JP2549508B2 - Closed loop drive control method for stepping motor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a closed loop drive control method for a stepping motor, which switches a phase excitation state based on a rotor position signal and a rotation command signal to drive a stepping motor to rotate.
More specifically, it relates to a closed loop drive control method for generating a braking force when the stepping motor is decelerated.

b. Prior Art FIG. 5 shows a conventionally known stepping motor driving device, in which 1 is a stepping motor, 2 is a rotor of the stepping motor 1, and 3 is a rotor 2.
An encoder (position detector) fixed coaxially to one end of 4, a light source 5, a photoelectric element 5, a control circuit 6, A ,,
B, is a winding for each phase of the motor. For example, 50 circular slits 7 are provided at the outer peripheral edge of the encoder 3 at intervals of 7.2 °.
Are formed, and four pairs of light sources 4 and photoelectric elements 5 are arranged to face each other on both sides of the circular slit 7.
Then, every time the rotor 2 rotates by 1.8 °, for example, high level signals are sequentially output from the four photoelectric elements 5.

The control circuit 6 described above includes a logic circuit that produces a predetermined excitation state based on the rotor position signal from the photoelectric element 5 and a stepping motor rotation command signal from a command circuit (not shown), and a winding current logic circuit. And a power switching circuit which is turned on / off based on the output of the control circuit 6. The control circuit 6 selectively energizes the windings A, B. That is, the phase excitation sequence most suitable for acceleration, deceleration or constant speed operation of the stepping motor 1 is determined by the rotor position signal and the stepping motor rotation command signal, whereby the stepping motor 1 is driven to rotate. ing. by the way,
Conventionally, when decelerating the stepping motor 1 in the high-speed rotation state, the lead angle is set to 0 step. Here, the "lead angle" is counted from the phase excitation switching point of the stepping motor 1,
It is a value indicating how many steps ahead or how many steps before is excited, and the unit is "step". More specifically, the "advance angle" is a term that represents the distance to the excitation stable point of the next excitation phase at the excitation switching point determined by the signal from the encoder or the like installed in the stepping motor. There are roughly two types of "advance angle", and there are "positive (+) advance angle" and "negative (-) advance angle". The positive advance angle generates acceleration torque for the rotor. The negative lead angle means that the excitation phase for generating the braking torque is selected.
In general, the electrical distance between the excitation phases is the electrical angle (eg,
In the case of a two-phase motor, it is expressed as 90 degrees), while the unit called "step" is often used when expressing the rotation angle of the rotor, and the rotor from the stable excitation point of one phase to the stable excitation point of the adjacent phase is The rotation angle is often expressed as one step (for example, in the case of a two-phase motor, the distance from the A-phase excitation stable point to the B-phase excitation stable point). However, in this specification, the display method of the concept as described above is not adopted,
The unit called "step" is used to indicate the electrical distance from the current excitation phase to the next excitation phase at the excitation switching point. That is, in the present specification, the magnitude of the electrical distance from the current excitation phase to the excitation stable point of the next excitation phase at the excitation switching point is displayed in the unit of "step". Note that there is one step between the mutually adjacent excitation phases.

Therefore, when exciting ahead of the phase excitation switching point, the lead angle becomes a positive value and the acceleration state occurs, and when exciting before that, the lead angle becomes a negative value and the deceleration state occurs. As described above, when the advance angle is set to 0 step during deceleration, the phase exhibiting the action of always stopping the rotating rotor 2 at the current position is automatically excited, and as a result, the braking force acts on the rotor 2. Will be done. Conventionally, the rotation of the rotor 2 is stopped at the time of deceleration by the braking action based on the advance angle of 0 step.

c. Problems to be Solved by the Invention However, since the acceleration and deceleration torques in the stepping motor are proportional to the phase difference between the excitation stable point and the rotor, when the lead angle is set to 0 step, the maximum phase difference is 1 step. (Range α from B in FIG. 4), the fluctuation of the torque acting in the direction opposite to the rotation direction of the rotor is large, and the average torque value is small. Further, it takes time for the exciting current to rise due to the influence of the inductance of the stepping motor winding.

Therefore, there has been a big problem that a strong and stable braking torque cannot be obtained by the deceleration with the advance angle of 0 step which has been conventionally performed.

Also, Japanese Patent Application Laid-Open No. 59-165993 proposes a system in which a braking torque is obtained by exciting a predetermined phase based on a control signal from a phase switching determiner during deceleration of a rotor. Had a problem in that a large pulsation was generated in the braking torque (the torque fluctuation was large) and the average value of the braking torque was small.

Further, in JP-A-49-62915, the excitation phase is switched at the point where the torques of the adjacent phases are equal to each other to generate the braking torque, whereby the largest braking torque is used in the range including the maximum negative torque. Although a control method of a stepping motor has been proposed, the content of it is premised on excitation under ideal conditions, and it is not always possible to obtain a negative maximum torque in actual implementation. Is the actual situation. The reason is that in controlling the exciting current, there is a considerable time delay in the exciting current due to the motor constant of the stepping motor and the constant of the drive circuit, so it is not always possible to always use the maximum negative torque. Because there is no.

The present invention has been made to solve the above problems, and an object thereof is to ensure a negative maximum torque during braking by selecting a negative lead angle according to the type of a stepping motor or the like. Closed-loop drive of a stepping motor that can obtain a braking torque that can be obtained and that can suppress a decrease in the braking torque due to the delay characteristic of the rising of the exciting current and that has a small torque fluctuation and a large average value torque. It is to provide a control method.

d. Means for Solving the Problems In order to solve the above-mentioned problems, in the present invention, a stepping motor that switches the excitation state and rotationally drives the stepping motor based on the rotor position signal and the rotation command signal. In the closed loop drive control method, the intermediate point of the excitation stable points adjacent to each other of the rotor is set as the excitation switching point, and the adjacent excitation phases are defined as one step. In the deceleration mode of the stepping motor, the excitation current for the stepping motor to be controlled is set. Depending on the time delay of the rising edge of, the negative maximum torque value is selected from the multiple negative lead angles of -0.5, -1.5, -2.5 and -3.5 steps which are the lead angles before the excitation switching point. By selecting a negative lead angle such that a negative torque that changes in the range including that acts on the rotor and switching the excitation phase, A reduction in braking torque due to a time delay is suppressed.

An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a block diagram of a stepping motor drive device for implementing a closed loop drive control system for a stepping motor according to the present invention. In FIG. 1, 10 is a stepping motor, 11 is a rotor, and 12 is a rotor 11. A position detector that detects the rotational position, 13 is a conversion circuit that outputs a rotation direction signal and a rotation speed signal based on the rotor position signal output from the position detector 12, and 14 is a phase excitation sequencer that drives and controls the stepping motor 10. Is.

The above-described phase excitation sequencer 14 is supplied with the rotor position signal output from the position detector 12 and the rotation direction signal and rotation speed signal output from the conversion circuit 13 as rotor rotation information signals, and Start / stop command signal, forward / reverse command signal and acceleration /
A stepping motor rotation command signal including a deceleration command signal and the like is supplied, and a predetermined phase excitation signal is supplied from the phase excitation sequencer 14 to the stepping motor 10 based on these signals.

FIG. 2 is a diagram showing the relationship between the excitation stable point and the rotor position signal output from the position detector 12 when the rotor 11 of the stepping motor 10 is rotating clockwise (CW direction). . In FIG. 2, A, B ,, indicate stepping motor windings, * indicates a stable point of the rotor 11 in the 1-2 phase excitation sequence, and S _{0 to} S ₇ indicate phase excitation in the 1-2 phase excitation. The excitation switching point (switching point) at which the sequence is switched is shown. As is clear from FIG. 2, the excitation switching points S _{0 to} S ₇ are set at the intermediate points of the region between the excitation stable points *. Also, in FIG. 2, channel A and channel B are A and B of the position detector.
The output signal of the channel is shown.

Next, the case of an ideal condition in which there is no time delay in the rise of the exciting current will be described first. In this example, when the rotor 11 is rotating clockwise in the deceleration region, a method is adopted in which the advance angle is excited so as to rotate the lead angle counterclockwise (CCW direction) in −1.5 steps. The figure shows the phase excitation sequence in this case.

The phase excitation sequence shown in FIG. 3 will be described below.

First, when a deceleration signal is input to the phase excitation sequencer 14, the rotor position signal output from the position detector 12 corresponding to the rotational position of the rotor 11 of the stepping motor 10 and the rotation command signal described above are used as the basis. And the phase excitation sequence is such that the lead angle becomes -1.5 steps.
Selected by. That is, the rotor 11 is, for example, the third
When passing the switching point S ₃ shown in the figure in the clockwise direction, the B-phase stepping motor winding B is excited. Therefore, the position of the stable points of the rotor 11 with respect to the stepping motor winding B is viewed from the switching point S ₃
It is 1.5 steps ahead (-1.5 steps). Thus, in the case of this example, always in all switching points S ₁ to S _7, is phase excitation at the lead angle of -1.5 steps. As a result, a braking torque that tries to rotate the rotor 11 in the opposite direction (counterclockwise) always acts on the rotor that rotates clockwise, and the rotor 11 becomes strong immediately after the phase excitation is switched. It will be stopped rapidly by the braking torque.

The reason for this will be described in more detail below with reference to FIG.

The torque generated by the stepping motor 10 can be expressed as shown in FIG. 4 based on its stiffness characteristic (angle-torque characteristic). In the stiffness characteristic diagram of the stepping motor shown in FIG. 4, the horizontal excitation indicates the phase excitation phase difference (angle) with the rotor 11 at a certain excitation stable point as the reference, and the vertical axis shows the generated torque at that time. And is usually approximated by a sine function. As is clear from the stiffness characteristics in FIG. 4, the phase difference (angle) is negative torque, that is, deceleration torque, in the range of 0 to -4 steps, and positive torque, that is, acceleration, in the range of 0 to +4 steps. It becomes torque. If the reference stable point of the rotor 11 is a phase here, a negative maximum deceleration torque is generated two steps before this, that is, when the B phase is excited. The maximum value of the acceleration torque is +2 steps.

In this example, since the advance angle at the time of deceleration of the stepping motor 10 is set to −1.5 step to perform the phase excitation as described above, the braking torque acts on the rotor 11, but the rotor 11 does not have the inertia of the load. The rotation in the clockwise direction is continued by, for example, from the switching point S ₃ to the next switching point S ₄ . The phase difference reaches 2.5 steps immediately before reaching the switching point S ₄ .

Therefore, the range of possible phase difference between the rotor 11 and the stable excitation point is -1.5 to -2.5 steps. Therefore, the braking torque at the time of deceleration, a continuous range around the negative maximum torque value (-T _H) in stiffness characteristic diagram of Figure 4 β
(In the prior art, the range is α), and it is possible to obtain an optimum braking torque with a small torque fluctuation and a large average torque value.

However, the above theory is valid only when the rising of the exciting current is under the ideal characteristics, and when a rising time of the rising of the exciting current occurs,
It may not be put to practical use. That is, in an actual control system, the excitation signal and the excitation current rarely coincide with each other on the time axis, and in many cases, the rise of the excitation current is delayed in time. Is determined by the motor constant of the stepping motor and the constant of the drive circuit, and it is difficult to accurately grasp the value. Even if there is a time delay in the rise of the exciting current in this way, when the stepping motor is driven by the excitation switching method defined under the ideal conditions as described above, when the stepping motor is decelerated, Therefore, it is not possible to obtain an optimum braking torque in a range including the maximum torque, that is, a small torque fluctuation and a large average torque value. Therefore, in order to deal with the delay phenomenon of the rising of the exciting current, it is practically effective to set the lead angle at the start of excitation to −0.5, −2.5 or −3.5 steps instead of limiting it to −1.5. Effective to obtain a braking torque in a range including the maximum torque of).

Therefore, in the present invention, the time delay of the rising of the exciting current of the stepping motor to be controlled is measured in advance by an experiment or the like, and the lead angle in the deceleration mode of the stepping motor is set based on the result. I am trying to do it. Specifically, according to the time delay of the rising of the exciting current for the stepping motor to be controlled, it is the lead angle before the excitation switching point -0.5, -1.5,
From multiple negative lead angles of −2.5 and −3.5 steps,
By selecting a negative lead angle such that a negative torque that changes in the range including the maximum negative torque value acts on the rotor, the excitation phase is switched. The reduction of the braking torque resulting from this is suppressed.

Although one embodiment of the present invention has been described above, the present invention is not limited to the embodiment described above, and various modifications and changes can be made based on the technical ideal of the present invention.

e. Effects of the Invention As described above, in the present invention, in the deceleration mode of the stepping motor, the advance angle before the excitation switching point is set according to the time delay of the rising of the excitation current for the stepping motor to be controlled. −0.5, −1.5, −2.5 and −
From a plurality of negative lead angles of 3.5 steps, a stepping motor that switches the excitation phase by selecting a negative lead angle such that a negative torque that changes in the range including the maximum negative torque value acts on the rotor Since the phase excitation is performed with a negative lead angle during deceleration, it is possible to effectively use the torque in the range including the smooth and largest negative torque as the braking torque, which has been conventionally performed. It is possible to obtain a braking torque with a small fluctuation (pulsation) of the braking torque and a large average value as compared with the case of the phase excitation with the lead angle of 0 step. Therefore, according to the present invention, the stepping motor can be stably and rapidly decelerated to be stopped suddenly, and in turn, the rotor can be quickly positioned.

Further, in particular, in the present invention, during braking, the numerical value of the negative lead angle is selectively set according to the time delay of the rising of the exciting current determined by the motor constant of the stepping motor and the constant of the drive circuit. Since the braking torque in the range including the negative maximum torque is applied to the rotor, a preferable negative torque range in one stiffness cycle can be selected and set reliably, and the characteristics of various stepping motors can be controlled. The most suitable braking torque for each can be applied to the rotor.

[Brief description of drawings]

1 to 4 are for explaining a closed loop drive control system of a stepping motor according to the present invention. FIG. 1 is a circuit diagram of a stepping motor drive circuit, and FIG. 2 is an excitation of the stepping motor. A time chart showing the relationship between the stable point and the output signal from the position detector, FIG. 3 is an explanatory diagram of a phase excitation sequence, FIG. 4 is a stiffness characteristic diagram of a stepping motor, and FIG. 5 is a conventionally known stepping motor drive. It is a block diagram of an apparatus. 10 …… Stepping motor, 11 …… Rotor, 12 …… Position detector, 13 …… Conversion circuit, 14 …… Phase excitation sequencer.

Claims (1)

(57) [Claims] 1. A closed loop drive control method for a stepping motor, wherein an excitation state is switched based on a rotor position signal and a rotation command signal to drive a stepping motor to rotate. In a method, a midpoint between adjacent excitation stable points of a rotor is excited. In the stepping motor deceleration mode, the advance point before the excitation switching point is set according to the time delay of the rising of the excitation current of the stepping motor to be controlled. Among a plurality of negative lead angles of -0.5, -1.5, -2.5 and -3.5 steps, a negative lead angle such that a negative torque varying in a range including the maximum negative torque value acts on the rotor. Is selected to switch the excitation phase to suppress the decrease in braking torque due to the time delay of the rising of the excitation current. Closed loop drive control method of the stepping motor, characterized in that.