JP3036646B2 - Cam grinder - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cam grinder for grinding a cam surface such as a cam used in a valve mechanism of an internal combustion engine.

2. Description of the Related Art In a cam grinding machine of this type, a relationship between a rotation angle of a main shaft on which a workpiece is mounted and a feed amount of a grinding wheel for grinding a cam surface of a workpiece according to a desired cam profile is shown. The control data is stored in a memory in advance, the spindle rotation angle is sequentially detected during machining, the grinding wheel feed amount with respect to the spindle rotation angle is obtained from the control data, and the grinding wheel feed amount is controlled to achieve high precision. There is a numerical control type that can perform cam grinding.

In such a numerically controlled cam grinder, for example, as disclosed in JP-A-2-30466, a grinding wheel is mounted on a grindstone table which reciprocates with a ball screw, and the ball screw is mounted on the basis of the control data. The feed of the grinding wheel is feedback-controlled by being rotationally driven by a servomotor.

Further, if the rotation speed of the spindle is constant, the moving speed of the grinding point on the cam surface fluctuates due to the rotation angle of the main shaft, which is not preferable for grinding. For control, the rotation of the spindle is also often subjected to feedback control by a servomotor.

Problems to be Solved by the Invention As described above, in the conventional cam grinder that performs feedback control of the feed of the grinding wheel and the rotation speed of the spindle, since a tracking delay occurs individually in the nuclear feedback loop, the mutual tracking delay causes Synchronization between the feed position of the grinding wheel and the rotation angle of the spindle is not synchronized.However, if the cutting depth is increased or the processing speed is increased to improve productivity, the following delay will increase and the processing accuracy will decrease. was there.

For example, as shown in FIG. 6, assuming that the target position (command value) of the feed position of the grinding wheel is a solid line A and the actual feed position is a broken line B due to a tracking delay (indicated by an arrow), a seventh line A profile error as shown in the figure will occur.

In addition, since the following delay occurs not only independently of each other in each feedback loop but also depends on machining conditions such as a cutting amount at that time, the control data is corrected in advance in anticipation of the following delay amount. It is extremely difficult. Further, it is possible to reduce the following delay amount to some extent by increasing the servo gain. However, if the servo gain is too large, the control system becomes unstable, and the machining accuracy deteriorates. .

Means for Solving the Problems In order to solve the above problems, a cam grinding machine according to the present invention grinds a spindle motor for rotating a spindle on which a workpiece is mounted and a cam surface of the workpiece. A grinding wheel feed servomotor for relatively moving a grinding wheel in a direction intersecting the main spindle, and the grinding wheel feed based on control data indicating a relationship between a main spindle rotation angle and a grinding wheel feed amount stored in advance according to a desired cam profile. And a control device for performing feedback control of a servo motor for a cam grinding machine for processing the cam surface into the desired cam profile in a plurality of grinding operations, the grinding wheel feed amount and the actual grinding operation in the control data. The difference from the wheel wheel feed amount at the time is calculated each time, multiplied by a predetermined learning function, and stored and updated as a learning correction value each time. A learning means for correcting the control data used in the next grinding operation based on the correction value is provided in the control device.

The difference between the wheel wheel feed amount and the actual wheel wheel feed amount in the control data is detected, the value is multiplied by a predetermined learning function to obtain a learning correction value, and the next processing in the control data is performed using the learning correction value. Correct the grinding wheel feed amount. And
In the next machining, the servo motor for grinding wheel feed is feedback-controlled based on the corrected control data, and the grinding of the cam surface of the workpiece by a predetermined amount is repeated a plurality of times, so that the cam surface has a desired cam profile. Process.

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

First, a schematic configuration of a cam grinder according to an embodiment will be described with reference to FIG. 1 is a headstock 3 on a table 2
And a spindle servomotor that rotationally drives a spindle 5 on which the workpiece 4 is mounted. Servomotor 1 for spindle
Is mounted with a pulse generator 6. The rotational speed of the spindle servomotor 1 is controlled by the pulse generator 6, a control unit 7 to which a position detection pulse of the pulse generator 6 is supplied, and a servo to which a speed command is supplied from the control unit 7. Feedback control is performed by a closed loop formed by the amplifier 8.

Reference numeral 9 denotes a ball screw fixedly mounted on a bed (not shown) for moving the grindstone head 10 in the X direction orthogonal to the rotation axis of the main shaft 5.
This is a grinding wheel feed servo motor that rotationally drives 11. The rotational position of the grinding wheel feed servo motor 9 is determined by a pulse generator 12 attached to the grinding wheel feed servo motor 9, a control unit 7 to which a position detection pulse of the pulse generator 12 is given, and a servo amplifier to which a speed command is given from the control unit 7. 13 is feedback-controlled by a closed loop formed by 13.

The grinding wheel head 10 is provided with a grinding wheel 14 and a motor 50 for rotating and driving the grinding wheel 14. As shown in FIG. 3, the cam surface 51 of the work 4 is ground by moving back and forth in the X direction in synchronization with the rotation of the main shaft 5.

Next, the feedback control of each of the servo motors 1 and 9 will be described in detail with reference to the functional block diagram of the control unit 7 in FIG. The control unit 7 is roughly constituted by a spindle servomotor control unit 15, a grinding wheel feed servomotor control unit 16, and a reference time generator 17.

First, the spindle servomotor control unit 15 will be described. The control data storage 18 previously stores spindle control data for controlling the spindle rotation speed such that the grinding point moving speed is substantially constant according to a desired cam profile. The spindle control data is stored as a target value of the spindle rotation position (a value obtained by integrating the target value of the spindle rotation speed) at each reference time (for example, every 1 ms) generated by the reference time generator 17. This target value is periodically (for example, every 1 ms) read out by the control data extractor 19 in accordance with the reference time generated by the reference time generator 17, and is added to the adder 2.
Given to 0.

In the adder 20, the read target value is corrected by adding a learning correction value described later, and the corrected target value is subtracted from the subtractor.
Given to 21. On the other hand, the position detection pulse of the pulse generator 6 is given to the position counter 22, and the position counter 22 calculates the current value of the main shaft rotation position by counting the position detection pulses, and supplies the current value to the subtractor 21.

The subtracter 21 subtracts the current value from the correction target value, and obtains the deviation. In the speed command setting unit 23 to which the deviation is given, a speed command to be output to the servo amplifier 8 by multiplying the deviation by a predetermined gain is set. With this speed command, the current value given to the servomotor 1 for the spindle by the servo amplifier 8 is set, and the rotation speed of the servomotor 1 for the spindle, that is, the rotation speed of the spindle 5 is controlled.

Next, the grinding wheel feed servo motor control unit 16 will be described. The control data storage 24 stores grinding wheel feed control data for controlling the X-direction position of the grinding wheel 14 in advance according to the desired cam profile. As shown in FIG. 4, the grinding wheel feed control data includes a reference time generator.
The target value of the X-direction position of the grinding wheel 14 at each reference time generated at 17 (the value corresponding to the target spindle rotational position at the same time stored in the control data storage 18) is stored. In FIG. 4, the position in the X direction when the base circle portion of the cam surface 51 is ground is "0". The target value is periodically read by the control data extractor 25 according to the reference time generated by the reference time generator 17 in synchronization with the reading of the spindle control data of the control data extractor 19, and the adder Given to 26.

In the adder 26, a learning correction value described later is added to the read target value, and the target value is corrected. The correction target value is given to the subtractor 27, and the pulse generator
The deviation from the present value of the X-direction position of the grinding wheel 14, which is the output of the position counter 28 to which the twelve position detection pulses are given, is obtained.

In the speed command setting device 29 to which the deviation is given, a speed command output to the servo amplifier 13 by multiplying the deviation by a predetermined gain is set. With this speed command, the servo amplifier
At 13, a current value given to the grinding wheel feed servomotor 9 is set, and the rotational position of the grinding wheel feed servomotor 9, that is, the X direction position of the grinding wheel 14 is controlled.

As described above, in this embodiment, the adder 20 of the spindle servomotor control unit 15 and the grinding wheel feed servomotor control unit are used.
The 16 adders 26 add the learning value to each target value and correct each target value. Hereinafter, the correction of each target value will be described.

In the spindle servomotor control unit 15, the current value of the spindle rotation position, which is the output of the position counter 22, is given to the subtractor 30, and the subtractor 30 outputs the current value of the spindle rotation position and the control data extractor 19. The deviation from the target value of the spindle rotational position given from the above is obtained at a predetermined cycle (for each reference time). Then, the deviation is given to the learning correction value setting unit 31, and the learning correction value is determined by multiplying the deviation by an appropriate learning function. The learning correction value obtained for each reference time is determined during one grinding operation (when the spindle 5
During the rotation, the learning correction value is stored in the learning correction value storage unit 32, and when the next grinding operation is started, the learning correction value extraction unit 33 gives the learning correction value to the adder 20 according to the reference time. After the learning correction value is once stored, the learning correction value is updated and stored in such a manner that a new learning correction value is added to the learning correction value.

In the grinding wheel feed servo motor control unit 16 as well, the current value of the grinding wheel X direction position, which is the output of the position counter 28, is given to the subtractor 34, and the subtractor 34 calculates the current value of the grinding wheel X direction position. The deviation between the current value and the target value of the position in the grinding wheel X direction provided from the control data extractor 25 is obtained for each reference time. And the deviation is the learning correction value setting unit 35
The learning correction value is obtained by multiplying the deviation by an appropriate learning function in the learning correction value setting unit 35. The learning correction value obtained for each reference time is stored in the learning correction value storage 36 during one grinding operation, and when the next grinding operation is started, the learning correction value extractor 37 outputs the learning correction value according to the reference time. Given to 26. After the learning correction value is once stored in the grinding wheel feed servo motor controller 16, the learning correction value is updated and stored in such a manner that a new learning correction value is added to the learning correction value.

With such a learning correction operation, for example, when learning correction is not performed in the first machining operation, as shown in FIG. 6, the X-direction target of the grinding wheel 14 with respect to the spindle rotational position (indicated by an angle in FIG. 6). Assuming that the position is a solid line A and the actual position is a broken line B due to a tracking delay (indicated by an arrow),
In the second machining operation in which the learning correction is performed, as shown in FIG. 5, the target position in the second machining operation indicated by the solid line C is corrected as indicated by a broken line D. Therefore, assuming that a follow-up delay occurs in the second machining operation as in the first machining operation (substantially the same if the machining conditions are not changed), the learning correction is performed in the second machining operation. The actual position in the grinding wheel X direction with respect to the spindle rotation position substantially coincides with the target position.

As described above, in this embodiment, since the learning correction operation as described above is performed, the profile error does not increase even if the cutting depth is increased or the processing speed is increased, so that the cam grinding without reducing the processing accuracy is performed. Can be performed, and the productivity can be improved.

In the above embodiment, the rotational speed of the spindle 5 is feedback-controlled. However, in the present invention, the spindle 5 may be rotationally driven by a motor at a constant speed, and only the feed of the grinding wheel 14 may be feedback-controlled. .

Effect of the Invention As is apparent from the above description, according to the cam grinder according to the present invention, the difference between the grinding wheel feed amount in the control data and the grinding wheel feed amount during actual grinding is determined and a predetermined value is determined. Is multiplied by a learning function to obtain a learning correction value, and the control data used in the next grinding operation is corrected using the learning correction value, so that a profile error caused by a tracking delay is reduced, and the processing accuracy during high-speed processing is improved. can do.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the function of a control unit according to an embodiment of the present invention, FIG. 2 is a perspective view schematically showing the overall configuration of the embodiment, and FIG. 3 is an enlarged view of a cam surface and a grinding wheel. FIG. 4 is a graph showing the relationship between the X-direction position of the grinding wheel and the reference time, and FIG. 5 is a graph showing the relationship between the X-direction position of the grinding wheel and the spindle rotation angle when learning correction is performed. FIG. 6 is a graph showing the relationship between the X-direction position of the grinding wheel and the spindle rotation angle when learning correction is not performed, and FIG. 7 is a graph showing a profile error. 1 ... Spindle servo motor, 4 ... Workpiece, 5 ... Spindle, 6,12 ... Pulse generator, 7 ... Control unit, 8,13 ... Servo amplifier, 9 ... Wheel servo motor , 11 ... ball screw, 10 ... grindstone head, 14 ...
Wheel, 20,34 …… Adder, 30,34 …… Subtractor, 31,35…
… Learning correction value setting device, 32,36 …… Learning correction value storage device, 33,
37: Learning correction value extractor, 51: Cam surface.

Claims (1)

(57) [Claims] A spindle motor for rotating a spindle on which a workpiece is mounted; a grinding wheel feed servomotor for relatively moving a grinding wheel for grinding a cam surface of the workpiece in a direction intersecting the spindle. A control device for feedback-controlling the grinding wheel feed servomotor based on control data indicating a relationship between the spindle rotation angle and the grinding wheel feed amount stored in advance according to a desired cam profile, and In a cam grinding machine for processing a cam surface into the desired cam profile, a predetermined learning function is obtained by calculating a difference between a grinding wheel feed amount in the control data and a grinding wheel feed amount during an actual grinding operation each time. The learning is performed by multiplying the stored learning correction value each time and updating the control data to be used in the next grinding operation based on the stored learning correction value. A cam grinder wherein means is provided in the control device.