Method and apparatus for detecting breaks in power lines of a servo motor

Abstract

This system quickly detects disconnections in the power lines connecting a motor control device (which servo-controls a motor) and the motor itself, while suppressing the occurrence of false detections. [Solution] A combination determination logic is provided that determines whether or not there is a break in the power line based on the combination of indicators, by obtaining a binary or ternary index for each of a plurality of items selected from the command value and the state value obtained for the motor. The combination determination logic includes, for example, an in-range comparator 41, selectors 42-46, AND circuits 47-50, sign inconsistency determination devices 51, 52, and OR circuits 53, 54.

Description

Technical Field

[0001] The present invention relates to a method and an apparatus for detecting disconnection of a power line in a servo motor used for driving an industrial robot (hereinafter referred to as a robot).

Background Art

[0002] Each axis of the robot is driven by a servo motor based on a command input to the robot control device. Each axis of the robot has an axis on which gravity does not act and an axis on which gravity acts. Here, the axis on which gravity does not act is, for example, an axis used only for moving a workpiece in a horizontal plane, and is an axis on which rotation due to gravity does not occur in a state where no driving force is applied by a motor connected to that axis. On the other hand, the axis on which gravity acts is, for example, an axis used for moving a workpiece in the vertical direction, and is an axis on which torque generated by a motor must be applied to prevent that axis from rotating due to gravity. The wiring for supplying the electric power for driving the servo motor from the robot control device or the motor drive device to the servo motor is called a power line.

[0003] When a robot is started, the robot control unit begins controlling each servo motor, and the mechanical brakes on each axis are released. If there is a break in the power line connected to a servo motor, that servo motor will not be driven even if control by the robot control unit begins, and therefore no torque will be generated. If an axis is not subject to gravity, a break in the power line connected to the servo motor on that axis will simply prevent the axis from moving. However, if there is a break in the power line connected to the servo motor on an axis that is subject to gravity, the brake will be released when servo control begins, causing the axis to move at a speed corresponding to the acceleration due to gravity and friction, which in many cases will result in the robot's arm or hand falling. When such an abnormality occurs, it is necessary to detect the abnormality and activate the brakes. If the brakes are activated only after detecting that a fall has actually occurred, there will be a delay between the detection of the abnormality and the stopping of the robot, increasing the braking distance and potentially causing damage to the fallen object. When a power line is broken, the dynamic brake by the motor will also not operate, so the braking distance tends to be longer. Therefore, early detection of power line breaks is required. Power lines can break during robot operation, and in such cases, early detection of power line breakage is desirable. Similarly, in equipment other than robots driven by servo motors, if gravity acts on the axis driven by the servo motor, falls and other incidents can occur, so early detection of power line breakage connected to the servo motor is required. In the case of a three-phase motor, if one of the three power lines breaks, current will flow through the other two, making it difficult to determine whether a break has occurred simply by detecting the motor current.

[0004] Patent Document 1 discloses a method for detecting a break in a power line when, for example, a servo motor is an AC motor, the current command value for the motor in any phase is greater than or equal to a predetermined value, and the actual detected motor current value is less than or equal to a predetermined value. Patent Document 2 discloses a method for detecting a break in a power line in an AC servo motor controlled based on a torque command, in which the current flowing through the motor is detected, the torque current component is extracted, and it is determined that the power line is broken when the difference between the torque command and the torque current component exceeds a set value. Patent Document 3 discloses a method for calculating an estimated torque value based on the motor current and voltage command value in an electric vehicle driven by multiple induction motors, and detecting miswiring of induction motors, etc., based on the calculated estimated torque value and torque command value. Patent Document 4 discloses a method for detecting a state quantity representing the operating state of the robot during program execution, issuing an alarm when the state quantity exceeds a threshold, and graphically displaying the location and frequency of alarm occurrences in the program, in order to facilitate the identification of the location of a break in a power line when a robot is controlled based on a program. Furthermore, the technology described in Patent Document 4 attempts to identify the location of a power line failure based on statistical trends, and is not intended to immediately detect a power line break when it occurs. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2008-141928 [Patent Document 2] Japanese Patent Publication No. 2004-320945 [Patent Document 3] International Publication No. 2019 / 130564 [Patent Document 4] Japanese Patent Publication No. 2019-916 [Overview of the project] [Problems that the invention aims to solve]

[0006] The technologies disclosed in Patent Documents 1 to 3 attempt to detect malfunctions such as broken power lines in a servo motor based on a specific command value for the servo motor and a value obtained by actual measurement on the motor side corresponding to that command value. However, with these technologies, depending on the content of the command to the motor, it may not be possible to quickly detect a broken power line in the motor. Furthermore, if thresholds or set values ​​are changed in an attempt to shorten the time required to detect a broken line, false detections may increase. For example, in the technology described in Patent Document 1, if a broken power line occurs and the motor stops generating torque when the current command value calculated based on the position command to the motor is originally small, the current command value will not increase unless the deviation from the position command becomes large, so it will take time to detect the broken line. Also, in the technology described in Patent Document 1, false detections may increase depending on the setting of the predetermined values ​​used for detection. Furthermore, tuning thresholds and set values ​​takes a lot of time, and if the number of values ​​to be set increases, the amount of work required for tuning will also increase accordingly.

[0007] The object of the present invention is to provide a method and apparatus that can quickly detect a break in a power line in a servo motor while suppressing the occurrence of false detections. [Means for solving the problem]

[0008] According to one aspect of the present invention, a method for detecting a break in a power line connected to a motor in a system that servo-controls a motor based on a command value involves determining a binary or ternary index for each of a plurality of items selected from the command value and the status value obtained for the motor, and detecting a break in the power line based on a combination of these indices.

[0009] According to another aspect of the present invention, a detection device for detecting a break in a power line connecting a motor control device and a motor in a system that includes a motor control device for servo-controlling a motor based on a command value includes a combination determination logic that determines a binary or ternary index for each of a plurality of items selected from the command value and the status value obtained with respect to the motor, and determines whether or not there is a break in the power line based on the combination of the indexes. [Effects of the Invention]

[0010] According to the present invention, it becomes possible to quickly detect a break in a power line in a servo motor while suppressing the occurrence of false detections. [Brief explanation of the drawing]

[0011] [Figure 1] This block diagram shows the configuration of a motor system to which one form of a wire break detection method is applied. [Figure 2] This is a block diagram illustrating the logical configuration of the wire break detection unit. [Modes for carrying out the invention]

[0012] Next, embodiments for carrying out the present invention will be described with reference to the drawings. Figure 1 is a block diagram showing the configuration of a motor system to which a wire break detection method according to one embodiment of the present invention is applied. The illustrated motor system receives AC power from an AC power source 10, and each of the multiple motors 30 is driven based on a command input from an external source (at least one of a position command and a speed command). The multiple motors 30 include motors 30 that drive axes not acted upon by gravity and motors 30 that drive axes acted upon by gravity. A motor control device 20 is provided for controlling the motors 30 based on the commands. An encoder 31 for detecting the position of the motor 30 is attached to the output shaft of each motor 30, and data indicating the position detected by the encoder 31 is fed back to the motor control device 20. If the motors 30 are motors that drive each axis of a robot, then the motor system described here is a robot system, and the motor control device 20 is a robot control device or robot controller that controls the robot.

[0013] There are various ways in which the motor control device 20 controls each motor 30, and the wire break detection method according to the present invention can detect a wire break in the power line 32 of the motor 30 regardless of which control mode is employed. The motor 30 may be an AC motor or a DC motor. Below, assuming that each motor 30 is a three-phase synchronous motor (or a three-phase induction motor), wire break detection will be described when the motor 30 is controlled by vector control or the like.

[0014] The motor control device 20 includes a full-wave rectifier circuit 21 that rectifies AC power received from an AC power source, and an inverter circuit 22 provided for each motor 30 that generates three-phase AC power supplied from the full-wave rectifier circuit 21 to drive the corresponding motor 30. The voltage of the DC power output by the full-wave rectifier circuit 21 is called the main circuit power supply voltage. The u-phase, v-phase, and w-phase outputs of the inverter circuit 22 are connected to the motors 30 via power lines 32 for each phase. Current sensors 23 and 24 are provided on the u-phase and v-phase power lines 32, respectively. Furthermore, the motor control device 20 includes a control calculation unit 26 provided in common for multiple motors 30, a wire break detection unit 28, and a current control unit 27 provided for each motor 30 that drives the switching elements in the inverter circuit 22. External position commands and speed commands are input to the motor control device 20 in the control calculation unit 26. Based on the input command values ​​such as position commands and speed commands, and the position data input from the encoder 31 attached to each motor 30, the control calculation unit 26 outputs a current command (for example, a d-axis current command and a q-axis current command) for each motor 30 to drive that motor 30. The control calculation unit 26 calculates command values ​​such as voltage commands and torque commands, also called internal command values, for the control of the motors 30. Current commands are also classified as true internal command values. The current command for each motor 30 is input to the current control unit 27 corresponding to that motor 30. The current control unit 27 receives the detected position value of the motor 30 from the encoder 31 and the detected current values ​​of each phase of the motor 30 from the current sensors 23 and 24. The current control unit 27 calculates the electrical angle of the motor 30 from the position of the motor 30, and drives the switching elements in the inverter circuit 22 based on the current values ​​of each phase and the input current command, thereby controlling the three-phase output from the inverter circuit 22.

[0015] Incidentally, the inverter circuit 22 and the motor 30 have rated values ​​such as rated power, and regardless of the voltage command or current command calculated by the control calculation unit 26, the motor 30 cannot be driven beyond these rated values. When the motor 30 rotates, a back electromotive force is generated in the motor 30, and if this exceeds the main circuit power supply voltage, current cannot flow from the inverter circuit 22 to the motor 30, regardless of the voltage command or current command related to the motor 30. These conditions can be described as the output of the motor control device 20 being saturated or limited with respect to the motor 30. Such saturation or limitation is detected by the control calculation unit 26.

[0016] The wire break detection unit 28 detects the occurrence of wire breaks in the power lines 32 that connect each of the multiple motors 30 connected to the motor control device 20, for example, a power line 32 provided for each motor 30. Previously, the presence or absence of a wire break was determined by comparing a single state quantity obtained for the motor with a threshold value. However, setting the threshold value to detect wire breaks more quickly resulted in many false detections, and setting the threshold value to suppress false detections resulted in a longer time until wire break detection. In contrast, in this embodiment, when servo-controlling the motor 30 based on a command value, binary or ternary indicators are obtained for each of several items related to the command value and the state value obtained for the motor 30, and wire breaks in the power lines are detected based on the combination of the obtained indicators. The command value includes both command values ​​given to the motor control device 20 from the outside and command values ​​generated internally by the motor control device 20. Command values ​​that can be used in this embodiment include, for example, position command values, speed command values, torque command values, current command values, and voltage command values. Examples of status values ​​obtained regarding the motor include the position measured by the encoder 31 (position feedback value) and the speed calculated from it (speed feedback value), the duty cycle of the PWM (pulse width modulation) in the inverter circuit 22, and whether or not saturation or limitation occurs in the motor 30.

[0017] If there is no break in the power line 32 and the motor 30 is operating normally, the command values ​​and state values ​​obtained for the motor 30 will generally exhibit a fixed behavior depending on the control mode of the motor 30. Therefore, by treating each of the multiple command values ​​and state values ​​as a binary index or a ternary index including 0, and then checking them using a combination condition with an AND (logical conjunction) condition, it is possible to determine whether those command values ​​and state values ​​are behaving as expected, and the presence or absence of an abnormality, specifically the presence or absence of a break in the power line 32, can be detected quickly. It is preferable to define the index for each item in a way that eliminates arbitrariness in threshold setting as much as possible. Therefore, as indexes, binary indexes indicating whether a value exists or not, binary indexes indicating whether a value is 0 or not, binary indexes indicating whether a value is positive or negative, ternary indexes indicating whether a value is positive, 0 or negative, and indexes indicating whether or not saturation or limitation has occurred with respect to the command value can be used. When using a ternary index, being non-zero is equivalent to being positive or negative. In this embodiment, it is preferable to use three or more binary or ternary indexes to detect the presence or absence of a break in the power line.

[0018] Considering the effects of noise and other factors, especially with values ​​based on actual measurements, it is necessary to consider a value as 0 if it falls within a certain range that includes 0, even if it is not strictly 0. Therefore, strictly speaking, a threshold is required to determine whether a value is 0 or not, but in this embodiment, an arbitrarily set threshold is not used to determine binary or ternary indicators. Instead, in this embodiment, a threshold may be set for the duration that the combination of conditions for determining a wire break persists, and a wire break may be determined to have occurred when the duration of this combination of conditions exceeds the threshold. The threshold related to duration is used to achieve the desired detection sensitivity while preventing an increase in false detections due to overshoot, noise, etc.

[0019] Hereinafter, specific examples will be described. As a plurality of indicators, for example, a three-valued indicator indicating whether the speed command value is positive, 0, or negative, a three-valued indicator indicating whether the speed feedback value is positive, 0, or negative, a two-valued indicator indicating whether saturation has occurred with respect to the voltage command calculated inside the control arithmetic unit 26, and a two-valued indicator indicating whether the torque command value is positive or negative are used. These command values and state values are input from the control arithmetic unit 26 to the disconnection detection unit 28. Regarding the state value, as shown by the broken line in FIG. 1, the position feedback value for each motor 30 is directly input from the encoder 31 connected to that motor 30 to the control arithmetic unit 26 corresponding to that motor 30, and the speed feedback value may be calculated from the position feedback value inside the disconnection detection unit 28. When the combination shown in Table 1 is established for these indicators, the disconnection detection unit 28 detects that a disconnection has occurred in the power line 32 and outputs the detection result to the outside. In the table, "not used" indicates that the corresponding indicator is not used.

[0020]

Table 1

[0021] Anomaly 1 corresponds to a state where, despite a speed command being input to move motor 30, the speed is 0 and the motor is not moving, and saturation occurs in the voltage command output to try to operate motor 30, which has been detected as not moving. In this state, since motor 30, which drives an axis not acted upon by gravity, is not being driven, it can be evaluated that a break has occurred in the power line 32 connected to motor 30. Anomalies 2 and 3 are simply different cases depending on whether the speed command value is positive or negative, i.e., whether the rotation direction of motor 30 is positive or negative, but they essentially indicate the same state. In the states indicated by Anomalies 2 and 3, although the rotation direction indicated by the externally input speed command value and the rotation direction intended by the control calculation unit 26 are the same, the actual rotation direction of motor 30 is in the opposite direction, and saturation occurs in the voltage command that tries to rotate motor 30 in the commanded direction. Therefore, in this state, when attempting to move the axis acting on gravity in the upward direction, the motor 30 on that axis is not driven, causing it to fall. Even if a voltage command is output to suppress this fall, saturation occurs, and it can be determined that a break has occurred in the power line 32 connected to the motor 30.

[0022] In abnormality 4, although the speed command value is zero, indicating the intention is to keep the shaft to which the motor 30 is connected still, the speed feedback value is not zero, meaning the shaft is actually moving, and saturation is occurring with respect to the voltage command output to stop the rotation of the shaft. In this state, even though the motor 30 is attempting to generate torque to keep the shaft, which is under the influence of gravity, stationary, no torque is actually being generated, the voltage command for generating torque is saturated, and it can be concluded that a break has occurred in the power line 32 connected to the motor 30 on that shaft.

[0023] Figure 2 illustrates the configuration for realizing a wire break detection unit 28 that detects wire breaks in the power line 32 based on the combination of indicators shown in Table 1, and shows the logical configuration for detecting a wire break in one motor 30 of the wire break detection unit 28. A wire break detection unit 28 with the logical configuration shown in Figure 2 is provided for each of the multiple motors 30. The wire break detection unit 28 is composed of a combination determination logic that determines whether or not the combination conditions shown in Table 1 are met, and can be configured as hardware by combining discrete components based on the logical configuration shown in Figure 2, but can also be realized by having a microprocessor or microcomputer execute software that realizes operation equivalent to the logical configuration shown in Figure 2. In the motor control device 20, the control calculation unit 26 and the current control unit 27 are also generally composed of software, so the software that realizes the wire break detection unit 28 may be incorporated into the software that realizes the control calculation unit 26 and the current control unit 27.

[0024] Assuming that a position command value is input to the control calculation unit 26 and the position of the motor 30 is fed back from the encoder 31, the speed command value is the difference between the previously input position command value and the currently input position command value, and the speed feedback value is the difference between the previously input position feedback value and the currently input position feedback value. The wire break detection unit 28 includes an in-range comparator 41, selectors 42 to 46, AND (logical conjunction) circuits 47 to 50, sign mismatch detectors 51 and 52, OR (logical disjunction) circuits 53 and 54, and an on-delay circuit 55.

[0025] The in-range comparator 41 is provided to determine whether the speed feedback value can be considered substantially zero. It outputs true if the rotational speed of the motor 30 is within a predetermined value that can be considered as the motor 30 not rotating, and false otherwise. The selector 42 outputs false if the speed feedback value is 0, and true if it is not 0. The selector 43 outputs true when saturation occurs with respect to the voltage command, and false otherwise. The AND (logical conjunction) circuit 47 calculates the logical OR of the output value of the in-range comparator 41 and the output value of the selector 43 and outputs it. The selector 44 outputs false if the speed command value is 0, and outputs the output of the AND circuit 47 as is if it is not 0. As a result, the output of the selector 44 becomes true when the above abnormality 1 condition is met, and false otherwise. Similarly, the AND circuit 48 calculates the logical OR of the output value of the selector 42 and the output value of the selector 43 and outputs it. The selector 45 outputs the output of the AND circuit 48 as is if the speed command value is 0, and outputs false if the speed command value is not 0. The output of selector 45 is true when the above abnormality 4 condition is met, and false otherwise. The OR (logical disjunction) circuit 53 calculates the logical OR of the output of selector 44 and the output of selector 45 and outputs the result. Therefore, the output of OR circuit 53 is true when the abnormality 1 or abnormality 4 condition is met, that is, when a break in the wire is detected, such as when the motor 30 is started.

[0026] The sign mismatch detectors 51 and 52 each have two inputs and output true if the signs of the two input values ​​are different, and false if they are the same. If either input or both inputs are 0, they output false. The sign mismatch detector 51 receives the speed command value and the speed feedback value as inputs, and the sign mismatch detector 52 receives the speed feedback value and the torque command value as inputs. The AND circuit 49 calculates the logical AND of the output of the sign mismatch detector 51 and the output of the sign mismatch detector 52 and outputs the result. The selector 46 outputs true when saturation occurs with respect to the voltage command, and false otherwise. The AND circuit 50 calculates the logical AND of the output of the selector 46 and the output of the AND circuit 49 and outputs the result. Therefore, the output of the AND circuit 50 becomes true when the conditions for abnormality 2 or abnormality 3 are met, that is, when a break in the wire is detected when the motor 30 is rotating in a direction of rotation against gravity on the axis on which gravity acts. Alternatively, the selector 46 may be omitted, and instead, the output of the selector 43 may be input to the AND circuit 50.

[0027] The OR circuit 54 calculates the logical OR of the output of the OR circuit 53 and the output of the AND circuit 50 and outputs the result. The output of the OR circuit 54 is true when any of abnormalities 1 to 4 are true, and false otherwise. The output of the OR circuit 54 is input to the ON delay circuit 55. The ON delay circuit 55 outputs the output of the OR circuit 54 with a delay of a preset ON delay time, but is reset if the output of the OR circuit 54 becomes false during that ON delay time. As a result, the output of the ON delay circuit 55 is true only when the output of the OR circuit 54 remains true for a period longer than the ON delay time. If the output of the ON delay circuit 55 is true, it indicates a broken wire abnormality state, and is output from the broken wire detection unit 28 as a detection result.

[0028] The above describes an example of a configuration for carrying out the present invention, but the above technology can take the following configuration.

[0029] (1) A method for detecting a break in a power line connected to a motor in a system that servo-controls a motor based on a command value, A binary or ternary index is determined for each of the multiple items selected from the command value and the state value obtained for the motor. A detection method for detecting a break in a power line based on a combination of the aforementioned indicators.

[0030] (2) The binary index includes at least one of the following: an index indicating whether a value exists or does not exist, an index indicating whether a value is zero or non-zero, an index indicating whether a value is positive or negative, and an index indicating whether saturation or limitation has occurred. The detection method described in (1), wherein the three-value index is an index that indicates whether the value is positive, zero, or negative.

[0031] (3) The detection method according to (1) or (2), wherein a break in the power line is determined to have occurred when the combination of indicators continues to satisfy predetermined conditions for a first period of time.

[0032] (4) The detection method according to (3), wherein the detection sensitivity is adjusted by adjusting the length of the first time.

[0033] (5) The detection method according to any one of (1)-(4), wherein with respect to the motor, it is determined that a break has occurred in the power line when saturation occurs with respect to the voltage command for the motor and the speed command value is zero and the speed feedback value is not zero, when saturation occurs with respect to the voltage command and the speed command value and the torque command value are of the same sign and the speed command value and the speed feedback value are of different signs.

[0034] (6) A detection device for detecting a break in a power line connecting a motor control device and a motor in a system that includes a motor control device that servo-controls a motor based on a command value, A detection device comprising a combination determination logic that determines whether or not there is a break in the power line based on a combination of the command value and a state value obtained with respect to the motor, for each of a plurality of items selected from the command value and the state value obtained with respect to the motor, and for each of the binary or ternary indicators.

[0035] (7) The binary index includes at least one of the following: an index indicating whether a value exists or does not exist; an index indicating whether a value is zero or non-zero; an index indicating whether a value is positive or negative; and an index indicating whether saturation or limitation has occurred. The detection device described in (6), wherein the three-value index is an index that indicates whether the value is positive, zero, or negative.

[0036] (8) The detection device according to (6) or (7), further comprising an on-delay circuit at the output of the combination determination logic, which notifies the outside that a break has occurred in the power line when the state in which the combination determination logic has determined that there is a break in the power line continues for a first period of time.

[0037] (9) The detection device according to (8), wherein the first time is adjustable for adjusting the sensitivity of the detection.

[0038] (10) The detection device according to any one of (6)-(9), wherein the combination determination logic is configured to detect, with respect to the motor, at least one of the following: saturation with respect to the voltage command for the motor occurs, the speed command value is zero and the speed feedback value is not zero; saturation with respect to the voltage command occurs, the speed command value and the torque command value have the same sign and the speed command value and the speed feedback value have different signs.

[0039] According to the configurations of (1) and (6), by using multiple binary or ternary indicators, it is possible to quickly determine whether the system is behaving as expected, thereby enabling rapid detection of breaks in power lines while suppressing false positives.

[0040] According to the configuration of (2) and (7), the arbitrariness in threshold setting is eliminated as much as possible when determining the index, so that false detections and rapid detection of disconnections can be achieved at the same time, while preventing a decrease in work efficiency that occurs when tuning multiple thresholds.

[0041] The configurations in (3) and (8) eliminate the possibility of false detections caused by noise, overshoot, etc., and in particular, the configurations in (4) and (9) allow for adjustment of detection sensitivity by adjusting only a single parameter, the first time.

[0042] According to the configurations of (5) and (10), a suitable combination of indicators for detecting breaks in power lines can be obtained, enabling faster detection of breaks in power lines while further suppressing false detections. [Explanation of symbols]

[0043] 10...AC power supply, 20...Motor control device, 21...Full-wave rectifier circuit, 22...Inverter circuit (INV), 23,24...Current sensor, 26...Control calculation unit, 27...Current control unit, 28...Wire break detection unit, 30...Motor, 31...Encoder, 32...Power line, 41...In-range comparator, 42~46...Selector, 47~50...AND circuit, 51,52...Sign mismatch detector, 53,54...OR circuit, 55...On delay circuit.

Claims

1. A method for detecting a break in a power line connected to a motor in a system that servo-controls a motor based on a command value, A binary or ternary index is determined for each of the multiple items selected from the command value and the state value obtained for the motor. A detection method for detecting a break in a power line based on a combination of the aforementioned indicators.

2. The aforementioned binary indicator includes at least one of the following: an indicator indicating whether a value exists or does not exist; an indicator indicating whether a value is zero or non-zero; an indicator indicating whether a value is positive or negative; and an indicator indicating whether saturation or limitation has occurred. The detection method according to claim 1, wherein the three-value index is an index that indicates whether the value is positive, zero, or negative.

3. The detection method according to claim 1 or 2, wherein it is determined that a break has occurred in the power line when the combination of the indicators described above continues to satisfy predetermined conditions for a first period of time.

4. The detection method according to claim 3, wherein the detection sensitivity is adjusted by adjusting the length of the first time period.

5. The detection method according to claim 1 or 2, wherein with respect to the motor, it is determined that a break has occurred in the power line when saturation occurs with respect to the voltage command to the motor, the speed command value is zero and the speed feedback value is not zero; when saturation occurs with respect to the voltage command, the speed command value and the torque command value are of the same sign and the speed command value and the speed feedback value are of different signs.

6. A detection device for detecting a break in a power line connecting a motor control device and a motor in a system that includes a motor control device that servo-controls a motor based on a command value, A detection device comprising a combination determination logic that determines whether or not there is a break in the power line based on a combination of the command value and a state value obtained with respect to the motor, for each of a plurality of items selected from the command value and the state value obtained with respect to the motor, and for each of the binary or ternary indicators.

7. The aforementioned binary indicator includes at least one of the following: an indicator indicating whether a value exists or does not exist; an indicator indicating whether a value is zero or non-zero; an indicator indicating whether a value is positive or negative; and an indicator indicating whether saturation or limitation has occurred. The detection device according to claim 6, wherein the three-value index is an index that indicates whether the value is positive, zero, or negative.

8. The detection device according to claim 6 or 7, further comprising an on-delay circuit at the output of the combination determination logic, and notifying an external party that a break has occurred in the power line when the state in which the combination determination logic has determined that there is a break in the power line continues for a first period of time.

9. The detection device according to claim 8, wherein the first time is adjustable for adjusting the sensitivity of the detection.

10. The detection device according to claim 6 or 7, wherein the combination determination logic is configured to detect, with respect to the motor, at least one of the following: saturation with respect to the voltage command for the motor occurs, the speed command value is zero and the speed feedback value is not zero; saturation with respect to the voltage command occurs, the speed command value and the torque command value have the same sign and the speed command value and the speed feedback value have different signs.

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