JPH0557562A - Gauge zero point compensation method in auto-sizing grinding - Google Patents

Abstract

PURPOSE:To improve the size accuracy by calculating a work expansion value from those of grinding power and both heat inflow and outflow constants in grinding operation, and making a zero point of an in-process gauge so as to be compensated as far as a portion of size equivalent to the expansion value. CONSTITUTION:An infeed driving part 6 is controlled by a feed driving control signal A out of an infeed control part 5, thus grinding takes place with a wheel spindle driving motor 4. In addition, a wheel spindle driving motor power signal B is inputted into a measuring device operational part 8 and the infeed control part 5 from the wheel spindle driving motor 4 via a grinding power measuring part 7. In succession, a size signal C is inputted into the measuring device operational part 8 from a size measuring part 10. This measuring device operational part 8 finds a work expansion value out of the extent of grinding power, compensating the size signal C, and it outputs a compensation size D to the infeed control part 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gauge zero point correcting method for eliminating a machining error caused by thermal expansion of a work due to grinding heat in automatic constant-size grinding.

[0002]

2. Description of the Related Art In a grinding machine equipped with an automatic sizing device, the dimensions of a workpiece being machined are continuously measured with an in-process gauge, and the measured value is fed back to the control mechanism of the grinding machine to cut the grinding wheel. The operation is controlled automatically. At this time, the set value (work finish dimension) of the in-process gauge is set in consideration of the expansion amount of the work due to the temperature rise due to the grinding heat.

However, the work temperature at the time of finishing the grinding may vary due to various causes, and the final finished dimension of the work may vary, resulting in defective machining. In order to suppress such variations in the final finishing dimensions, rough grinding and fine grinding are repeated twice, or sparking after rough grinding is lengthened to provide a cooling period.
Attempts have been made to eliminate variations in the work temperature at the finish of grinding, but there were drawbacks such as an increase in the number of grinding processes and a long cycle time.

In order to eliminate these drawbacks, Japanese Patent Application Laid-Open No. 59-209759 discloses the following conventional technique. In other words, most of the grinding work is converted into heat, and some of that flows into the work, but the heat generated by this grinding is known to be proportional to the tangential grinding resistance, and the grinding heat is calculated from the grinding power. Can be obtained by Therefore, the grinding power is detected during grinding, the grinding heat is calculated from this, the expansion amount of the work is calculated from the grinding heat thus obtained, and the dimension corresponding to the expansion amount of this work is set as the in-process gauge. The feedback is used to correct the gauge zero point.

Here, focusing on the fluctuation of grinding power during cutting feed, the amount of rough grinding power and the finished size of the work after fine polishing are in a substantially proportional relationship in short-time automatic grinding.
That is, when the grinding power amount during rough grinding increases, the work size measured at the time of finishing expands in proportion to the work temperature, so that the work after cooling after cooling is finished to a negative size. When the fine grinding is started, the work temperature is gradually lowered, but the fine grinding is completed while leaving the variation due to the work temperature at the time of the rough grinding. Therefore, if the zero point of the gauge is corrected by the end of rough grinding, it is possible to suppress variations in final finished dimensions due to thermal expansion. Based on such knowledge, the above-mentioned conventional technique corrects the zero point of the in-process gauge by the end of rough grinding.

[0006]

The above-mentioned prior art is based on the fact that the grinding power and the grinding heat are in a proportional relationship, so that the grinding power can be directly calculated from the grinding power without the work temperature being directly measured, and the thermal expansion of the work. Although the amount of heat is calculated to correct the gauge zero point, only the amount of heat flowing into the work is taken into consideration, and the amount of heat flowing out of the work surface due to coolant or the like is not taken into consideration. Moreover, as shown in FIG. 1, the amount of temperature rise of the work draws a curve that is slightly behind the grinding power. Therefore, the true amount of thermal expansion cannot be obtained only from the grinding power.

An object of the present invention is to further suppress the dimensional variation due to the influence of heat and enable the grinding process with higher accuracy.

[0008]

The feature of the present invention resides in that the gauge zero point is corrected in consideration of the amount of heat flowing out from the surface of the work. That is, this invention is
In automatic sizing grinding that measures the size of the workpiece being ground with an in-process gauge and performs feedback control of the motor power of the grindstone axis drive motor so that grinding is automatically terminated when the specified size is reached. The expansion amount of the work is calculated from the grinding power during grinding, the heat inflow constant, and the heat outflow constant, and the zero point of the in-process gauge is corrected by the dimension corresponding to the expansion amount of the work.

[0009]

[Function] By taking into account the amount of heat flowing out from the surface of the work, more precise dimensional control becomes possible. The temperature rise gradient of the workpiece during grinding is the formula dθ / dt = αP
It is represented by -βθ. Here, α: heat inflow constant β: heat outflow constant P: grinding power θ: workpiece temperature αP: heat flow into the work βθ: heat flow out from the work surface

Sequential calculation of the temperature rise during processing based on the above equation {(thermal expansion amount) = (workpiece diameter) × (linear expansion coefficient) ×
θ} to obtain the amount of thermal expansion, and from that the work size (= gauge size-thermal expansion amount) in the cold state after processing is determined. Thus, by considering not only the inflowing heat amount but also the outflowing heat amount, a more accurate thermal expansion amount of the work can be grasped, and thereby machine control in an actual dimension becomes possible. The heat inflow constant α is determined by the work material and processing conditions. The heat outflow constant β is determined by the work material and the coolant.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is to take into consideration not only the inflowing heat amount but also the outflowing heat amount when performing the zero point correction of the gauge in order to eliminate a processing error due to the thermal expansion of the work due to the influence of the grinding processing heat. Therefore, it can be applied to various dimension control methods. In the following, JP-A-59-20
It was applied to the dimension control method described in Japanese Patent Publication No. 9759, that is, by controlling the rough grinding power to a constant level to replace the amount of grinding power at the time of rough grinding with time and correcting the gauge zero point at regular intervals. Examples will be described.

First, referring to the block diagram of FIG. 2, the grindstone 1 has a grindstone base 3 slidable on a machine bed 2.
Mounted on the wheel, driven by the whetstone shaft drive motor 4,
A cutting operation is given by a cutting feed drive unit 6 controlled by a feed drive control signal A from the cutting feed control unit 5. When the grindstone shaft driving motor 4 starts grinding, a grindstone shaft driving motor power signal B is output, and this signal B is input to the measuring device computing unit 8 and the cutting feed control unit 5 via the grinding power measuring unit 7. On the other hand, the dimension measuring unit (in-process gauge) 10 outputs a dimension signal C and inputs it to the cutting feed control unit 5 via the measuring device computing unit 8. At this time,
The measuring device calculator 8 calculates the amount of thermal expansion of the workpiece from the grinding power and corrects the dimension signal C to calculate the corrected dimension D.

Next, the dimension control method will be described with reference to FIG. In the figure, the horizontal axis represents time and the vertical axis represents the power of the grindstone shaft drive motor 4 (grinding power).

The cycle is started, and the grindstone 1 is rapidly cut by cutting to the power zero level hold point a, where the power of the grindstone shaft drive motor 4 is held to bring the power to zero level, and the cutting fast feed is switched. When the grinding wheel 1 grinding power reaches the grinding start point b, it switches to the cutting rough feed,
Start actual grinding. Along with this, when the power of the grindstone shaft driving motor 4 rises and the power of the grindstone shaft driving motor 4 rises to the peak power control level d, the cutting and roughing feed is made slower than usual to lower the power, so that the power is zero gauge. The grinding power is controlled to a constant level by repeating the operation of returning to the normal cutting and roughing feed and increasing the power when the level has fallen to the correction level. Then, the zero point correction of the dimension measuring unit (in-process gauge) 10 is repeatedly performed until the grinding completion point g at every predetermined time Δt. The correction amount at that time is calculated by the formula d as described above.
θ / dt = the amount of thermal expansion of the work obtained based on αP−βθ. By such gauge zero point correction, the work size in the cold state after processing (= gauge size-thermal expansion amount)
Will be controlled based on. After that, the cycle is completed through operations such as cutting back.

[0015]

As described above, according to the present invention, the size of a workpiece being ground is measured by an in-process gauge, and the grinding wheel drive motor power is feedback-controlled to automatically perform grinding when a predetermined size is reached. In the automatic sizing grinding that is finished at the above step, the expansion amount of the work is calculated from the grinding power during grinding, the heat inflow constant and the heat outflow constant, and the zero point of the in-process gauge is corrected by the dimension corresponding to this work expansion amount. Therefore, it is possible to extremely reduce the variation in the finished work dimension after finishing due to the variation in the work temperature during the grinding finish. In particular, by taking into account the outflow heat amount as well, more accurate thermal expansion of the work can be grasped, and machine control in actual dimensions becomes possible, so that it is more accurate than the conventional dimension control that only considers the inflow heat amount. Grinding has become possible.

[Brief description of drawings]

FIG. 1 is a diagram showing the grinding depth, the grinding power, and the temperature rise in association with each other.

[Fig. 2] Control block diagram of the grinding machine

[Fig. 3] Grinding power diagram

[Explanation of symbols]

 1 Grindstone 2 Machine bed 3 Grindstone base 4 Drive motor 5 Control unit 6 Feed drive unit 7 Grinding power measuring unit 8 Measuring device arithmetic unit 9 Workpiece 10 Dimension measuring unit (in-process gauge)

Claims (1)

[Claims] 1. Automatic sizing in which the size of a workpiece being ground is measured with an in-process gauge and the grinding wheel drive motor power is feedback-controlled so that the grinding is automatically terminated when the size reaches a predetermined size. In the grinding process, the expansion amount of the work is calculated from the grinding power during grinding, the heat inflow constant and the heat outflow constant, and the zero point of the in-process gauge is corrected by the dimension corresponding to this work expansion amount. Gauge zero correction method in automatic constant-size grinding.