JPS61161998A - Load detecting method of stepping motor - Google Patents

Abstract

PURPOSE:To prevent a stepout phenomenon and to presume the amplitude or an external load torque or variation by continuously detecting a load from a counterelectromotive force and a drive voltage signal. CONSTITUTION:A drive circuit 22 drives a step motor 8 by drive voltage signals E1, E2. A counterelectromotive force detector 23 detects a counterelectromotive force generated at the motor 8. A calculator 24 obtains a period function with the phase difference delta of the position of a rotor as variable from phase drive voltage signals E1, E2 and phase counterelectromotive force signals V1, V2. A controller 20 detects the load of the motor 8 from the phase difference deltacontained in a period function obtained by the calculator 24, and varies the drive frequency of a step motor for preventing, for example, a stepout in response to the load.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a step motor load detection method, and is particularly suitable for use in controlling step motors widely used in numerical control (hereinafter referred to as NO) machine tools and servo mechanisms of peripheral equipment of electronic computers. , relates to a method for detecting the load of a step motor driven by a multi-phase periodic drive signal.

[Conventional technology]

In addition to acting as an actuator, step motors have the function of converting digital pulses given by pulse trains into mechanical positions, and are widely used in peripheral equipment for NO machine tools and electronic computers as servo motors most suitable for numerical control. It's starting to look like this. This step motor is
The major feature is that open-loop control is possible, and the servo mechanism can be configured easily and with high precision without using feedback elements such as encoders or potentiometers.

[Problems to be solved by the invention]

However, until now, no suitable method has been proposed to detect the load applied to the step motor, and therefore, it is necessary to prevent the so-called step-out phenomenon in which the step motor cannot rotate fully when an unexpected external force or load is applied. In addition, in processing machines, etc., constant tightening has the problem that it is difficult to stop the feed by a step motor with force. That is, if the load on the step motor can be detected, for example, if the step motor is close to losing synchronization due to load fluctuations, it is possible to prevent the step motor from losing synchronization by lowering the drive frequency of the step motor and increasing the torque. However, since it was not possible to detect the load in the past, the drive frequency could only be determined based on experience, and no effective countermeasures could be taken against load fluctuations during use. There wasn't. In order to solve such problems, the applicant has already proposed in Japanese Patent Application No. 59-87283, which detects the stable point position signal of the step motor, calculates the phase difference between the periodic drive signal and the stable point position signal, and A method is proposed for detecting the load of a step motor based on the phase difference and the drive frequency.However, in the load detection method proposed in this patent application No. 59-87283, the step motor is stabilized from the zero cross point of the back electromotive force. If a point position signal is obtained, there is no need to attach a rotary encoder, but it is not possible to detect a load change at the zero cross point.On the other hand,
If a rotary encoder is attached to obtain a stable point position signal, information between zero cross points can also be obtained by using a rotary encoder with high resolution, but the information obtained is intermittent. The problem remains that it is.

[Purpose of the invention] The present invention has been made in order to solve the above-mentioned conventional problems, and is capable of continuously detecting the load of a step motor. Therefore, it is possible to detect the load with high precision and high resolution, and also to detect the load after detection. It is an object of the present invention to provide a step motor load detection method that can be widely used for measuring force detection of measuring instruments, constant torque tightening devices, etc. without adding correction. [Means to solve the problem]

When detecting the load of a step motor driven by a periodic drive signal of multiple phases, the present invention detects a back electromotive force signal of a phase corresponding to each phase of the drive signal, as shown in FIG. Detect and calculate the product sum or product difference of each phase drive signal and each phase back electromotive force signal, and from the product sum or product difference, generate a periodic function whose variable is the phase difference between the excitation voltage and the position of the rotor of the step motor. The above object is achieved by determining the phase difference included in the periodic function and detecting the load of the step motor. Further, in an embodiment of the present invention, the periodic function is a sine function so that small loads can be detected with high accuracy. Alternatively, in another embodiment of the present invention, the periodic function is a cosine function, so that the load can be reliably detected even when the range of change in the load is large.

[Effect]

There are basically two types of step motors: variable roughtance (hereinafter referred to as VR) type and permanent magnet (hereinafter referred to as PM) type, but PM type step motors also include a type commonly called hybrid type. Basically, it is a two-phase alternating current one-synchronous motor, and the model shown in FIG. 2 can be applied. In FIG. 2, 10 is the rotor of the step motor 8, and 12 is the stator. In this type of motor, the mutual inductance between the first and second phases can be ignored, the static torque curve can be approximated by a sinusoidal waveform, and the PM type step motor motion is expressed by the following equation: It can be expressed as LIt+RIt-KsinNθ・θ−E + ・= (
1) Jθ+Dθ+Ti −−KSlnNθφI 1+ KO08Nθ・I2・・
・ (3) Here, Shi is the self-inductance of the stator winding, R is the resistance of the stator winding including the load resistance, 1i is the current of the i-phase, and Ei is the excitation of the first phase 1 m! pressure, K is the torque constant, N
is the number of magnetic pole pairs of the rotor <m), θ is the rotation angle of the rotor shaft, J is the moment of inertia of the load and rotor, D is the viscous drag coefficient, and TI is the load torque including frictional force. In general, the input voltages El and El are given as rectangular waves as shown in FIG. 3, but in the analysis below, we will focus on their fundamental harmonic components, which will be expressed by the following equation. E+−VcosωL...(4)E2
-Vsin cc+j -(5) Since the harmonic components of the excitation voltage are attenuated in the motor windings and the portion of the output torque used can be considered to be due to the fundamental harmonic components, the excitation 1ItiN pressure is ), (5)
It can be said that the results obtained when given as in the equation are also meaningful for phenomena in the case of rectangular wave input. Drive voltage signals E1 and El such as equations (4) and (5)
When given, the detected back electromotive force signals V+, Vz are as follows:
For example, as shown in FIG. 4, it is basically expressed by the following equation. V+--KSIro (ω

[−δ−φ) ・θ・・・
(6) V 2- K 005 (ω is one δ-φ)・
θ (7) Here, δ is the delay angle of the rotor 10 with respect to the excitation voltage due to the load, and φ is the phase delay of the voltage detection signal due to the L1R component, which is expressed by the following equation. φ−wtan−'τω ...(8)τ−
L/R (9) Further, the phase difference δ can be determined from a linear equation. Tβ+Dω/N-vK/(Rr+r'cn')-5in
(δ−φ)−K2ω/(NR(1+τ2ω2))・・
-(10) This equation (10) indicates that the rotor 10 rotates with a delay angle of δ, and this delay angle δ
has a relationship with the load torque TJ2, so the frequency ω
If is constant, the load torque Tλ can be easily determined. A periodic function with the phase difference δ as a variable, for example, a sine function S
One method for determining in (δ-φ) is to calculate the sum of products of each phase drive voltage signal Ez, El and each phase back electromotive force signal V1, V2, as shown in the following equation. E+ ΦV++Ez aVz −-sin (ωL-6-φ)cosωt+cos
(ωt-6-φ) sin ωt-5in (δ+φ)
...(11) The method for finding the sine function (δ+φ) using the phase difference δ as a variable is to calculate the sine function δ+φ−90 as shown in FIG.
Considering that it is a monotonically increasing single-valued function in the region up to ``, it is suitable when the load is small.Also, other periodic functions using the phase difference δ as a variable, such as the cosine function COS (δ+φ ) can be obtained by taking the product difference between each phase drive voltage signal E1, El and each phase back electromotive force signal Vl, V2, as shown in the following equation: El・Vz−El・Vl− cos(6+φ)...(1
2) This product difference creates a cosine function aOS with the phase difference δ as a variable.
The method for determining (δ+φ) is to take into account that the cosine function is a monotonically increasing monovalent function in the region up to δ+φ−1800, as shown in Figure 6, when the load changes over a wide range. It is suitable. Also, δ+φ−90”
Nearby detection accuracy is high. Note that in this case, there is a possibility that the detection accuracy when the load is small is slightly reduced, but this does not pose much of a problem since there is almost no risk of step-out when the load is small. In the case of equations (11) and (12) above, the periodic function includes the phase delay φ due to R, so if the frequency ω is not constant, it must be corrected. On the other hand, if the device detects the drive current signals 1+ and 12 shown in the following equations obtained by solving equations (1) to (5) above, in principle, the phase delay φ due to R is zero. Therefore, it is possible to obtain the load torque regardless of the frequency ω. I+=V/(Rr w ) xcos(ω(-φ) +ω/(NRrgo+z'goi completion)
・ (13) I2-V/(R+r w
)
ωt −a−φ) (14) In other words, in this case, only the periodic function regarding the position δ of the row 910 that does not include the phase delay φ due to L and R can be obtained, for example, as shown in the following equation. For example, by using the relationship between COS and load as shown in FIG. 7, more accurate measurement is possible. I+ ・Vz-12-Vt-cosδ ・(15)
Therefore, depending on the load detected continuously with high resolution,
By lowering the drive frequency of the step motor and increasing its torque, you can prevent step-out phenomena, stop the step motor from feeding with a constant tightening force, monitor the movement of the step motor, and detect torque abnormalities. It is possible to detect this and make an emergency stop of the step motor. Furthermore, it is also possible to perform optimal control during acceleration and deceleration. The present invention has been made based on the above findings. Embodiments Hereinafter, embodiments of a PM type step motor controlled WJVi device in which the load detection method according to the present invention is adopted will be described in detail with reference to the drawings. In this embodiment, as shown in FIG.
A drive circuit 22 with a multi-phase excitation method and drive method for driving the step motor 8, a back electromotive force detection circuit 23 for detecting the back electromotive force generated in the step motor 8, and a drive circuit from the control circuit 20 22 and each phase back electromotive force signal V1, Vz detected by the back electromotive force detection circuit 23, the product sum or product difference is calculated from the product sum or product difference. , an arithmetic unit 24 that calculates a periodic function using a phase difference δ between the excitation voltage and the position of the rotor of the step motor as a variable, and a load of the step motor 98 from the phase difference δ included in the period rIAa determined by the arithmetic unit 24. and a control section 20 that detects the load and changes the driving frequency of the step motor 8 according to the load so as to prevent tax adjustment, for example. The counter electromotive force detection circuit 23 is composed of a detection auxiliary winding 23A wound over the excitation winding 14 of the step motor 8, and a transformer 23B, as shown in detail in FIG. 9, for example. FIG. 9 shows a detection circuit for the first phase back electromotive force 1 corresponding to the first phase voltage E1 and the first phase current 11, but the second phase back electromotive force V2 is also detected in the same way. It is possible to detect the detected two-phase back electromotive force V
1, Vz has a waveform as shown in FIG. 4 mentioned above, for example. Note that the method for detecting the back electromotive force is not limited to this, and it is also possible to calculate the back electromotive force by configuring a circuit that derives it from the above equations (1) and (2), for example. In this case, a sensor such as a transformer is not required. The arithmetic unit 24 is, for example, as shown in detail in FIG.
Drive voltage signals E1 and Ez of each phase and back electromotive force signals Vl and V
Multipliers 24A and 24B that calculate the product of z, and the multiplier 24
It is composed of an adder 24G that adds the outputs of A and 24B. The operation of the embodiment will be explained below. The step motor 8 is driven via the drive circuit 22 by drive voltage signals E1 and Ez given from the control section 20. The back electromotive force (1) and (2) generated during the driving are detected by the back electromotive force detection circuit 23. The back electromotive force detection circuit 2
The product sum of the back electromotive force signals V+, Vz detected in step 3 and the drive voltage signals E+, Ez given to the drive circuit 22 is determined by the calculator 24. A periodic function whose variable is the phase difference δ between the excitation voltage Ia output from the calculator 24 and the position of the rotor of the step motor is input to the control section 20, where the load on the step motor 8 is detected. Depending on the detected load, the control unit 20 changes the drive frequency of the step motor 8 so as to prevent synchronization, for example. [Effects of the Invention] As explained above, according to the present invention, it is possible to continuously detect the load of the step motor. Therefore, it becomes possible to detect the load of the step motor with high accuracy and high resolution, and it becomes possible to prevent step-out phenomena in open-loop driving and to estimate the magnitude and fluctuation of external load torque. Also, an automatic screw tightening machine that rotates until a predetermined torque is reached.
It becomes possible to use a step motor for a device that tightens pulp until the internal pressure reaches a predetermined value. Furthermore, it has excellent effects such as being able to stop the table and conveyance device when an abnormal load occurs.

[Brief explanation of drawings]

FIG. 1 is a flowchart showing the gist of the step motor load detection method according to the present invention, FIG. 2 is a front view showing a PM type step motor model configuration for explaining the present invention in detail, and FIG. Similarly, the figure is a miniature diagram showing the waveform of the step motor input voltage, FIG. , FIG. 6, which is a miniature diagram showing the waveform of the sine function, is the same. FIG. 7 is a diagram showing the waveform of a cosine function. Similarly, FIG. 7 is a diagram showing an example of the relationship between a load and a cosine function including a phase difference. FIG. Motor-controlled WJ
FIG. 9 is a block diagram showing the configuration of an embodiment of the device; FIG. 9 is a circuit diagram showing the configuration of the back electromotive force detection circuit used in the embodiment; FIG. 10 is a block diagram showing the configuration of the arithmetic unit. FIG. 8... Step motor, 20... Control part, 22
... Drive circuit, El, E2... Drive voltage signal, If, 12... Drive current signal, 23... Back electromotive force detection circuit, Vl, V2... Back electromotive force signal, 24... - Arithmetic unit, 24A124B... Multiplier, 24C... Adder, δ... Phase difference.

Claims (3)

[Claims] (1) When detecting the load of a step motor driven by multiple-phase periodic drive signals, detect the back electromotive force signal of the phase corresponding to each phase of the drive signal, and compare each phase drive signal with each phase. Find the sum of products or difference of products of the phase back electromotive force signal, find a periodic function whose variable is the phase difference between the excitation voltage and the position of the rotor of the step motor from the sum of products or difference of products, and calculate the periodic function that is included in the periodic function. A method for detecting a load on a step motor, characterized in that the load on the step motor is detected from the phase difference. (2) A step motor load detection method according to claim 1, wherein the periodic function is a sine function. (3) A step motor load detection method according to claim 1, wherein the periodic function is a cosine function.