JPH0640755B2 - Step motor load detection method - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to a step motor load detection method, and is particularly suitable for use in controlling a step motor that is widely used in a servo mechanism of a peripheral device of a numerical control (hereinafter referred to as NC) machine tool or an electronic computer. , A method of detecting the load of a step motor driven by a plurality of cyclic drive signals.

[Prior art]

The step motor, which has the function of converting the digital value given by the pulse train to the mechanical position in addition to its function as an actuator, is widely used as a servo motor most suitable for numerical control in peripheral equipment of NC machine tools and electronic computers. It is becoming like this. This step motor is
It has a great feature that open loop control is possible and the servo mechanism can be configured easily and with high accuracy without using feed back elements such as an encoder and a potentiometer.

[Problems to be Solved by the Invention]

However, conventionally, an appropriate method for detecting the load applied to the step motor has not been proposed. Therefore, when an unexpected external force or load is applied, the step motor cannot be prevented from turning completely, that is, so-called step-out phenomenon is prevented. Or
Further, in a processing machine or the like, it is difficult to stop the feeding by the step motor with a constant tightening force. That is, if the load of the step motor can be detected,
For example, when it is close to step-out due to load fluctuation or the like, it is possible to prevent step-out by lowering the drive frequency of the step motor and improving the torque. Since it could not be detected, the drive frequency was only determined according to experience, and no effective countermeasures could be taken against load fluctuation during use. In order to solve such a problem, the applicant has already proposed in Japanese Patent Application No. 59-87283 that the stable point position signal of the step motor is detected and the phase difference between the periodic drive signal and the stable point position signal is obtained. We propose a method to detect the load of the step motor based on the phase difference and the driving frequency. However, in the load detecting method proposed in this Japanese Patent Application No. 59-87283, when the stable point position signal is obtained from the zero cross point of the back electromotive force of the step motor, it is not necessary to attach a rotary encoder, but the zero cross point is required. The load change between points cannot be detected. on the other hand,
When a rotary encoder is attached to obtain a stable point position signal, the information between zero cross points can be obtained by using a rotary encoder with high resolution, but the obtained information is intermittent. There was a problem that it was no different.

[Object of the Invention]

The present invention has been made to solve the above-mentioned conventional problems, and can continuously detect the load of the step motor. Therefore, it is possible to detect the load with high accuracy and high resolution, and to detect the load. An object of the present invention is to provide a step motor load detection method that can be widely used for detecting a measuring force of a measuring instrument, a tightening device with a constant torque, and the like without adding a subsequent correction.

[Means for solving problems]

According to the present invention, when detecting the load of a step motor driven by a plurality of phase drive signals, the counter electromotive force generated in the step motor is detected by the drive signal as shown in FIG. Detecting for each phase corresponding to each phase, obtain the product sum or product difference between each phase of the drive signal and each phase of the counter electromotive force signal, from the product sum or product difference, the excitation voltage and the step motor The object is achieved by obtaining a continuous periodic function having a phase difference from the position of the rotor as a variable and detecting the load of the step motor from the phase difference included in the periodic function. Further, according to an embodiment of the present invention, the periodic function is a sine function so that a small load can be accurately detected. Alternatively, another embodiment of the present invention is such that the periodic function is a cosine function so that the load can be reliably detected even when the change width of the load is large.

[Action]

Basically, there are two types of step motors, a variable reluctance (hereinafter referred to as VR) type and a permanent magnet (hereinafter referred to as PM) type. The PM type step motor including a type usually called a hybrid type is basically Specifically, it is a two-phase AC 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 phase and the second phase can be neglected, and the static torque curve can be approximated by a sinusoidal waveform, and the motion of the PM type stepper motor can be expressed by the following equation. Can be expressed as L ₁ + RI ₁ −Ksin Nθ · = E ₁ (1) L ₂ + RI ₂ + Kcos Nθ · = E ₂ (2) J + D + Tl = −Ksin Nθ · I ₁ + Kcos Nθ · I ₂ (3) where L Is the self-inductance of the stator winding, R is the resistance of the stator winding including the load resistance, Ii is the current of the i-th phase, Ei is the excitation voltage of the I-phase, K is the torque constant, and N is the magnetic pole pair of the rotor. Number (number of teeth), θ is the rotation angle of the rotor shaft,
J is the moment of inertia of the load and the rotor, D is the viscous drag coefficient, and Tl is the load torque including the frictional force. In general, the input voltages E ₁ and E ₂ are given as rectangular waves as shown in FIG. 3, but in the following analysis, its fundamental harmonic component is focused and expressed by the following equation. E ₁ = Vcos ωt (4) E ₂ = Vsin ωt (5) It can be considered that the harmonic component of the excitation voltage is attenuated in the motor winding and that the output torque is used in the fundamental harmonic component. Therefore, the excitation voltage is given in (4) and (5) above.
It can be said that the result obtained when given as the formula is meaningful for the phenomenon in the case of rectangular wave input. The drive voltage signals E ₁ and E ₂ as in the above equations (4) and (5)
Is given, the detected back electromotive force signals V ₁ and V ₂ are
For example, as shown in FIG. 4, it is basically expressed by the following equation. _{V 1 = -Ksin (ωt -δ-} φ) · ... (6) V 2 = Kcos (ωt -δ-φ) · ... (7) where, [delta], the rotor 10 against the excitation voltage by the load
Is the delay angle of φ, and φ is the phase delay of the voltage detection signal due to the L and R components expressed by the following equation. φ = tan ⁻¹ τω (8) τ = L / R (9) The phase difference δ can be calculated from the following equation. The expression (10) indicates that the rotor 10 rotates with a delay angle of δ, and this delay angle δ is related to the load torque Tl. Therefore, if the frequency ω is constant, The load torque Tl can be easily obtained. As one method of obtaining a continuous periodic function having the phase difference δ as a variable, for example, a sine function sin (δ-φ), as shown in the following equation, the drive voltage signals E ₁ and E ₂ of each phase and each phase The product of the counter electromotive force signals V ₁ and V ₂ can be calculated. E ₁ · V ₁ + E ₂ · V ₂ = −sin (ωt −δ−φ) cos ωt + cos (ωt −δ−φ) sin ωt = sin (δ + φ) (11) The phase difference δ is varied by this product sum. Sine function sin (δ
The method of obtaining + φ) is suitable when the load is small considering that the sine function becomes a monovalent function of monotonically increasing in the region up to δ + φ = 90 ° as shown in FIG. Further, another continuous periodic function having the phase difference δ as a variable,
For example, as one method of obtaining the cosine function cos (δ + φ), the product difference between the phase drive voltage signals E ₁ and E ₂ and the phase counter electromotive force signals V ₁ and V ₂ is calculated as shown in the following equation. it can. E ₁ · V ₂ −E ₂ · V ₁ = cos (δ + φ) (12) Cosine function cos (δ) with the phase difference δ as a variable due to this product difference
+ Φ) is calculated by considering that the cosine function is a monotonically increasing monovalent function in the region up to δ + φ = 180 °, as shown in Fig. 6, when the load changes over a wide range. It is suitable. Further, the detection accuracy is high near δ + φ = 90 °. In this case, the detection accuracy may be slightly reduced when the load is small, but when the load is small, there is almost no risk of step-out, so this is not a serious problem. In the case of the above equations (11) and (12), since the term of the phase delay φ due to L and R is also included in the periodic function, the correction is necessary when the frequency ω is not constant. On the other hand, if the drive current signals I ₁ and I ₂ shown in the following equations, which are obtained by solving the above equations (1) to (5), are detected, the phase delay φ due to L and R is theoretically obtained. Is zero, the load torque can be obtained regardless of the frequency ω. That is, in this case, for example, as shown in the following equation, it is possible to obtain only the periodic function relating to the position δ of the rotor 10 that does not include the phase delay φ due to L and R. For example, cos δ as shown in FIG. More accurate measurement can be performed by using the load relationship. I ₁ · V ₂ −I ₂ · V ₁ = cos δ (15) Therefore, according to the load continuously detected with high resolution,
By reducing the drive frequency of the step motor and improving the torque, step-out phenomenon can be prevented, feeding by the step motor can be stopped with a constant tightening force, the movement of the step motor can be monitored, and abnormal torque can be detected. It becomes possible to detect and stop the step motor in an emergency. It is also possible to perform optimum control during acceleration / deceleration.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a PM type stepping motor control device adopting the load detecting method according to the present invention will be described in detail below with reference to the drawings. In this embodiment, as shown in FIG. 8, the stepping motor 8 is driven by drive voltage signals E ₁ and E ₂ provided from the controller 20.
A drive circuit 22 of a multi-phase excitation system and a drive system for driving the motor, a back electromotive force detection circuit 23 for detecting a back electromotive force generated in the step motor 8, and a drive circuit from the control circuit 20. 22. The sum of products or the product difference of the phase drive voltage signals E ₁ and E ₂ input to 22 and the phase back electromotive force signals V ₁ and V ₂ detected by the counter electromotive force detection circuit 23 is calculated, and the product sum Alternatively, an arithmetic unit 24 for obtaining a continuous periodic function whose variable is the phase difference δ between the excitation voltage and the rotor position of the step motor from the product difference, and the phase difference included in the periodic function obtained by the arithmetic unit 24. A control unit 20 that detects the load of the step motor 8 from δ and changes the drive frequency of the step motor 8 according to the load so as to prevent step-out, for example.
It consists of and. As shown in detail in FIG. 9, the counter electromotive force detection circuit 23 is composed of a detection auxiliary winding 23A wound around the excitation winding 14 of the step motor 8 and a transformer 23B. Figure 9 is shows a first detection circuit SogyakuOkoshi power V ₁ corresponding to the first phase voltage E ₁ and a first phase current I _1, also the counter electromotive force V ₂ of the second phase It is possible to detect in the same manner, and the detected back electromotive force V for two phases is detected.
₁ and V ₂ have waveforms as shown in FIG. 4, for example. The method for detecting the back electromotive force is not limited to this, and it is also possible to form the circuit derived from the above equations (6) and (7) and calculate it. In this case, a sensor such as a transformer is unnecessary. The arithmetic unit 24 is, for example, as shown in detail in FIG.
Drive voltage signals E ₁ and E _{2 of} each phase and back electromotive force signals V ₁ and V
Multipliers 24A and 24B for obtaining the product of _{2 and} the multiplier 24
It is composed of an adder 24C for adding the outputs of A and 24B. The operation of the embodiment will be described below. The stepping motor 8 is driven via the drive circuit 22 by the drive voltage signals E ₁ and E ₂ provided from the control section 20. The counter electromotive forces V ₁ and V ₂ generated during the driving are detected by the counter electromotive force detection circuit 23. The sum of products of the counter electromotive force signals V ₁ and V ₂ detected by the counter electromotive force detection circuit 23 and the drive voltage signals E ₁ and E ₂ applied to the drive circuit 22 is obtained by the calculator 24. A continuous periodic function whose variable is the phase difference δ between the excitation voltage output from the calculator 24 and the rotor position of the step motor is input to the control unit 20, where the load on the step motor 8 is detected. In accordance with the detected load, the control unit 20 changes the drive frequency of the step motor 8 so as to prevent step-out, for example.

【The invention's effect】

As described 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, prevent the step-out phenomenon in the open loop drive, and estimate the magnitude and fluctuation of the external load torque. Further, the step motor can be used for an automatic screw tightener that rotates until a predetermined torque is reached, a device that tightens a valve until the internal pressure reaches a predetermined value, and the like. Further, there is an excellent effect that the table and the transport device can be stopped when an abnormal load occurs.

[Brief description of drawings]

FIG. 1 is a flow chart showing the gist of a step motor load detection method according to the present invention, and FIG. 2 is a front view showing a model configuration of a PM type step motor for explaining the principle of the present invention. The same figure is a diagram showing the waveform of the step motor input voltage, FIG. 4 is a diagram showing an example of the change state of each phase drive signal and each phase counter electromotive force signal, and FIG.
Similarly, a diagram showing a waveform of a sine function, FIG. 6 is a diagram showing a waveform of a cosine function, and FIG. 7 is a line showing an example of a relationship between a load and a cosine function including a phase difference. 8 and 9 are block diagrams showing the construction of an embodiment of a PM type stepping motor control device to which the present invention is applied, and FIG.
Similarly, FIG. 10 is a block diagram showing the configuration of the computing unit, which is a circuit diagram showing the configuration of the back electromotive force detection circuit used in the embodiment. 8 ...... step motor, 20 ...... controller, 22 ...... driving circuit, _E 1, _{E 2} ...... drive voltage signal, _I 1, _{I 2} ...... drive current signal, 23 ...... counter electromotive force detecting circuit, V ₁ , V ₂ ... Back electromotive force signal, 24 ... Computing unit, 24A, 24B ... Multiplier, 24C ... Adder, .delta .... Phase difference.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-55-71196 (JP, A) JP-A-53-30720 (JP, A) JP-A-59-181999 (JP, A) JP-A-55- 97198 (JP, A)

Claims (3)

[Claims] 1. When detecting a load of a step motor driven by a plurality of phase drive signals, a back electromotive force generated in the step motor is detected for each phase corresponding to each phase of the drive signal. Then, the product sum or product difference of each phase of the drive signal and each phase of the counter electromotive force signal is obtained, and the phase difference between the excitation voltage and the rotor position of the step motor is changed from the product sum or product difference. The step motor load detecting method is characterized in that the load of the step motor is detected from the phase difference included in the periodic function. 2. The step motor load detection method according to claim 1, wherein the periodic function is a sine function. 3. A load detecting method for a step motor according to claim 1, wherein the periodic function is a cosine function.