10 as described above, faults in the monitoring circuit as well as faults in the driver circuits can be detected. Due to the fact that,

13
during the tests, opposite input signals are required at input terminal 22 (Pin 1) of microprocessor 18 for the "Passed" function, any short circuit or disconnection of discrete parts of the monitoring circuit will result in a safe OFF state. Permanent energization either of control switch 14 or circuit breaker 16 leads to the same fault as short-circuiting the control switch or the circuit breaker. If microprocessor 18 fails to output a control signal on line 28 and line 30 to energize control switch 14 and circuit breaker 16, then this produces the same result as disconnecting control switch 14 or circuit breaker 16. It is not possible to start the motor in this case, either.
In the circuits according to Fig. 1, it is essential that circuit breaker 16 be switched off again immediately if a malfunction is detected during the second test, when circuit breaker 16 is energized while control switch 14 is not energized. If there is any delay in switching off circuit breaker 16 on detection of a fault during the second test, this may result in the motor being started, which could be disadvantageous in certain circumstances.
To eliminate this possibility, motor 10a in Fig. 4 is also provided with means 36 for high-impedance bridging of circuit breaker 16.
When test 1 has been completed (voltage at Pin 1 is within the threshold range when the circuit breaker and the monitoring circuit are not energized), circuit breaker 16 is merely bridged with a high impedance with the aid of circuit 36, instead of being energized. It is possible in this way to perform a functional test of control switch 16 without any risk arising of the motor immediately starting up if control switch 16 is short circuited.
As an alternative to circuit 36 for high-impedance bridging of control switch 16, a means for monitoring the speed of rotation of the motor is shown as a further modification in Fig. 5, where it is labeled in its entirety with reference numeral 10b.

14
To this end, a shunt resistor R5 can be provided in series with field windings 13. If, during the second test, i.e. when switching on circuit breaker 16 in order to check control switch 14, a voltage drop across shunt resistor R5 between pole 26 of the alternating voltage and line 52 is registered, energization of circuit breaker 16 is immediately interrupted to prevent the motor from starting up.
Alternatively (or additionally), a rotational speed sensor 54 that monitors the rotor speed of the motor could be provided, as indicated by the broken line in Fig. 5. If rotational speed sensor 54 receives a signal during test 2, i.e. when circuit breaker 16 is energized in order to check control switch 14, then energization of circuit breaker 16 is immediately interrupted to stop the electric motor from running. The circuit of motor 10b is otherwise identical to the circuit of motor 10a.
Another embodiment of an electric motor according to the invention is shown in Fig. 6, where it is referenced in its entirety with numeral 10c.
In this case, a fusible cutout 56 is provided that can be tripped by a circuit breaker 16 in the event of a fault in control switch 14. For this purpose, circuit breaker 16 is connected in parallel, immediately behind fuse 56, to the two poles 24 and 26 of the supply voltage source. The drop in voltage potential across control switch 14 is monitored, in turn, by a protection circuit 20, as explained above. The output from monitoring circuit 20 is supplied, in turn, to Pin 1 of microprocessor 18. Although a complete functional test is not possible with the circuit in Fig. 6, because fuse 56 would immediately respond, the driver circuit for circuit breaker 16 can nevertheless be tested by preventing the circuit breaker or triac 16 from triggering.
To this end, the gate 28 of triac 16 is connected via two series resistors R6 and R7 to an output terminal (Pin 3) of microprocessor 18. The point of connection between the two resistors R6, R7 is connected via a line 62 to a measurement input (Pin 4) of microprocessor 18. A transistor 60, the base of which can be driven via an output

15
terminal (Pin 2) of microprocessor 18, is disposed between the gate 28 of circuit breaker 16 and pole 26 of the supply voltage.
For testing purposes, the monitoring circuit 20 is firstly assessed. The test is performed in the manner as described in conjunction with Figs. 2 and 2a. If a fault is detected during said test, circuit breaker 16 is triggered in order to trip fuse 56.
If no fault is detected in the prior test, the driver circuit for circuit breaker 16 is then tested in the following manner:
In a first step, transistor 60 is powered at its base 64 via Pin 2 of microprocessor 18. This prevents triac 16 from triggering. Gating pulses are now outputted via Pin 3, whereby transistor 60 prevents any triggering. The voltage between resistors R6, R7 can now be detected at Pin 4 of microprocessor 18. The output voltage at Pin 3 corresponds approximately to the supply voltage VCc- If no voltage is now applied at Pin 4, then either resistors R6, R7 have been disconnected or no gating pulse is out-putted, which means that a fault is present. Assuming that resistors R6, R7 are identical, approximately half the supply voltage Vz VCc must be applied to Pin 4 while the gate trigger current is flowing. In this case, the driver circuit for triac 16 is working properly. If the full supply voltage Vcc is applied to Pin 4 when gating pulses are being outputted at Pin 3, then resistor R6 is disconnected, which again means there is a fault.
If no fault is detected, powering of transistor 60 via Pin 2 is cancelled in order that
the circuit breaker or triac 16 can work during operation to enable control switch 14
to trip fuse 56 in the event of a fault. Control switch 14 can then be switched on in
order to switch on the motor. If control switch 14 is not longer energized, i.e. no
gating pulses are being outputted via line 30, then the voltage drop across control
switch 14 must rise above a predefined threshold value. Otherwise, control switch 14
is defective. If a defect in control switch 14 is detected when switching it off, circuit
breaker 16 is triggered via Pin 3 of control circuit 18 in order to trip fuse 56.

16
Claims
1. A series motor, in particular for a power tool, comprising a first electronic
switch (control switch) (14) for switching the motor on and off (10, 10a, 10b),
a second electronic switch (circuit breaker) (16) connected in series to the con
trol switch (14), a monitoring circuit (20, 20') that monitors the function of
the switches (14, 16) and analyzes the voltage potential at the connection
point of the control switch (14) and the circuit breaker (16), and further com
prising an electronic controller (18), preferably a microprocessor, that is cou
pled to the two switches (14, 16) and the monitoring circuit (20, 20') and
forces at least one of the switches (14, 16) into an OFF state when the moni
toring circuit (20, 20') registers a malfunction in one of the switches (14, 16).
2. The series motor according to claim 1, comprising a means (36) for bridging
the switch path of the circuit breaker (16) with a high impedance in order to
allow a functional test of the control switch (14) without having to start the
motor (10, 10a, 10b).
3. The series motor according to claim 2, in which the means (36) for high-
impedance bridging includes an optocoupler, preferably an optotriac (38), that
is connected in parallel via a resistor (R4) to the main terminals (42, 44) of the
circuit breaker (16).
4. The series motor according to one of the preceding claims, comprising a
means for monitoring the rotation of the motor (10, 10a, 10b), said means be
ing coupled to the controller (18) in order to force at least one of the two
switches (14, 16) into an OFF state in the event that the motor (10, 10a, 10b)
starts when the circuit breaker (16) is energized without the control switch
(14) being energized.

17
5. The series motor according to claim 4, wherein the means for monitoring the
rotation of the motor is embodied as a rotational speed sensor (54).
6. The series motor according to claim 4, wherein the means for monitoring the
rotation of the motor monitors the motor current.
7. The series motor according to claim 6, wherein the means for monitoring the
rotation of the motor is a shunt resistor (R5) that is connected in series to the
armature (12) and whose voltage drop is monitored.
8. The series motor according to one of the preceding claims, wherein the
monitoring circuit (20) includes a voltage divider with two resistors (Ri, R2)
connected in series, the first resistor (Ri) being connected to a first pole of an
auxiliary voltage supply (Vcc) and the second resistor (R2) being connected to
one of the main terminals of the control switch (14) and to the second pole of
the auxiliary voltage, the connection point between the two resistors (Ri, R2)
being connected via a third resistor (R3) to the other main terminal of the con
trol switch (14) and supplied as the output of the monitoring circuit to an in
put terminal (22) of the controller (18).
9. A series motor, in particular for an power tool, comprising a fuse (56) via
which the armature (12) is connected via a first electronic switch (control
switch) (14) to the supply voltage in order to switch the motor on and off
(10c), a second electronic switch (circuit breaker) (16) connected in parallel to
the armature (12) and to the control switch (14) in order to trip the fuse (56)
in the event of a fault, an electronic controller (18), preferably a microproces
sor coupled to the switches (14, 16), a means (16) for blocking the circuit
breaker (16) and for testing the function of the circuit breaker (16) in the
blocked state, and a monitoring circuit (20) that analyzes the voltage drop at
the control switch (14) and whose output signal is supplied to the electronic

18
controller (18) to force the circuit breaker (16) to trip the fuse (56) if the monitoring circuit (16) registers a malfunction of the control switch (14).
10. The series motor according to claim 9, wherein a transistor (60) which can be
made conductive in order to test the circuit breaker (16) by measuring its con
trol current is connected with its emitter and collector between the control
terminal (28) and a main terminal (44) of the circuit breaker (16) in order to
prevent the fuse (56) from tripping when the circuit breaker (16) is being
tested.
11. The series motor according to one of the preceding claims, wherein the
switches (14, 16) are embodied as triacs.
12. A method for controlling a series motor, preferably for a power tool, compris
ing the following steps:

(a) connecting the motor (12) to a supply voltage via a first electronic
switch (control switch) (14) for switching the motor on and off, and a
second electronic switch (circuit breaker) (16),
(b) monitoring the voltage potential across the control switch (14),
(c) blocking the switches (14, 16) if the voltage potential across the control
switch (14) takes on values outside a predefined threshold range when
both switches (14, 16) are in the switched-off state,
(d) first switching on the circuit breaker (16) if the voltage potential across
the control switch (14) is within the threshold range when both
switches (14, 16) are in the switched-off state,
(e) switching on the control switch (14) if the voltage potential across the
control switch (14) takes on values outside the threshold range and
(f) blocking both switches (14, 16) if the voltage potential across the con
trol switch (14) does not take on values outside the threshold range.

19
13. The method according to claim 12, wherein the circuit breaker (16) is imme
diately switched off again if the voltage potential does not increase when
switching on the circuit breaker (16) with the control switch (14) switched off.
14. The method according to claim 12 or 13, wherein rotation of the motor is
monitored in order to switch off the motor again immediately if rotation of
the motor is registered when switching on the circuit breaker (16) with the
control switch (14) switched off.
15. The method according to one of claims 12 to 14, wherein the circuit breaker
(16) is first bridged by a high impedance in order to test the control switch
(14), and a test is carried out to determine whether the voltage potential
across the control switch (14) increases to the predefined threshold value.
16. A method for controlling a series motor, preferably for a power tool, compris
ing the following steps:

(a) connecting the armature (12) to a supply voltage via a fuse (56) and a
first electronic switch (control switch) (14) for switching the motor on
and off, and connecting a second electronic switch (circuit breaker)
(16) to the supply voltage via the fuse (56),
(b) before switching on the control switch (14), first blocking the circuit
breaker (16) and testing whether the circuit breaker (16) works by ener
gizing the circuit breaker (16) and testing the control current,
(c) removing the block on the circuit breaker (16) if the circuit breaker (16)
is found to be working properly, and switching on the control switch
(14) in order to switch on the motor,
(d) forcing the switch (14, 16) into an OFF state if a malfunction is de
tected in the course of step (b),
(e) monitoring the voltage drop at the control switch (14) and triggering
the circuit breaker (16) in order to trip the fuse (56) if the voltage drop
when switching off the control switch (14) does not increase beyond a
predefined threshold value.

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Patent Number

259501

Indian Patent Application Number

3165/KOLNP/2006

PG Journal Number

12/2014

Publication Date

21-Mar-2014

Grant Date

14-Mar-2014

Date of Filing

31-Oct-2006

Name of Patentee

C.& E.FEIN GMBH

Applicant Address

HANS-FEIN-STRASSE 81 73529 SCHWAEBISCH GMUENT-BARGAU GERMANY

Inventors:

#	Inventor's Name	Inventor's Address
1	CHRISTOF KRESS	OEHRWIESENWEG 11 73779 DEIZISAU GERMANY.
2	MARTIN BEICHTER	LEO-FALL-WEG 15 70195 STUTTGART GERMANY.

PCT International Classification Number

H02H 7/08

PCT International Application Number

PCT/EP2005/003237

PCT International Filing date

2005-03-26

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	10 2004 018 966.8	2004-04-13	Germany