Detection method and detection device

Abstract

The present invention addresses the problem of providing a detection method and a detection device that suppress the occurrence of erroneous detection and quickly detect disconnection of a power line connecting a motor control device for servo-controlling the motor and the motor. In the present invention, a combination determination logic is provided that obtains a binary index or a ternary index for each of a plurality of items selected from a command value and a state value obtained with respect to a motor, and determines the presence or absence of a power line break line on the basis of a combination of the indexes. The combination determination logic includes, for example, an in-range comparator (41), selectors (42-46), AND circuits (47-50), sign inconsistency determiners (51, 52), and OR circuits (53, 54).

Description

Technical Field

[0001] This invention relates to a method and apparatus for detecting broken power lines in servo motors used to drive industrial robots (hereinafter referred to as robots). Background Technology

[0002] Each axis of the robot is driven by servo motors based on commands input to the robot control unit. The robot's axes include axes where gravity does not affect movement and axes where gravity does affect movement. Here, axes where gravity does not affect movement are those used only for example, moving a workpiece in a horizontal plane; these axes will not rotate due to gravity unless a driving force generated by the motor connected to them is applied. On the other hand, axes where gravity affects movement are, for example, axes used to move a workpiece vertically; to prevent these axes from rotating due to gravity, a torque generated by the motor must be applied to them. The wiring that supplies power from the robot control unit or motor drive unit to the servo motors is called the power line.

[0003] When the robot starts, the robot control unit begins to control each servo motor and releases the mechanical brakes on each axis. If there is a break in the power line connected to the servo motor, the servo motor will not be driven, and therefore no torque will be generated, even if the robot control unit begins control. For axes where gravity does not play a role, even if the power line connected to the servo motor is broken, the axis will simply remain stationary. However, for axes where gravity plays a role, if the power line connected to the servo motor is broken, the brakes are released when servo control begins, causing the axis to move at a speed corresponding to gravitational acceleration and friction. In most cases, the robot's arm or hand may fall. When this anomaly occurs, it is necessary to detect the anomaly and initiate braking. In practice, if braking is initiated only after a fall is detected, there is a time delay between anomaly detection and robot stopping, increasing the braking distance and the risk of damage to fallen objects. When the power line is broken, dynamic braking by the motor is also not initiated, thus often increasing the braking distance. Therefore, the industry strives to detect power line breaks as early as possible. There are also instances where the power lines break during robot operation, and in such cases, early detection of the breakage is desirable. In machines other than those driven by servo motors, the same applies when gravity acts on the shaft driven by the servo motor; falls and other accidents can occur. Therefore, early detection of breaks in the power lines connected to the servo motor is crucial. In the case of a three-phase motor, even if one of the three power lines breaks, current will still flow in the other two, making it difficult to determine the presence of a breakage solely by detecting the motor current.

[0004] Patent Document 1 discloses the following: Assuming the servo motor is, for example, an AC motor, in a certain phase, when the current command value for the motor is determined to be above a specified value, and the actual detected motor current value is below the specified value, a break in the power line is detected. Patent Document 2 discloses the following: In a method for detecting a break in the power line of an AC servo motor based on torque command control, the current flowing in the motor is detected and the torque current component is extracted. When the difference between the torque command and the torque current component exceeds a set value, a break in the power line is determined. Patent Document 3 discloses the following: In an electric vehicle driven by multiple induction motors, a torque estimate is calculated based on the motor current and voltage command values. Based on the calculated torque estimate and torque command value, miswiring related to the induction motors is detected. Patent Document 4 discloses the following: In a program-controlled robot, to easily determine the location of a break in the power line, state variables representing the robot's operating state during program execution are detected. When the state variable exceeds a threshold, an alarm is issued, and the location and frequency of the alarm in the program are graphically displayed. Furthermore, the technology described in Patent Document 4 aims to determine the location of the fault in the power line based on statistical trends, rather than to detect the breakage immediately when the power line breaks.

[0005] [Existing Technical Documents]

[0006] [Patent Literature]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2008-141928

[0008] [Patent Document 2] Japanese Patent Application Publication No. 2004-320945

[0009] [Patent Document 3] International Publication No. 2019 / 130564

[0010] [Patent Document 4] Japanese Patent Application Publication No. 2019-916 Summary of the Invention

[0011] [The problem the invention aims to solve]

[0012] The technologies disclosed in Patent Documents 1 to 3 aim to detect faults 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 at the motor side corresponding to that command value. However, in these technologies, depending on the content of the command for the motor, there are situations where it is not possible to quickly detect broken power lines. Moreover, when trying to shorten the time required to detect a broken line by changing thresholds or setting values, false detections increase. For example, in the technology described in Patent Document 1, if the current command value calculated based on the position command for the motor is already small, and a broken power line occurs but the motor does not generate torque, the current command value will also be small if the deviation from the position command is small, thus the detection of the broken line will take time. Furthermore, in the technology described in Patent Document 1, the number of false detections increases depending on the setting of the prescribed values ​​used for detection. Consequently, adjusting thresholds or setting values ​​takes a lot of time, and if the number of values ​​to be set increases, the workload for adjustment also increases accordingly.

[0013] The purpose of this invention is to provide a method and apparatus that can suppress false detections and quickly detect broken power lines in a servo motor.

[0014] [Technical means to solve the problem]

[0015] According to an embodiment of the present invention, the method for detecting a broken wire in the power line connected to the motor in a system that performs servo control of the motor based on command values ​​is to calculate a binary or ternary index from multiple items selected from the command values ​​and the state values ​​obtained about the motor, and to detect the broken wire in the power line based on the combination of the indexes.

[0016] According to other embodiments of the present invention, a detection device for detecting the breakage of a power line connecting the motor control device and the motor in a system including a motor control device that performs servo control of the motor based on command values ​​has the following combined determination logic, which calculates a binary index or a tri-valued index for multiple items selected from the command value and the state value obtained about the motor, and determines the presence or absence of a breakage in the power line based on the combination of the indexes.

[0017] [The effects of the invention]

[0018] According to the present invention, false detections can be suppressed and broken power lines in servo motors can be detected quickly. Attached Figure Description

[0019] Figure 1 This is a block diagram illustrating the structure of a motor system for a wire breakage detection method according to one embodiment of the application.

[0020] Figure 2This is a block diagram illustrating the logic structure of the wire breakage detection unit.

[0021] Explanation of icon numbers

[0022] 10: AC power supply

[0023] 20: Motor control device

[0024] 21: Full-wave rectifier circuit

[0025] 22: Inverter circuit (INV)

[0026] 23, 24: Current sensor

[0027] 26: Control and Computation Department

[0028] 27: Current Control Section

[0029] 28: Wire Breakage Detection Department

[0030] 30: Motor

[0031] 31: Encoder

[0032] 32: Power Line

[0033] 41: Range comparator

[0034] 42-46: Selectors

[0035] 47-50: AND circuit

[0036] 51, 52: Sign Inconsistency Determiner

[0037] 53, 54: OR circuit

[0038] 55: Turn-on delay circuit Detailed Implementation

[0039] The embodiments for carrying out the present invention will then be described with reference to the accompanying drawings. Figure 1This is a block diagram illustrating the structure of a motor system for a wire breakage detection method according to an embodiment of the present invention. The illustrated motor system receives AC power from an AC power source 10 and drives multiple motors 30 based on externally input commands (at least one of position and speed commands). The multiple motors 30 include motors 30 that drive axes where gravity is not applied and motors 30 that drive axes where gravity is applied. A motor control device 20 is provided for command-based control of the motors 30. An encoder 31 is mounted on the output shaft of each motor 30 to detect the position of the motor 30, and data indicating the position detected by the encoder 31 is fed back to the motor control device 20. In the case where the motors 30 are motors driving the axes of a robot, the motor system described herein is referred to as a robot system, and the motor control device 20 is referred to as a robot control device or robot controller.

[0040] The motor control device 20 controls each motor 30 in various configurations. Based on the wire breakage detection method of the present invention, wire breakage in the power line 32 of the motor 30 can be detected in any of these control configurations. The motor 30 can be an AC motor or a DC motor. Hereinafter, assuming each motor 30 is a three-phase synchronous motor (or a three-phase induction motor), wire breakage detection will be described when the motor 30 is controlled by vector control or the like.

[0041] The motor control device 20 includes a full-wave rectifier circuit 21 that rectifies the AC power received from the AC power source, and a three-phase AC inverter circuit 22 installed in each motor 30 that receives DC power from the full-wave rectifier circuit 21 and generates DC power to drive the corresponding motor 30. The voltage of the DC power output from the full-wave rectifier circuit 21 is called the main circuit power supply voltage. The outputs of the u-phase, v-phase, and w-phase of the inverter circuit 22 are connected to the motor 30 via the power lines 32 of each phase. Current sensors 23 and 24 are respectively installed on the power lines 32 of the u-phase and v-phase. Furthermore, the motor control device 20 includes a control calculation unit 26, a wire break detection unit 28, which are common to the multiple motors 30, and a current control unit 27 installed in each motor 30 to drive the switching elements in the inverter circuit 22. Position or speed commands from the external motor control device 20 are input to the control calculation unit 26. Based on the input position or speed commands and position data input from the encoder 31 attached to each motor 30, the control calculation unit 26 outputs current commands (e.g., d-axis current commands and q-axis current commands) to drive each motor 30. In the control calculation unit 26, voltage commands, torque commands, and other command values, also known as internal command values, are calculated for motor 30 control. Current commands are also classified as internal command values. The current commands for each motor 30 are input to the current control unit 27 corresponding to that motor 30. For the current control unit 27, the detected position value of the motor 30 is input from the encoder 31, and the detected current values ​​of each phase of the motor 30 are input from the current sensors 23 and 24. The current control unit 27 calculates the electrical angle of the motor 30 based on the position of the motor 30, and drives the switching elements in the inverter circuit 22 based on the current value of each phase and the input current command, thereby controlling the three-phase output from the inverter circuit 22.

[0042] Furthermore, the inverter circuit 22 and the motor 30 have rated values ​​such as rated power. Regardless of the voltage or current command calculated in the control calculation unit 26, if these rated values ​​are exceeded, the motor 30 cannot be driven. If the motor 30 rotates, it generates a back electromotive force (EMF). If this back EMF exceeds the main circuit power supply voltage, current will not flow from the inverter circuit 22 to the motor 30, regardless of the voltage or current command associated with the motor 30. These states can be considered as output saturation or limitation states of the motor control device 20 for the motor 30. Such saturation or limitation is detected in the control calculation unit 26.

[0043] For the plurality of motors 30 connected to the motor control device 20, a wire breakage detection unit 28 is provided in each motor 30 to detect the occurrence of a wire breakage in the power line 32 connecting the motor 30 to the motor control device 20. Currently, the presence or absence of a wire breakage is determined by comparing a single state quantity obtained about the motor with a threshold value, but this leads to the following problems: if a threshold value is set to detect wire breakage more quickly, false detections increase; if a threshold value is set to suppress false detections, the time required to detect wire breakage increases. In this embodiment, when servo control of the motor 30 is performed based on a command value, binary or tri-valued indicators are obtained for each of the multiple items related to the command value and the state value obtained about the motor 30, and the wire breakage in the power line is detected based on the combination of the obtained indicators. The command value can be either a command value externally assigned to the motor control device 20 or a command value generated internally by the motor control device 20. Examples of command values ​​that can be used in this embodiment include position command values, speed command values, torque command values, current command values, and voltage command values. Examples of state values ​​obtained by the motor include, for example, the position (position feedback value) measured by the encoder 31 or the speed calculated therefrom (speed feedback value), the duty cycle of the pulse width modulation (PWM) in the inverter circuit 22, and whether saturation or limitation occurs in the motor 30.

[0044] If there is no break in the power line 32 and the motor 30 operates normally, the command value or the state value obtained about the motor 30 indicates a roughly determined action based on the control mode of the motor 30. Therefore, by setting multiple command values ​​or state values ​​as binary indicators or ternary indicators including 0, and confirming the combination conditions obtained using AND gate conditions, it is possible to determine whether an action that could have yielded these command values ​​or state values ​​has been performed, and thus quickly detect the presence or absence of anomalies, specifically the presence or absence of a break in the power line 32. The indicators for each item are preferably determined in a way that minimizes arbitrariness in the threshold setting. Therefore, as indicators, binary indicators indicating whether a value exists or does not exist, binary indicators indicating whether a value is 0 or not, binary indicators indicating whether a value is positive or negative, ternary indicators indicating whether a value is positive, 0, or negative, and indicators indicating whether the command value has saturated or been limited, etc., can be used. When using ternary indicators, non-zero is equivalent to positive or negative. In this embodiment, it is preferable to use three or more binary or ternary indicators to detect the presence or absence of a break in the power line.

[0045] Considering the effects of noise, especially in values ​​based on measured values, even if the value is not strictly zero, it should still be considered zero as long as it falls within a certain range including zero. Therefore, strictly speaking, a threshold is necessary to determine whether a value is zero. However, in this embodiment, to obtain binary or ternary indices, an arbitrarily set threshold is not used. Instead, in this embodiment, a threshold can be set for the duration of the combined conditions used to determine if a disconnection has occurred. If the duration of the combined conditions exceeds the threshold, a disconnection is determined to have occurred. The duration-related threshold is used to prevent an increase in false detections caused by overshoot or noise, and to set the detection sensitivity to the desired level.

[0046] The following is a specific example. As multiple indicators, for example, a three-value indicator indicating whether the speed command value is positive, 0, or negative; a three-value indicator indicating whether the speed feedback value is positive, 0, or negative; a two-value indicator indicating whether the voltage command calculated internally by the control calculation unit 26 has saturated; and a two-value indicator indicating whether the torque command value is positive or negative. These command values ​​or status values ​​are input from the control calculation unit 26 to the disconnection detection unit 28. Regarding status values, such as... Figure 1 As shown by the dashed line, the position feedback values ​​for each motor 30 can be directly input from the encoder 31 connected to the motor 30 to the control calculation unit 26 corresponding to that motor 30. The speed feedback value is calculated internally by the wire breakage detection unit 28 based on the position feedback values. When the combination of these indicators shown in Table 1 is met, the wire breakage detection unit 28 detects a wire break in the power line 32 and outputs the detection result to the outside. "Not used" in the table indicates that the corresponding indicator is not used.

[0047] [Table 1]

[0048]

[0049] Anomaly 1 corresponds to the following state: although a speed command to move motor 30 is input, the speed is 0, the motor does not move, and the voltage command output to operate the detected non-moving motor 30 saturates. This state is one in which the motor 30, which does not drive a shaft that does not act on gravity, is not being driven, and therefore can be assessed as a state where the power line 32 connected to the motor 30 is broken. Anomalies 2 and 3 are derived according to the sign of the speed command value, i.e., whether the rotation direction of the motor 30 is positive or negative, and essentially represent the same state. In the states represented by anomalies 2 and 3, although the rotation direction represented by the externally input speed command value is the same as the rotation direction intended by the control calculation unit 26, the actual rotation direction of the motor 30 is opposite, and the voltage command to rotate the motor 30 relative to the commanded direction saturates. Therefore, in the stated state, when the shaft is to be moved in the upward direction by gravity, it will fall because the motor 30 is not driving the shaft. Even if a voltage command is output to suppress the fall, it can be determined that saturation has occurred, and it can be assessed that the power line 32 connected to the motor 30 has broken.

[0050] In anomaly 4, the speed command value is zero. Therefore, although there is no intention to move the shaft connected to motor 30, the shaft will actually move because the speed feedback value is not zero, and the voltage command output to stop the shaft's rotation becomes saturated. The state is as follows: even if torque is to be generated in motor 30 to keep the shaft stationary due to gravity, no torque is actually generated, and the voltage command used to generate torque is saturated. This can be assessed as a break in the power line 32 connecting the shaft to motor 30.

[0051] Figure 2 The structure of the wire breakage detection unit 28, which implements the combined detection of power line 32 based on the indicators shown in Table 1, will be described. The logic structure for detecting wire breakage in one motor 30 using the wire breakage detection unit 28 will be shown. Separate units will be provided for multiple motors 30. Figure 2 The disconnection detection unit 28, as shown in the logic structure, includes combination determination logic that determines whether the combination conditions shown in Table 1 are true. It can also be configured based on... Figure 2 The logic structure shown represents hardware assembled from discrete components, which can also be implemented using a microprocessor or microcomputer. Figure 2 The logic structure shown is equivalent to the software that operates. In the motor control device 20, the control calculation unit 26 and the current control unit 27 usually also include software, so the software that implements the wire breakage detection unit 28 can also be incorporated into the software that implements the control calculation unit 26 and the current control unit 27.

[0052] If the encoder 31 provides feedback on the position of the motor 30, the speed command value is the difference between the previously input position command value and the current input position command value. The speed feedback value is the difference between the previously input position feedback value and the current input position feedback value. The disconnection detection unit 28 includes a range comparator 41, selectors 42 to 46, AND gate circuits 47 to 50, a sign inconsistency arbitrator 51, a sign inconsistency arbitrator 52, an OR gate circuit 53, an OR gate circuit 54, and an on-delay circuit 55.

[0053] The range comparator 41 is configured to determine whether the speed feedback value can be substantially considered zero. If the rotational speed of the motor 30 is within a specified value that can be considered as the motor 30 not rotating, it outputs true; otherwise, it outputs false. If the speed feedback value is 0, selector 42 outputs false; otherwise, it outputs true. Selector 43 outputs true when the voltage command has saturated and false when it has not. The AND gate circuit 47 calculates and outputs the logical sum of the output values ​​of the range comparator 41 and selector 43. If the speed command value is 0, selector 44 outputs false; otherwise, it directly outputs the output of the AND circuit 47. As a result, the output of selector 44 is true when the condition of exception 1 is met, and false otherwise. Similarly, the AND circuit 48 calculates and outputs the logical sum of the output values ​​of selector 42 and selector 43. If the speed command value is 0, selector 45 directly outputs the output of the AND circuit 48; otherwise, it outputs false. The output of selector 45 is true when condition 4 of exception is met, and false otherwise. The OR (or gate) circuit 53 calculates the logical sum of the outputs of selector 44 and selector 45 and outputs the result. Therefore, the output of OR circuit 53 is true when conditions 1 or 4 of exception are met, i.e. when a disconnection is detected, such as when motor 30 starts.

[0054] Both the sign inconsistency arbiter 51 and sign inconsistency arbiter 52 have two inputs. They output true if the two input values ​​have different signs, and false if they have the same sign. False is output when either or both inputs are 0. The sign inconsistency arbiter 51 receives the speed command value and the speed feedback value, while the sign inconsistency arbiter 52 receives the speed feedback value and the torque command value. The AND circuit 49 calculates and outputs the logical product of the outputs of sign inconsistency arbiter 51 and sign inconsistency arbiter 52. The selector 46 outputs true when the voltage command saturates, and false when saturation does not occur. The AND circuit 50 calculates and outputs the logical product of the outputs of selector 46 and AND circuit 49. Therefore, the output of AND circuit 50 becomes true when the conditions of exception 2 or exception 3 are met, i.e., when the motor 30 rotates in the direction opposite to gravity in the shaft where gravity is applied, a broken wire is detected. Alternatively, selector 46 can be omitted, and the output of selector 43 can be input to AND circuit 50 instead.

[0055] OR circuit 54 calculates and outputs the logical sum of the outputs of OR circuit 53 and AND circuit 50. The output of OR circuit 54 is true when any of exceptions 1 to 4 is true, otherwise it is false. The output of OR circuit 54 is input to turn-on delay circuit 55. Turn-on delay circuit 55 outputs the output of OR circuit 54 after a preset turn-on delay time, but if the output of OR circuit 54 is false during the turn-on delay time, it is reset. As a result, the output of turn-on delay circuit 55 is also true only when the output of OR circuit 54 is true for a period longer than the turn-on delay time. If the output of turn-on delay circuit 55 is true, the output of turn-on delay circuit 55 indicates a disconnection fault state and is output from disconnection detection unit 28 as a detection result.

[0056] The above has described one example of a structure used to implement the present invention, but the technology may take the form of the following structures.

[0057] (1) A detection method for detecting a break in the power line connected to the motor in a system that performs servo control of the motor based on command values.

[0058] For each of the multiple items selected from the command value and the state values ​​obtained about the motor, a binary or ternary index is calculated.

[0059] The broken wires in the power line are detected based on a combination of the aforementioned indicators.

[0060] (2) The detection method as described in (1), wherein 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.

[0061] The three-value index represents whether the value is positive, 0, or negative.

[0062] (3) The detection method as described in (1) or (2), wherein when the combination of the indicators satisfies the specified conditions for a first time, it is determined that a break has occurred in the power line.

[0063] (4) The detection method as described in (3), wherein the detection sensitivity is adjusted by adjusting the length of the first time.

[0064] (5) The detection method described in any one of (1) to (4), wherein, with respect to the motor, a break in the power line is determined to have occurred when: saturation related to the voltage command for the motor occurs, the speed command value is zero, and the speed feedback value is not zero; the saturation related to the voltage command occurs, the speed command value is not zero, and the speed feedback value is zero; and the saturation related 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.

[0065] (6) A detection device for detecting a break in a power line connecting the motor control device to the motor in a system including a motor control device that performs servo control on the motor based on command values.

[0066] The system includes a combination determination logic. For multiple items selected from the instruction value and the state value obtained about the motor, the combination determination logic calculates a binary index or a ternary index respectively, and determines the presence or absence of a broken wire in the power line based on the combination of the indexes.

[0067] (7) The detection device as described in (6), wherein 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.

[0068] The three-value index represents whether the value is positive, 0, or negative.

[0069] (8) The detection device as described in (6) or (7), wherein the output of the combined determination logic includes an on-delay circuit that notifies the outside that a break has occurred in the power line when the combined determination logic determines that the power line is in a state of disconnection for a first time.

[0070] (9) The detection device as described in (8), wherein the first time can be adjusted in order to adjust the sensitivity of the detection.

[0071] (10) The detection device described in any one of (6) to (9), wherein the combined determination logic is configured to detect at least one of the following conditions with respect to the motor: saturation related to a voltage command for the motor occurs, the speed command value is zero, and the speed feedback value is not zero; the saturation related to the voltage command occurs, the speed command value is not zero, and the speed feedback value is zero; and the saturation related 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.

[0072] Based on the structure of (1) and (6), by using multiple binary or ternary indices, it is possible to quickly determine whether the system performs the expected action, thereby suppressing false detections and quickly detecting broken lines in the power line.

[0073] Based on the structure of (2) and (7), the arbitrariness in the threshold setting can be eliminated as much as possible to obtain the index. Therefore, it can take into account both the suppression of false detection and the rapid detection of disconnection, and prevent the reduction in workability that comes with the adjustment of multiple thresholds.

[0074] Based on the structures of (3) and (8), the possibility of false detection caused by noise or overshoot can be eliminated. In particular, based on the structures of (4) and (9), the detection sensitivity can be adjusted by adjusting only the single parameter of the first moment.

[0075] Based on the structures of (5) and (10), a suitable combination of indicators can be obtained for the detection of broken power lines, which can further suppress false detections and detect broken power lines more quickly.

Claims

1. A detection method of detecting disconnection of a power line connected to a motor in a system in which a motor is servo-controlled based on command values, in the detection method, for a plurality of items selected from the command values and state values obtained with respect to the motor, a binary index or a ternary index is respectively calculated, disconnection of the power line is detected based on a combination of the indexes.

2. The detection method according to claim 1, wherein the binary index includes at least one of an index indicating presence or absence of a value, an index indicating whether a value is zero or not, an index indicating whether a value is positive or negative, and an index indicating whether saturation or limitation has occurred, the ternary index is an index indicating whether a value is positive, zero, or negative.

3. The detection method according to claim 1 or 2, wherein when the combination of the indexes satisfies a prescribed condition for a first time, it is determined that disconnection of the power line has occurred.

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

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

6. A detection device of detecting disconnection of a power line connecting a motor control device and a motor in a system including the motor control device that servo-controls a motor based on command values, the detection device includes combination determination logic that, for a plurality of items selected from the command values and state values obtained with respect to the motor, respectively calculates a binary index or a ternary index, and determines the presence or absence of disconnection of the power line based on a combination of the indexes.

7. The detection device according to claim 6, wherein the binary index includes at least one of an index indicating presence or absence of a value, an index indicating whether a value is zero or not, an index indicating whether a value is positive or negative, and an index indicating whether saturation or limitation has occurred, the ternary index is an index indicating whether a value is positive, zero, or negative.

8. The detection device according to claim 6 or 7, wherein an output of the combination determination logic includes an on-delay circuit that, when the combination determination logic determines that a state in which disconnection of the power line has occurred has continued for a first time, notifies an outside that disconnection of the power line has occurred.

9. The detection device according to claim 8, wherein the first time is adjustable in order to adjust the sensitivity of detection.

10. The detection apparatus of claim 6 or 7, wherein the combination decision logic is structured in a manner that is capable of detecting at least one of the following conditions with respect to the motor: saturation related to a voltage command for the motor has occurred, a speed command value is zero, and a speed feedback value is not zero; the saturation related to the voltage command has occurred, the speed command value is not zero, and the speed feedback value is zero; and the saturation related to the voltage command has occurred, the speed command value is the same sign as a torque command value, and the speed command value is a different sign than the speed feedback value.

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