JPH04112306A - Control system for velocity loop integration - Google Patents

Abstract

PURPOSE:To prevent the oscillation of a velocity loop in a normal velocity control state by setting different velocity loop gains of a spindle control circuit in both velocity and position control states respectively and switching properly both gains to each other. CONSTITUTION:A compensator which controls the proportion/integration of a spindle motor 1 consists of a velocity loop proportion gain 2 and two integration gains 3 and 4. The velocity feedback signal received from the motor 1 is inputted to an adder 6 via a velocity loop 5. At the same time, a velocity command VCMD contained in the numerical control command given from a CNC device is inputted to the adder 6 via a changeover switch S2. The output terminal of the adder 6 can be connected to the gain 2 and also to one of gains 3 and 4 via a changeover switch S1. When the motor 1 is controlled by the numerical control command given from the CNC device, the switch S2 is turned on if it is judges that the command VCMD is inputted to a spindle control circuit. Then the gain 3 is selected by the switch S1. Thus the oscillation of a velocity loop can be prevented.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a main shaft control circuit using a PI as a speed loop compensator.
The present invention relates to a speed loop integral control method that performs (proportional integral) control, and particularly relates to a speed loop integral control method in which the gain of a position determination servo is set large for a main shaft motor.

[Conventional technology]

Generally, the spindle motor of an NC machine tool is required to rotate the spindle at an accurately set rotation speed. Therefore, a PI control circuit is used as a speed loop compensator in a spindle control circuit that controls the spindle motor.

In recent years, it has been considered to use such a spindle motor to perform position control by constructing a position loop outside the speed loop, and to also perform C-axis contour machining with one spindle motor. As a result, positioning of the main shaft can be performed without adding a C-axis circumferential servo motor. Therefore, there is no need to add new hardware to the CNC for spindle positioning.

In this case, when a speed command is given to the spindle control circuit, the position loop is disabled, and when a position command is given, such as in C-axis contour control, the feedback pulse from the position detector attached to the spindle motor is sent to the position loop. It is used as a position feedback signal via the

[Problem to be solved by the invention]

When performing PI sub-control of the spindle motor using a spindle control circuit that has such a speed loop and a position loop, the integral gain does not need to be that large in order to perform normal speed control, but for C-axis contour machining, etc. In position control, the cutting load from an end mill etc. is applied to the spindle, so the integral gain of the speed loop must be set large.

However, in the conventional speed loop integral control method, the same speed loop integral gain is selected in the position control mode and the normal speed control mode. Therefore, if you try to increase the integral gain of the speed loop during position control to improve position accuracy, when the command control mode is switched to speed control, the integrator will become saturated for low-speed rotation commands, and the speed loop will become saturated. could cause oscillation.

The present invention has been made in view of these points, and is designed to reduce position fluctuations caused by disturbance torque applied to the main shaft during position control.
It is an object of the present invention to provide a speed loop integral control method that can effectively suppress the speed loop by using the integral gain of the speed loop.

[The island's means of solving problems]

In order to solve the above-mentioned problems, the present invention provides a speed loop-integral control method that performs proportional-integral control on a spindle control circuit having a speed loop and a position loop. a determining means for determining whether the command control mode for the spindle control circuit is the position control mode or the speed control mode; A speed loop integral control method is provided, which is characterized by having a switching means for switching the means to a large integral gain and to a small integral gain when in a speed control mode.

[Effect]

In the speed loop integral control method of the present invention, the two large and small integral gains of the proportional integral means provided in the speed loop are set separately for the speed control mode and the position control mode, and when position control is performed, the Based on the signal indicating that control is in progress, an integral gain larger than that of normal speed control can be selected to effectively suppress position fluctuations caused by disturbance torque.

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on the drawings.

The drawing is a block diagram showing a spindle control circuit having a velocity loop and a position loop.

The compensator that performs proportional-integral control on the main shaft motor 1 is composed of a speed loop proportional gain 2 and two integral gains 3.4, and the speed feedback signal from the main shaft motor 1 is input to the adder 6 via the speed loop 5. are doing. This adder 6
Further, a speed command VCMD included in a numerical control command from a CNC device (not shown) is inputted via a changeover switch S2, and the output terminal of the adder 6 is connected to the speed loop proportional gain 2, and the changeover switch It is configured to be connectable to either of two integral gains 3 or 4 via SI.

These two integral gains 3.4 are, the former consists of 1 for the speed loop integral gain during normal speed control, and the latter consists of 2 for the position control mode loop integral gain, and K2 is 1 for each gain. The relationship is Kl<K2. The outputs of these two integral gains of 3.4 are added to the output of the velocity loop proportional gain of 2 in an adder 7. This adder 7 is connected to the torque constant circuit 8 of the servo motor 1 and outputs a drive command to the main shaft motor 1.

Note that Jm is motor inertia.

The main shaft motor 1 is connected to the main shaft via a gear mechanism 9, etc., and its position signal is fed back through a position loop 10 as an output of an integral element (1/S). The adder 11 calculates the difference between the position command PCMD from the CNC device and the position signal of the spindle motor 1, and the output of the difference is manually input to the position gain 12.

Further, this position gain 12 is connected to the adder 6 via a changeover switch S3 on the output side.

When the spindle motor 1 is controlled by a numerical control command from a CNC device, if it is determined that the speed command VCMD is manually input to this spindle control circuit, the changeover switch S2 is turned on, and the changeover switch S1 is activated to control the integral gain. 3
is selected. In other words, in order to accurately control the speed of the spindle motor 1 when the turning mode is commanded and normal speed control is performed, it is not necessary to make the integral gain 1 that large, and to prevent oscillation when low speed rotation is commanded. In order to do this, for example, in the case of a main shaft motor of about 10 kW, the band frequency (in terms of integral gain) may be set to about 5 to 10 Hz.

When the numerical control command from the CNC device is switched to, for example, a C-axis contour machining command, the position command P CMD is sent to the adder 11.
The changeover switch S1 is switched to the integral gain 4 side, and the changeover switches S2 and S3 are switched to the states shown in the figure. That is, when the command control mode becomes the position control mode, the position control speed loop integral gain 4 is selected. Main shaft motor 1 is 10k
If it is about W, by setting the band frequency of 2 for the integral gain to about 20 to 30 Hz, even if cutting load from an end mill etc. is applied, position fluctuation can be effectively suppressed by the compensation function in the proportional-integral circuit. can.

In this way, in the present invention, the gains are set separately depending on the control mode. Therefore, in the conventional speed loop integral control method, the same speed loop integral gain was used as during speed control even if the mode was switched to position control mode, but in the present invention, parameters can be set separately depending on the application. With the gain, it is possible to select an integral gain that suppresses positional fluctuations due to disturbance torque during cutting in the C-axis control mode, and prevents the speed loop from oscillating even at low speed rotation during normal speed control. Note that for a main shaft motor with a motor output greater than 10 kW, the velocity loop integral gain 4 during position control may be set smaller than 20 to 30 Hz.

Furthermore, when returning from the position control mode to the speed control mode, errors (differences) accumulated in the position loop of the spindle control circuit are cleared.

Note that the present invention is not limited to the above embodiments,
The present invention can be widely applied to spindle control circuits having a velocity loop and a position loop, and the magnitude of the integral gain is appropriately determined depending on the application.

〔Effect of the invention〕

As explained above, according to the speed loop integral control method of the present invention, the speed loop integral gain of the spindle control circuit is set separately for speed control and position control, and can be used by switching between them. As a result, optimal integral control can be performed according to the command control mode, and there is no risk of speed loop oscillation even during normal speed control.

[Brief explanation of drawings]

The drawing is a block diagram showing one embodiment of the present invention. 1. Main shaft motor 2 Speed loop proportional gain 3.4-...-integral gain 31% velocity loop position loop S2, S3 changeover switch Patent applicant: FANUC Corporation Agent: Patent Attorney: Takeshi Hattori

Claims (2)

[Claims] (1) In a speed loop integral control method that performs proportional-integral control of a spindle control circuit having a speed loop and a position loop, a proportional-integral means provided in the speed loop and including two switchable large and small integral gains; a discriminating means for discriminating whether the command control mode for the control circuit is a position control mode or a speed control mode; and a discriminating means for determining whether the command control mode to the control circuit is a position control mode or a speed control mode; and a discriminating means for controlling the proportional and integral means to a large integral gain in the position control mode based on the discrimination result of the discriminating means; A speed loop integral control method comprising: switching control means for switching to a small integral gain when in mode; and a speed loop integral control method. (2) The determining means determines the normal speed control mode when the numerical control command is a turning command, and determines the position control mode when the numerical control command is a C-axis contour machining command. velocity loop integral control method.