MOTOR CONTROL DEVICE AND METHOD FOR DETERMINING MOTOR LIFE

Abstract

To provide a motor controller which can determine life of a motor, and a life determination method of the motor.SOLUTION: A determination unit 30 determines failure patterns S1 to S3 of a motor 2 when the motor 2 is driven with current of the motor 2 maintained constant by a motor control unit 10. The determination unit 30 further calculates a failure level C on the basis of the failure patterns of the motor 2 and calculates an accumulated failure count value TC from the failure level C. An operational expression of the accumulated failure count value TC includes: an addition term for accumulating the failure levels; and a subtraction term A for subtracting the accumulated failure count value when the failure level is zero. The determination unit 30 further determines a life of the motor 2 on the basis of the accumulated failure count value TC.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a motor control device and a method for determining the lifespan of a motor. [Background technology]

[0002] Japanese Patent Laid-Open Publication No. 7-71261 (Patent Document 1) discloses a warning device for a motor (rotating electric machine) attached to a turbocharger. This warning device measures the power generation output of the motor when no load is applied, and if the measured value is below a reference value, it is determined that the rotor has been demagnetized and a warning is issued to the driver. This allows the driver to notice the motor failure and take measures (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 7-71261 Summary of the Invention [Problem to be solved by the invention]

[0004] The warning device described in Patent Document 1 is useful in that it can warn the driver of a motor failure, but it does not judge the life of the motor and issue a warning. Being able to judge the life of the motor rather than accidental failure is useful for users.

[0005] The present disclosure has been made to achieve this objective, and an object of the present disclosure is to provide a motor control device that is capable of determining the lifespan of a motor, and a method for determining the lifespan of a motor. [Means for solving the problem]

[0006] The motor control device of the present disclosure includes a control unit that drives the motor, and a determination unit that determines the lifespan of the motor. When the motor is driven by the control unit with a constant current to the motor, the determination unit determines a predetermined motor fault pattern at a predetermined timing, calculates a fault level indicating a value equal to or greater than zero according to the degree of fault occurring in the motor based on the fault pattern, and calculates a cumulative fault count value indicating a cumulative value of the fault level using the fault level. The calculation formula for the cumulative fault count value includes an increase term that accumulates the fault level, and a subtraction term that subtracts the cumulative fault count value when the fault level is zero. The determination unit further determines that the motor has a short lifespan when the cumulative fault count value is higher than a threshold value, and determines that the motor has a long lifespan when the cumulative fault count value is lower than the threshold value.

[0007] In the motor control device, a fault level is calculated based on the motor's fault pattern, and a cumulative fault count value is calculated from the fault level. The life of the motor is then determined based on the cumulative fault count value. Since the formula for the cumulative fault count value includes a subtraction term that subtracts the cumulative fault count value when the fault level is zero, the cumulative fault count value is subtracted for faults that occur accidentally. Therefore, with this motor control device, the life of the motor can be determined without being due to an accidental failure.

[0008] The subtraction term may have a larger value the longer the time the fault level is at zero, or the subtraction term may have a larger value the more consecutive times the fault level is at zero.

[0009] The longer the fault level is at zero, or the more consecutive times the fault level is at zero, the more likely it is that the fault is accidental and not the end of the motor's life. Therefore, the motor's life can be determined more accurately.

[0010] The determination unit may determine the obstacle pattern based on at least one of the first to third parameters. The first parameter is a magnitude of angular acceleration of the motor. The second parameter is a speed underachievement time indicating a time during which the angular velocity of the motor continues to be below a target. The third parameter is a speed underachievement count indicating the number of times the angular velocity of the motor falls below the target. The determination unit may determine the obstacle patterns, which are the first to third obstacle patterns, based on the first to third parameters. The obstacle level may be a value obtained by adding a predetermined weighted value to each of the first to third obstacle patterns.

[0011] With the above configuration, it is possible to adjust the relationship between each of the first to third parameters and the fault level, and further the relationship between each parameter and the motor lifespan, thereby making it possible to more accurately determine the motor lifespan.

[0012] The thresholds may include a first threshold and a second threshold smaller than the first threshold. The determination unit may determine that the motor's life is short when the cumulative failure count value is higher than the first threshold, determine that the motor's life is long when the cumulative failure count value is lower than the second threshold, and determine that the motor's life is neither short nor long when the cumulative failure count value is lower than the first threshold and higher than the second threshold.

[0013] By adopting the above-mentioned configuration, the life of the motor can be appropriately determined.

[0014] The lifespan determination method of the present disclosure is a method for determining the lifespan of a motor, and includes a first step of determining a predetermined motor fault pattern at a predetermined timing when the motor current is constant, a second step of calculating a fault level indicating a value equal to or greater than zero according to the degree of fault occurring in the motor based on the fault pattern, and a third step of calculating a cumulative fault count value indicating a cumulative value of the fault level from the fault level. The calculation formula for the cumulative fault count value in the third step includes an increase term for accumulating the fault level, and a subtraction term for subtracting the cumulative fault count value when the cumulative fault count value is smaller than the minimum value of the fault level that is non-zero and the fault level is zero. The lifespan determination method further includes a fourth step of determining that the motor lifespan is short when the cumulative fault count value is higher than a threshold value, and a fifth step of determining that the motor lifespan is long when the cumulative fault count value is lower than the threshold value.

[0015] In the above-mentioned lifespan determination method, a fault level is calculated based on the motor's fault pattern, and a cumulative fault count value is calculated from the fault level. The lifespan of the motor is then determined based on the cumulative fault count value. Since the calculation formula for the cumulative fault count value includes a subtraction term that subtracts the cumulative fault count value when the fault level is zero, the cumulative fault count value is subtracted for faults that occur accidentally. Therefore, this lifespan determination method makes it possible to determine the lifespan of the motor that is not due to accidental failure.

[0016] The first step may determine a failure pattern based on at least one of the first to third parameters. The first parameter is a magnitude of angular acceleration of the motor. The second parameter is a speed underachievement time indicating a time during which the angular velocity of the motor continues to be below a target. The third parameter is a speed underachievement count indicating a number of times the angular velocity of the motor falls below the target. The first step may determine first to third failure patterns, which are failure patterns of the motor, based on the first to third parameters, respectively, and the second step may add a predetermined weighted value to each of the first to third failure patterns.

[0017] With the above configuration, it is possible to adjust the relationship between each of the first to third parameters and the fault level, and further the relationship between each parameter and the motor lifespan, thereby making it possible to more accurately determine the motor lifespan.

[0018] The thresholds may include a first threshold and a second threshold smaller than the first threshold. A fourth step may determine that the motor has a short life if the cumulative failure count value is higher than the first threshold, and a fifth step may determine that the motor has a long life if the cumulative failure count value is lower than the second threshold. The life determination method may further include a sixth step of determining that the motor has neither a short life nor a long life if the cumulative failure count value is lower than the first threshold and higher than the second threshold.

[0019] By adopting the above-mentioned configuration, the life of the motor can be appropriately determined. Effect of the Invention

[0020] According to the motor control device and motor life determination method of the present disclosure, the life of the motor can be determined with high accuracy. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 illustrates an example of a configuration of a motor control device according to an embodiment of the present disclosure. [Diagram 2] FIG. 11 is a diagram showing changes in the rotation angle, angular velocity, and angular acceleration of a motor when the motor is normal (no fault is occurring). [Diagram 3] 11A and 11B are diagrams showing changes in the rotation angle, angular velocity, and angular acceleration of a motor when a fault occurs in the motor. [Figure 4] 11A and 11B are diagrams showing changes in the rotation angle, angular velocity, and angular acceleration of a motor when a fault occurs in the motor. [Diagram 5]11A and 11B are diagrams showing changes in the rotation angle, angular velocity, and angular acceleration of a motor when a fault occurs in the motor. [Figure 6] 11A and 11B are diagrams showing changes in the rotation angle, angular velocity, and angular acceleration of a motor when a fault occurs in the motor. [Figure 7] 11A and 11B are diagrams showing changes in the rotation angle, angular velocity, and angular acceleration of a motor when a fault occurs in the motor. [Figure 8] 11A and 11B are diagrams showing changes in the rotation angle, angular velocity, and angular acceleration of a motor when a fault occurs in the motor. [Figure 9] FIG. 11 is a diagram illustrating an example of a transition of a failure level. [Figure 10] 10 is a diagram showing a transition of a cumulative fault count value calculated based on the fault levels shown in FIG. 9. FIG. [Figure 11] 5 is a flowchart showing an example of a procedure for a motor life determination process executed in the motor control device. [Figure 12] 11A and 11B are diagrams showing changes in the rotation angle, angular velocity, and angular acceleration when the motor current is increased after the motor has stopped due to a fault. [Figure 13] 13 is a flowchart showing an example of a fault pattern S2 determination process in the first modification. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference characters and their description will not be repeated.

[0023] 1 is a diagram showing an example of a configuration of a motor control device according to an embodiment of the present disclosure. With reference to Fig. 1, motor control device 1 includes a motor control unit 10, a rotation angle sensor 15, calculation units 20 and 25, a determination unit 30, a storage unit 35, and a timer 40.

[0024] The motor control unit 10 generates a current command Im for driving the motor 2, and controls the motor 2 in accordance with the generated current command Im. The motor 2 is, for example, an AC motor, but may also be a DC motor.

[0025] The rotation angle sensor 15 detects the rotation angle θ of the rotor of the motor 2. A known rotation angle sensor can be used as the rotation angle sensor 15. The calculation unit 20 calculates the angular velocity ω of the motor 2 by calculating the differential value dθ / dt of the rotation angle θ detected by the rotation angle sensor 15. The calculation unit 25 calculates the angular acceleration α of the motor 2 by calculating the differential value dω / dt of the angular velocity ω calculated by the calculation unit 20.

[0026] The judgment unit 30 receives the calculated values ​​of the angular velocity ω and angular acceleration α of the motor 2 from the calculation units 20, 25, respectively. The judgment unit 30 then judges the fault pattern occurring in the motor 2 based on the angular velocity ω and angular acceleration α of the motor 2, and judges the life of the motor 2 based on the fault pattern judgment result. Note that as shown in the figure, the judgment unit 30 may receive the rotation angle θ of the motor 2 from the rotation angle sensor 15, and the calculations by the calculation units 20, 25 may be performed in the judgment unit 30. The methods for judging the fault pattern and life of the motor 2 will be described in detail later.

[0027] The memory unit 35 is a storage for storing various data, and in this embodiment, stores a cumulative fault count value TC described below. The memory unit 35 is, for example, a hard disk drive (HDD: Hard Disk Drive) or a solid state drive (SSD: Solid State Drive). The timer 40 is used by the determination unit 30 to measure a certain period for counting a speed underachievement time T and a speed underachievement count N described below.

[0028] The motor control unit 10, the determination unit 30, and the calculation units 20 and 25 are configured, for example, by an electronic control unit (ECU (Electronic Control Unit)) including a CPU (Central Processing Unit) and a memory. The memory includes a ROM (Read Only Memory) that stores processing programs and the like, and a RAM (Random Access Memory) that temporarily stores data. The CPU deploys the program stored in the ROM into the RAM and executes it. The program stored in the ROM describes various processes to be executed by the motor control unit 10, the determination unit 30, and the calculation units 20 and 25. An ECU may be provided for each of the motor control unit 10, the determination unit 30, and the calculation units 20 and 25, or may be configured as a single ECU including the functions of the motor control unit 10, the determination unit 30, and the calculation units 20 and 25.

[0029] <Determining the fault pattern of Motor 2> The fault pattern and lifespan of the motor 2 are determined when the motor 2 is driven with the current of the motor 2 constant. By keeping the current of the motor 2 constant, it is possible to determine the level of the fault occurring in the motor 2 from the state in which the angular velocity ω of the motor 2 has not reached the target and the magnitude of the angular acceleration α of the motor 2.

[0030] A fault in the motor 2 can be detected from the magnitude of the angular acceleration α of the motor 2 as follows. For the motor 2, the following equation of motion holds true.

[0031] J×α=Tm-TL …(1) In the above equation, J is the moment of inertia of the rotating body, Tm is the torque generated by motor 2, and TL is the load torque acting on the rotating body including motor 2. By transforming equation (1) as Tm = k × Im (k is a constant), the following equation is obtained.

[0032] TL = k × Im-J × α … (2) When the current of the motor 2 is constant at Im, if the motor 2 is normal, the motor 2 rotates at a constant angular velocity, so that the angular acceleration α is 0 and TL = k × Im (constant value).

[0033] On the other hand, if some fault occurs in motor 2 and the load torque TL fluctuates even though the current of motor 2 is constant at Im, the fluctuation in the load torque TL appears in the second term on the right side of equation (2), i.e., the angular acceleration α, because the first term on the right side of equation (2) is a constant value. Therefore, under conditions where the current of motor 2 is constant, the fluctuation in the load torque TL can be detected from the angular acceleration α of motor 2, and one of the faults in motor 2 (fluctuations in the load torque TL even though the current of motor 2 is constant) can be detected based on the angular acceleration α.

[0034] Each of Fig. 2 to Fig. 8 is a diagram showing an example of the transitions of the rotation angle θ, angular velocity ω, and angular acceleration α of the motor 2. Fig. 2 shows the transitions when the motor 2 is normal (no fault occurs). Fig. 3 to Fig. 8 show the transitions when some fault occurs in the motor 2. Note that each diagram shows the transitions of the rotation angle θ, angular velocity ω, and angular acceleration α when the current Im of the motor 2 is constant.

[0035] 2, when motor 2 is normal, after time t1 when current Im becomes constant, angular velocity ω is constant along a target (a value corresponding to the magnitude of current Im), and angular acceleration α is zero.

[0036] 3, this example shows a case where the current Im is constant after time t11, but at time t12, some major load abnormality occurs, causing the motor 2 to suddenly stop, and the stopped state of the motor 2 continues after time t12. In this case, the angular velocity ω remains at 0 after time t12, and the angular acceleration α has a large value at time t12.

[0037] 4, this example shows a case where at time t22, some major load abnormality occurs and motor 2 suddenly stops, but motor 2 starts moving again shortly thereafter and returns to a normal state at time t23. In this case, angular velocity ω decreases between times t22 and t23, but returns to a normal value after time t23, and angular acceleration α has a large value at time t22.

[0038] 5, this example shows a case where the current Im is constant after time t31, but some load abnormality occurs at time t32, causing the motor 2 to slowly stop at time t33 and the stopped state of the motor 2 to continue after time t33. In this case, the angular velocity ω remains at 0 after time t33. As for the angular acceleration α, since the motor 2 slowly stops, the fluctuation of the angular acceleration α is small.

[0039] 6, this example shows a case where at time t42, some load abnormality occurs, causing motor 2 to slowly stop, but then motor 2 starts moving again shortly thereafter, and returns to a normal state at time t43. In this case, angular velocity ω decreases between times t42 and t43, but returns to a normal value after time t43. As for angular acceleration α, since motor 2 slowly stops, the fluctuation of angular acceleration α is small.

[0040] 7, in this example, after time t51, the current Im is constant at the same magnitude as in the other examples, but the angular velocity ω continues to be below the target (a value corresponding to the magnitude of the current Im) indicated by the dotted line due to some load abnormality occurring in the motor 2. However, because the fluctuation in the angular velocity ω is small, the angular acceleration α is approximately 0.

[0041] 8, in this example, at time t62, some major load abnormality occurs and motor 2 suddenly stops, but motor 2 starts moving again shortly thereafter, and at time t63, it returns to a normal state. After that, at time t64, some major load abnormality occurs again and motor 2 suddenly stops, but motor 2 starts moving again shortly thereafter, and at time t65, it returns to a normal state. In this example, such sudden stops of motor 2 and subsequent recovery are repeated. In this case, angular velocity ω decreases every time motor 2 stops. Angular acceleration α increases every time motor 2 suddenly stops.

[0042] In this way, when a fault occurs in the motor 2, the angular velocity ω and the angular acceleration α change in various ways. In other words, various states of a fault occurring in the motor 2 can be detected based on the angular velocity ω and the angular acceleration α of the motor 2. Therefore, in this embodiment, the level of the fault occurring in the motor 2 is determined by three parameters based on the angular velocity ω and the angular acceleration α.

[0043] The first parameter is the magnitude of the angular acceleration α of the motor 2. When the current Im is constant, it is considered that the greater the magnitude of the angular acceleration α occurring in the motor 2, the greater the degree of the damage occurring in the motor 2 (for example, the deeper and larger the scratches occurring on the contact surface of the rotating body). Therefore, it is considered that the greater the magnitude of the angular acceleration α, the greater the damage pattern of the motor 2 (hereinafter referred to as "fault pattern S1"). For example, in a comparison between the situation shown in FIG. 3 and the situation shown in FIG. 5, the situation in FIG. 3, where the magnitude of the angular acceleration α is greater, is determined to have a greater damage pattern S1 than the situation in FIG. 5. In a comparison between the situation shown in FIG. 4 and the situation shown in FIG. 6, the situation in FIG. 4, where a large angular acceleration α occurs, is determined to have a greater damage pattern S1 than the situation in FIG. 6.

[0044] The second parameter is the speed underachievement time, which indicates the time during which the angular velocity ω of the motor 2 continues to be below the target (a value corresponding to the magnitude of the current Im). It is considered that the longer the speed underachievement time, the greater the degree of the fault that has occurred in the motor 2 (for example, the motor 2 continues to be stopped due to a fault). Therefore, it is considered that the longer the speed underachievement time, the greater the fault pattern of the motor 2 (hereinafter referred to as "fault pattern S2"). For example, in the situation shown in FIG. 3 or FIG. 5 and the situation shown in FIG. 4, the fault pattern S2 is determined to be greater in the situations shown in FIG. 3 and FIG. 5, where the speed underachievement time is longer, than in the situation shown in FIG. 4. In addition, in the situation shown in FIG. 4 and the situation shown in FIG. 7, the fault pattern S2 is determined to be greater in the situation shown in FIG. 7, where the speed underachievement time is longer, than in the situation shown in FIG. 4.

[0045] The third parameter is the number of times the speed does not reach the target, which indicates the number of times the angular velocity ω of the motor 2 falls below the target. It is considered that the greater the number of times the speed does not reach the target, the greater the degree of the fault that has occurred in the motor 2 (e.g., the motor 2 is repeatedly stopped and restarted). Therefore, it is considered that the greater the number of times the speed does not reach the target, the greater the fault pattern of the motor 2 (hereinafter referred to as "fault pattern S3"). For example, when comparing the situation shown in FIG. 4 and the situation shown in FIG. 8, the situation in FIG. 8, which has a greater number of times the speed does not reach the target, is determined to have a greater fault pattern S3 than the situation in FIG. 4.

[0046] Each of the obstacle patterns S1 to S3 is judged, for example, into five stages. That is, the obstacle pattern S1 is judged into five stages according to the magnitude of the angular acceleration α that occurred. The obstacle patterns S2 and S3 are also judged into five stages according to the length of the speed underachievement time and the number of times the speed underachievement occurs. The five-stage judgment is just an example, and there may be more or less than five stages.

[0047] <Determining the lifespan of Motor 2> In this embodiment, the life of the motor 2 is judged based on the fault patterns S1 to S3 determined as described above. Specifically, the life of the motor 2 is judged as follows.

[0048] In this embodiment, first, a fault level C indicating the degree of fault occurring in the motor 2 is calculated based on the fault patterns S1 to S3. This fault level C indicates the overall degree of fault taking into account the fault patterns S1 to S3. The fault level C is expressed as a function of the fault patterns S1 to S3 by the following equation.

[0049] Disturbance level C = f(S1, S2, S3) … (3) Various formulas can be used for the function f, but in this embodiment, the following formula is used, which adds a weighted value to each of the failure patterns S1 to S3.

[0050] Disability level C = S1 × w1 + S2 × w2 + S3 × w3 … (4) wi (i=1 to 3) indicates a weight for the trouble pattern Si. The weight wi can be set appropriately, for example, w2>w3>w1. That is, the weight w2 of the trouble pattern S2 based on the speed underachievement time is the largest, followed by the weight w3 of the trouble pattern S3 based on the speed underachievement count. However, the order of magnitude of the weight wi is not limited to the above order.

[0051] This fault level C indicates the degree of fault in the motor 2 at a certain point in time, and in this embodiment, a cumulative fault count value TC is calculated by accumulating the fault levels C. The cumulative fault count value TC is calculated based on the fault level C using the following formula.

[0052] TC(current value) = TC(previous value) + C (when C>0) ... (5-1) TC(current value) = TC(previous value) - A (when C = 0) ... (5-2) Note that A is a positive constant and is a subtraction term that subtracts the cumulative fault count value TC when the fault level C is 0 (no fault has occurred in the motor 2, and all of the fault patterns S1 to S3 are 0). The magnitude of A is set to a value smaller than the minimum value of the non-zero fault level C. Calculations of the fault level C and the cumulative fault count value TC are performed at each predetermined calculation cycle, and TC (previous value) indicates the value of the cumulative fault count value TC calculated at the previous calculation timing.

[0053] In this embodiment, the life of the motor 2 is determined based on this cumulative fault count value TC. Specifically, the greater the cumulative value of the fault level C, which indicates the degree of fault occurring in the motor 2, the shorter the life of the motor 2 is determined to be.

[0054] Here, as shown in equation (5-2), in this embodiment, the calculation equation for the cumulative fault count value TC includes a subtraction term A that subtracts the cumulative fault count value TC when the fault level C is 0. As a result, for an accidentally (single) fault, the cumulative fault count value TC temporarily increases when the fault occurs, but is thereafter subtracted by the subtraction term A each time the cumulative fault count value TC is calculated. Therefore, according to this embodiment, when determining the life of the motor 2, accidentally occurring faults can be ignored, and the true life can be determined, not due to accidental failures.

[0055] Fig. 9 is a diagram showing an example of the transition of the fault level C. Referring to Fig. 9, the fault level C indicates the degree of a fault occurring in the motor 2 at a certain point in time, and in this example, it is shown that a fault occurs in the motor 2 at each of times t1 to t7. Note that, since the magnitude of the fault level C differs between times t1 to t5 and times t6 and t7, it can be understood that the level or type of the fault occurring is different.

[0056] Fig. 10 is a diagram showing the transition of the cumulative fault count value TC calculated based on the fault level C shown in Fig. 9. Referring to Fig. 10, at time t1, the cumulative fault count value TC increased in response to the fault level C becoming > 0, but thereafter, as the fault level C = 0 continued, the cumulative fault count value TC gradually decreases to 0 without exceeding the threshold value L1.

[0057] Threshold values L1 and L2 (L1 < L2) are threshold values indicating the life of motor 2. When the cumulative failure count value TC is lower than threshold value L1, it is determined that the life of motor 2 is still long. When the cumulative failure count value TC exceeds threshold value L2, it is determined that the life of motor 2 is short. When the cumulative failure count value TC is higher than threshold value L1 and lower than threshold value L2, it is determined that the life of motor 2 is neither short nor long. In this example, two threshold values L1 and L2 (L1 < L2) are provided, but L1 = L2 may also be used.

[0058] Also at times t2 and t3, the cumulative failure count value TC does not exceed threshold value L1 and then decreases to 0. On the other hand, after time t4, the failure level C > 0 continues, and the cumulative failure count value TC increases due to the accumulation of the failure level C. And the cumulative failure count value TC exceeds threshold value L2, and it is determined that the life of motor 2 is short.

[0059] FIG. 11 is a flowchart showing an example of the procedure of the motor life determination process executed in the motor control device 1. Referring to FIG. 11, first, the determination unit 30 of the motor control device 1 determines whether to perform the life determination of motor 2 (step S10). In this embodiment, since the life determination of motor 2 is performed with the current of motor 2 kept constant, for example, it is performed during the offline operation of the rotation control by motor 2 or the like.

[0060] And when it is determined that the life determination of motor 2 is to be performed (YES in step S10), a command indicating that the life determination of motor 2 is to be performed is output from the determination unit 30 to the motor control unit 10. In response to the command, the motor control unit 10 controls the current of motor 2 to a predetermined constant value in order to perform the life determination (step S15). The magnitude of the constant value can be set as appropriate. In this embodiment, motor 2 is an AC motor, and the effective value of the motor current is controlled to be constant.

[0061] Next, the determination unit 30 obtains the angular velocity ω and angular acceleration α of the motor 2 from the calculation units 20 and 25, respectively (step S20). The angular velocity ω of the motor 2 is calculated by the calculation unit 20 from the rotation angle θ detected by the rotation angle sensor 15. Moreover, the angular acceleration α of the motor 2 is calculated by the calculation unit 25 from the angular velocity ω calculated by the calculation unit 20.

[0062] Then, based on the acquired angular velocity ω, the judgment unit 30 calculates a speed underachievement time T indicating the time during which the angular velocity ω continues to fall below the target (step S30). The target angular velocity ω is an angular velocity corresponding to the magnitude of the current Im of the motor 2, which is controlled to a constant value. Furthermore, based on the angular velocity ω, the judgment unit 30 calculates a speed underachievement count N indicating the number of times the angular velocity ω falls below the target within a predetermined fixed period (step S35). The length of the fixed period can be set appropriately. The speed underachievement time T and the fixed period are measured using a timer 40.

[0063] Next, the determination unit 30 determines a trouble pattern S1 according to the magnitude of the angular acceleration α based on the angular acceleration α acquired in step S20 (step S40). When the angular acceleration α is approximately 0, the trouble pattern S1 is determined to be 0.

[0064] Furthermore, the determination unit 30 determines a trouble pattern S2 according to the length of the speed underachievement time T based on the speed underachievement time T calculated in step S30 (step S45). When the speed underachievement time T is approximately 0, the trouble pattern S2 is determined to be 0.

[0065] Furthermore, the determination unit 30 determines a trouble pattern S3 according to the number of times N of speed underachievement calculated in step S35 (step S45). When the number of times N of speed underachievement is approximately 0, the trouble pattern S3 is determined to be 0.

[0066] Then, the determining unit 30 calculates the fault level C based on the fault patterns S1 to S3 determined in steps S40 to S50 (step S55). In this embodiment, the fault level C is calculated by the above formula (4).

[0067] Next, the determination unit 30 calculates the cumulative fault count value TC by the above formulas (5-1) and (5-2) based on the calculated fault level C (step S60). The calculated cumulative fault count value TC is temporarily stored in the memory unit 35. The cumulative fault count value TC stored in the memory unit 35 is used as the previous value in the next calculation. Then, the determination unit 30 determines whether the calculated cumulative fault count value TC is smaller than a threshold value L1 (step S65).

[0068] If it is determined that the cumulative fault count value TC is smaller than the threshold value L1 (YES in step S65), the determination unit 30 determines that the life of the motor 2 is still long (step S70). On the other hand, if it is determined in step S65 that the cumulative fault count value TC is equal to or greater than the threshold value L1 (NO in step S65), the determination unit 30 proceeds to step S75.

[0069] Next, the judgment unit 30 judges whether the calculated cumulative fault count value TC is greater than the threshold value L2 (L2>L1) (step S75). If it is judged that the cumulative fault count value TC is greater than the threshold value L2 (YES in step S75), the judgment unit 30 judges that the life of the motor 2 is short (step S80). On the other hand, if it is judged that the cumulative fault count value TC is equal to or less than the threshold value L2 (NO in step S75), the judgment unit 30 returns the process to step S10 without executing step S80. Note that the process also returns to step S10 after executing step S80.

[0070] As described above, in this embodiment, the fault level C is calculated based on the fault patterns S1 to S3 of the motor 2, and the cumulative fault count value TC is calculated from the fault level C. The life of the motor 2 is then determined based on the cumulative fault count value TC, and since the calculation formula for the cumulative fault count value TC includes a subtraction term A that subtracts the cumulative fault count value TC when the fault level C is zero, the cumulative fault count value TC is subtracted for faults that occur accidentally. Therefore, according to this embodiment, the life of the motor 2 can be determined for faults that are not accidental malfunctions.

[0071] [Variation 1] In the above embodiment, the fault pattern S2 is determined based on the length of the speed not-reaching time T of the motor 2. However, when the rotation of the motor 2 has stopped due to a fault (angular velocity ω=0), the fault pattern S2 may also be determined based on whether the current Im of the motor 2 is increased and the motor 2 rotates.

[0072] Fig. 12 is a diagram showing the transition of the rotation angle θ, angular velocity ω, and angular acceleration α when the current Im of the motor 2 is increased after the motor 2 stops due to a fault. Referring to Fig. 12, in this example, at time t72, the motor 2 stops due to a fault. Thereafter, while the motor 2 is stopped, the motor current Im is increased at time t73. Fault pattern S2 is determined depending on whether the motor 2 rotates due to this increase in current Im.

[0073] In this example, the motor 2 starts rotating due to the increase in the current Im at time t73. Therefore, the fault pattern S2 is determined to be lower than the case where the motor 2 continues to be stopped even if the current Im is increased (not shown).

[0074] Fig. 13 is a flowchart showing an example of a determination process of the fault pattern S2 in this modified example 1. Referring to Fig. 13, the determination unit 30 determines whether or not the angular velocity ω of the motor 2 is 0 (step S110). When the angular velocity ω is not 0 (NO in step S110), the fault pattern S2 is determined to be "0" (step S115).

[0075] If it is determined in step S110 that the angular velocity ω is 0 (YES in step S110), the determination unit 30 outputs a current increase command to the motor control unit 10, and the motor control unit 10 increases the current of the motor 2 by a predetermined amount (step S120).

[0076] Then, the determination unit 30 determines whether the angular velocity ω of the motor 2 is 0 or not (step S125). When the angular velocity ω is not 0 (NO in step S125), that is, when the motor 2 starts to rotate due to the increase in the current of the motor 2, the fault pattern S2 is determined to be "1" (step S130).

[0077] If it is determined in step S125 that the angular velocity ω is still 0 (YES in step S125), the determination unit 30 further increases the current of the motor 2 by a predetermined amount (step S135).

[0078] Then, the determination unit 30 determines again whether the angular velocity ω of the motor 2 is 0 or not (step S140). When the angular velocity ω is not 0 (NO in step S140), that is, when the motor 2 starts to rotate by increasing the current of the motor 2 again, the fault pattern S2 is determined to be "2" (step S145). On the other hand, when it is determined in step S140 that the angular velocity ω is still 0 (YES in step S140), the fault pattern S2 is determined to be "3" (step S160).

[0079] The above series of processes may be performed when the speed underachievement time T of the motor 2 exceeds a predetermined time.

[0080] In this way, in the first modification, when the rotation of the motor 2 is stopped due to a fault (angular velocity ω=0), the current of the motor 2 is increased stepwise to determine the fault pattern S2 depending on whether the motor 2 rotates or not. Since consideration is given not only to the length of the speed underachievement time T (the time the motor 2 is stopped) but also to whether the motor 2 rotates depending on the current, the fault pattern S2 can be determined in detail. As a result, the life of the motor 2 can also be determined in more detail.

[0081] [Variation 2] In the above embodiment, the trouble pattern and life of the motor 2 are determined based on the angular velocity ω and angular acceleration α of the motor 2. That is, the trouble patterns S1 to S3 are determined based on the angular acceleration α (first parameter), and the speed underachievement time T (second parameter) and the speed underachievement count N (third parameter) calculated based on the angular velocity ω, and the trouble patterns S1 to S3 are used to determine the life of the motor 2.

[0082] As a modification of this, the obstacle pattern and life of the motor 2 may be determined based on any one or two of the angular acceleration α (first parameter), the speed underachievement time T (second parameter), and the speed underachievement count N (third parameter). For example, the life of the motor 2 may be determined using only the obstacle pattern S1 determined based on the angular acceleration α, or the obstacle pattern S1 determined based on the angular acceleration α and the obstacle pattern S2 determined based on the speed underachievement time T. Alternatively, the life of the motor 2 may be determined using the obstacle pattern S1 determined based on the angular acceleration α and the obstacle pattern S3 determined based on the speed underachievement count N, or the obstacle pattern S2 determined based on the speed underachievement time T and the obstacle pattern S3 determined based on the speed underachievement count N.

[0083] [Variation 3] In the above embodiment, the subtraction term A of the cumulative fault count value TC shown in equation (5-2) is a constant, but the value of subtraction term A may be increased the longer the time that fault level C is 0 or the greater the number of consecutive times that fault level C is 0. The longer the time that fault level C is 0 or the greater the number of consecutive times that fault level C is 0, the more likely it is that the previous fault was accidental and not the end of the motor's life. Therefore, by making subtraction term A variable as described above, the life of motor 2 can be determined more accurately.

[0084] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The technical scope of the present disclosure is defined by the claims, not by the description of the embodiments described above, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0085] 1 motor control device, 2 motor, 10 motor control unit, 15 rotation angle sensor, 20, 25 calculation unit, 30 judgment unit, 35 memory unit, 40 timer.

Claims

1. A control unit that drives the motor; A determination unit that determines the life of the motor, The determination unit is When the motor is driven by the control unit with a constant current to the motor, a predetermined fault pattern of the motor is determined at each predetermined timing, calculating a fault level indicating a value equal to or greater than zero according to the degree of the fault occurring in the motor based on the fault pattern; calculating a cumulative fault count value indicating a cumulative value of the fault level using the fault level; the calculation formula for the cumulative fault count value includes an increment term for accumulating the fault level, and a decrement term for decrementing the cumulative fault count value when the fault level is zero, The determination unit further If the cumulative fault count value is higher than a threshold value, it is determined that the motor has a short lifespan; A motor control device that determines that the motor has a long life when the cumulative fault count value is lower than the threshold value.

2. The motor control device according to claim 1 , wherein the subtraction term has a larger value as the time during which the fault level is zero becomes longer.

3. The motor control device according to claim 1 , wherein the subtraction term has a larger value as the number of consecutive times that the fault level is zero increases.

4. the determination unit determines the fault pattern based on at least one of first to third parameters; the first parameter is a magnitude of angular acceleration of the motor; the second parameter is a speed underachievement time indicating a time during which the angular velocity of the motor continues to be below a target; the third parameter is a speed underachievement count indicating the number of times that the angular velocity of the motor falls below the target; the determination unit determines first to third fault patterns, which are the fault patterns, based on the first to third parameters, respectively; 4. The motor control device according to claim 1, wherein the fault level is a value obtained by adding a predetermined weighted value to each of the first to third fault patterns.

5. The threshold value is a first threshold value; a second threshold value less than the first threshold value; The determination unit is If the cumulative fault count value is higher than the first threshold value, it is determined that the motor has a short lifespan; determining that the motor has a long life when the cumulative fault count value is lower than the second threshold value; 5. The motor control device according to claim 1, wherein when the cumulative fault count value is lower than the first threshold value and higher than the second threshold value, it is determined that the life of the motor is neither short nor long.

6. A method for determining a lifespan of a motor, comprising the steps of: A first step of determining a predetermined fault pattern of the motor at each predetermined timing when a current of the motor is constant; a second step of calculating a fault level indicating a value equal to or greater than zero according to the degree of the fault occurring in the motor based on the fault pattern; and a third step of calculating, from the fault level, a cumulative fault count value indicating a cumulative value of the fault level, The calculation formula for the cumulative fault count value in the third step includes an increment term for accumulating the fault level, and a decrement term for decrementing the cumulative fault count value when the fault level is zero and is smaller than a non-zero minimum value of the fault level, and further includes a fourth step of determining that the motor has a short life if the cumulative fault count value is higher than a threshold value; a fifth step of determining that the motor has a long life if the cumulative fault count value is lower than the threshold value.

7. The first step includes determining the fault pattern based on at least one of first to third parameters; the first parameter is a magnitude of angular acceleration of the motor; the second parameter is a speed underachievement time indicating a time during which the angular velocity of the motor continues to be below a target; the third parameter is a speed underachievement count indicating the number of times that the angular velocity of the motor falls below the target; The first step includes determining first to third fault patterns, which are fault patterns of the motor, based on the first to third parameters, respectively; 7. The motor life judgment method according to claim 6, wherein said second step adds a predetermined weighted value to each of said first to third fault patterns.

8. The threshold value is a first threshold value; a second threshold value less than the first threshold value; the fourth step is to determine that the motor has a short life when the cumulative fault count value is higher than the first threshold value; The fifth step determines that the motor has a long life when the cumulative fault count value is lower than the second threshold value, and further comprises:

8. The motor life judgment method according to claim 6 or claim 7, further comprising a sixth step of judging that the motor life is neither short nor long when the cumulative fault count value is lower than the first threshold value and higher than the second threshold value.

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