EP4635070A1 - Compact safe torque off circuit for electric motor - Google Patents

Compact safe torque off circuit for electric motor

Info

Publication number
EP4635070A1
EP4635070A1 EP23833317.3A EP23833317A EP4635070A1 EP 4635070 A1 EP4635070 A1 EP 4635070A1 EP 23833317 A EP23833317 A EP 23833317A EP 4635070 A1 EP4635070 A1 EP 4635070A1
Authority
EP
European Patent Office
Prior art keywords
electric
circuit
sto
output
motor
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP23833317.3A
Other languages
German (de)
French (fr)
Inventor
Mikal Jesper NIELSEN
Sérgio Filipe do Vale Guimarães TELES
Jens Uwe MARGGRANDER
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Grundfos Holdings AS
Original Assignee
Grundfos Holdings AS
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Grundfos Holdings AS filed Critical Grundfos Holdings AS
Publication of EP4635070A1 publication Critical patent/EP4635070A1/en
Pending legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P29/00—Arrangements for regulating or controlling electric motors, appropriate for both AC and DC motors
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P29/00—Arrangements for regulating or controlling electric motors, appropriate for both AC and DC motors
    • H02P29/20—Arrangements for regulating or controlling electric motors, appropriate for both AC and DC motors for controlling one motor used for different sequential operations
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P3/00—Arrangements for stopping or slowing electric motors, generators, or dynamo-electric converters

Definitions

  • the present invention relates to safety circuits for electric motors, such as electric motors for driving a pump or the like. Especially, the invention relates to a compact safety circuit which can prevent an electric motor from generating torque without the need to cut off the main supply.
  • Electric motors are used in a wide range of applications and in a variety of setups where they have to comply with safety regulations,
  • a safety function can be implemented by interrupting power supply to the electric motor. However, this means a slow start-up when returning to normal operation after a safety stop, since a rebooting of the motor control will be required.
  • a safety circuit for Safe Torque Off can be used.
  • IEC 61508-1 2010, Saftety Integrity Level (SIL) 3, following the guidelines of EN ISO 13849-1 : 2015 for Performance Level e, category 3, such circuit requires bulky components. This means that it is not possible to integrate the safety circuit into a compact housing of an electric motor device, or a combined electric motor and pump device.
  • SIL Saftety Integrity Level
  • a first aspect of the invention provides an electric Safe Torque Off circuit arranged for connection to a motor drive of an electric motor, wherein the Safe Torque Off circuit is arranged to cause the electric motor to stop generating torque in case at least one out of at least two conditions is detected, the Safe Torque Off circuit comprising
  • a pulse generator connected to the second electric input and being arranged to generate an oscillating electric output voltage at an output when powered from the second electric input
  • a modulator connected to the first electric input and the output of the pulse generator, wherein the modulator is arranged to generate an electric output signal being a modulated version of an electric voltage at the first input at a rate defined by the pulse generator controlled by the second input,
  • an electric isolator component connected to receive the electric output signal from the modulator and being arranged to generate an electric output signal accordingly, wherein the electric output signal is electrically isolated from the electric output signal from the modulator.
  • Such safety circuit is advantageous, since it can be implemented with only few rather simple components, and thus the circuit is suited for low cost implementation and occupies a minimum of space.
  • the circuit is Performance Level e category 3 compliant according to EN ISO 13849-1:2015, even though it can be implemented with only one single signal transfer between two electrically circuits, e.g. one single optocoupler as electric isolator connecting the low voltage side of the safety circuit with the power module including the motor driver.
  • This is made possible with the pulsed signal resulting from the modulator as deriver for the electric isolator (e.g. optocoupler) and its detection after the electric isolator.
  • a possible failure of the electric isolator e.g. optocoupler
  • circuit is a hardware only solution and thus software independent, which makes it easy to integrate into various electric motors and applications.
  • the safety function can for example be integrated within the housing of an electric motor along with e.g. the motor drive.
  • the electric motor can have a built-in safety function which makes it easy to integrate with various applications where e.g. electric switches in a protection door or the like can be connected to the electric motor in a simple way to provide a high degree of safety without the need for external safety circuits.
  • the Safe Torque Off circuit is arranged for connection to the motor drive to cause the electric motor to stop generating torque in case of failure of a single component of the electric Safe Torque Off circuit.
  • the Safe Torque Off circuit has only one single electric isolator component, preferably one single optocoupler, connected between the first and second electric inputs and an electric output arranged for connection to the motor drive.
  • the Safe Torque Off circuit is arranged to cause the electric motor to stop generating torque in case of failure of a single component by use of one single electric isolator component.
  • the output of the electric isolator component is applied for deriving control signals for controlling the motor drive to cause the electric motor (MT) to stop generating torque in case of failure of a single component.
  • the output of the electric isolator component may be applied for controlling respective high and low gate driver outputs accordingly for driving respective high and low gate driver parts of the motor drive.
  • the Safe Tourque Off circuit preferably comprises first and second logic comparator blocks both being arranged to receive said electric output signal from the electric isolator component and to provide respective first and second logic outputs accordingly.
  • the logic comparator blocks may especially be implemented as electronic logic components that receive a voltage at the input and generates a an output voltage according to a predetermined scheme. These logic comparator blocks allow the detection of any fault in response to receiving the output from the electric isolator, e.g. optocoupler.
  • each of the first and second logic comparator blocks preferably comprises a pulse detector connected to receive said electric output signal from the electric isolator component, and wherein the first and second logic comparator blocks are arranged to generate the respective first and second logic outputs in accordance with outputs of the respective pulse detectors.
  • the circuit may comprise first and second interconnected logic comparators arranged to receive respective first and second pulse detection outputs from the respective pulse detector and to respective first and second logic outputs accordingly.
  • the first and second logic comparator blocks may be arranged to gate respective high and low gate driver outputs accordingly for driving respective high and low gate driver parts of the motor drive in response to the first and second logic outputs.
  • the first and second logic comparator blocks are arrange to drive both of the high and low gate driver parts of the motor drive only in case both of the first and second pulse detection output indicate that a pulse signal is detected by both of the first and second pulse detectors.
  • the circuit may comprise respective first and second logic gates, preferably AND gates, arranged to receive the respective first and second logic outputs and to gate respective high and low gate driver outputs accordingly for driving respective high and low gate driver parts of the motor drive.
  • the high and low gate driver outputs are preferably applied to the high and low gate driver parts of all three phases of the motor drive.
  • the pulse generator may be arranged to generate an output voltage switching between two levels. Specifically, the pulse generator may be arranged to oscillate at a frequency of 1-100 kHz, such as 10-50 kHz, such as 10-20 kHz, such as 14- 16 kHz. The pulse generator is preferably arranged to generate an output voltage switching between a DC voltage and electrical ground (zero V), such as a DC voltage of 10-50 V, such as 20-30 V, such as 24 V.
  • the electric isolator component is implemented by an optocoupler. Especially, it is noted that the electric isolator component can be implemented using only one signle optocoupler, and still the Safe Torque Off circuit can be EN ISO 13849- 1: 2015; category 3 compliant.
  • the invention provides a method for causing an electric motor to stop generating torque in case at least one out of at least two conditions is detected.
  • the method comprising
  • an electrical isolator component such as an optocoupler
  • the method preferably comprises providing said electrically isolated signal to first and second interconnected comparator blocks.
  • the method may comprise controlling gate driver signals to high and low gate driver parts of a motor drive in response to outputs from said first and second logic comparator blocks.
  • the method may comprise applying respective first and second logic outputs from the comparator blocks for gating respective high and low gate driver signals to the motor drive, so as to drive both of the high and low gate driver parts of the motor drive only in case both of the first and second pulse detection output indicate that a pulse signal is detected by both of the first and second pulse detectors.
  • the method preferably comprises driving respective high and low gate driver parts of each electric phase of the three-phase motor drive.
  • the method comprises applying an output from only one electric isolator component to inputs of both of first and second logic blocks.
  • the method comprises applying controlling both of high and and low gate driver parts of the motor drive in response to an output from only one electric isolator component.
  • the method comprises applying the electrically isolated signal to first and second logic blocks having outputs connected to the motor drive so as to cause the electric motor to stop generating torque in case it is detected by any one of the first and second logic blocks that either the electrically isolated signal is not present or that the electrically isolated signal represents a state where at least one of the first and second external electric switches or contacts indicates a fault state.
  • the method may comprise controlling respective high and low gate driver outputs for driving respective high and low gate driver parts of the motor drive in response to outputs from the first and second logic blocks.
  • the invention provides a system comprising
  • an electric motor e.g. a three-phase electric motor, arranged to rotate a shaft
  • a motor drive connected to the electric motor and being arranged for driving the electric motor by means of high and low set of gate drivers controlled by respective high and low gate driver signals, and
  • the electric motor may be a permanent magnet electric motor, however the electric motor is not limited to that.
  • the electric motor may be arranged for being powered by an AC electric power source providing a 100 V AC to 500 V AC electric power input, e.g., the public grid.
  • the electric motor may be configured to receive an electric power input in the form of a DC voltage, e.g. in the form of a positive and a negative DC voltage.
  • the electric motor may be in the electric power range of 1 W to 100 W, however the invention is also advantageous for electric motors in the electric power range 100 W to 1 kW, or for electric motors in the electric power range of 1-50 kW or even more.
  • the system may comprise a housing forming an enclosure in which the motor drive and the Safe Torque Off circuit are positioned, wherein the housing is attached to the electric motor.
  • a compact electric motor with an integrated safety function can be provided.
  • the system comprises rotational pump mechanism arranged for pumping a fluid between a fluid inlet and a fluid outlet, and wherein the shaft of the electric motor is arranged to rotate the rotational pump mechanism.
  • the rotational pump mechanism may be based on any known pump technology.
  • the rotational pump mechanism may comprise an impeller arranged to rotate inside an impeller housing for pumping fluid, e.g., liquid such as water, from a fluid inlet to a fluid outlet, upon rotation.
  • the housing around the rotational pump mechanism may be partly or fully integrated with the electrically conductive motor housing.
  • the motor drive and Safe Torque Off circuit may be enclosed within such housing, thus providing a pump device with an integrated safety function.
  • the pump device may comprise a casing enclosing at least the electric inverter.
  • the casing preferably encloses all electronic components of the pump device, however it may further enclose more components, e.g. part of or all of the electric motor, part of or all of the rotational pump mechanism.
  • the casing preferably has openings to allow electric connection to an electric power source, e.g. it may have pipe connections for fluid inlet and fluid outlet.
  • the casing may be made of a composite or another electrically non-conductive material.
  • the system may comprise first and second switches or contacts connected to the first and second electric inputs of the Safe Torque Off circuit.
  • the first and second electric contacts may be arranged for position to detect opening of a door or port, thus implementing a safety stop feature on to stop the electric motor in generating torque if the door is opened.
  • FIG. 1 shows a block diagram of the Safe Torque Off circuit connected to external swithes and a motor drive of an electric motor
  • FIG. 2 shows a functional block diagram serving to explain the function of a Safe Torque Off circuit embodiment
  • FIG. 3 shows steps of a method embodiment.
  • FIG. 1 shows a block diagram of the the Safte Torque Off circuit STO of the invention which is connected with its outputs to motor drive MD arranged to drive an electric motor MT.
  • the purpose of the circuit STO is to provide a safety function of the electric motor, which causes the electric motor to stop generating torque in case one of the switches SW1, SW2 is detected to be closed.
  • the circuit STO is preferably implemented so as to comply with the requirements in EN ISO 13849- 1: 2015 PL e category 3.
  • the invention provides a circuit STO which eliminates the need for using two optocouplers for EN ISO 13849-1:2015 PL e category 3 compatibility. Embodiments of the circuit STO will be described in more details in the following.
  • the Safe Torque Off circuit STO is shown connected at its two input terminals II, 12 to respective electric switches SW1, SW2, such as safety switches serving to detect opening of a door, or the like, which should be detected and trigger the circuit STO to switch to safety mode, where the electric motor MT is disabled from generating torque.
  • the switches SW1, SW2 are connected to the Safe Torque Off circuit STO so that the circuit STO can react and switches to safety mode in case at least one of the two switches SW1, SW2 is activated, thus the circuit STO can switch to safety mode if one out of two conditions is met: 1) both switches SW1, SW2 are activated, 2) one of the switches SW1, SW2 is activated. In this way a fail of one of the switches SW1, SW2 can be tolerated and still cause the circuit STO to switch to safety mode.
  • the Safe Torque Off circuit STO is connected to the motor drive MD of the electric motor MT, more specifically the Safe Torque Off circuit STO is arranged to provide outputs GD_H, GD_L to the motor drive MD for driving respective high and low gate driver parts of the motor drive MD.
  • these outputs GD_H, GD_L can manipulate, e.g. gate or not gate, the high and low gate drivers of the motor drive MD to cause the motor to stop generating torque, if the Safe Torque Off circuit STO detects close of any one of the safety switches SW1, SW2. In case just one of the high and low gate drivers is not gated to drive the electric motor MT, the electric motor MT will stop generate torque, and thus be in safety mode.
  • FIG. 2 shows a Safe Torque Off circuit STO embodiment illustrated with a block diagram serving to explain the function of the circuit STO.
  • the circuit has two electric inputs II, 12. These input II, 12 are connected to two safety switches SW1, SW2. As seen, the two switches SW1, SW2 are interconnected at a midpoint which is connected to a fixed DC voltage DCV, e.g. 10-30 V, e.g. 24 V from a voltage supply, and this voltage DCV may be used in general as supply for the electric components of the Safe Torque Off circuit STO.
  • DCV DC voltage
  • a pulse generator PG is connected to the second electric input (12) and being arranged to generate an oscillating electric output voltage, oscillating at 15 kHz between electric ground (zero V) and 24 V when powered from the second electric input 12.
  • a modulator MOD is connected to the first electric input II and the output of the pulse generator PG, and the modulator MOD generates an electric output signal being a modulated version of an electric voltage at the first input II at a rate defined by the pulse generator PG controlled by the second input 12.
  • An electric isolator component e.g. an optocoupler OPT, is connected to receive the electric output signal from the modulator MOD and being arranged to generate an electric output signal accordingly which is electrically isolated from the electric output signal from the modulator MOD.
  • First and second logic comparator blocks Bl, B2 are both being arranged to receive the output from the optocoupler OPT and to provide respective first and second logic outputs 01, 02 accordingly.
  • Each of the two logic comparator blocks Bl, B2 comprises a pulse detector PD1, PD2 connected to receive the output from the optocoupler OPT and being arranged to generate the respective logic outputs 01, 02 in accordance with outputs of the respective pulse detectors PD1, PD2.
  • the pulse detectors PD1, PD2 provide logic outputs indicating if pulses are received or not.
  • First and second interconnected logic comparators LI, L2 are arranged to receive the respective outputs from the first and second pulse detectors PD1, PD2. These logic comparators LI, L2 are arranged to compare signals from the pulse detectors PD1, PD2 with approval limits, and if just one of the comparators LI, L2 detects and error, it is interconnected with the other one of the comparators LI, L2 such that both of the logic output 01, 02 will indicate an error, and thus even a failure in one of the pulse detectors PD1, PD2 will cause both logic outputs 01, 02 to indicate an error.
  • first and second logic gates LG1, LG2 receive the respective logic outputs 01, 02 and these logic gates LG1, LG2 are arranged to allow the respective high and low gate driver outputs (Hl, H2, H3, LI, L2, L3) to pass for driving respective high and low gate driver parts of the motor drive, e.g. an IGBT based motor drive.
  • the logic gates LG1, LG2 are preferably implemented by AND gates.
  • the safety compliance is obtained by the use of one single optocoupler.
  • An optocoupler is a bulky component to fit into the housing of compact device.
  • the implementation of the safety function with one single optocoupler allows the Safe Function Off circuit to be integrated in the housing attached to an electric motor or a pump device.
  • the safety circuit STO can preferably be implemented on one circuit board and connected to an input of an optocoupler which is implemented on another circuit board along with components forming the motor drive. However, all of these components may be implemented on one single circuit board, if preferred.
  • FIG. 3 shows steps of a method embodiment, i.e. a method for causing an electric motor to stop generating torque in case at least one out of at least two conditions is detected.
  • the method comprises sensing S_U_I2 electric signals at first and second electric inputs connected to respective first and second external electric switches or contacts. Further, the method comprises generating G_OSC_V an oscillating electric output voltage at an output of a pulse generator when powered from the second electric input. Further, generating G_MOD an electric signal being a modulated version of an electric voltage at the first electric input and an output of the pulse generator.
  • G_EI an electrically isolated signal corresponding to said electric signal being a modulated version of said electric voltage at the first electric input and said output of the pulse generator by means of a single optocoupler. Further, providing P_CB1_CB2 said electrically isolated signal to first and second interconnected comparator blocks. Further, controlling C_GDS gate driver signals to high and low gate driver parts of a motor drive in response to outputs from said first and second logic comparator blocks.
  • the method may comprise gating first and second logic outputs from the comparator blocks with respective high and low gate driver signals to the motor drive, so as to drive both of the high and low gate driver parts of the motor drive only in case both of the first and second pulse detection outputs indicate that a pulse signal is detected by both of the first and second pulse detectors.
  • the Safe Torque Off circuit is suitable for integration with such as three-phase electric motors in the electric power range of such as 1-50 kW. Especially, such motors can form part of a pump device in which the safety function can be integrated easily, since the circuit is compact, and still the circuit complies with high demands of safety regulations.
  • the invention provides an electric Safe Torque Off circuit (STO) arranged for connection to a motor drive (MD) of an electric motor (MT), wherein the Safe Torque Off circuit (STO) is arranged to cause the electric motor (MT) to stop generating torque in case at least one out of at least two conditions is detected.
  • the circuit (STO) is based on connection of first and second electric inputs (II, 12) arranged for connection to respective first and second external electric switches (SW1, SW2).
  • a pulse generator (PG) connects to the second electric input (12) and generates an oscillating electric output voltage when powered from the second electric input (2).
  • a modulator generates an electric output signal being a modulated version of an electric voltage at the first input (II) at a rate defined by the pulse generator (PG) controlled by the second input (12).
  • the output from the modulator (MOD) is applied to an optocoupler (OPT) which generates an electrically isolated output which is applied to two logic comparator blocks (Bl, B2).
  • These blocks (Bl, B2) serve to drive respective high and low gate driver parts of the motor drive (MD) only in case both of the first and second pulse detection output indicate that a pulse signal is detected by both of the first and second pulse detectors (PD1, PD2).
  • This provides a compact safety function, e.g. for integration into the housing of an electric motor along with its motor drive.
  • the circuit (STO) is compliant with EN ISO 13849-1:2015, PL e category 3 and IEC 61800-5-2:2016 SIL 3.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Control Of Electric Motors In General (AREA)

Abstract

An electric Safe Torque Off circuit (STO) arranged for connection to a motor drive (MD) of an electric motor (MT), wherein the Safe Torque Off circuit (STO) is arranged to cause the electric motor (MT) to stop generating torque in case at least one out of at least two conditions is detected. The circuit (STO) is based on connection of first and second electric inputs (I1, I2) arranged for connection to respective first and second external electric switches (SW1, SW2). A pulse generator (PG) connects to the second electric input (I2) and generates an oscillating electric output voltage when powered from the second electric input (2). A modulator (MOD) generates an electric output signal being a modulated version of an electric voltage at the first input (I1) at a rate defined by the pulse generator (PG) controlled by the second input (I2). The output from the modulator (MOD) is applied to an optocoupler (OPT) which generates an electrically isolated output which is applied to two logic comparator blocks (B1, B2). These blocks (B1, B2) serve to drive respective high and low gate driver parts of the motor drive (MD) only in case both of the first and second pulse detection output indicate that a pulse signal is detected by both of the first and second pulse detectors (PD1, PD2). This provides a compact safety function, e.g. for integration into the housing of an electric motor along with its motor drive. Still, the circuit (STO) is compliant with EN ISO 13849-1:2015, PL e category 3 and IEC 61800-5-2:2016 SIL 3.

Description

COMPACT SAFE TORQUE OFF CIRCUIT FOR ELECTRIC MOTOR
FIELD OF THE INVENTION
The present invention relates to safety circuits for electric motors, such as electric motors for driving a pump or the like. Especially, the invention relates to a compact safety circuit which can prevent an electric motor from generating torque without the need to cut off the main supply.
BACKGROUND OF THE INVENTION
Electric motors are used in a wide range of applications and in a variety of setups where they have to comply with safety regulations,
A safety function can be implemented by interrupting power supply to the electric motor. However, this means a slow start-up when returning to normal operation after a safety stop, since a rebooting of the motor control will be required.
A safety circuit for Safe Torque Off can be used. However for complying with the safety requirements of e.g. IEC 61508-1 : 2010, Saftety Integrity Level (SIL) 3, following the guidelines of EN ISO 13849-1 : 2015 for Performance Level e, category 3, such circuit requires bulky components. This means that it is not possible to integrate the safety circuit into a compact housing of an electric motor device, or a combined electric motor and pump device.
Thus, to provide a safety function in an application involving an electric motor, external components are required, e.g. for connection to switches for detection of opening of a door or the like, where person safety requires the electric motor to be stopped.
OBJECT OF THE INVENTION
Following the above, it may be seen as an object of the present invention to provide a compact safety circuit for electric motors which complies with the safety regulations of some standards, such as the IEC 61508 (SIL 3), EN ISO 13849 (category 3).
SUMMARY OF THE INVENTION
A first aspect of the invention provides an electric Safe Torque Off circuit arranged for connection to a motor drive of an electric motor, wherein the Safe Torque Off circuit is arranged to cause the electric motor to stop generating torque in case at least one out of at least two conditions is detected, the Safe Torque Off circuit comprising
- a first and second electric inputs arranged for connection to respective first and second external electric switches or contacts,
- a pulse generator connected to the second electric input and being arranged to generate an oscillating electric output voltage at an output when powered from the second electric input,
- a modulator connected to the first electric input and the output of the pulse generator, wherein the modulator is arranged to generate an electric output signal being a modulated version of an electric voltage at the first input at a rate defined by the pulse generator controlled by the second input,
- an electric isolator component connected to receive the electric output signal from the modulator and being arranged to generate an electric output signal accordingly, wherein the electric output signal is electrically isolated from the electric output signal from the modulator.
Such safety circuit is advantageous, since it can be implemented with only few rather simple components, and thus the circuit is suited for low cost implementation and occupies a minimum of space.
Especially, the circuit is Performance Level e category 3 compliant according to EN ISO 13849-1:2015, even though it can be implemented with only one single signal transfer between two electrically circuits, e.g. one single optocoupler as electric isolator connecting the low voltage side of the safety circuit with the power module including the motor driver. This is made possible with the pulsed signal resulting from the modulator as deriver for the electric isolator (e.g. optocoupler) and its detection after the electric isolator. A possible failure of the electric isolator (e.g. optocoupler) will always result in a safe state. This guarantees that any fault before the optocoupler, or even at the optocoupler, results in a safe state. In this way, the need for redundancy at the optocoupler has been eliminated, and still the safety circuit complies with the category 3 saftey requirements.
Furthermore, the circuit is a hardware only solution and thus software independent, which makes it easy to integrate into various electric motors and applications.
The small space required allows the Safe Torque Off circuit to be implemented at least partially integrated with the motor drive. Thus, the safety function can for example be integrated within the housing of an electric motor along with e.g. the motor drive. Hereby, the electric motor can have a built-in safety function which makes it easy to integrate with various applications where e.g. electric switches in a protection door or the like can be connected to the electric motor in a simple way to provide a high degree of safety without the need for external safety circuits.
In the following, preferred embodiments and features will be described.
Preferably, the Safe Torque Off circuit is arranged for connection to the motor drive to cause the electric motor to stop generating torque in case of failure of a single component of the electric Safe Torque Off circuit.
Preferably, the Safe Torque Off circuit has only one single electric isolator component, preferably one single optocoupler, connected between the first and second electric inputs and an electric output arranged for connection to the motor drive.
Preferably, the Safe Torque Off circuit is arranged to cause the electric motor to stop generating torque in case of failure of a single component by use of one single electric isolator component. Preferably, the output of the electric isolator component is applied for deriving control signals for controlling the motor drive to cause the electric motor (MT) to stop generating torque in case of failure of a single component. Especially, the output of the electric isolator component may be applied for controlling respective high and low gate driver outputs accordingly for driving respective high and low gate driver parts of the motor drive.
The Safe Tourque Off circuit preferably comprises first and second logic comparator blocks both being arranged to receive said electric output signal from the electric isolator component and to provide respective first and second logic outputs accordingly. The logic comparator blocks may especially be implemented as electronic logic components that receive a voltage at the input and generates a an output voltage according to a predetermined scheme. These logic comparator blocks allow the detection of any fault in response to receiving the output from the electric isolator, e.g. optocoupler. Especially, wherein each of the first and second logic comparator blocks preferably comprises a pulse detector connected to receive said electric output signal from the electric isolator component, and wherein the first and second logic comparator blocks are arranged to generate the respective first and second logic outputs in accordance with outputs of the respective pulse detectors. Especially, the circuit may comprise first and second interconnected logic comparators arranged to receive respective first and second pulse detection outputs from the respective pulse detector and to respective first and second logic outputs accordingly. Especially, the first and second logic comparator blocks may be arranged to gate respective high and low gate driver outputs accordingly for driving respective high and low gate driver parts of the motor drive in response to the first and second logic outputs. Hereby, the first and second logic comparator blocks are arrange to drive both of the high and low gate driver parts of the motor drive only in case both of the first and second pulse detection output indicate that a pulse signal is detected by both of the first and second pulse detectors. More specifically, the circuit may comprise respective first and second logic gates, preferably AND gates, arranged to receive the respective first and second logic outputs and to gate respective high and low gate driver outputs accordingly for driving respective high and low gate driver parts of the motor drive. In case of a three-phase electric motor, it is to be understood that the high and low gate driver outputs are preferably applied to the high and low gate driver parts of all three phases of the motor drive.
The pulse generator may be arranged to generate an output voltage switching between two levels. Specifically, the pulse generator may be arranged to oscillate at a frequency of 1-100 kHz, such as 10-50 kHz, such as 10-20 kHz, such as 14- 16 kHz. The pulse generator is preferably arranged to generate an output voltage switching between a DC voltage and electrical ground (zero V), such as a DC voltage of 10-50 V, such as 20-30 V, such as 24 V.
The electric isolator component is implemented by an optocoupler. Especially, it is noted that the electric isolator component can be implemented using only one signle optocoupler, and still the Safe Torque Off circuit can be EN ISO 13849- 1: 2015; category 3 compliant.
In a second aspect, the invention provides a method for causing an electric motor to stop generating torque in case at least one out of at least two conditions is detected. The method comprising
- sensing electric signals at first and second electric inputs connected to respective first and second external electric switches or contacts,
- generating an oscillating electric output voltage at an output of a pulse generator when powered from the second electric input,
- generating an electric signal being a modulated version of an electric voltage at the first electric input and an output of the pulse generator, and
- generating an electrically isolated signal corresponding to said electric signal being a modulated version of said electric voltage at the first electric input and said output of the pulse generator by means of an electrical isolator component, such as an optocoupler.
The method preferably comprises providing said electrically isolated signal to first and second interconnected comparator blocks. Especially, the method may comprise controlling gate driver signals to high and low gate driver parts of a motor drive in response to outputs from said first and second logic comparator blocks. More specifically, the method may comprise applying respective first and second logic outputs from the comparator blocks for gating respective high and low gate driver signals to the motor drive, so as to drive both of the high and low gate driver parts of the motor drive only in case both of the first and second pulse detection output indicate that a pulse signal is detected by both of the first and second pulse detectors. Especially, in case of a three-phase electric motor, the method preferably comprises driving respective high and low gate driver parts of each electric phase of the three-phase motor drive.
In preferred embodiments, the method comprises applying an output from only one electric isolator component to inputs of both of first and second logic blocks.
In preferred embodiments, the method comprises applying controlling both of high and and low gate driver parts of the motor drive in response to an output from only one electric isolator component.
In preferred embodiments, the method comprises applying the electrically isolated signal to first and second logic blocks having outputs connected to the motor drive so as to cause the electric motor to stop generating torque in case it is detected by any one of the first and second logic blocks that either the electrically isolated signal is not present or that the electrically isolated signal represents a state where at least one of the first and second external electric switches or contacts indicates a fault state. Especially, the method may comprise controlling respective high and low gate driver outputs for driving respective high and low gate driver parts of the motor drive in response to outputs from the first and second logic blocks.
In a third aspect, the invention provides a system comprising
- an electric motor, e.g. a three-phase electric motor, arranged to rotate a shaft,
- a motor drive connected to the electric motor and being arranged for driving the electric motor by means of high and low set of gate drivers controlled by respective high and low gate driver signals, and
- the Safe Torque Off circuit according to the first aspect connected to the motor drive.
The electric motor may be a permanent magnet electric motor, however the electric motor is not limited to that. The electric motor may be arranged for being powered by an AC electric power source providing a 100 V AC to 500 V AC electric power input, e.g., the public grid. In some embodiments, e.g. for solar powering, the electric motor may be configured to receive an electric power input in the form of a DC voltage, e.g. in the form of a positive and a negative DC voltage.
The electric motor may be in the electric power range of 1 W to 100 W, however the invention is also advantageous for electric motors in the electric power range 100 W to 1 kW, or for electric motors in the electric power range of 1-50 kW or even more.
The system may comprise a housing forming an enclosure in which the motor drive and the Safe Torque Off circuit are positioned, wherein the housing is attached to the electric motor. Hereby, a compact electric motor with an integrated safety function can be provided.
In one embodiment, the system comprises rotational pump mechanism arranged for pumping a fluid between a fluid inlet and a fluid outlet, and wherein the shaft of the electric motor is arranged to rotate the rotational pump mechanism. Especially, the rotational pump mechanism may be based on any known pump technology. E.g., the rotational pump mechanism may comprise an impeller arranged to rotate inside an impeller housing for pumping fluid, e.g., liquid such as water, from a fluid inlet to a fluid outlet, upon rotation. Especially, the housing around the rotational pump mechanism may be partly or fully integrated with the electrically conductive motor housing. Specifically, the motor drive and Safe Torque Off circuit may be enclosed within such housing, thus providing a pump device with an integrated safety function.
The pump device may comprise a casing enclosing at least the electric inverter. The casing preferably encloses all electronic components of the pump device, however it may further enclose more components, e.g. part of or all of the electric motor, part of or all of the rotational pump mechanism. The casing preferably has openings to allow electric connection to an electric power source, e.g. it may have pipe connections for fluid inlet and fluid outlet. Especially, the casing may be made of a composite or another electrically non-conductive material.
The system may comprise first and second switches or contacts connected to the first and second electric inputs of the Safe Torque Off circuit. The first and second electric contacts may be arranged for position to detect opening of a door or port, thus implementing a safety stop feature on to stop the electric motor in generating torque if the door is opened.
The skilled person will know how to implement the invention based on the disclosure of the present description and the general knowledge in the technical field.
The mentioned aspects of the present invention may be combined. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.
BRIEF DESCRIPTION OF THE FIGURES
The saftey circuit according to the invention will now be described in more detail with regard to the accompanying figures. The figures show one way of implementing the present invention and is not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.
FIG. 1 shows a block diagram of the Safe Torque Off circuit connected to external swithes and a motor drive of an electric motor,
FIG. 2 shows a functional block diagram serving to explain the function of a Safe Torque Off circuit embodiment, and
FIG. 3 shows steps of a method embodiment.
DETAILED DESCRIPTION OF AN EMBODIMENT
FIG. 1 shows a block diagram of the the Safte Torque Off circuit STO of the invention which is connected with its outputs to motor drive MD arranged to drive an electric motor MT. The purpose of the circuit STO is to provide a safety function of the electric motor, which causes the electric motor to stop generating torque in case one of the switches SW1, SW2 is detected to be closed. The circuit STO is preferably implemented so as to comply with the requirements in EN ISO 13849- 1: 2015 PL e category 3. Especially, the invention provides a circuit STO which eliminates the need for using two optocouplers for EN ISO 13849-1:2015 PL e category 3 compatibility. Embodiments of the circuit STO will be described in more details in the following.
The Safe Torque Off circuit STO is shown connected at its two input terminals II, 12 to respective electric switches SW1, SW2, such as safety switches serving to detect opening of a door, or the like, which should be detected and trigger the circuit STO to switch to safety mode, where the electric motor MT is disabled from generating torque. The switches SW1, SW2 are connected to the Safe Torque Off circuit STO so that the circuit STO can react and switches to safety mode in case at least one of the two switches SW1, SW2 is activated, thus the circuit STO can switch to safety mode if one out of two conditions is met: 1) both switches SW1, SW2 are activated, 2) one of the switches SW1, SW2 is activated. In this way a fail of one of the switches SW1, SW2 can be tolerated and still cause the circuit STO to switch to safety mode.
The Safe Torque Off circuit STO is connected to the motor drive MD of the electric motor MT, more specifically the Safe Torque Off circuit STO is arranged to provide outputs GD_H, GD_L to the motor drive MD for driving respective high and low gate driver parts of the motor drive MD. Thus, these outputs GD_H, GD_L can manipulate, e.g. gate or not gate, the high and low gate drivers of the motor drive MD to cause the motor to stop generating torque, if the Safe Torque Off circuit STO detects close of any one of the safety switches SW1, SW2. In case just one of the high and low gate drivers is not gated to drive the electric motor MT, the electric motor MT will stop generate torque, and thus be in safety mode.
FIG. 2 shows a Safe Torque Off circuit STO embodiment illustrated with a block diagram serving to explain the function of the circuit STO. The circuit has two electric inputs II, 12. These input II, 12 are connected to two safety switches SW1, SW2. As seen, the two switches SW1, SW2 are interconnected at a midpoint which is connected to a fixed DC voltage DCV, e.g. 10-30 V, e.g. 24 V from a voltage supply, and this voltage DCV may be used in general as supply for the electric components of the Safe Torque Off circuit STO.
A pulse generator PG is connected to the second electric input (12) and being arranged to generate an oscillating electric output voltage, oscillating at 15 kHz between electric ground (zero V) and 24 V when powered from the second electric input 12.
A modulator MOD is connected to the first electric input II and the output of the pulse generator PG, and the modulator MOD generates an electric output signal being a modulated version of an electric voltage at the first input II at a rate defined by the pulse generator PG controlled by the second input 12.
An electric isolator component, e.g. an optocoupler OPT, is connected to receive the electric output signal from the modulator MOD and being arranged to generate an electric output signal accordingly which is electrically isolated from the electric output signal from the modulator MOD.
First and second logic comparator blocks Bl, B2 are both being arranged to receive the output from the optocoupler OPT and to provide respective first and second logic outputs 01, 02 accordingly.
Each of the two logic comparator blocks Bl, B2 comprises a pulse detector PD1, PD2 connected to receive the output from the optocoupler OPT and being arranged to generate the respective logic outputs 01, 02 in accordance with outputs of the respective pulse detectors PD1, PD2. The pulse detectors PD1, PD2 provide logic outputs indicating if pulses are received or not.
First and second interconnected logic comparators LI, L2 are arranged to receive the respective outputs from the first and second pulse detectors PD1, PD2. These logic comparators LI, L2 are arranged to compare signals from the pulse detectors PD1, PD2 with approval limits, and if just one of the comparators LI, L2 detects and error, it is interconnected with the other one of the comparators LI, L2 such that both of the logic output 01, 02 will indicate an error, and thus even a failure in one of the pulse detectors PD1, PD2 will cause both logic outputs 01, 02 to indicate an error.
Hereby, it can be ensured to drive both of the high and low gate driver parts of the motor drive only in case both of the first and second logic outputs 01, 02 indicate that a pulse signal is detected by both of the first and second pulse detectors PD1, PD2. Thus, the interconnection between the logic comparators LI, L2 ensures a fail safe function even though only one single input signal from the single optocoupler OPT is provided to the logic comparator blocks.
Finally, first and second logic gates LG1, LG2 receive the respective logic outputs 01, 02 and these logic gates LG1, LG2 are arranged to allow the respective high and low gate driver outputs (Hl, H2, H3, LI, L2, L3) to pass for driving respective high and low gate driver parts of the motor drive, e.g. an IGBT based motor drive. The logic gates LG1, LG2 are preferably implemented by AND gates.
In the illustrated case three high gate driver outputs (Hl, H2, H3) and three low gate deriver outputs (LI, L2, L3) are generated to be connected to the three- phase motor drive for driving a three-phase electric motor. In case of a one-phase electric motor and motor drive, only a single output is generated for the respective high and low gate driver parts.
The skilled person will know how to implement the functional blocks illustrated and described in connection with FIG. 2 by means of electric circuits. All elements can be implemented by simple electric components occupying only a small amount of space and can be implemented at low cost.
The safety compliance is obtained by the use of one single optocoupler. An optocoupler is a bulky component to fit into the housing of compact device. Thus, the implementation of the safety function with one single optocoupler allows the Safe Function Off circuit to be integrated in the housing attached to an electric motor or a pump device.
The safety circuit STO can preferably be implemented on one circuit board and connected to an input of an optocoupler which is implemented on another circuit board along with components forming the motor drive. However, all of these components may be implemented on one single circuit board, if preferred.
FIG. 3 shows steps of a method embodiment, i.e. a method for causing an electric motor to stop generating torque in case at least one out of at least two conditions is detected. The method comprises sensing S_U_I2 electric signals at first and second electric inputs connected to respective first and second external electric switches or contacts. Further, the method comprises generating G_OSC_V an oscillating electric output voltage at an output of a pulse generator when powered from the second electric input. Further, generating G_MOD an electric signal being a modulated version of an electric voltage at the first electric input and an output of the pulse generator. Next, generating G_EI an electrically isolated signal corresponding to said electric signal being a modulated version of said electric voltage at the first electric input and said output of the pulse generator by means of a single optocoupler. Further, providing P_CB1_CB2 said electrically isolated signal to first and second interconnected comparator blocks. Further, controlling C_GDS gate driver signals to high and low gate driver parts of a motor drive in response to outputs from said first and second logic comparator blocks.
Especially, the method may comprise gating first and second logic outputs from the comparator blocks with respective high and low gate driver signals to the motor drive, so as to drive both of the high and low gate driver parts of the motor drive only in case both of the first and second pulse detection outputs indicate that a pulse signal is detected by both of the first and second pulse detectors.
The Safe Torque Off circuit is suitable for integration with such as three-phase electric motors in the electric power range of such as 1-50 kW. Especially, such motors can form part of a pump device in which the safety function can be integrated easily, since the circuit is compact, and still the circuit complies with high demands of safety regulations.
To sum up, the invention provides an electric Safe Torque Off circuit (STO) arranged for connection to a motor drive (MD) of an electric motor (MT), wherein the Safe Torque Off circuit (STO) is arranged to cause the electric motor (MT) to stop generating torque in case at least one out of at least two conditions is detected. The circuit (STO) is based on connection of first and second electric inputs (II, 12) arranged for connection to respective first and second external electric switches (SW1, SW2). A pulse generator (PG) connects to the second electric input (12) and generates an oscillating electric output voltage when powered from the second electric input (2). A modulator (MOD) generates an electric output signal being a modulated version of an electric voltage at the first input (II) at a rate defined by the pulse generator (PG) controlled by the second input (12). The output from the modulator (MOD) is applied to an optocoupler (OPT) which generates an electrically isolated output which is applied to two logic comparator blocks (Bl, B2). These blocks (Bl, B2) serve to drive respective high and low gate driver parts of the motor drive (MD) only in case both of the first and second pulse detection output indicate that a pulse signal is detected by both of the first and second pulse detectors (PD1, PD2). This provides a compact safety function, e.g. for integration into the housing of an electric motor along with its motor drive. Still, the circuit (STO) is compliant with EN ISO 13849-1:2015, PL e category 3 and IEC 61800-5-2:2016 SIL 3.
Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms "comprising" or "comprises" do not exclude other possible elements or steps. The mentioning of references such as "a" or "an" etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.

Claims

1. An electric Safe Torque Off circuit (STO) arranged for connection to a motor drive (MD) of an electric motor (MT), wherein the Safe Torque Off circuit (STO) is arranged to cause the electric motor (MT) to stop generating torque in case at least one out of at least two conditions is detected, the Safe Torque Off circuit (STO) comprising
- a first and second electric inputs (II, 12) arranged for connection to respective first and second external electric switches or contacts (SW1, SW2),
- a pulse generator (PG) connected to the second electric input (12) and being arranged to generate an oscillating electric output voltage at an output when powered from the second electric input (12),
- a modulator (MOD) connected to the first electric input (II) and the output of the pulse generator (PG), wherein the modulator (MOD) is arranged to generate an electric output signal being a modulated version of an electric voltage at the first electric input (II) at a rate defined by the pulse generator controlled by the second electric input (12),
- an electric isolator component (OPT), such as an optocoupler, connected to receive the electric output signal from the modulator (MOD) and being arranged to generate an electric output signal accordingly, wherein the electric output signal is electrically isolated from the electric output signal from the modulator (MOD).
2. The electric Safe Torque Off circuit (STO) according to claim 1, wherein the Safe Torque Off circuit (STO) is arranged for connection to the motor drive (MD) to cause the electric motor (MT) to stop generating torque in case of failure of a single component of the electric Safe Torque Off circuit (STO).
3. The electric Safe Torque Off circuit (STO) according to claim 1 or 2, wherein the Safe Torque Off circuit (STO) has only one single electric isolator component (OPT) connected between the first and second electric inputs (II, 12) and an electric output arranged for connection to the motor drive (MD).
4. The electric Safe Torque Off circuit (STO) according to any of the preceding claims, being arranged to cause the electric motor (MT) to stop generating torque in case of failure of a single component by use of one single electric isolator component (OPT).
5. The electric Safe Torque Off circuit (STO) according to any of the preceding claims, wherein the output of the electric isolator component (OPT) is applied for deriving control signals for controlling the motor drive (MD) to cause the electric motor (MT) to stop generating torque in case of failure of a single component.
6. The electric Safe Torque Off circuit (STO) according to claim 5, wherein the output of the electric isolator component (OPT) is applied for controlling respective high and low gate driver outputs (LI, L2, L3, Hl, H2, H3) accordingly for driving respective high and low gate driver parts of the motor drive (MD).
7. The electric Safe Tourque Off circuit (STO) according to any of the preceding claims, further comprising
- first and second logic comparator blocks (Bl, B2) both being arranged to receive said electric output signal from the electric isolator component (OPT) and to provide respective first and second logic outputs (01, 02) accordingly.
8. The electric Safe Tourque Off circuit (STO) according to claim 7, wherein each of the first and second logic comparator blocks (Bl, B2) comprises a pulse detector (PD1, PD2) connected to receive said electric output signal from the electric isolator component (OPT), and wherein the first and second logic comparator blocks (Bl, B2) are arranged to generate the respective first and second logic outputs (01, 02) in accordance with outputs of the respective pulse detectors (PD1, PD2).
9. The electric Safe Tourque Off circuit (STO) according to claim 8, wherein the first and second logic comparator blocks (Bl, B2) comprise respective first and second interconnected logic comparators (LI, L2) arranged to receive respective first and second pulse detection outputs from the respective pulse detectors (PD1, PD2).
10. The electric Safe Tourque Off circuit (STO) according to any of claims 7-9, wherein the first and second logic comparator blocks (Bl, B2) are arranged to receive the respective first and second logic outputs (01, 02) and gate respective high and low gate driver outputs (LI, L2, L3, Hl, H2, H3) accordingly for driving respective high and low gate driver parts of the motor drive (MD).
11. The electric Safe Torque Off circuit (STO) according to claim 10, wherein the first and second logic comparator blocks (Bl, B2) are arranged to drive both of the high and low gate driver parts of the motor (MD) drive only in case both of the first and second pulse detection outputs indicate that a pulse signal is detected by both of the first and second pulse detectors (PD1, PD2).
12. The electric Safe Tourque Off circuit (STO) according to claim 10 or 11, comprising respective first and second logic gates (LG1, LG2) arranged to compare the respective first and second logic outputs (01, 02) with respective first and second gate driver signals to the motor drive (MD) and to generate respective high and low gate driver outputs (LI, L2, L3, Hl, H2, H3) accordingly for driving respective high and low gate driver parts of the motor drive (MD).
13. The electric Safe Tourque Off circuit (STO) according to any of the preceding claims, wherein the pulse generator (PG) is arranged to generate an output voltage switching between two levels, such as the pulse generator (PG) being arranged to generate an output voltage switching between a DC voltage (DCV) and electrical ground, such as a DC voltage (DCV) of 10-50 V.
14. A method for causing an electric motor to stop generating torque in case at least one out of at least two conditions is detected, the method comprising - sensing (S_U_I2) electric signals at first and second electric inputs connected to respective first and second external electric switches or contacts,
- generating (G_OSC_V) an oscillating electric output voltage at an output of a pulse generator when powered from the second electric input,
- generating (G_MOD) an electric signal being a modulated version of an electric voltage at the first electric input and an output of the pulse generator, and
- generating (G_EI) an electrically isolated signal corresponding to said electric signal being a modulated version of said electric voltage at the first electric input and said output of the pulse generator by means of an electrical isolator component, such as an optocoupler.
15. The method according to claim 14, comprising applying an output from only one electric isolator component to inputs of both of first and second logic blocks (Bl, B2).
16. The method according to claim 14 or 15, comprising controlling both a high and a low gate driver parts of the motor drive (MD) in response to an output from only one electric isolator component (OPT).
17. The method according to any of claims 14-16, comprising applying the electrically isolated signal to first and second logic blocks (Bl, B2) having outputs connected to the motor drive (MD) so as to cause the electric motor (MT) to stop generating torque in case it is detected by any one of the first and second logic blocks (Bl, B2) that either the electrically isolated signal is not present or that the electrically isolated signal represents a state where at least one of the first and second external electric switches or contacts indicates a fault state.
18. The method according to claim 17, comprising controlling respective high and low gate driver outputs (LI, L2, L3, Hl, H2, H3) for driving respective high and low gate driver parts of the motor drive (MD) in response to outputs from the first and second logic blocks (Bl, B2).
19. A system comprising
- an electric motor arranged to rotate a shaft,
- a motor drive connected to the electric motor and being arranged for driving the electric motor by means of high and low set of gate drivers controlled by respective high and low gate driver signals, and
- the Safe Torque Off circuit according to any of claims 1-13 connected to the motor drive.
EP23833317.3A 2022-12-15 2023-12-13 Compact safe torque off circuit for electric motor Pending EP4635070A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DKPA202270618 2022-12-15
PCT/EP2023/085496 WO2024126544A1 (en) 2022-12-15 2023-12-13 Compact safe torque off circuit for electric motor

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EP4635070A1 true EP4635070A1 (en) 2025-10-22

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EP23833317.3A Pending EP4635070A1 (en) 2022-12-15 2023-12-13 Compact safe torque off circuit for electric motor

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EP (1) EP4635070A1 (en)
CN (1) CN120476542A (en)
WO (1) WO2024126544A1 (en)

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP3179625A1 (en) * 2015-12-07 2017-06-14 ABB Technology Oy A method and apparatus for testing safe torque off circuitry in electric drives
CN207884588U (en) * 2018-01-02 2018-09-18 浙江海利普电子科技有限公司 Safe torque breaking circuit

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