JPH04201063A - Cam grinder - Google Patents

Abstract

PURPOSE:To prevent the uncorrect correction of each target value by stopping the correction motion of each target value, while a grinding motion is in a transit state by the stop command on the way of the grinding motion or the re-starting command from the stoppage thereof. CONSTITUTION:A stop command is outputted from an emergency stop/start switch 31 on the way of a grinding motion, the work speed is reduced from an ordinary speed, while the transient period until the work motion is completely stopped, or while the transient period when the work speed is accelerated to the ordinary speed from the stoppage state on the way of the work by a restarting command, the correction motion of the target value by learning correction value setters 26, 46 is stopped is stopped by an adjustable speed control part 30. Consequently, the uncorrect correction of each target value of the spindle rotating position of a servomotor 1 for spindle and the feeding position of the grinding wheel of a servomotor 9 for grinding wheel feeding can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to a cam grinder for grinding a cam surface of a cam or the like used in a valve mechanism of an internal combustion engine.

Conventional technology In this type of cam grinding machine, the relationship between the rotation angle of the main shaft on which the workpiece is mounted and the feed amount of the grinding wheel that grinds the cam surface of the workpiece is shown according to the desired cam profile. By storing control data in advance in memory, sequentially detecting the spindle rotation angle during machining, determining the grinding wheel feed amount for that spindle rotation angle from the control data, and controlling the grinding wheel feed amount, high precision can be achieved. There is a numerically controlled type that can perform cam grinding.

In such a numerically controlled cam grinding machine, for example, as seen in Japanese Patent Application Laid-open No. 2-30466, the grinding wheel is mounted on a grinding wheel head that reciprocates using a ball screw, and the ball screw is rotated based on the control data. The feed position of the grinding wheel is controlled by feedback by rotating it with a servo motor.

Furthermore, if the rotation speed of the spindle is constant, the speed of movement of the grinding point on the cam surface will vary depending on the rotation angle of the spindle, which is unfavorable for grinding. For control purposes, the rotational speed of the main shaft is also feedback-controlled by a servo motor.

Problems to be Solved by the Invention As mentioned above, in conventional cam grinding machines that feedback control the feed position of the grinding wheel and the rotation speed of the main shaft, tracking delays occur individually in each feedback loop.
Either the feed position of the grinding wheel and the spindle rotation angle become out of synchronization due to the mutual tracking delay, or if the depth of cut is increased or the machining speed is increased to improve productivity, the tracking delay increases. There was a problem that led to a decrease in processing accuracy.

For example, as shown in Fig. 8, the target position (command value) of the grinding wheel feed position is the solid line A, and the follow-up delay (indicated by the arrow)
If the actual feeding position is the broken line B, then
A profile error as shown in FIG. 9 will occur.

Note that this follow-up delay not only occurs in each feedback loop independently of each other, but also depends on the machining conditions such as the depth of cut at that time, so the control data should be corrected in advance in anticipation of the follow-up delay amount. That is extremely difficult. In addition, it is possible to reduce the amount of follow-up delay to a certain extent by increasing the servo gain, but there is a limit because if the servo gain is increased too much, the control system will become unstable and the machining accuracy will deteriorate. .

Means for Solving the Problems In order to solve the above-mentioned problems, the cam grinding machine according to the present invention includes a main spindle servo motor that rotates the main spindle on which a workpiece is mounted, and a cam grinder that grinds the cam surface of the workpiece. A servo motor for feeding the grinding wheel moves the grinding wheel relative to the main shaft in a direction crossing the main shaft, and a servo motor for moving the grinding wheel relative to the main shaft. A control device that sets target values for a spindle rotational position and a grinding wheel feed position in a grinding operation, and performs feedback control of the spindle servo motor and the grinding wheel feed servo motor based on the target values, In a cam grinder that processes the cam surface into the desired cam profile through multiple grinding operations, the target values for the next grinding operation are determined based on the deviations between the target values and their actual values. While the grinding operation is in a transient state due to a learning means for each correction and a stop command during the grinding operation or a restart command from the stop,
The present invention is characterized in that the control device is provided with learning stop means for stopping the target value correction operation of the learning means.

The action learning means sets a correction value based on the deviation between the target value and the actual value of the spindle rotational position detected in the spindle rotational position feedback loop, and uses the correction value to adjust the grinding wheel feed position in the next grinding operation. Correct the target value. In addition, a correction value is set based on the deviation between the target value and the actual value of the grinding wheel feed position detected in the feedback loop of the grinding wheel feed position, and the correction value is used as the target value for the grinding wheel feed position in the next grinding operation. Correct the value. However, when a stop command is issued during the grinding operation, the machining speed is decelerated from the normal speed, and during the transition period until the machining operation is completely stopped, or due to a restart command, the machining speed is reduced from the stopped state during the machining process. During the transition period during which the speed is accelerated to the normal speed, the correction operation of the target value by the learning means is stopped.

Embodiment FIG. 2 is a perspective view showing a schematic configuration of an embodiment of a cam grinder according to the present invention.

In FIG. 2, reference numeral 1 denotes a spindle servo motor which is fixed to a headstock 3 on a table 2 and rotationally drives a spindle 5 on which a workpiece 4 is mounted. A pulse generator 6 is attached to the main shaft servo motor 1, and the rotational speed of the main shaft servo motor 1 is determined by the pulse generator 6, a control unit 7 to which position detection pulses of the pulse generator 6 are given, and a speed control unit 7. Feedback control is performed by a closed loop formed by the servo amplifier 8 to which commands are given.

Reference numeral 9 denotes a ball screw 1 which is fixed on a bed (not shown) and moves the grindstone head 10 in the X direction perpendicular to the rotational axis of the main shaft 5.
1 shows a servo motor for rotating the grinding wheel. The rotational position of the grinding wheel feeding servo motor 9 is determined by a pulse generator 12 attached to this grinding wheel feeding servo motor 9.
Feedback control is performed by a closed loop formed by a control unit 7 to which a position detection pulse from a pulse generator 12 is applied, and a servo amplifier 13 to which a speed command is applied from the control unit 7.

The grinding wheel head 10 is provided with a grinding wheel 14 and a motor 50 for rotationally driving the grinding wheel 14, and a servo motor 9 for feeding the grinding wheel is controlled by the control unit l-7.
As shown in FIG. 3, the grinding wheel 14 moves back and forth in the X direction in synchronization with the rotation of the main shaft 5, and the cam surface 51 of the workpiece 4 is ground.

Next, 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 shown in FIG.

The control unit 7 includes a spindle servo motor control section 15. The grindstone feeding servo motor control section 16 is roughly composed of a reference time generator 17 and an acceleration/deceleration control section 30.

Control data storage 18 of main shaft servo motor control section 15
Main shaft control data is stored in advance in accordance with a desired cam profile for controlling the main shaft rotational speed so that the grinding point moving speed becomes substantially constant. This spindle control data includes each reference time (
For example, the target value of the spindle rotational position (a value obtained by integrating the target value of the spindle rotational speed) at each time (for example, every 1 mS) is stored. This target value is read out periodically (for example, every 1 mS) by the control data extractor 19 according to the reference time generated by the reference time generator 17, and is provided to the adder 20.

In the adder 20, the read target value is corrected by adding a learning correction value, which will be described later, and the corrected target value is given to the subtracter 21. Further, 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 (actual value) of the spindle rotational position by counting the position detection pulse. given to.

A subtracter 21 subtracts the current value from the corrected target value to obtain the deviation. The speed command setter 23 to which this deviation is given sets a speed command to be output to the servo amplifier 8 by multiplying the deviation by a predetermined gain. Based on this speed command, the current value given to the spindle servo motor 1 by the servo amplifier 8 is set, and the rotation speed of the spindle servo motor 1, that is, the rotation speed of the spindle 5 is controlled.

On the other hand, the control data storage unit 38 of the grinding wheel feeding servo motor control unit 16 stores information in advance for controlling the X-direction position of the grinding wheel 14 (hereinafter referred to as the grinding wheel feeding position) according to the desired cam profile. Grindstone feed control data is stored.

As shown in FIG. 4, this grinding wheel feed control data includes a target value of the grinding wheel feeding position at each reference time generated by the reference time generator 17 (a target value of the grinding wheel feed position at the same time stored in the control data storage device 18). (value corresponding to the rotational position). In FIG. 4, the feed position when grinding the base circle portion of the cam surface 51 is set at "0". This target value is periodically read out by the control data extractor 39 in accordance with the reference time generated by the reference time generator 17 in synchronization with the readout of the spindle control data by the control data extractor 19, and the adder given to 40.

The adder 40 adds a learning correction value, which will be described later, to the read target value, thereby correcting the target value. The correction target value is given to a subtracter 41, and a position counter 42 to which a position detection pulse of the pulse generator 12 is given.
The deviation from the current value (actual value) of the grinding wheel feed position, which is the output of , is determined.

The speed command setter 43 to which this deviation is given sets a speed command to be output to the servo amplifier 13 by multiplying the deviation by a predetermined gain. Based on this speed command, the current value given to the grindstone feeding servo motor 9 by the servo amplifier 13 is set, and the rotational position of the grinding wheel feeding servo motor 9, that is, the grinding wheel feeding position is controlled.

As described above, in this embodiment, the adder 20 of the spindle servo motor control section 15 and the adder 40 of the grindstone feeding servo motor control section 16 add the learning value to each target value, and each target value Correct. Hereinafter, correction of each target value will be explained.

In the main shaft servo motor control section 15, the position counter 22
The current value of the spindle rotational position which is the output of is given to the subtractor 24, and the subtractor 24 calculates the deviation between the current value of the spindle rotational position and the target value of the spindle rotational position given from the control data extractor 19. is obtained at a predetermined period (each reference time). Then, the deviation is given to the learning correction value setter 26 via the switch 25, and the learning correction value setting device 26 applies an appropriate learning function to the deviation to obtain a learning correction value.

The learning correction value obtained at each reference time is sequentially stored in the learning correction value storage 27 during the -grinding operation (while the main spindle 5 makes one revolution). Then, during the next grinding operation, the learning correction value is read out by the learning correction value extractor 28 according to the reference time, and is provided to the adder 20 via the switch 29. After the - degree learning correction value is stored, it is updated and stored in a form in which a new learning correction value is added to the learning correction value for each -grinding operation.

On the other hand, also in the grindstone feeding servo motor control section 16,
Similarly, the current value of the grinding wheel feed position which is the output of the position counter 42 is given to a subtracter 44, and the subtracter 44 combines the current value of the grinding wheel feed position with the control data extractor 39.
The deviation from the target value of the grinding wheel feed position given by is determined at each reference time. And that deviation is switch 45
The deviation is given to the learning correction value setter 46 via the learning correction value setter 46, and the learning correction value is determined by applying an appropriate learning function to the deviation.

The learning correction value obtained for each reference time is stored in the learning correction value storage device 47 during the grinding operation, and when the next grinding operation begins, the learning correction value extractor 48 retrieves the learning correction value according to the reference time. It is applied to the adder 40 via the switch 49. In this grindstone feeding servo motor control unit 16 as well, after the - degree learning correction value is stored, it is updated and stored in a form in which a new learning correction value is added to the learning correction value for each -grinding operation. .

The acceleration/deceleration control section 30 has an emergency stop/start switch 31 (
(not shown in FIG. 2), each of the above-mentioned switches 25, 29,
45.49 and the reference time generator 17. The emergency stop/start switch 31 outputs a stop command when the machining operation is to be stopped urgently for some reason during the grinding operation, or outputs a restart command when the machining operation is restarted from the stopped state. When a stop command is given, the acceleration/deceleration control unit 30 switches each switch 25, 29, 45° 49 to
At the same time, the generation cycle of the reference time is gradually lengthened for the reference time generator 17 so that the processing speed is decelerated from the normal speed and the processing operation is stopped after a predetermined period of time. Give a command to stop the occurrence. In addition, when a restart command is given, the reference time generator 17 is started to generate a reference time so that the processing speed is accelerated from a stopped state and returns to normal speed in a predetermined period. A control command is given to gradually shorten the cycle to a normal cycle, and after the predetermined period, each switch 25, 29,
45. Set 49 to "closed".

When each switch 25, 29, 45.49 becomes "open", the adder 20.40 corrects each target value by the learning correction value - and the learning correction value storage 27. Update storage of the '47 learning correction value is stopped.

In the above configuration, the learning correction operation is performed as follows.

For example, when learning correction is not performed in the first grinding operation, as shown in Fig. 8, the target position of the grinding wheel feed position with respect to the spindle rotational position (indicated by angle in Fig. 8) is a solid line A, and the tracking Suppose that due to the delay (indicated by the arrow), the actual position is on the dashed line B. Then, in the second grinding operation in which the learning correction is performed, as shown in FIG. The target position is corrected as shown by the broken line using a learning correction value based on the deviation. Therefore, if a follow-up delay occurs during the second grinding operation in the same way as during the first grinding operation, the grinding wheel feed relative to the spindle rotation position will be adjusted during the second grinding operation using the learning correction described above. The actual position of a position will approximately correspond to its target position.

In order to perform such a learning correction operation, in this embodiment,
Even if the depth of cut is increased or the machining speed is increased, the profile error does not increase, so cam grinding can be performed without reducing machining accuracy, and productivity can be improved.

Next, with reference to FIGS. 6 and 7, the operation at the time of emergency stop and restart by operating the emergency stop/start switch 31 will be described.

When a stop command is given during the grinding operation by operating the emergency stop/start switch 31, the generation cycle of the reference time gradually increases as described above, so that the grinding wheel 14 stops as shown in FIG. As the feed rate (indicated by the solid line) decreases, the rotational speed of the main spindle 5 decreases in synchronization with the decrease, and finally the machining operation is stopped. During this transition period, the speed decrease causes the follow-up delay amount to be smaller than the follow-up delay amount that occurred in the previous grinding operation, so if learning correction is performed, the correction amount will be too large and the profile error will not be reduced. However, in this embodiment, the learning correction is stopped by keeping the switches 29 and 49 open during the transition period, so that the profile error can be kept small.

Furthermore, if the learning correction value is updated and stored during the transition period, the correction amount is set to be small due to the above-mentioned reason, and therefore the correction amount will be too small in the next grinding operation, resulting in a large profile error.

However, in this embodiment, during the transition period, the switch 25.4
5 is set to "open" to stop updating the learning correction value, in the next grinding operation, the target value will be corrected using the learning correction value from the previous time only during the period corresponding to the transition period. , the profile error does not become large.

On the other hand, when a restart/stop command is given by operating the emergency stop/start switch 31, the generation of the reference time starts and the period gradually decreases, so that the grinding wheel stops as shown in FIG. As the feed rate of the wheel 14 (indicated by the solid line) increases, the rotational speed of the main shaft 5 increases in synchronization with it, and eventually returns to the normal machining speed.

During this transition period, the amount of follow-up delay is smaller than the amount of follow-up delay that occurred in the previous grinding operation, so when learning correction is performed, the correction amount is too large and the profile error does not become small, but the same as when stopped. During that transition period, the switch 29
．． 49 is set to "open" to stop learning correction, profile errors can be kept small.

In addition, during the transition period, the switch 25.45 is set to ``open'' to stop updating the learning correction value, similar to when stopping, so that in the next grinding operation, the switch 25.45 is opened during the transition period. Only during the corresponding period, the target value is corrected using the learned correction value from the time before the previous one, so that the profile error does not become large.

Effects of the Invention As is clear from the above explanation, according to the cam grinder according to the present invention, the next grinding operation is performed according to each deviation between each target value and each actual value of the spindle rotation position and grinding wheel feed position. Since each of the target values is corrected, the machining accuracy during high-speed machining can be improved. In addition, since the correction operation of each target value is stopped while the grinding operation is in a transient state due to a stop command in the middle of the grinding operation or a restart command from the stop, unauthorized correction of each target value is prevented. Ru.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the functions of a control unit in 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 the cam surface and grinding wheel. 4 is a graph showing the relationship between the grinding wheel feed position and the reference time, and FIG. 5 is a graph showing the relationship between the grinding wheel feed position and the spindle rotation angle when learning correction is performed.
FIG. 6 is a graph showing the relationship between the reference time and the grinding wheel feed speed when the machining operation is stopped, and FIG. 7 is a graph showing the relationship between the reference time and the grinding wheel feed speed when restarting the machining operation.
FIG. 8 is a graph showing the relationship between the grinding wheel feed position and the spindle rotation angle without learning correction, and FIG. 9 is a graph showing the profile error in relation to FIG. 8. ■...Spindle servo motor, 4...Workpiece, 5...
・Main shaft, 6.12...Pulse generator, 7...
Control unit, 8.13... Servo amplifier,
9... Servo motor for grinding wheel feeding, 11... Ball screw, 10... Grinding wheel head, 14... Grinding wheel, 17...
Reference time generator, 20.40...Adder, 24.44
...Subtractor, 25.29, 45.49...Switch,
26.46...Learning correction value setter, 27.47...
Learning correction value storage device, 28.48... Learning correction value extractor, 30... Acceleration/deceleration control unit, 51... Cam surface.

Claims (1)

[Claims] (1) A servo motor for the main shaft that rotates the main shaft on which the workpiece is mounted, a servo motor for feeding the grindstone that moves the grinding wheel that grinds the cam surface of the workpiece relative to the main shaft in a direction crossing the main shaft; The target values for the spindle rotation position and grinding wheel feed position for each grinding operation are set based on the control data that indicates the relationship between the spindle rotation angle and the grinding wheel feed amount, which are stored in advance according to the cam profile to be used. and a control device that performs feedback control of the spindle servo motor and the grindstone feeding servo motor based on the above, and processes the cam surface into the desired cam profile through a plurality of grinding operations, A learning means for correcting each target value of the next grinding operation based on each deviation between each target value and each actual value, and a stop command in the middle of the grinding operation or a restart command from the stop. A cam grinding machine characterized in that the control device is provided with learning stopping means for stopping the target value correction operation of the learning means while the grinding operation is in a transient state.