JPH04201057A - Cam grinder - Google Patents

Abstract

PURPOSE:To reduce a profile errorcaused with the follow-up delay, and to increase the work accuracy at a high speed working time by correcting the control data used in the next time grinding motion based on the difference in the grinding wheel feeding quantity in control data and that in the actual grinding time. CONSTITUTION:In a servomotor control part 16 for feeding a grinding wheel, the present value of the grinding wheel X directional position which is the output of a position counter 28 is given to a substracter 34. Then the deviation in the present value of this grinding wheel X directional position and the target value of the grinding wheel X directional position given from a control data offtaker 25 is found on each reference time. At this time, a learning correction value is found with a proper learning function being acted on this deviation by a learning correction value setter 35, this learning correction value is stored in a memory 36, while one grinding motion, and given to an adder 26 according to the reference time by an offtaker 37 when coming into the next prinding motion. The servomotor 9 for grinding wheel feeding is thus controlled based on this correction control data in the next work.

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 is reciprocated by a ball screw, and the ball screw is adjusted based on the control data. The feed of the grinding wheel is controlled by feedback by rotating it with a servo motor.

In addition, if the rotational speed of the main spindle is constant, the moving speed of the grinding point on the cam surface will vary depending on the rotational angle of the main shaft, which is unfavorable for grinding. In order to control this, the rotation of the main shaft is also often feedback-controlled using a servo motor.

Problems to be Solved by the Invention As mentioned above, in conventional cam grinding machines that feedback control the feed of the grinding wheel and the rotational speed of the main shaft, each feedback loop has an individual follow-up delay. The feed position of the grinding wheel and the rotation angle of the spindle are out of synchronization, but when increasing the depth of cut or increasing the machining speed to improve productivity, the follow-up delay increases, leading to a decrease in machining accuracy. was there.

For example, as shown in Fig. 6, 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. 7 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. Also, it is possible to reduce the amount of follow-up delay to a certain extent by increasing the servo gain, but if the servo gain is increased too much, the control system will become unstable and the machining accuracy will deteriorate, so there is a limit. .

Means for Solving the Problems In order to solve the above problems, a cam grinding machine according to the present invention includes a spindle motor that rotates a spindle on which a workpiece is mounted, and a spindle motor that grinds a cam surface of the workpiece. A grindstone feeding servo motor that relatively moves the grinding wheel in a direction crossing the main shaft, and a grinding wheel feeding based on control data indicating the relationship between the main shaft rotation angle and the grinding wheel feed amount stored in advance according to a desired cam profile. In a cam grinding machine that processes the cam surface into the desired cam profile through multiple grinding operations, the grinding wheel feed amount in the control data and the actual grinding operation are The present invention is characterized in that the control device is provided with a learning means for determining the difference between the grinding wheel feed amount and the grinding wheel feed amount at the time of the grinding operation, and correcting the control data to be used in the next grinding operation based on this difference.

The difference between the grinding wheel feed amount in the action control data and the actual grinding wheel feed amount is detected, and the grinding wheel feed amount for the next processing in the control data is corrected based on the difference, and the next processing is performed based on the corrected control data. The cam surface of the workpiece is processed into a desired cam profile by feedback-controlling the grinding wheel feeding servo motor and repeating the process of grinding the cam surface of the workpiece by a predetermined amount a plurality of times.

Embodiment An embodiment of the present invention will be explained based on FIGS. 1 to 5.

First, with reference to FIG. 2, a schematic configuration of a cam grinder according to an embodiment will be described. Reference numeral 1 denotes a spindle servo motor that is fixedly installed on a headstock 3 on a table 2 and rotates 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 rotation speed of the main shaft servo motor 1 is as follows.
This pulse generator6. Feedback control is performed by a closed loop formed by a control unit 7 to which a position detection pulse of the pulse generator 6 is applied, and a servo amplifier 8 to which a speed command is applied from the control unit 7.

Reference numeral 9 denotes a grinding wheel feeding servo motor which is fixed on a bed (not shown) and rotationally drives a ball screw 11 that moves the grinding wheel head 10 in the X direction perpendicular to the rotational axis of the main shaft 5.

The rotational position of the grinding wheel feeding servo motor 9 is determined by the 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 that rotationally drives the grinding wheel 14. Under the control of the control unit 7, the grinding wheel 14 is rotated by the rotational drive of the grinding wheel feeding servo motor 9. As shown in FIG. 3, the cam surface 51 of the workpiece 4 is ground by moving back and forth in the X direction in synchronization with the rotation of the main shaft 5.

Next, feedback control of each of the servo motors 1.9 will be described in detail with reference to the functional block diagram of the control unit 7 shown in FIG.

The control unit 7 is roughly composed of a spindle servo motor control section 15, a grindstone feeding servo motor control section 16, and a reference time generator 17.

First, the spindle servo motor control section 15 will be explained. The control data storage device 18 stores in advance spindle control data for controlling the spindle rotational speed so that the grinding point movement speed becomes substantially constant according to a desired cam profile. This spindle control data is stored as a target value of the spindle rotational position (a value obtained by integrating the target value of the spindle rotational speed) at each reference time (for example, every 1 ms) generated by the reference time generator 17. 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 provided to the subtracter 21. On the other hand 1. <The position detection pulses of the pulse generator 6 are applied to the position counter 22.The position counter 22 calculates the current value of the spindle rotational position by counting the position detection pulses, and the current value is applied to the subtracter 21.

The 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.

Next, the grindstone feeding servo motor control section 16 will be explained. The control data storage device 24 stores in advance grindstone feed control data for controlling the position of the grindstone wheel 14 in the X direction according to the desired cam profile. As shown in FIG. 4, this grinding wheel feed control data includes the target value of the X-direction position of the grinding wheel 14 at each reference time generated by the reference time generator 17 (the same time stored in the control data storage 18). (a value corresponding to the target spindle rotational position at ). In FIG. 4, the position in the X direction when grinding the base circle portion of the cam surface 51 is set at "0". This target value is determined by the control data extractor 19 mentioned above.
In synchronization with the readout of the spindle control data, the control data extractor 25 periodically reads out the reference time according to the reference time generated by the reference time generator 17 and provides it to the adder 26 .

The adder 26 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 27, and a position counter 28 to which a position detection pulse of the pulse generator 12 is given.
The deviation from the current value of the X-direction position of the grinding wheel 14, which is the output of the grinding wheel 14, is determined.

The speed command setter 29 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 position of the grinding wheel 14 in the X direction is controlled.

As described above, in this embodiment, the adder 20 of the spindle servo motor control section 15 and the adder 26 of the grindstone feed servo motor control section 16 add the learning value to each target value, and each target value Correct. Correction of each target value will be described below.

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 obtained at a predetermined period (each reference time). The deviation is then given to the learning correction value setter 31, which applies an appropriate learning function to the deviation to obtain a learning correction value. The learning correction value obtained at each reference time is stored in the learning correction value storage 32 during the grinding operation (during one revolution of the main spindle 5);
When the next grinding operation starts, the learning correction value extractor 33
It is applied to the adder 20 according to the reference time. Note that 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.

Similarly, in the grinding wheel feeding servo motor control section 16, the current value of the grinding wheel X-direction position, which is the output of the position counter 28, is given to the subtracter 34. The deviation between the current value and the target value of the grinding wheel X-direction position given from the control data extractor 25 is determined at each reference time. And that deviation is the learning correction value setting @? 35, and the learning correction value setter 35 applies an appropriate learning function to the deviation to obtain a learning correction value. The learning correction value obtained for each reference time is −
During the grinding operation, the learning correction value is stored in the learning correction value storage 36, and when the next grinding operation begins, the learning correction value extractor 37 provides the learning correction value to the adder 26 according to the reference time. In addition, in this grindstone feeding servo motor control section 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.

With such a learning correction operation, for example, when learning correction is not performed in the first machining operation, as shown in Fig. 6,
Assuming that the target position of the grinding wheel 14 in the X direction with respect to the spindle rotational position (indicated by an angle in FIG. 6) is a solid line A, and its actual position is a broken line B due to a follow-up delay (indicated by an arrow), learning correction is performed. In the second machining operation, as shown in FIG. 5, the target position is corrected as shown by the broken line with respect to the target position in the second machining operation shown by the solid line C.

Therefore, if a follow-up delay occurs during the second machining operation in the same way as during the first machining operation (it will be almost the same unless the machining conditions change), the learning correction will be applied during the second machining operation. , the actual position of the grinding wheel in the X direction with respect to the rotational position of the main shaft almost coincides with its target position.

As described above, in this embodiment, since the learning correction operation described above is performed, the profile error does not increase even if the depth of cut is increased or the machining speed is increased.
Cam grinding can be performed without reducing machining accuracy, and productivity can be improved.

Note that in the above-described embodiment, the rotational speed of the main shaft 5 is feedback-controlled, but in the present invention, the main shaft 5 may be rotated at a constant speed by a motor, and only the feed of the grinding wheel 14 may be feedback-controlled. .

Effects of the Invention As is clear from the above explanation, the cam grinder according to the present invention determines the next grinding process based on the difference between the grinding wheel feed amount in the control data and the grinding wheel feed amount during the actual grinding process. Since the control data used in the operation is corrected, profile errors caused by tracking delay are reduced,
Machining accuracy during high-speed machining can be improved.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the functions 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 the cam surface and grinding wheel. FIG. 4 is a graph showing the relationship between the X-direction position of the grinding wheel and reference time, and FIG. 5 is a graph showing the relationship between the grinding wheel's X-direction position 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 without learning correction, and FIG. 7 is a graph showing the profile error. ■...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 stand, 14... Grinding wheel, 20.34
...Adder, 30.34...Subtractor, 31.35.
...Learning correction value setter, 32.36...Learning correction value storage, 33゜37...Learning correction value extractor, 51...
cam surface. Outside 3 Figure 4 Retreat Figure 5 Retreat Mu forward Sat w @LgI Private Moon

Claims (1)

[Claims] (1) A spindle motor that rotates a spindle on which a workpiece is attached, and a grindstone feeding servo motor that moves a grindstone that grinds a cam surface of a workpiece relative to the spindle in a direction crossing the spindle, as desired. a control device that performs feedback control of the grinding wheel feeding servo motor based on control data indicating the relationship between the spindle rotation angle and the grinding wheel feed amount stored in advance according to the cam profile; In the cam grinding machine that processes the cam profile into the desired cam profile, the difference between the grinding wheel feed amount in the control data and the grinding wheel feed amount during the actual grinding operation is determined, and the difference is used in the next grinding operation based on this difference. A cam grinding machine characterized in that the control device is provided with learning means for correcting the control data.