JP3857425B2 - Servo motor demagnetization inspection method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a servo motor demagnetization inspection method capable of inspecting a demagnetization of a permanent magnet used in a servo motor easily and in a short time.
[0002]
[Prior art]
As is well known, an electromagnetic force motor configured as a servo motor includes a stator (stator) or a rotor {rotor (for a rotary servo motor)}, a slider {slider (for a linear servo motor)}. Alternatively, permanent magnets are widely used for vibrators {vibrators (in the case of vibration type servo motors)}.
[0003]
By the way, a permanent magnet may have a decrease in magnetic force (demagnetization) due to external factors such as temperature, humidity, and impact. For example, in a rotary servo motor, if demagnetization occurs, the torque constant of the servo motor is reduced, so that a desired torque for an arbitrary torque current cannot be obtained. As a method according to a conventional example for inspecting such demagnetization, the following technique is used.
[0004]
In other words, when position control or speed control is performed on a servo motor, the demagnetization is inspected by utilizing the fact that the effect of demagnetization appears in the form of a tracking abnormality with respect to the position command or speed command.
[0005]
[Problems to be solved by the invention]
However, in the conventional technique described above, since the demagnetization inspection is performed based on the follow-up abnormality with respect to the position command or the speed command, this technique cannot be applied when torque control is performed on the servo motor.
[0006]
The present invention has been made in view of such problems, and an object of the present invention is to provide a servo motor demagnetization inspection method capable of easily and in a short time performing a demagnetization inspection on a servo motor. To do.
[0007]
[Means for Solving the Problems]
In the present invention, the position of the permanent magnet is detected based on the rotation angle of the rotor of the servo motor, and the torque current value supplied to the servo motor, the frictional force generated in the servo motor, and the acceleration of the servo motor are calculated. Obtaining the calculated inertia of the servo motor from the torque current value, the frictional force and the acceleration, and a torque constant defined as a value specific to the servo motor, and obtaining the calculated inertia and the servo motor A permanent inertia used for the servo motor is compared with each detected position of the permanent magnet determined as a specific value, and the position of the permanent magnet where demagnetization occurs is determined. The demagnetization of the magnet is inspected.
[0008]
In this case, the torque current value, the frictional force, and the acceleration can be obtained by calculation while driving the servomotor based on an arbitrary speed plan or torque plan. Is possible.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[0010]
First, a servo motor drive system 10 to which an embodiment of the present invention is applied will be described with reference to FIG.
[0011]
The servo motor drive system 10 basically includes a servo motor 20 and a control device 40 that controls the drive of the servo motor 20 and functions as a demagnetization inspection device. In the servo motor drive system 10, an AC servo motor is used as the servo motor 20.
[0012]
Here, the servo motor 20 basically includes a rotor 22 having a rotating shaft 21 and a stator 30 disposed so as to surround the rotor 22.
[0013]
The rotor 22 has four magnets 24a to 24d arranged at 90 ° intervals. Specifically, the magnets 24a to 24d have their outer (stator 30 side) ends separated from each other by 90 ° with respect to the rotation direction of the rotor 22, and the outer ends are alternately N poles. , S pole, N pole, and S pole. Actually, the outer ends of the magnets 24a and 24c are N poles, and the outer ends of the magnets 24b and 24d are S poles. A magnetic pole position detector (encoder, resolver, etc.) 26 for detecting the rotation angle of the rotor 22, in other words, the positions of the magnets 24 a to 24 d (magnetic pole position Pm) is attached to the rotating shaft 21 of the rotor 22. ing.
[0014]
The stator 30 of the servo motor 20 has three coils 32u, 32v, 32w arranged at intervals of 120 °. These coils 32u, 32v, 32w are connected to an inverter 46, which will be described later, via cables 34u, 34v, 34w. From the inverter 46 to the coils 32u, 32v, 32w, U-phase, V Phase and W phase alternating currents are supplied. Also, current sensors 38u and 38v are attached to the cables 34u and 34v, respectively, and the current sensors 38u and 38v supply the coils 32u and 32v from the inverter 46 via the cables 34u and 34v. Current values Iu and Iv of the U-phase and V-phase alternating currents are detected. The current value Iw of the W-phase alternating current is obtained from the current values Iu and Iv. Further, the torque current value I indicating the torque generated in the servo motor 20 is obtained from the current values Iu, Iv and Iw.
[0015]
On the other hand, the control device 40 determines the magnitude of torque to be generated by the servo motor 20 based on the magnetic pole position Pm from the magnetic pole position detector 26 and the current values Iu and Iv from the current sensors 38u and 38v. A controller 42 for obtaining a current command value I0 to be output, and a PWM generating circuit for outputting an alternating current signal Sp having a pulse train based on the current command value I0 from the controller 42 and the magnetic pole position Pm from the magnetic pole position detector 26 44 and an inverter 46 for supplying three-phase (U-phase, V-phase, W-phase) alternating current based on the alternating current signal Sp from the PWM generating circuit 44 to the coils 32u, 32v, 32w.
[0016]
Next, the operation of the servo motor drive system 10 will be described.
[0017]
The controller 42 obtains a current command value I0 based on the magnetic pole position Pm from the magnetic pole position detector 26 and the current values Iu and Iv from the current sensors 38u and 38v. The PWM generation circuit 44 outputs an alternating current signal Sp having a pulse train based on the current command value I0 from the controller 42 and the magnetic pole position Pm from the magnetic pole position detector 26. The inverter 46 supplies three-phase (U-phase, V-phase, W-phase) AC currents based on the AC current signal Sp from the PWM generation circuit 44 to the coils 32u, 32v, 32w. The rotor 22 of the servo motor 20 rotates by generating a torque based on the current value of the three-phase alternating current.
[0018]
Next, a method for inspecting the demagnetization of the servo motor 20 will be described with reference to FIGS.
[0019]
In the present embodiment, the servo motor 20 is driven based on a predetermined speed plan or torque plan, and at that time, inertia identification (calculation of inertia) of the servo motor 20 is performed to perform demagnetization inspection.
[0020]
First, the equation of motion of the servo motor 20 expressed by the following equation (1) is obtained.
[0021]
K × I−m × α−μ (V) = 0 (1)
Here, m is a calculated inertia which is an actual inertia of the rotor 22 (hereinafter also referred to as a calculated inertia). I is a torque current value, and is obtained from current values Iu and Iv detected by the current sensors 38u and 38v. Further, μ (V) is a friction (frictional force) and is approximated as a function (for example, a linear function) of the rotational speed V. The rotational speed V is obtained by differentiating the magnetic pole position Pm detected by the magnetic pole position detector 26 with a predetermined minute time. Furthermore, α is the acceleration of the rotor 22 and is obtained by differentiating the rotational speed V by a predetermined minute time. K is a torque constant, and is defined as a value unique to the servo motor 20.
[0022]
The following equation (2) is obtained by modifying the equation (1).
[0023]
m = {K × I−μ (V)} / α (2)
Here, the torque current value I, the friction μ (V), and the acceleration α can be obtained by calculation as described above. Since the torque constant K is a predetermined value, the calculated inertia m is the torque current value I, It is obtained by substituting the friction μ (V), the acceleration α and the torque constant K into the equation (2). However, when a load (not shown) is connected to the rotating shaft 21 of the rotor 22 of the servo motor 20, the calculated inertia m may be obtained including this load.
[0024]
Next, FIG. 2A shows an example of a speed plan for demagnetization inspection when position control or speed control of the servomotor 20 is performed.
[0025]
In this speed plan, the rotational speed (angular speed) V of the rotor 22 of the servo motor 20 increases linearly from 0 to + V1 in the period from time t0 to t1, and linear from + V1 to 0 in the period from time t1 to t2. And decreases linearly from 0 to -V1 in the period from time t2 to t3, increases linearly from -V1 to 0 in the period from time t3 to t4, and from 0 in the period from time t4 to t5 The sawtooth wave speed plan is linearly increased from + V1 and linearly decreased from + V1 to 0 in the period from time t5 to time t6.
[0026]
In this case, as shown in FIG. 2B, the acceleration (angular acceleration) α of the rotor 22 is + α1 in the period from the time point t0 to t1, becomes −α1 in the period from the time point t1 to t3, and in the period from the time point t3 to t5. + Α1 and −α1 in the period from time t5 to t6. However, the time ΔT in each period is the same.
[0027]
When the servo motor 20 is driven based on such a speed plan, the rotor 22 of the servo motor 20 rotates by a predetermined angle θ in one direction (positive direction) during the period from time t0 to t2, and from time t2 to t4. During this period, it rotates by a predetermined angle θ in the other direction (negative direction) and returns to the original position (position at time t0). Then, during the period from the time point t4 to the time point t6, as in the period from the time point t0 to the time point t2, the rotation is stopped by rotating by a predetermined angle θ in the positive direction. By repeating the operation in the period from the time point t0 to the time point t6 after the time point t6, the rotor 22 rotates in the forward direction while repeating forward and reverse rotations at every predetermined angle θ.
[0028]
2B, an AC current having a torque current value I proportional to the acceleration α is supplied to the rotor 22 of the servo motor 20. That is, as shown in FIG. 2C, the torque current value I is approximately + I1 during the period from the time point t0 to t1, is approximately −I1 during the period from the time point t1 to t3, and is approximately + I1 during the period from the time point t3 to t5. In the period from t5 to t6, it is approximately −I1.
[0029]
Here, when demagnetization occurs in a part of the magnets 24a to 24d of the rotor 22, the torque current value I includes the torque current value I (in this case, + I1 or -I1 as shown in FIG. 2C). ) In the direction in which the absolute value increases, a peak P1 of size Ip1 occurs. As described above, the peak P1 occurs in the direction in which the absolute value of the torque current value I increases. When the magnets 24a to 24d are demagnetized, more torque than usual is obtained to obtain the desired rotational speed V. This is because the current value I is required. Further, as shown in FIG. 2C, the peak P1 occurs at the discrete magnetic pole positions Pm because the magnitude of the torque applied to each of the magnets 24a to 24d is between the magnets 24a to 24d and the coils 32u, 32v, and 32w. This is because it changes in accordance with the positional relationship, that is, the magnetic pole position Pm of the rotor 22.
[0030]
In FIG. 2C, in a time region where the peak P1 does not occur in the torque current value I, the calculated inertia m obtained based on the equation (2) is an inertia (default inertia) defined as a value unique to the servo motor 20. It is the same value as m0. However, when the calculated inertia m is obtained including the connected load, the predetermined inertia m0 is also set in consideration of the load.
[0031]
On the other hand, in the time domain in which the peak P1 occurs, the torque current value I is a large value with respect to the other time domains, so the calculated inertia m is also a large value with respect to the predetermined inertia m0. Therefore, the demagnetization test can be performed by comparing the calculated inertia m and the predetermined inertia m0 at each magnetic pole position Pm.
[0032]
Actually, the calculated inertia m is obtained for each magnetic pole position Pm while rotating the rotor 22 of the servo motor 20 based on the speed plan shown in FIG. 2A. In this case, the calculated inertia m at each magnetic pole position Pm may be calculated a plurality of times while repeating the operation in the period from the time point t0 to the time t4, and the average of these may be compared with the predetermined inertia m0.
[0033]
Subsequently, the calculated inertia m and the predetermined inertia m0 are compared for each magnetic pole position Pm, and the magnetic pole position Pm in which the influence of demagnetization occurs is specified. In this case, the calculated inertia m is obtained, and this is compared with the predetermined inertia m0 to perform a series of processes for specifying the magnetic pole position Pm where the demagnetizing effect occurs, and the demagnetization is performed at each magnetic pole position Pm. It is also possible to obtain the probability of the influence and determine the presence or absence of demagnetization based on this probability.
[0034]
On the other hand, FIG. 3A shows an example of a torque plan when the torque control of the servo motor 20 is performed. In this case, the torque plan is actually set by the torque current value I.
[0035]
In the torque plan, the torque current value I supplied to the coils 32u, 32v, 32w of the servo motor 20 is + I2 during the period from the time point t10 to t11, and is −I2 during the period from the time point t11 to t12 and from the time point t12 to t13. It is + I2 during the period from time t13 to t14 and from time t14 to t15, and is −I2 during the period from time t15 to t16.
[0036]
In this case, since the acceleration α of the rotor 22 of the servo motor 20 is proportional to the torque current value I, as shown in FIG. 3B, it becomes approximately + α2 during the period from time t10 to t11, and substantially during the period from time t11 to t13. −α2, approximately + α2 during the period from time t13 to t15, and −α2 during the period from time t15 to t16.
[0037]
By the way, when demagnetization occurs in the magnets 24a to 24d of the rotor 22, the absolute value of the acceleration α (in this case, + α2 or −α2 in this case) decreases as shown in FIG. 3B. Then, a peak P2 having a size αp2 is generated. As described above, the peak P2 is generated in the direction in which the absolute value of the acceleration α decreases, because when the magnets 24a to 24d are demagnetized, a desired torque cannot be obtained with respect to the torque current value I. It is.
[0038]
In FIG. 3B, in a time region where the peak α2 does not occur in the acceleration α, the calculated inertia m obtained based on the equation (2) has the same value as the predetermined inertia m0. On the other hand, in the time region where the peak P2 occurs, the acceleration α is a small value relative to the other time regions, so the calculated inertia m is a large value with respect to the predetermined inertia m0. Therefore, the demagnetization test can be performed by comparing the calculated inertia m and the predetermined inertia m0 at each magnetic pole position Pm.
[0039]
Next, an example of a processing operation performed by the controller 42 when performing a demagnetization inspection while performing position control on the servo motor 20 will be described with reference to a flowchart of FIG.
[0040]
Here, the processing operations in the following steps S1 to S7 are started when an inspection mode is selected for an input device (not shown).
[0041]
First, in the controller 42, a speed plan is made based on the position command (see FIG. 2A), and a torque current value I (see FIG. 2C) obtained based on the speed plan is supplied to the servo motor 20. Thus, the drive of the servo motor 20 is started (step S1).
[0042]
Subsequently, in FIG. 2A, the operation in the period from the time point t0 to t4 is repeatedly performed a plurality of times, and the rotor 22 rotates forward and backward a plurality of times during a predetermined angle θ (for example, 45 °). At this time, the calculated inertia m for each magnetic pole position Pm is obtained based on the equation (2) (step S2). When the calculated inertia m for each magnetic pole position Pm is obtained a predetermined number of times (for example, 10 times) (step S3), the operation in the period from time t4 to t6 is performed in FIG. Only in the positive direction and stop (step S4). As a result, the magnetic pole position Pm for obtaining the calculated inertia m is updated.
[0043]
Then, when the processes of steps S2 to S4 are sequentially performed and the calculated inertia m at all the magnetic pole positions Pm of the rotor 22 is obtained, the drive of the servo motor 20 is stopped (step S5).
[0044]
Next, the average of the calculated inertia m is obtained for each magnetic pole position Pm (step S6), and these are respectively compared with the predetermined inertia m0 to determine whether or not the magnets 24a to 24d are demagnetized. (Step S7). Here, in step S6, the total average of the calculated inertia m at all the magnetic pole positions Pm may be obtained, and in step S7, this may be compared with the predetermined inertia m0.
[0045]
Thus, in the present embodiment, the torque current value I obtained from the current values Iu and Iv detected by the current sensors 38u and 38v and the magnetic pole position Pm detected by the magnetic pole position detector 26 are differentiated. The friction μ (V) calculated as a function of the rotational speed V obtained by the equation (1), the acceleration α of the rotor 22 obtained by differentiating the rotational speed V, and values inherent to the servo motor 20 are predetermined. The calculated inertia m of the rotor 22 is obtained from the torque constant K, and the calculated inertia m is compared with a predetermined inertia m0 that is predetermined as a value inherent to the servo motor 20, thereby checking the demagnetization.
[0046]
In this case, the torque current value I, the friction μ (V), and the acceleration α can be obtained by calculation while driving the servo motor 20 based on an arbitrary speed plan or torque plan, and therefore reduced to the magnets 24a to 24d. It is possible to easily and quickly check whether or not magnetism has occurred.
[0047]
Note that the present invention is not limited to the above-described embodiment, and various configurations can be adopted without departing from the gist of the present invention.
[0048]
【The invention's effect】
As described above, according to the present invention, it is possible to inspect the demagnetization of the permanent magnet used in the servomotor easily and in a short time.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a schematic configuration of a servo motor drive system to which an embodiment of the present invention is applied.
FIG. 2A is a graph showing a speed plan for demagnetization inspection when position control or speed control of the servo motor is performed, and FIG. 2B is a graph showing acceleration of the servo motor based on this speed plan. FIG. 2C is a graph showing torque current values based on this speed plan.
FIG. 3A is a graph showing a torque plan for demagnetization inspection in the case where torque control of the servo motor is performed, and FIG. 3B is a graph showing acceleration of the servo motor based on this torque plan.
FIG. 4 is a flowchart showing a processing operation performed by a controller when performing a demagnetization inspection while performing position control on a servo motor.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Servo motor drive system 20 ... Servo motor 22 ... Rotor 24a-24d ... Magnet 26 ... Magnetic pole position detector 30 ... Stator 32u, 32v, 32w ... Coil 34u, 34v, 34w ... Cable 38u, 38v ... Current sensor 40 ... Control device 42 ... Controller 44 ... PWM generation circuit 46 ... Inverter

Claims (1)

A method for inspecting the demagnetization of a permanent magnet used in a servo motor,
Detecting the position of the permanent magnet based on the rotation angle of the rotor of the servo motor;
The torque current value supplied to the servo motor, the friction force generated in the servo motor, and the acceleration of the servo motor are obtained, and these torque current value, friction force and acceleration, and values inherent to the servo motor are defined. Obtaining a calculated inertia of the servo motor based on the torque constant being
Comparing the obtained calculated inertia and a predetermined inertia set as a value unique to the servo motor for each detected position of the permanent magnet, and identifying the position of the permanent magnet where demagnetization occurs; and ,
A demagnetization inspection method for a servo motor, comprising:

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