Fault detection device and fault detection procedure

Abstract

Fault detection device (12) comprising: an oscillation signal transmitter unit (30) configured to send an oscillation signal (Os) that causes a rotating shaft of a servomotor (24) to rotate and oscillate in a predetermined pattern to a motor control unit (20) configured to control the servomotor (24); a measuring unit (32) which is set up to measure a physical quantity (Ps) which represents a state of the servomotor (24) when the rotating shaft is set into oscillation; a comparison unit (34) configured to compare a measurement signal (Ms) of the measured physical quantity (Ps) with a reference signal (Ss) configured to represent a periodically varying value corresponding to the oscillation signal (Os) in order to calculate a difference (D) between them; and a fault detection unit (36) which is configured to detect the occurrence of a fault in a drive system (10) comprising the servo motor (24) and the motor control unit (20) and extending from a driven object (28) to be driven by the servo motor (24) to the motor control unit (20), based on a comparison result from the comparison unit (34), wherein the fault detection unit (36) is configured to determine that the drive system (10) has a fault when the difference (D) is greater than or equal to a threshold (TH), wherein the comparison unit (34) is set up to calculate a sum (D1) of the differences at given multiple time points, and wherein the fault detection unit (36) is set up to determine that the drive system (10) has a fault when the sum (D1) of the differences is greater than or equal to the threshold (TH).

Description

Background of the invention

[0001] The present invention relates to a fault detection device and a fault detection method for detecting a fault of a drive system comprising a servo motor and the like. Description of the state of the art:

[0002] JP H11-095820 A discloses a machine tool equipped with an operation recording function that measures electrical currents supplied to a spindle motor and a rotating tool as load data, displays a warning when the measured current exceeds a warning threshold, and stores the measured current as load data. It is also disclosed that when the measured current exceeds a fault threshold, the machine tool indicates the occurrence of a fault, quickly retracts the base of the rotating tool from the workpiece, and stores the measured current as load data.

[0003] DE 10 2005 024 385 A1 discloses a method for monitoring an automated industrial system by detecting and analyzing control signals. First, the expected signal characteristic for the course of a particular control signal is defined. A current signal characteristic is created from the course of the current control signal and compared with the expected signal characteristic. If there is an unacceptable deviation between these two characteristics, the current signal characteristic is classified as an anomalous signal characteristic. Summary of the invention

[0004] However, according to the previous JP H11-095820 A, since only the motor fault is detected based on the motor current value and the threshold value, detecting the drive system fault including the motor is not possible. For example, a fault due to a loose screw in the drive system, etc., cannot be detected.

[0005] An object of the present invention is therefore to provide a fault detection device and a fault detection method that can detect a fault in a drive system comprising a motor.

[0006] According to the present disclosure, fault detection devices and fault detection methods are provided according to the independent claims. Developments are presented in the dependent claims.

[0007] The foregoing and other objects, features and advantages of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example. Short description of the drawings Fig. 1 is a diagram illustrating a failure detection system including a drive system and a failure detection device for detecting a failure of the drive system according to a first embodiment. Fig. Figure 2 shows a diagram illustrating an example of a Fig. 1 shown oscillation signal transmitted oscillation signal transmitting unit. Fig. 3 shows a diagram illustrating an example of a Fig. 1 shown measuring unit measured physical quantity. Fig. Figure 4 shows a diagram illustrating an example of a reference signal. Fig. 5 shows a diagram for explaining a first comparison method by a Fig. 1 comparison unit shown. Fig. Fig. 6 is a diagram for explaining a second comparison method by a Fig. 1 comparison unit shown. Fig. Fig. 7 shows a diagram for explaining a third comparison method by a Fig. 1 comparison unit shown. Fig. Fig. 8 is a diagram for explaining a fourth comparison method by a Fig. 1 comparison unit shown. Fig. 9 is a flowchart showing the operation of a failure detection apparatus according to the first embodiment. Fig. 10 is a diagram showing a failure detection system according to a second embodiment. Fig. 11 is a flowchart showing the operation of the failure detection apparatus according to the second embodiment. Fig. 12 is a diagram showing another example of an oscillation signal. Description of the preferred embodiments

[0008] Hereinafter, a failure detection apparatus and a failure detection method according to the present invention will be explained by describing the preferred embodiments with reference to the accompanying drawings. [First embodiment]

[0009] Fig. 1 is a diagram illustrating a failure detection system 14 including a drive system 10 and a failure detection device 12 for detecting a failure of the drive system 10. The drive system 10 is installed in a robot or a processing machine (such as a machine tool or an injection molding machine). For example, in a machine tool, the drive system 10 is a drive system for axially moving a driven object 28 such as a table, a tool, or the like. In an injection molding machine, the drive system 10 is a drive system for rotating the screw as the driven object 28 and / or for moving it back and forth. In a robot, the drive system 10 is a mechanism for bending an arm as the driven object 28 at a joint or rotating the arm.

[0010] The drive system 10 includes a motor control unit 20, a servo amplifier 22, a servo motor 24, a driving force transmission mechanism 26, and a driven object 28. That is, the drive system 10 consists of various mechanisms, elements, parts, and others ranging from the driven object 28 to the motor control unit 20.

[0011] The servo amplifier 22 drives the servo motor 24, and the motor control unit 20 controls the servo amplifier 22 to thereby control the rotation of the servo motor 24.

[0012] The driving force transmission mechanism 26 transmits the driving force (rotational force) of the servo motor 24 to the driven object 28, thereby driving the driven object 28. The driving force transmission mechanism 26 can convert the rotational force of the servo motor 24 into linear motion and transmit it to the driven object 28, or can directly transmit the rotational force of the servo motor 24 to the driven object 28. Therefore, the driving force transmission mechanism 26 can include a ball screw, a gear, and / or a disk.

[0013] The fault detection device 12 includes an oscillation signal transmitting unit 30, a measuring unit 32, a comparing unit 34, a fault detection unit 36, a notification unit 38, and a measurement start control unit 40. The fault detection device 12 includes at least one processor such as a CPU and a storage medium for storing a fault detection program therein. The processor executes the fault detection program, thus serving as the fault detection device 12 of the first embodiment.

[0014] The oscillation signal transmitting unit 30 sends an oscillation signal Os to the motor control unit 20 for causing the rotary shaft of the servo motor 24 to rotate and oscillate (rotate forward and backward) in a predetermined pattern. The oscillation signal Os is a signal whose signal value changes periodically. Here, the oscillation signal Os is a control signal that controls the motor control unit 20 to cause the rotary shaft of the servo motor 24 to rotate by a predetermined angle in the forward direction and then rotate by a predetermined angle in the reverse direction repeatedly with the current rotational position of the rotary shaft (hereinafter referred to as the reference position) as a reference. The value of the oscillation signal Os indicates a command position (command rotational position) of the rotary shaft of the servo motor 24.

[0015] Fig. Fig. 2 is a diagram showing an example of the oscillation signal Os transmitted from the oscillation signal transmitting unit 30. As shown in Fig. As shown in Figure 2, the oscillation signal Os is a command signal that causes the rotary shaft of the servo motor 24 to rotate backward and forward in a predetermined pattern. Since the oscillation signal Os sent to the motor control unit 20 is a command signal that gradually increases in amplitude and frequency over time, the oscillation of the rotary shaft based on the oscillation signal Os also increases in amplitude and frequency over time. As the oscillation amplitude increases, the rotation angle of the rotary shaft increases; as the oscillation frequency increases, the rotation speed of the rotary shaft increases.

[0016] The amplitude (rotational position, rotation angle) of the rotation in the forward and reverse directions from the reference position, i.e., the amplitude of the oscillation, gradually increases over time. The frequency of the oscillation also gradually increases over time. Even if a disturbance can only be detected with a specific amplitude and / or at a specific frequency, such a disturbance can be detected by varying the amplitude and frequency. Thus, various disturbances occurring in the drive system 10 can be detected.

[0017] The value "0" of the oscillation signal Os indicates the reference position. The value of the oscillation signal Os with the (+) sign (plus sign) indicates the command position of the rotary shaft rotating in the forward direction from the reference position. The value of the oscillation signal Os with the (-) sign (minus sign) indicates the command position of the rotary shaft rotating in the reverse direction from the reference position. As the direction position moves away from the reference position "0", the rotation angle of the rotary shaft increases from the reference position. When this oscillation signal Os is input to the motor control unit 20, the motor control unit 20 causes the rotary shaft of the servo motor 24 to rotate and oscillate according to the oscillation signal Os.

[0018] The measuring unit 32 measures a physical quantity Ps to represent the state of the servo motor when the rotary shaft of the servo motor 24 is vibrated. As shown in Fig. As shown in Figure 3, the measurement signal Ms for indicating the physical quantity Ps measured by the measuring unit 32 varies periodically according to the oscillation signal Os. The measuring unit 32 outputs the measurement signal Ms to the comparison unit 34.

[0019] Examples of the physical quantity Ps representing the state of the servo motor 24 include electric current flowing through the servo motor 24 and a torque, a rotational position, a speed, an acceleration, and an inertia of the rotating shaft of the servo motor 24. When measuring the current flowing in the servo motor 24, the measuring unit 32 may include a current sensor, and when measuring the torque of the rotating shaft of the servo motor 24, the measuring unit 32 may include a torque sensor. The measuring unit 32 may calculate the torque from the measured current value. Further, when measuring the rotational position of the rotating shaft of the servo motor 24, the measuring unit 32 may include a transmitter for detecting the rotational position. The measuring unit 32 may calculate the speed and acceleration from the rotational position. Further, the measuring unit 32 may calculate the inertia from the current value and the rotational position.

[0020] The measuring unit 32 can measure the torque, position, rotational speed, acceleration, or inertia of the driven object 28 as a physical quantity Ps. This is because the physical quantity Ps of the driven object 28 also represents the state of the servo motor 24. In short, the measuring unit 32 can measure the physical quantity Ps to represent the state of the servo motor 24. The first embodiment is described assuming that the measuring unit 32 measures the current flowing through the servo motor 24 as a physical quantity Ps.

[0021] When a measurement signal (signal indicating the current value) Ms indicating the current (physical quantity) Ps flowing through the servo motor 24 is sent from the measurement unit 32 to the comparison unit 34, the comparison unit 34 compares the received measurement signal Ms with the reference signal Ss. The reference signal Ss is stored in a storage unit 34a of the comparison unit 34. As shown in Fig. As shown in Figure 4, the reference signal Ss varies periodically according to the oscillation signal Os.

[0022] The reference signal Ss may be a measurement signal Ms measured by the measuring unit 32 when the rotary shaft of the servo motor 24 is oscillated according to the oscillation signal Os, provided that no disturbance occurs in the drive system 10 (for example, at the time of assembly). Alternatively, the reference signal Ss may be a measurement signal Ms measured by the measuring unit 32 in the past, or may be the average value thereof. The comparison unit 34 compares the measurement signal Ms with the reference signal Ss to calculate a difference D (absolute value) therebetween. The comparison unit 34 outputs the comparison result (difference D) to the disturbance determination unit 36. The comparison unit 34 will be specifically described later.

[0023] Upon receiving the comparison result from the comparison unit 34, the fault determination unit 36 ​​determines whether a fault exists in the drive system 10 based on the transmitted comparison result. The fault determination unit 36 ​​determines that the drive system 10 is faulty if the difference D calculated by the comparison unit 34 is greater than or equal to a threshold TH, and determines that the drive system 10 is normal if the difference Dis is less than the threshold TH.

[0024] When there is no disturbance in the drive system 10, the measured measurement signal Ms and the reference signal Ss essentially agree with each other completely, or they do not agree with each other completely but to an acceptable degree. However, there are cases where a disturbance occurs in the drive system 10. For example, due to loosening (disturbance) or the like of a screw for supporting a member arranged in the servo motor 24 or the driving force transmission mechanism 26 for generating or transmitting the driving force, the load applied to the servo motor 24 may fluctuate. When the load on the servo motor 24 fluctuates, the detected measurement signal Ms deviates from that during normal operation. Furthermore, when there is a disturbance in the servo amplifier 22 or the motor control unit 20, it is not possible to control the servo motor 24 according to the oscillation signal Os, so the detected measurement signal Ms deviates from the measurement signal obtained under normal conditions.

[0025] Therefore, if a fault occurs in the drive system 10, the difference D between the measurement signal Ms and the reference signal Ss is outside a permissible range. Thus, if the difference between the measurement signal Ms and the reference signal Ss is greater than or equal to the threshold TH, the fault determination unit 36 ​​determines that the drive system 10 is faulty. Upon determining that the drive system 10 is faulty, the fault determination unit 36 ​​outputs a fault signal ER to the notification unit 38.

[0026] When the fault signal ER is sent from the fault detection unit 36, the notification unit 38 notifies the operator that the drive system 10 is faulty. The notification unit 38 may include a display device so that, upon receiving the fault signal ER, the notification unit can display the fact that the drive system 10 is faulty on the display device, thereby notifying the operator. Furthermore, the notification unit 38 may include a communication unit so that, upon receiving the fault signal ER, the notification unit can send the fault signal ER to another external device (e.g., a PC, a smartphone, etc.) via the communication unit to notify the operator. In this case, the operator detects the fault of the drive system 10 via the external device. Additionally, the notification unit 38 may be equipped with a loudspeaker.Upon receiving the fault signal ER, the notification unit 38 may output an audible alarm signal (indicating that a fault has occurred) from the loudspeaker to thereby notify the operator.

[0027] The measurement start control unit 40 manages the time to start measuring the drive system 10. When the measurement start time is reached, the measurement start control unit 40 sends a measurement start signal ST to the oscillation signal transmitting unit 30 and the measuring unit 32. Upon receiving the measurement start signal ST, the oscillation signal transmitting unit 30 sends the oscillation signal Os to the motor control unit 20. Upon receiving the measurement start signal, the measuring unit 32 measures the current Ps of the servo motor 24.

[0028] When the operator operates an unillustrated input unit to execute the operation to start the disturbance detection, the measurement start control unit 40 may be configured to determine that the time to start the measurement has arrived and send the measurement start signal ST to the oscillation signal transmission unit 30 and the measurement unit 32. Furthermore, when the disturbance detection is performed periodically, the measurement start control unit 40 may send the measurement start signal ST to the oscillation signal transmission unit 30 and the measurement unit 32 when the measurement start time has arrived. In this case, the measurement start control unit 40 periodically sends the measurement start signal ST to the oscillation signal transmission unit 30 and the measurement unit 32.

[0029] The comparison unit 34 is described in detail below. In the first embodiment, four examples of the comparison method by the comparison unit 34 are described below; however, other methods for performing the comparison may also be used. Fig. 5 shows a diagram for explaining a first comparison method, Fig. 6 shows a diagram for explaining a second comparison method, Fig. Fig. 7 shows a diagram for explaining a third comparison method and Fig. Figure 8 shows a diagram for explaining a fourth comparison method. The solid lines in Fig. The waveforms shown in Figures 5 to 8 represent the measured signal Ms and the waveforms shown by dashed lines represent the reference signal Ss. <Erstes Vergleichsverfahren>

[0030] The first comparison procedure is described below. In the first comparison procedure (see Fig. 5) The comparison unit 34 obtains a difference (absolute value) between the measurement signal Ms and the reference signal Ss at each of a predetermined plurality of times and calculates a sum D1 of the obtained differences. The predetermined plurality of times may be times within a predetermined time interval. When the drive system 10 is free of disturbances, the sum D1 of the differences (comparison result) has a smaller value (for example, 0) than the threshold TH. Thus, if the sum D1 of the differences calculated by the comparison unit 34 is equal to or greater than the threshold TH, the disturbance determination unit 36 ​​determines that the drive system 10 is in a disturbance. If the sum D1 of the differences is less than the threshold TH, the drive system 10 is determined to be normal.

[0031] The comparison unit 34 calculates the sum (summation) D1 of the differences at respective points in time in a time interval of time t m at time t n by using the following mathematical formula (1). Here, f(t i ) the measurement signal Ms at time t i and g(t i ) represents the reference signal Ss at time t i where i = m to n, m < n. In Fig. The example shown in Figure 5 is: t m = 0. D1=∑i=mn|f(ti)−g(ti)|

[0032] In the first comparison method, the time points within a given time interval are set to a predetermined number of times; however, the multiple times do not have to be consecutive. The predetermined multiple times can be chosen arbitrarily or at regular intervals.

[0033] The threshold TH in the first comparison method is determined depending on the oscillation signal (Os) and the predetermined multiple times. This is due to the fact that the amplitude and frequency of the oscillation signal Os sent to the engine control unit 20 gradually decrease with the passage of time, as shown in Fig. 2; the longer the time length from the beginning of the oscillation, the greater the difference between the measurement signal Ms and the reference signal Ss as in Fig. 5 shown. <Zweites Vergleichsverfahren>

[0034] In the second settlement procedure (see Fig. 6) The comparison unit 34 calculates an integral value D2 of the difference (absolute value) between the measurement signal Ms and the reference signal Ss at a predetermined time interval. Also in this case, when the drive system 10 is free of disturbances, the integral value D2 of the difference has a smaller value (e.g., 0) than the threshold TH. Thus, if the integral value (comparison value) D2 of the difference calculated by the comparison unit 34 is equal to or greater than the threshold TH, the disturbance determination unit 36 ​​determines that the drive system 10 is in a disturbance. If the integral value D2 of the difference is less than the threshold TH, the drive system 10 is determined to be normal.

[0035] The comparison unit 34 calculates the integral value D2 of the difference between the measurement signal Ms and the reference signal Ss in the time interval from time t1 to time t2 by using the following formula (2). Here, f(t) represents the measurement signal Ms at time t, and g(t) represents the reference signal Ss at time t, where t1 < t2. Fig. In the example shown in Figure 6, t1 = 0. D2=∫t1t2|f(t)−g(t)|

[0036] The threshold TH in the second comparison method is determined depending on the oscillation signal Os and the specified time interval (time t1 to t2). This is due to the fact that the amplitude and frequency of the oscillation signal Os sent to the engine control unit 20 gradually decrease over time, as shown in Fig. 2; the longer the time length from the beginning of the oscillation, the greater the difference between the measurement signal Ms and the reference signal Ss as in Fig. 6 shown. <Drittes Vergleichsverfahren>

[0037] In the third settlement procedure (see Fig. 7) the comparison unit 34 compares the N-th period T f (N) of the measurement signal Ms with the N-th period T g (N) of the reference signal Ss, in order to calculate the difference between them (absolute value) D3. In Fig. In the example shown in Figure 7, the comparison unit 34 compares the 1.5(=N)-th period T f (1,5) of the measurement signal Ms with the 1.5(=N)-th period T g(1,5) of the reference signal Ss. That is, the comparison unit 34 compares a period starting at a time point that is half a cycle late from the first period of the measurement signal Ms with a period starting at a time point that is half a cycle late from the first period of the reference signal Ss. Also in this case, when the drive system 10 is free of disturbances, the period difference D3 has a smaller value (for example, 0) than the threshold TH. Therefore, when the difference (comparison result) D3 of one period calculated by the comparison unit 34 is equal to or greater than the threshold TH, the disturbance determination unit 36 ​​determines that the drive system 10 is in a disturbance, and when the difference D3 of one period is less than the threshold TH, the drive system 10 is determined to be normal.

[0038] The comparison unit 34 calculates the difference D3 between the N-th period T f(N) of the measurement signal Ms and the N-th period T g (N) of the reference signal S2 using the mathematical formula (3) shown below. D3=|Tf(N)−Tg(N)|

[0039] The threshold TH in the third comparison method is determined depending on the oscillation signal Os and the value N. This is due to the fact that the amplitude and frequency of the oscillation signal Os sent to the engine control unit 20 gradually decrease with the passage of time as shown in Fig. 2; the longer the time length from the beginning of the oscillation, the shorter the periods of the measurement signal Ms and the reference signal Ss as in Fig. 7 shown. <Viertes Vergleichsverfahren>

[0040] In the fourth settlement procedure (see Fig. 8) the comparison unit 34 compares the N-th peak amplitude A f (N) of the measurement signal Ms with the Nth peak amplitude A g(N) of the reference signal Ss, thereby calculating a difference (absolute value) D4 therebetween. Fig. 8 shows an example in which the comparison unit 34 detects the 5(=N)-th peak amplitude A f (5) of the measurement signal Ms with the 5(=N)-th peak amplitude A g (5) of the reference signal Ss. Also in this case, when the drive system 10 is free of disturbances, the amplitude difference D4 has a smaller value (for example, 0) than the threshold TH. Therefore, if the amplitude difference (comparison result) D4 calculated by the comparison unit 34 is greater than or equal to the threshold TH, the disturbance determination unit 36 ​​determines that the drive system 10 is disturbed, and if the amplitude difference D4 is less than the threshold TH, the drive system 10 is determined to be normal.

[0041] The comparison unit 34 calculates the difference D4 between the Nth amplitude A f(N) of the measurement signal Ms and the Nth amplitude A g (N) of the reference signal Ss using the formula (4) shown below. D4=|Af(N)−Ag(N)|

[0042] The threshold TH in the fourth comparison method is determined depending on the oscillation signal Os and the value N. This is due to the fact that the amplitude and frequency of the oscillation signal Os sent to the engine control unit 20 gradually decrease with the passage of time as shown in Fig. 2; the longer the time length from the beginning of the oscillation, the larger the amplitudes of the measurement signal Ms and the reference signal Ss as in Fig. 8 shown.

[0043] The following describes the operation of the fault detection device 12 with respect to Fig. 9 briefly describes. In step S1, the measurement start control unit 40 determines whether it is time to start the measurement. If it is determined in step S1 that the measurement start time has not yet arrived, control returns to step S1. Conversely, if it is determined in step S1 that the measurement start time has arrived, control proceeds to step S2. At this time, if it is determined that it is time to start the measurement, the measurement start control unit 40 sends the measurement start signal ST to the oscillation signal transmission unit 30 and the measurement unit 32.

[0044] In step S2, the oscillation signal transmitting unit 30 transmits the oscillation signal Os to the motor control unit 20 of the drive system 10. In step S3, the measuring unit 32 measures the current (physical quantity) Ps of the servo motor 24 of the drive system 10.

[0045] Subsequently, the comparison unit 34 compares the measurement signal Ms of the current Ps measured in step S3 with the reference signal Ss stored in the storage unit 34a (step S4), and the failure determination unit 36 ​​performs a failure determination process based on the comparison result to determine whether the drive system 10 is in failure (step S5). In step S4, the comparison unit 34 compares the measurement signal Ms and the reference signal Ss to thereby calculate the difference D therebetween (any one of D1 to D4), and in step S5, the failure determination unit 36 ​​judges that a failure has occurred in the drive system 10 when the difference (comparison result) D is equal to or greater than the threshold TH.

[0046] If it is determined in step S5 that a malfunction has occurred in the drive system 10, the notification unit 38 notifies the operator of the occurrence of the malfunction (step S6), and control returns to step S1 (back). If it is determined in step S5 that no malfunction has occurred in the drive system 10, control returns directly to step S1 (back). [Second embodiment]

[0047] A second embodiment is described below. In the first embodiment, the measurement signal Ms of the current (for the physical quantity) Ps measured in the past in the drive system 10 to be examined for faults is used as the reference signal Ss. However, the second embodiment differs from the first embodiment in that the physical quantity (current) Ps measured in another drive system or other drive systems 10 is used as the reference signal Ss.

[0048] Fig. Figure 10 is a diagram illustrating a fault detection system 14 according to the second embodiment. The same components as in the first embodiment are denoted by the same reference numerals, and only different features are described.

[0049] The fault detection device 12 detects the fault of a plurality (N) of drive systems 10. The plurality of drive systems 10 are drive systems used for the same purpose and, for example, for multiple processing machines or robots of the same model. In particular, the plurality of drive systems 10 may be drive systems that rotate or move the respective injection molding screws or move the respective movable molds in the injection molding machines of the same model. Here, to distinguish the plurality of drive systems 10 from each other, the N drive systems 10 may be referred to as drive systems 101 to 10 Nin some cases. The oscillation signal transmitting unit 30 transmits the same oscillation signal Os to each of the motor control units 20 of the plurality of drive systems 10 (101 to 10 N ).

[0050] The measuring unit 32 measures a physical quantity (also assumed to be the current in the second embodiment) Ps for representing the state of the servo motor 24 when the rotary shaft of the servo motor 24 in each of the plurality of drive systems 10 (101 to 10 N ) oscillates. This means that the current Ps flowing through the servo motor 24 of each drive system 10 is measured. The measuring unit 32 outputs the measurement signal Ms from each of the drive systems 10 to the comparison unit 34. In this case, the currents Ps of the plurality of drive systems 101 to 10 N as currents Ps1 to Ps N to distinguish them from each other, and the measurement signals Ms can be designated as Ms1 to Ms N be referred to.

[0051] The comparison unit 34 stores in the memory unit 34a the measurement signals Ms (Ms1 to Ms N ) of the currents Ps (Ps1 to Ps N ) in the corresponding drive systems 10 (101 to 10 N ). The comparison unit 34 selects one of the plurality of drive systems 10 as the target of the fault detection and uses at least one of the measurement signals Ms of the other non-selected drive systems 10 as the reference signal Ss. Of the measurement signals Ms (Ms1 to Ms N ), the comparison unit 34 compares the measurement signal Ms of the selected drive system 10 with at least one of the measurement signals Ms (reference signal Ss) of the other non-selected drive systems 10.

[0052] If the comparison unit 34 selects, for example, the drive system 101 as the target of the fault detection, at least one of the measurement signals Ms of the currents Ps of the drive systems 102 to 10 N used as a reference signal Ss. Subsequently, the comparison unit 34 compares the reference signal Ss with the measurement signal Ms1 of the drive system 101 selected as the target of the fault detection. In this way, the comparison unit 34 sequentially selects each of the plurality of drive systems 10 as a target of the fault detection and compares the measurement signal Ms of the drive system 10 selected as the target of the fault detection with at least one of the measurement signals Ms (reference signal Ss) of the other drive systems 10 that are not selected as the target of the fault detection.

[0053] If the measurement signals Ms of two or more drive systems 10 are used as the reference signal Ss by the other drive systems 10 that are not selected as the target of the disturbance detection, the average value of the multiple measurement signals Ms can also be set as the reference signal Ss. The average value of all measurement signals Ms (Ms1 to Ms N ) of the currents Ps (Ps1 to Ps N ) of the drive systems 10 (101 to 10 N ) can also be used as the reference signal Ss, regardless of whether they are selected as the target of the disturbance detection or not.

[0054] The comparison unit 34 calculates the difference D (D1 to D4) between the measurement signal Ms and the reference signal Ss by using one of the four comparison methods described in the foregoing first embodiment.

[0055] The fault determination unit 36 ​​performs a fault determination for each of the plurality of drive systems based on the comparison result (difference D) from the comparison unit 34.

[0056] The following is with regard to Fig. 11 describes the operation of the failure detection device 12 in the second embodiment. In step S11, the measurement start control unit 40 determines whether it is time to start measurement. If it is determined in step S11 that the measurement start time has not yet arrived, control returns to step S11. Conversely, if it is determined in step S11 that the measurement start time has arrived, control proceeds to step S12. At this time, if it is determined that it is time to start measurement, the measurement start control unit 40 sends the measurement start signal ST to the oscillation signal transmission unit 30 and the measurement unit 32.

[0057] In step S12, the oscillation signal transmitting unit 30 transmits the same oscillation signal Os to the motor control units 20 of the plurality of drive systems 10 (101 to 10 N ) and in step S13, the measuring unit 32 measures the currents Ps (Ps1 to Ps N ) of the servo motors 24 of the drive systems 10 (101 to 10 N ).

[0058] Subsequently, in step S14, the comparison unit 34 stores the measurement signals Ms (Ms1 to Ms N ) of the currents Ps (Ps1 to Ps N ) of the drive systems 10 (101 to 10 N ).

[0059] Subsequently, in step S15, the comparison unit 34 selects a drive system 10 as the target of the fault detection.

[0060] Subsequently, in step S16, the comparison unit 34 compares the measurement signal Ms of the currently selected drive system 10 as the target of the fault detection with one of the measurement signals Ms of the other drive systems 10 that are not currently selected as the target of the fault detection. That is, one of the measurement signals Ms of the other drive systems 10 that are not currently selected as the target of the fault detection serves as the reference signal Ss. If the measurement signals Ms of two or more drive systems 10 of the plurality of drive systems 10 that are not currently selected as the target of the fault detection are used as the reference signal Ss, the average value of the two or more measurement signals Ms can be set as the reference signal Ss. The average value of the measurement signals Ms (Ms1 to Ms N ) of all drive systems 10 (101 to 10 N) can be used as the reference signal Ss, regardless of whether they are selected as the target of the disturbance detection or not.

[0061] Subsequently, in step S17, the fault determination unit 36 ​​determines whether a fault exists in the currently selected drive system 10 based on the comparison result in step S16 (difference D between the measurement signal Ms and the reference signal Ss). If the difference D (any one of D1 to D4) calculated by the comparison unit 34 comparing the measurement signal Ms and the reference signal Ss is greater than or equal to the threshold TH, the fault determination unit 36 ​​determines that a fault exists in the currently selected drive system 10.

[0062] If it is determined in step S17 that a fault exists in the currently selected drive system 10, the notification unit 38 notifies the operator of the occurrence of the fault (step S18), and control proceeds to step S19. Conversely, if it is determined in step S17 that no fault exists in the currently selected drive system 10, control proceeds directly to step S19.

[0063] In step S19, the comparison unit 34 determines whether there are any drive systems 10 that have not yet been selected as the target of failure detection. If it is determined in step S19 that there is a drive system 10 that has not yet been selected as the target of failure detection, the comparison unit 34 selects one of the drive systems 10 that has not yet been selected as the target of failure detection (step S20), control proceeds to step S16, and the previously described sequence of steps is repeated. On the other hand, if it is determined in step S19 that there is no drive system 10 that has not yet been selected as the target of failure detection, control returns directly to step S11 (Back).

[0064] In Fig. 11 immediately notifies the notification unit 38 if the drive system 10 selected as the target of a fault detection turns out to be faulty. However, the notification unit 38 can collectively report the presence of a fault in one or more drive systems 10 after the fault detection has been completed for all drive systems 10. [Modifications]

[0065] The foregoing embodiments may be modified as follows. (Modification 1)

[0066] As in Fig. As shown in Figure 12, the oscillation signal Os sent to the motor control unit 20 may be a command signal that gradually increases in amplitude and frequency with the passage of time. In particular, the oscillation signal Os may be a command signal whose amplitude and frequency gradually increase with each predetermined number of cycles (in Fig. 12 every three cycles). As previously described, since the amplitude and frequency change gradually with each predetermined number of cycles, the disturbance of the parts constituting the drive system 10 can be more reliably detected. (Modification 2)

[0067] Although in the foregoing embodiments, the oscillation signal Os is specified as a command signal whose amplitude and frequency gradually increase with the passage of time, the oscillation signal Os may be a command signal whose amplitude and frequency vary with the passage of time. (Modification 3)

[0068] The oscillation signal Os can be a command signal in which the amplitude or frequency changes with time (for example, increases gradually). (Modification 4)

[0069] Although in the preceding embodiments, the amplitude and frequency of the oscillation signal Os are specified as changing with time, the amplitude and frequency may be fixed. Since such disturbances can only be detected at a certain specific frequency or amplitude, the amplitude and frequency of the oscillation signal may change each time a disturbance detection occurs, that is, each time the sequence of operations in Fig. 9 or Fig. 11 is carried out. (Modification 5)

[0070] The failure detection device 12 may be provided in a processing machine or a robot having the drive system 10. In this case, the numerical controller provided in the processing machine or robot for controlling the drive system 10 may be provided to serve as the failure detection device 12. When a plurality of drive systems 10 are provided as in the second embodiment, the failure detection device 12 may be provided for each of the plurality of processing machines or robots including the plurality of drive systems 10, or the failure detection device 12 may be provided for at least one of the plurality of processing machines or robots including the plurality of drive systems 10. (Modification 6)

[0071] The previous modifications 1 to 5 can be combined in any way as long as no inconsistencies occur.

[0072] The disturbance detection device 12 thus described with the foregoing embodiments and modifications includes: an oscillation signal transmission unit 30 configured to transmit an oscillation signal Os, which causes a rotary shaft of a servo motor 24 to rotate and oscillate in a predetermined pattern, to a motor control unit 20 for controlling the servo motor 24; a measuring unit 32 configured to measure a physical quantity Ps representing the state of the servo motor 24 when the rotary shaft of the servo motor 24 is oscillated; a comparing unit 34 configured to compare a measurement signal Ms of the measured physical quantity Ps with a reference signal Ss;and a fault detection unit 36 ​​configured to detect the occurrence of a fault in a drive system 10 comprising the servo motor 24 and the motor control unit 20, which extends from a driven object 28 to be driven by the servo motor 24 to the motor control unit 20, based on the comparison result from the comparison unit 34;

[0073] In this way, the physical quantity Ps representing the state of the servo motor 24 when the rotating shaft of the servo motor 24 is vibrated is measured, and the measurement signal Ms of the measured physical quantity Ps is compared with the reference signal Ss. Thus, disturbances in the drive system 10 including the servo motor 24 can be detected.

[0074] The reference signal Ss may be a periodically varying value corresponding to the oscillation signal Os. The comparison unit 34 may be configured to compare the measurement signal Ms with the reference signal Ss to thereby calculate a difference D therebetween. The fault detection unit 36 ​​may determine that the drive system 10 has a fault if the difference D is greater than or equal to a threshold TH. Thus, a fault in the drive system 10 can be accurately detected.

[0075] The comparison unit 34 can calculate a sum D1 of the differences at a predetermined number of points in time. The fault detection unit 36 ​​can determine that the drive system 10 has a fault if the sum D1 of the differences is greater than or equal to the threshold TH. In this case, the threshold TH can be determined depending on the oscillation signal Os and the predetermined number of points in time. Thus, a fault can be accurately detected.

[0076] The comparison unit 34 can calculate an integral value D2 of the difference between the measurement signal Ms and the reference signal Ss within a predetermined time interval. The fault detection unit 36 ​​can determine that the drive system 10 has a fault if the integral value D2 of the difference is greater than or equal to the threshold TH. In this case, the threshold TH can be determined depending on the oscillation signal Os and the predetermined time interval. Thus, a fault can be accurately detected.

[0077] The comparison unit 34 can determine the N-th period T f (N) of the measurement signal Ms with the N-th period T g(N) of the reference signal Ss to thereby calculate a difference D3 therebetween. The disturbance determination unit 36 ​​can determine that the drive system 10 has a disturbance if the difference D3 is greater than or equal to the threshold TH. In this case, the threshold TH can be determined depending on the oscillation signal Os and the value N. Thus, a disturbance can be accurately detected.

[0078] The comparison unit 34 can determine the Nth amplitude A f (N) of the measurement signal Ms with the Nth amplitude A g (N) of the reference signal Ss to thereby calculate a difference D4 therebetween. The disturbance determination unit 36 ​​can determine that the drive system 10 has a disturbance if the difference D4 is greater than or equal to the threshold TH. In this case, the threshold TH can be determined depending on the oscillation signal Os and the value N. Thus, a disturbance can be accurately detected.

[0079] The oscillation signal Os can be a command signal for causing the rotary shaft of the servo motor 24 to oscillate so that the amplitude and / or frequency of the oscillation varies gradually over time. Thus, various disturbances in the drive system 10 can be detected.

[0080] The oscillation signal Os can be a command signal for causing the rotary shaft of the servo motor 24 to oscillate so that the amplitude and / or frequency of the oscillation gradually increases over time. If the rotary shaft of the servo motor 24 is initially oscillated at a large angle and at a high speed, there is a risk that parts of the drive system 10 may be damaged. The above feature makes it possible to prevent damage to these parts.

[0081] The reference signal Ss may be the measurement signal Ms of the physical quantity Ps, which was previously measured by the measuring unit 32 when the rotary shaft of the servo motor 24 was vibrated. Thus, a disturbance can be accurately detected.

[0082] The fault detection device 12 can be provided in a processing machine or a robot with the drive system 10. Thus, the fault location can be clarified without disassembling the processing machine or robot. In addition, the present invention can be easily implemented by using integrated controllers and display devices.

[0083] The oscillation signal transmission unit 30 can transmit the oscillation signal Os to each of the motor control units 20 of the plurality of drive systems 10 used for the same purpose. The measurement unit 32 can measure the physical quantity Ps in each of the plurality of drive systems 10. The comparison unit 34 can use one of the plurality of drive systems 10 as a target of fault detection, at least one of the measurement signals Ms of the physical quantity Ps of the other non-selected drive systems 10 as a reference signal Ss, and compare the measurement signal Ms of the drive system 10 selected as the fault detection target with the reference signal Ss. Thus, a fault in the plurality of drive systems 10 can be detected.

[0084] The fault detection device 12 can be provided for at least one of a plurality of processing machines or robots of the same model with the multiple drive systems 10. This allows faulty parts to be located without disassembling a plurality of processing machines or robots. Additionally, the present invention can be easily implemented by using integrated control or display devices.

Claims

[1] Fault detection device (12) comprising: an oscillation signal transmitting unit (30) configured to transmit an oscillation signal (Os) causing a rotary shaft of a servo motor (24) to rotate and oscillate in a predetermined pattern to a motor control unit (20) configured to control the servo motor (24); a measuring unit (32) configured to measure a physical quantity (Ps) representing a state of the servo motor (24) when the rotary shaft is vibrated; a comparison unit (34) configured to compare a measurement signal (Ms) of the measured physical quantity (Ps) with a reference signal (Ss) configured to represent a periodically varying value corresponding to the oscillation signal (Os), thereby calculating a difference (D) therebetween; and a fault detection unit (36) configured to detect an occurrence of a fault in a drive system (10) comprising the servo motor (24) and the motor control unit (20) and extending from a driven object (28) to be driven by the servo motor (24) to the motor control unit (20), based on a comparison result from the comparison unit (34), wherein the fault detection unit (36) is configured to detect that the drive system (10) has a fault if the difference (D) is greater than or equal to a threshold (TH), wherein the comparison unit (34) is arranged to calculate a sum (D1) of the differences at predetermined multiple times, and wherein the fault detection unit (36) is configured to detect that the drive system (10) has a fault when the sum (D1) of the differences is greater than or equal to the threshold (TH). [2] Fault detection device (12) comprising: an oscillation signal transmitting unit (30) configured to transmit an oscillation signal (Os) causing a rotary shaft of a servo motor (24) to rotate and oscillate in a predetermined pattern to a motor control unit (20) configured to control the servo motor (24); a measuring unit (32) configured to measure a physical quantity (Ps) representing a state of the servo motor (24) when the rotary shaft is vibrated; a comparison unit (34) configured to compare a measurement signal (Ms) of the measured physical quantity (Ps) with a reference signal (Ss) configured to represent a periodically varying value corresponding to the oscillation signal (Os), thereby calculating a difference (D) therebetween; and a fault detection unit (36) configured to detect an occurrence of a fault in a drive system (10) comprising the servo motor (24) and the motor control unit (20) and extending from a driven object (28) to be driven by the servo motor (24) to the motor control unit (20), based on a comparison result from the comparison unit (34), wherein the fault detection unit (36) is configured to detect that the drive system (10) has a fault if the difference (D) is greater than or equal to a threshold (TH), wherein the comparison unit (34) is arranged to calculate an integral value (D2) of the difference between the measurement signal (Ms) and the reference signal (Ss) in a predetermined time interval, and wherein the fault detection unit (36) is configured to detect that the drive system (10) has a fault when the integral value (D2) of the difference is greater than or equal to the threshold (TH). [3] The fault detection device (12) according to claim 1 or 2, wherein the threshold value (TH) is determined depending on the oscillation signal (Os) and the predetermined plurality of times or the predetermined time interval. [4] The fault detection device (12) according to any one of claims 1 to 3, wherein the oscillation signal (Os) is a command signal for causing the rotary shaft to oscillate so that an amplitude and / or a frequency in the oscillation varies gradually with the passage of time. [5] The fault detecting device (12) according to claim 4, wherein the oscillation signal (Os) is a command signal for causing the rotary shaft to oscillate so that the amplitude and / or the frequency in the oscillation gradually increases with the passage of time. [6] The disturbance detecting device (12) according to any one of claims 1 to 5, wherein the reference signal (Ss) is the measurement signal (Ms) of the physical quantity (Ps) measured at previous times by the measuring unit (32) when the rotary shaft was vibrated. [7] The fault detection device (12) according to any one of claims 1 to 6, wherein the fault detection device (12) is provided in a processing machine or a robot having the drive system (10). [8] Fault detection device (12) according to one of claims 1 to 5, wherein: the oscillation signal transmitting unit (30) is arranged to transmit the oscillation signal (Os) to each of the motor control units (20) of a plurality of drive systems (10) used for the same purpose; the measuring unit (32) is arranged to measure the physical quantity (Ps) in each of the drive systems (10); and the comparison unit (34) is configured to select one of the drive systems (10) as a target of the fault detection, to use at least one of the measurement signals (Ms) of the physical quantity (Ps) of the other non-selected drive systems (10) as the reference signal (Ss), and to compare the measurement signal (Ms) of the one drive system (10) selected as the target of the fault detection with the reference signal (Ss). [9] The failure detection device (12) according to claim 8, wherein the failure detection device (12) is provided for at least one of a plurality of processing machines or robots of a same model having the plurality of drive systems (10). [10] Fault detection procedures, including: a transmission step (S2, S12) of transmitting an oscillation signal (Os) causing a rotary shaft of a servo motor (24) to rotate and oscillate in a predetermined pattern to a motor control unit (20) configured to control the servo motor (24); a measuring step (S3, S13) of measuring a physical quantity (Ps) representing a state of the servo motor (24) when the rotary shaft is vibrated; a comparison step (S4, S16) of comparing a measurement signal (Ms) of the measured physical quantity (Ps) with a reference signal (Ss) configured to represent a periodically varying value corresponding to the oscillation signal, thereby calculating a difference therebetween; and a determination step (S5, S17) of determining an occurrence of a fault in a drive system (10) comprising the servo motor (24) and the motor control unit (20) and ranging from a driven object (28) to be driven by the servo motor (24) to the motor control unit (20), based on a comparison result in the comparison step, wherein in the determination step it is determined that the drive system has a fault if the difference is greater than or equal to a threshold, wherein in the comparison step a sum (D1) of the differences is calculated at predetermined times, and wherein in the determination step it is determined that the drive system (10) has a fault if the sum (D1) of the differences is greater than or equal to the threshold (TH). [11] Fault detection procedures, including: a transmission step (S2, S12) of transmitting an oscillation signal (Os) causing a rotary shaft of a servo motor (24) to rotate and oscillate in a predetermined pattern to a motor control unit (20) configured to control the servo motor (24); a measuring step (S3, S13) of measuring a physical quantity (Ps) representing a state of the servo motor (24) when the rotary shaft is vibrated; a comparison step (S4, S16) of comparing a measurement signal (Ms) of the measured physical quantity (Ps) with a reference signal (Ss) configured to represent a periodically varying value corresponding to the oscillation signal, thereby calculating a difference therebetween; and a determination step (S5, S17) of determining an occurrence of a fault in a drive system (10) comprising the servo motor (24) and the motor control unit (20) and ranging from a driven object (28) to be driven by the servo motor (24) to the motor control unit (20), based on a comparison result in the comparison step, wherein in the determination step it is determined that the drive system has a fault if the difference is greater than or equal to a threshold, wherein in the comparison step an integral value (D2) of the difference between the measurement signal (Ms) and the reference signal (Ss) is calculated in a predetermined time interval, and wherein in the determination step it is determined that the drive system (10) has a fault if the integral value (D2) of the difference is greater than or equal to the threshold (TH).

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