JPH10128661A - Grinding control method and device for grinding machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To determine a cut retreat amount, eliminate worsening of work efficiency, so that accurate stable work can be realized, and simplify a device constitution, taking into consideration a change of grinding wheel sharpness and a response delay of a mechanical system and an electric control system. SOLUTION: A device is applied to a grinding control method of a grinding machine in which when rough grinding work is completed, cut retreat is performed, thereafter so as to perform finish grinding work, a depth of cut is controlled. While measuring a prescribed item relating to a workpiece and the grinding machine during rough grinding work, by this measured value, and amount of cut retreat, which must be performed, is calculated. When the rough grinding work is completed, cut retreat is performed by the calculated cut retreat amount. The device is constituted by an NC cut control device 21 and a measuring control device 22 calculating the cut retreat amount. In the NC cut control device 21, during the time a cut of rough grinding work is performed, an external input of the cut retreat amount xbo is always supervised, and a preset cut retreat amount is rewritten.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a grinding machine having a weak machining system, such as an inner surface grinding machine, a grinding machine having a weak workpiece rigidity and a low supporting system rigidity, and the like, in which the bending due to the machining force becomes large. The present invention relates to a grinding control method and apparatus for a grinding machine for performing control to retract a cut in order to release bending after roughing. In particular, the present invention relates to a grinding control method and apparatus for continuously processing a large amount of the same workpiece.

[0002]

2. Description of the Related Art A grinding machine performs rough processing and finish processing to process one workpiece, thereby ensuring processing efficiency and processing accuracy. The grinding system has a low rigidity, particularly in the case of an inner surface grinding machine. As described above, the cutting time can be shortened by performing the cutting and retreating before the finishing processing. In FIG. 9, the state of the bending of the grinding system is exaggerated. In the inner surface grinding, the grinding wheel shaft 9a is bent by the processing force, and an uncut portion corresponding to the bending δ occurs in the workpiece W with respect to the cut X1 (t). The processing dimension X2 (t) is expressed as a function of the cut X1 (t) and the grinding time constant τ (sec) as follows. dX2 (t) / dt = (1 / τ) · (X1 (t) −X2 (t)) Here, the grinding time constant τ is the sharpness (working efficiency) of the grindstone,
It depends on the workpiece material, workpiece shape, etc.

FIG. 10 shows a processing state (process) in a case where the bending is released by cutting back and in a case where bending is not performed.
This is shown in comparison with (A) and (B). In order to maintain the grinding accuracy, it is necessary to make the deflection δ (t) at the end of the cut into a certain value or less. When there is no retraction, it takes about three times the grinding time constant to recover the deflection during the finishing. When the cut-in retreat is made, it is possible to take an extra cut in the rough processing and to recover the bending before the finishing processing, so that the bending can be recovered quickly in the finishing processing. This makes it possible to shorten the processing time. In conventional grinding machines, there are two typical methods for determining the amount of cut retreat. One is a method of determining a cutting retreat amount so as to stabilize a processing cycle and processing accuracy while repeating a grinding experiment, and is the most general method. Secondly, when the machining force or machining power is controlled, for example, in power control, when the rough machining setting power Pr (kW) and the finishing setting power Pf (kW), the cutting retreat amount Xbo = control As the constant of the system x (Pr-Pf), the cutback is automatically performed.

[0004] However, with these cutting retreat amounts, if the finishing cutting speed is reduced or the finishing setting power is reduced, the cycle becomes unstable and the dispersion of the finishing time becomes very large. For this reason, it is necessary to increase the finishing allowance and lengthen the cutting time so that the retreat amount of the cutting becomes smaller. Also, as in the case of a CBN grindstone, the cycle becomes unstable even when the sharpness of the grindstone changes greatly before and after dressing or when the machining allowance varies.

[0005]

In view of the above situation, it has been desired to develop a method of determining the amount of retraction of the cutting which can realize a stable grinding cycle even for these causes of instability.
Therefore, a method of determining the amount of cut retraction as follows was considered. The basic characteristics of the grinding process are the workpiece size generation speed V (t) = dX2 (t) / dt and the grinding deflection δ (t) = X1 (t) −X2 (t). (T) = δ (t) / τ... Since this can also be interpreted as δ (t) = τ · V (t), the grinding deflection is the workpiece dimension generation speed (this is the cutting speed dX1 (t) / d when the deflection is stable).
(substantially equal to t) multiplied by the grinding time constant. Now, since the cutting retreat amount is set in order to make the rough grinding deflection into the finish grinding deflection, during the rough machining, the workpiece dimension generation speed V (t) or the cutting speed dX1 is obtained.
If (t) / dt and the grinding time constant τ are known, the deflection δ (t) can be calculated, and the optimum cut-in retreat amount Xbo to shift to finish processing can be calculated.

However, the retraction amount X calculated as described above is calculated.
When performing control using bo, there is a problem that there is no NC device capable of changing the cutback amount during cutting. In the NC apparatus, the speed can be switched by an override or the like in order to determine a path at the start of machining, but there is no apparatus that can change the position during machining. Therefore, it is necessary to develop an NC device capable of changing the amount of cut-back after roughing is completed during roughing. In addition, since the finish processing is predicted and controlled during the rough processing, a delay in the control system and the mechanical system is also a serious problem. Of course, the grinding time constant rarely changes drastically, so it is possible to use the value during the previous machining.However, in order to improve the accuracy, the grinding time constant for the workpiece currently being machined must be changed. It is desirable to ask.

Therefore, an in-process measurement method for obtaining a grinding time constant of a workpiece currently being machined will be considered. In the grinding process, the grinding efficiency, the so-called "grinding wheel sharpness", changes due to wear and fall of the abrasive grains as a tool. The change in the sharpness changes the grinding time constant and the control gain of the grinding system. When controlling the machining process, it is necessary to accurately grasp this change. Now, the grinding time constant τ is expressed as follows. τ = α / [(grinding system rigidity Kg) × (grinding wheel sharpness Λ)] where α: constant determined by the workpiece Λ = (working efficiency Z (mm ³ / sec)) / (grinding force Fn
(N)) That is, the grinding time constant τ is inversely proportional to the grinding wheel sharpness 石. When processing the same workpiece continuously,
It is considered that the constants α and Kg are the same, and if the sharpness 砥 of the grinding wheel is known, the grinding time constant τ can be determined.

[0008] Consider the change in the sharpness of the grinding wheel. Assuming that the grinding time constant at the standard grinding wheel sharpness Λ0 is τ0 depending on the workpiece, the grinding time constant τt when the grinding wheel sharpness becomes Λa during machining is τt = τ0 × (Λa / Λ0). A specific method of calculating the sharpness of the grinding wheel during processing will be described later in the description of the embodiment of the invention.

A method of calculating the cutting speed V (t) will be described.
The cutting speed V (t) is the processing speed of the workpiece, and dX2
It can be easily understood that (t) / dt. When there is an in-process gauge, the cutting speed can be easily obtained by differentiating the size signal. If there is no in-process gauge and only power or processing force is detected, the following is obtained. That is,
In FIG. 10, the deflection δ (t) is the same as the grinding power and the grinding resistance.
Since (t) ≒ dX2 (t), dX1 (t) / dt may be obtained by judging that the power or machining force has become steady.

A method for determining the amount of cut retraction will be considered. When the grinding time constant τ and the cutting speed V can be detected, the grinding deflection δ (t)
Can be calculated by δ (t) = τ × V (t). This grinding deflection δ (t) may be set as the cutback retreat amount.
In the case where an NC device capable of changing the retraction amount of the cut after the completion of the roughing can be developed during the roughing described as one of the problems described above, the value of the grinding deflection δ (t) is reduced during the roughing. The set value of NC is stored again as the retraction amount Xbo.

However, at this time, the delay of the cutting system becomes a serious problem. In a general NC device, a delay time of several tens of msec occurs when shifting from roughing to cutting retreat or finishing. This is because the delay of the mechanical system and the delay of the electric control system are combined, though the variation is small. Furthermore, a change in the grinding time constant is added, and an unstable phenomenon of the grinding cycle such as a variation in the finishing time occurs. If the cycle is unstable, the processing accuracy will vary, so it is necessary to make adjustments such as reducing the cutting speed.

The present invention has been made in view of the above-mentioned circumstances, and has been applied to unstable elements such as a change in a finishing cutting speed and a finishing setting power.
An object of the present invention is to provide a grinding control method and apparatus for a grinding machine capable of setting a cutting retreat amount capable of realizing a stable grinding cycle. Another object of the present invention is to be able to determine the retraction amount of the cut in consideration of the response delay of the mechanical system and the electric control system,
An object of the present invention is to provide a grinding control method and apparatus for a grinding machine capable of performing stable processing with high accuracy without lowering the processing efficiency. Still another object of the present invention is to provide a grinding machine control device that can change the setting of the amount of cutback after roughing is completed during roughing, has a simple configuration, and has high versatility, and components of this device. To provide a grinding machine cutting control device.

[0013]

SUMMARY OF THE INVENTION A grinding control method for a grinding machine according to the present invention is directed to a grinding control method for performing a cutting retreat when a rough grinding process is completed, and thereafter controlling the cutting so as to perform a finish grinding process. While performing the measurement of the predetermined items for the workpiece and the grinding machine during the rough grinding, the cut-in retreat amount to perform the cut-back is calculated by the measured value, and the above-described calculation is performed when the rough grinding is completed. This is a method of performing cutback with the cutback amount. In this manner, the measurement value during the rough grinding process is used to calculate the cutting retreat amount at the completion of the rough grinding process, and to perform the cutting retreat, the optimum cutting retreat amount according to the change in the sharpness of the grinding wheel and the like. be able to. Further, the optimum cutting retreat amount can be obtained without being affected by unstable factors such as a change in finishing cutting speed and finishing setting power, and a stable grinding cycle can be realized.
Therefore, there is no need to wastefully increase the finishing allowance, and high-speed machining can be realized.

In this grinding control method, as follows:
It is desirable to use a substantial processing dimension obtained by correcting the processing dimension of the workpiece obtained by the in-process gauge by the thermal expansion amount of the workpiece as the value of the processing dimension used for calculating the amount of cut retreat. That is, in the process of calculating the amount of cutting retreat, a grinding time constant τ represented by the following equation τ = α / [(grinding system rigidity) × (grinding wheel sharpnessΛ)] is used, where α is a constant determined by the workpiece. . The sharpness of the whetstone
Is a value represented by Λ = (processing force) / (processing efficiency), and the processing force is a value of a grinding power or a grinding force. The processing efficiency is a value represented by the product of the amount of change per unit time of the processing dimension and the processing circumference. As the value of the processing dimension used in this calculation, the actual processing dimension obtained by correcting the thermal expansion amount of the workpiece is used. As a result, the grinding wheel sharpness can be accurately evaluated, an accurate grinding time constant can be obtained, and a more appropriate cutting retreat amount can be calculated.

In these control methods, the grinding time constant τ, the rough grinding speed Vr, the machine response delay time t
2, 2, and t3, and the finishing processing conditions obtained from the finishing cutting speed Vf or the finishing grinding set power Pf, the cutting retreat amount Xbo may be obtained by the following equation. Xbo = δr × exp (−t2 / τ) −δ3 × exp (t3 / τ) = Vr × τ × exp (−t2 / τ) −δf × τ × exp (t3 / τ) However, the finishing cutting speed Vf When setting: δf =
Vf × τ When setting the finish grinding power Pf: δf = δr × Pf
× / Pr t2: Delay time from rough cutting to shifting to cutting retreat t3: Delay time from cutting retreat to finishing grinding start δr: Deflection at the end of rough grinding δf: Deflection at finishing Pr : Roughing setting power This grinding control method is a method of predicting the finishing process during the roughing process and controlling the cutback retreat amount Xbo, so that the response delay between the control system and the mechanical system becomes a major problem. As shown in the above relational expression, by setting the cut-back amount Xbo in consideration of each delay time, it is possible to set the cut-back amount Xbo more appropriately. Therefore, stable processing can be realized without lowering the processing efficiency.

A grinding control device for a grinding machine according to the present invention comprises a cutting control device for a grinding machine and a measurement / control device.
The cutting control device performs a cutting retreat by the set cutting retreat amount at the time of the completion of the rough grinding, and then performs a cutting control means for numerically controlling the cutting so as to perform the finish grinding. A cutting-in retreat amount rewriting means for monitoring an external input of the cutting retraction amount and rewriting the cut-in retraction amount set by the cutting control means to the external input value each time the external input value is changed. The measurement / control device measures predetermined items for the workpiece and the grinding machine during the roughing, calculates a cut retreat amount from the measured value, and sends the calculated cut retreat amount to the cut control device. It shall be output. According to this configuration, the cut control device
In order to constantly monitor the external input of the retraction amount of the cutting while performing the cutting of the coarse grinding process,
When the external input is changed, the retraction amount can be changed in real time. Therefore, it is possible to perform the cut-in retreat while minimizing the response delay of the control system. In addition, a cutting control device that performs numerical control and a measurement and calculation that calculates the cutting retreat amount that is the processing condition
Since the control device is provided independently, each device can have a simple configuration and can have high versatility.

A cutting control device for a grinding machine according to the present invention is a device constituting the above-mentioned grinding control device, and performs a cutting retreat by a set cutting retreat amount at the time of completion of a rough grinding process, and then performs a finish grinding process. Cutting control means for numerically controlling the cutting so as to perform the cutting control means for monitoring the external input of the cutting retreat amount during rough grinding and changing the external input value each time the external input value is changed Cutting retreat amount rewriting means for rewriting the set cutting retreat amount.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a plan view of a grinding apparatus to which the grinding control method for a grinding machine is applied, and includes a grinding machine 1 and a control board 2. The grinding machine 1 is composed of an inner surface grinding machine, and is mounted on a bed 6 such that an advancing / retreating table 4 on which a headstock 3 is mounted can advance and retreat in a cutting direction (X-axis direction) orthogonal to the spindle 5. The headstock 3 is driven forward and backward by a cutting drive motor 7 together with the forward / backward stand 4. The grindstone head 8 is equipped with a grindstone drive motor 10 for rotating a grindstone 9.
Is set on the bed 6 so as to be able to advance and retreat in the axial direction (Z-axis direction) of the main shaft 3 corresponding to the predetermined machining position, and is driven forward and backward by the grinding wheel drive motor 11. A dressing device 12 and an in-process gauge 13 for measuring the inner diameter of the workpiece W are mounted on the advance / retreat table 4 on which the headstock 3 is installed.
4 is installed.

The workpiece W is an outer ring of a rolling bearing such as a ball bearing. The workpiece W is rotatably supported on a rotation support table 15 composed of shoes 15a and 15b on the lower surface and side faces of the workpiece described above with reference to FIG. Is attracted to a driving plate 16 having an electromagnet at the tip of the shaft and is driven to rotate together with the main shaft 5. Further, a work supply / discharge device 17 that supplies a new workpiece W and discharges the processed workpiece W to the spindle 5 at the processing position is provided. Whetstone 9 is a workpiece W
And makes a horizontal cut while rotating. The processing dimension of the workpiece W is captured by a gauge contact 13a in the workpiece W and measured by the in-process gauge 13. The processing force (grinding force) is measured by the grinding dynamometer 34 of the grinding wheel drive motor 10 (FIGS. 1 and 2) and the deflection sensor 19 of the grinding wheel shaft 9a.

The control panel 2 controls the whole of the grinding machine 1. FIG. 2 is a conceptual diagram showing a part of a grinding control device for controlling the cutting in the control panel 2. As shown in FIG. The grinding control device includes a cutting control device 21 including a computer-based NC device,
The cut-in control device 21 is constituted by a measurement / control device 22 composed of another computer serving as a high-order control means.

After describing the outline of the grinding control device, individual components will be described. As shown in FIGS. 5 and 6, the grinding control device performs the finishing grinding by performing the cutting retraction after the rough grinding, and performs the rough grinding to set an appropriate cutting retreat amount Xbo. The measurement and control device 22 is provided with a cut-in retreat calculating means 29 for calculating during machining.
In addition, in order to realize a high-speed response of the cutting retraction, the cutting control device 21 monitors an external input of the cutting retraction amount during the rough grinding processing and rewrites the set cutting retraction amount. 24 are provided. The measurement / control device 22 further includes:
As means for high-speed machining for keeping the finishing machining time within the target time while ensuring machining accuracy, a finishing machining power control means 30, a time shift amount change allowance changing means 32, and a rough machining cut stop judging means 31 are provided. It is provided. The finishing power control means 30 is means for linearly reducing the power P (t) at the time of finishing, as shown by the straight line portion Pt4 in FIG. The time shift amount change allowance changing means 32 is a means for changing the set value of the finish allowance g1 for determining the completion of the rough grinding in accordance with the shift amount between the target value of the finish processing time and the actual finish processing time. When the machining dimension reaches the completion judgment finishing allowance g1 that is the set value,
This is a means for outputting the roughing stop signal s1 to the cut control device 21.

As will be described later, the cutting retraction calculating means 29 and the finishing power control means 30 use the grindstone sharpness Λ and the grinding time constant τ in an arithmetic expression. , A pre-calculation section 29a, a cut-in retreat amount calculation section 29b, and a database section 29c. The pre-calculating section 29a includes a calculating section 29aa for calculating the grinding wheel sharpness と and a calculating section 29ab for calculating the grinding time constant τ and the cutting speed. The finishing power control means 30 and the time lag amount change allowance changing means 32 share the pre-calculating section 29a and the database 29c in the cut-in retreat calculating means 29, or independently calculate the grinding wheel sharpness 研 削 and the grinding time constant τ. It shall have means and a database.

The cutting control device 21 comprising an NC device includes a cutting control means 23 and a cutting retreat amount rewriting means 24. The cut control means 23 is means for performing a cut retreat by the set cut retreat amount at the time of completion of the rough grinding, and numerically controlling the cut so as to perform the finish grinding thereafter. Cutting retreat control unit 26 and finishing processing control unit 2
7. Each of the control units 25, 26, and 27 controls the cutting in the rough machining cycle, the cutting retreat cycle, and the finishing machining cycle in accordance with the position command and the speed command of the machining program. Have been. The output of the cutting command from each of the control units 25, 26, 27 is given to the cutting drive motor 7 via the servo controller 28. Cut retreat amount rewriting means 24
Is a means for monitoring the external input of the cutting retreat amount during rough grinding and rewriting the set cutting retreat amount of the cutting control means to the external input value each time the external input value is changed. 3
As shown in (1), it is incorporated in the control cycle of the rough machining control unit 25.

FIG. 3 is a conceptual configuration diagram showing a portion related to the control of cutting retraction in the grinding control device of FIG.
As shown in the figure, the cut-in retreat amount rewriting means 24 reads a cut-in retreat amount Xbo which is an external input, and executes a step S1 of the cut-in retreat control unit 26 to read the value of the cut-in retreat amount Xbo. It comprises a step S2 for rewriting the retreat amount set value, and a determination step S3 for returning to the reading step S1 until a rough processing completion signal is obtained. I / O device 35
Is the retraction amount Xbo discharged from the measuring / measuring device 22.
Is always read and transferred to the cut-in retreat amount rewriting means 24.

The pre-computing unit 29a of the cutting retraction amount computing means 29 in the measuring / measuring device 22 calculates the grinding wheel from the measured values of the predetermined monitoring items of the grinding machine 1 and the data stored in the database 29c according to the following formula. This is a means for calculating the sharpness (processing efficiency) Λ, the grinding time constant τ, and the grinding wheel speed. The cut-in retreat amount calculating section 29b is provided with
Is a means for calculating a cutting retraction amount Xbo from the grinding time constant τ and the cutting speed calculated in the above and the stored data of the database 29c in accordance with a calculation formula described later, and discharging it to the cutting control device 21. The database 29c stores each of the arithmetic units 29
a, 29b, means for storing, for example, a grinding time constant τ0 at the reference wheel sharpness, a machine response delay time, and finishing processing conditions (set cutting speed, power, etc.).

With respect to the machining process having the above-described structure, the retraction of the cut will be described mainly with reference to FIG. When the cut X1 (t) is started, the machining of the workpiece is started, and the workpiece dimension g
(T) changes gradually. At this time, grinding deflection δ
(T) = X1 (t) -g (t), the deflection δ (t) gradually increases, and eventually converges to a constant value. In this way, when the in-process gauge 13 detects that the workpiece dimension has reached the completion determination finish allowance g1, the measurement / control device (FIG. 2, FIG. 3) 22 shifts the cut to the cut retreat. It instructs the cut control device 21. However, until the cutting speed is switched, the time t1 during which the rough grinding is performed and the time t2 when the cutting is stopped until the cutting retreat is delayed. The time t3 is also required between the time when the cut is set back and the finish cut is started.
There is a delay. Of course, even at the end of the grinding, t is maintained until the in-process gauge 13 detects the completed dimension g0 and completes the cutting.
5 and the finished dimension ga is the completed dimension g0
Will be different. These delay times t1 to t3
Is constant from machine to machine and can be used in calculations as a known value.

The rough grinding speed Vr and the finish grinding speed Vf
(This is the design value of the grinding cycle), the deflection δr at the end of rough grinding, and the deflection δf at the time of finishing (also the design value of the grinding cycle), the grinding allowance r1 and the deflection amount δr at time t1. R1 = Vr × t1 δr = Vr × τ The allowance r2 and the amount of deflection δ2 at time t2 are: r2 = Vr × τ × (1-exp (−t2 / τ)) δ2 = δr × exp (−t2 // τ) The removal allowance r3 and the amount of deflection δ3 at time t3 are as follows: δ3 = (δr × exp (−t2 / τ) −Xbo) × exp (−t3
/ Τ) = δfr3 = δ2-δ3-Xbo∴Xbo = δr × exp (−t2 / τ) −δ3 × exp (t3 / τ) = Vr × τ × exp (−t2 / τ) −δf × τ × exp (t3 / τ). δf is determined by the finish processing conditions, for example: * When setting the finish cutting speed Vf: δf = Vf × τ * When setting the finish grinding power Pf: δf = δr × P
fx / Pr or the like.

As described above, during the roughing, the retreat amount X
It is possible to calculate bo, and switch the cutting retreat amount Xbo of the NC cutting control device 21 immediately before the cutting retraction to construct an optimum cutting cycle. Note that the user can use a user macro or the like to calculate and set the cutting retreat amount Xbo as a machining program to be executed by the cutting control device 21 including an NC device. The time and its variation increase, which is not preferable when a large number of workpieces are continuously processed. In order to realize a high-speed response, it is preferable that the numerical control system for executing the machining program incorporates the method of calculating and setting the cutting retreat amount Xbo in the cutting control device 21 including an NC device. In this case, the NC device is not versatile and very expensive. On the other hand, in the present invention, independently of the NC cutting control device 21,
The calculation of the machining conditions is performed by a measuring / control device 22 comprising a separate computer device, and the NC cutting control device 21 constantly monitors the external input of the retraction amount of the cutting while performing the cutting of the rough grinding. In addition, since the set cutback amount is rewritten, the NC cutoff control device 21 can realize high-speed response.
Can be made highly versatile.

Next, control of the finish grinding process will be described. The grinding control method for this finishing process controls the grinding time to the target value and stabilizes the processing accuracy even if there is a change in the machining allowance or the sharpness of the grinding wheel (processing efficiency). How to do. First, problems of general finish processing will be described, and then a finish grinding control method of this embodiment will be described.

In FIG. 5, after the cutting retreat is performed as described above, the remaining allowance Xf (= g3) becomes Xf = g1-r
1-r2-r3. At this time, although there is a unit of μm, there are variations in the amount of retraction of the cut and measurement errors of the in-process gauge 13. Even if the error is about 5 μm, if the finishing cut speed is 5 μm / sec, a variation in the processing time of 1 second occurs. In this case, it is difficult to manage the processing site and standardize the processing conditions. If the value of the finishing allowance g1 is small due to a large cutting delay, finishing may not be possible. In the past grinding work, for such a problem, the finishing allowance was increased and the finishing cutting speed was set earlier. In addition, since there is a delay in cutting even after finishing processing, if the processing resistance is large or the workpiece processing speed is high, the processing accuracy is deteriorated. Until now, so-called spark-out grinding has been performed by stopping cutting to maintain processing accuracy, but this requires extra processing time.

Therefore, in this embodiment, the machining resistance at the time of finishing machining is reduced so that the machining time is constant by measuring the remaining machining allowance after the retraction of the cut and the accuracy of the workpiece is improved. Control to make the value. That is, in this embodiment, before the start of the finish cut, the remaining amount of the workpiece finish grinding remaining is measured, and an optimum finish cut pattern is determined to perform the cut. As apparent from the above-mentioned problem, in the current grinding machine, at the start of the finishing operation, the variation in the finishing allowance necessarily occurs, and the finishing machining allowance must be set to a relatively large value. Remove this large machining allowance in the shortest time,
In addition, at the end of the finishing process, it is necessary to reduce the working resistance to as close to zero as possible in order to improve the working accuracy. Therefore, the processing state was set as shown in FIG.

As shown in FIG. 6, when roughing is performed with the roughing power Pr and the cutting speed Vr (= dX2 (t) / dt), the in-process gauge signal g (t) = g1. Control is performed so as to end the rough machining and switch the cycle from the retraction of the cutting to the finishing cutting. Even if the g (t) = g1 gauge signal is output, there are delay times t1, t2, and t3, and the process does not immediately change to finishing. In addition, there are variations in measurement and control, and the finish allowance g3 varies. A state in which the finishing allowance g3 does not become smaller than the processing dimension g0 and the finishing processing does not occur may occur. Therefore, in the finishing operation, the depth of cut is controlled so that the processing power decreases linearly from the processing power Ph at the start of the finishing processing to the processing power Pl at the end of the finishing processing.

The depth of cut in which the processing power (cutting force) is reduced linearly from Ph to Pl in the finish grinding is calculated by the basic characteristic equation dX2 (t) / dt = (X1 (t) -X2 (t)) / τ dP (t) / dt = (Ph−Pl) / t4 = constant
If the ^{d 2 X2 (t) / d} 2 t = k × (Ph-Pl) / t4 these, in initial conditions t = 0, X1 (0) = Xr dX
Solving for 2 (t) / dt = Vr gives Becomes That is, it can be seen that the cut is a quadratic curve.

Further, as described above, the cutback retreat amount Xbo is given by: Xbo = δr × exp (−t2 / τ) −δ3 × exp (t3 / τ) = Vr × τ × exp (−t2 / τ) −δf × τ × exp (t3 / τ) The rough grinding completion dimension g1 is Becomes

In this embodiment, the value of the processing dimension g3 after the retraction of the cut is measured by the in-process gauge 13,
By controlling the finishing cut as in the following equation, stable accuracy and a processing cycle are realized. By performing such a cut, the machining resistance at the end of the finishing machining is stabilized in a low state. When the sharpness (working efficiency) 砥 of the grindstone gradually changes, the value of the above equation k changes, so that the processing time gradually changes. In order to prevent this, the value of k may be increased when the sharpness of the grinding wheel becomes poor, and the value of k may be decreased when it becomes better. As will be described later, since the sharpness of the grinding stone can be accurately performed during the rough grinding, the above-described change in the value of k can be easily performed.

As described above, the means for measuring the value of the processing dimension g3 and controlling the cutting to linearly reduce the processing power (cutting force) from Ph to Pl is provided by the measuring / control device 22 shown in FIG. The finishing power control means 30. The command s2 of the finishing speed by the means 30 is given to the finishing controller 27 of the cutting control device 21 as a speed override command.

In this embodiment, the finishing time can be controlled to a target time. This can be easily realized by giving an offset to the rough grinding completion dimension g1. This is a set value g1 of a finish grinding allowance for determining completion of rough grinding with respect to a measured value g (t) of a processing dimension obtained by the in-process gauge 13 during rough grinding.
Is changed by a predetermined calculated value corresponding to the deviation amount Δ between the target value Tsec of the finishing time and the actual finishing time Ta. For example, when the actual finishing time Ta is slower than the target finishing time Tsec, the amount proportional to the deviation (difference) △ sec is subtracted from the set value g1. For details, Is set to the value of g1 calculated by The value of the constant α is
Set to a value of 1 or less to prevent hunting. The difference Δ is a predetermined statistical calculation value such as the finish processing time of the preceding work or the average finish processing of the work up to a predetermined number.

The time lag amount change allowance changing means 32 shown in FIG.
Is a means for measuring a deviation amount Δ between the target value Tsec of the finishing time and the actual finishing time Ta, and changing the set value g1 of the roughing cut stop determining means 31 according to the above equation. . The roughing cut stop determining means 31 calculates the measured value g of the working dimension obtained by the in-process gauge 13 during the rough grinding.
This is a means for monitoring (t) and sending a rough machining stop signal to the finishing machining control section 27 of the cutting control device 21 when the set value g1 is reached.

Next, a method for evaluating the sharpness of the grinding stone will be described. Grinding wheel sharpness 、 is the machining efficiency defined as Λ = (working power) / (working efficiency), and the grinding time constant τ
It is necessary for calculation of. However, it is difficult to accurately obtain the grinding wheel sharpness during grinding by the conventional evaluation method of the grinding wheel sharpness. Therefore, in this embodiment, a method for evaluating the sharpness of a grinding stone has been devised and adopted as follows. First,
Problems of the conventional method for evaluating the sharpness of a grindstone will be described, and then the method for evaluating the sharpness of a grindstone employed in this embodiment will be described.

As shown in FIG. 7, when the processing dimension of the workpiece W is captured by the gauge contact 13a in the workpiece W and measured by the in-process gauge 13, the processing position (processing point) of the grinding stone 9 and the processing position are measured. The measurement points of the process gauge 13 do not coincide, and an error occurs in the measurement value of the in-process gauge 13 due to the thermal expansion of the workpiece W. Therefore, the following problem occurs. As shown in FIG. 8, when the roughing is started by the cut X, the working force P increases and the working dimension (observed value) g changes. The processing force P becomes almost constant at the end of the roughing, but the grinding friction heat flows into the workpiece, so that the processing dimensions are more than actually processed. Although the machining dimension that can be observed is g, the actual machining dimension is g− since the dimension including the thermal expansion of the workpiece σ (the vertical axis is enlarged in the figure) is measured.
σ (indicated by a dotted line). The thermal expansion amount σ of the workpiece W has a large time lag as compared with the processing force, and as shown in FIG.
For example, oil-based coolant has a thermal expansion of 10 μm or more, and water-soluble coolant has a thermal expansion of about 5 μm.

The machining force can be obtained by measuring the grinding power and the grinding resistance. To calculate the machining efficiency Z,
Assuming that the workpiece processing diameter is D, generally, Z = π × D × (dg / dt) mm ³ / (mm · sec), and the effect of thermal expansion of the workpiece is ignored. for that reason,
Accurate whetstone sharpness evaluation is not performed. In particular, the expansion and contraction of the workpiece W is large during the finishing processing before the rough processing is completed,
The calculated value of the sharpness of the grinding stone (processing efficiency) has a remarkable degree of inaccuracy. The error of the sharpness of the grinding stone does not become a big problem in the case of low-speed machining.However, in order to machine a large number of workpieces at high speed, such as bearing races, and to meet strict precision requirements, It is necessary to accurately calculate the sharpness of the grindstone. In particular, when controlling the amount of cut retreat as described above for high-speed machining and controlling the change of the cutting speed at the time of finishing, etc., if accurate grinding stone sharpness is not obtained, stable control is performed. Becomes impossible.

Therefore, in this embodiment, the grindstone sharpness 定 め る is determined as follows. FIG. 4 shows details of the grindstone sharpness calculating unit 29aa of FIG.
Is to calculate an accurate grinding stone sharpness after thermal expansion correction as follows. That is, the grinding wheel sharpness Λ is calculated as Λ = (working power) / (working efficiency), and the working power is a value of the grinding power or the grinding power. The processing efficiency is a value represented by the product of the amount of change per unit time of the processing dimension and the processing circumference. In this case, as the value of the processing dimension, the actual processing dimension of the workpiece obtained by correcting the processing dimension of the workpiece obtained by the in-process gauge 13 by the thermal expansion of the workpiece is used, and the thermal expansion of the workpiece is the grinding power. Shall be calculated from The thermal expansion of the workpiece is calculated from the amount of heat flowing into and out of the workpiece. According to this, the amount of thermal expansion of the workpiece during machining can be accurately calculated in real time, and the actual machining efficiency can be obtained by correcting the in-process gauge signal. The details will be described.

The workpiece temperature θ (t) during grinding is expressed by the following equation. dθ (t) / dt = α · P (t) −β · θ (t) where α: heat inflow constant β: heat outflow constant P (t): grinding power θ (t): workpiece temperature During processing Then, measure the grinding power and calculate the workpiece temperature θ using the above formula.
(T) can be calculated. From this work piece temperature, the work piece thermal expansion δ (t) can be obtained by δ (t) = (work piece thermal expansion coefficient) × working diameter × θ (t).
g (t) _real is obtained by subtracting δ (t) from the workpiece size g (t) by the in-process gauge during processing. g (t) _real = g (t) −δ (t) Since the machining efficiency Z is obtained by Z = π × D × (dg (t) _real / dt), the sharpness of the grinding stone (processing efficiency) A is a function of the grinding power. A = P (t) / Z For the normal direction grinding force Fn, A = Fn / Z. By correcting the thermal expansion of the workpiece in this manner, the evaluation of the sharpness of the grinding stone (machining efficiency) becomes accurate, and is effective as a parameter for evaluating and controlling the machining process. The method of calculating the thermal expansion amount of the workpiece from the grinding power during grinding and the heat inflow constant and heat outflow constant is described in Japanese Patent Application No. Hei. 219728).

[0044]

According to the grinding control method for a grinding machine of the present invention, the amount of cutback at the completion of rough grinding is calculated based on the measured value during rough grinding, and the cutting retreat is performed. Alternatively, even for unstable factors such as a change in finish cutting speed and finish setting power, an optimum cut retreat amount capable of realizing a stable grinding cycle can be set. According to a second aspect of the present invention, there is provided a grinding control method, wherein a processing dimension of a workpiece obtained by an in-process gauge is used as a processing dimension value for calculating a grinding wheel sharpness used for calculating a cutting retreat amount. Since the actual work dimensions of the work corrected by the above are used, the sharpness of the grinding wheel can be calculated accurately, and the cutting retreat amount can be set more appropriately. In the grinding control method according to the third aspect of the present invention, the cutting retreat amount can be determined in consideration of the response delay of the mechanical system and the electric control system, thereby realizing stable machining with no reduction in machining efficiency. it can. The grinding control device of the grinding machine according to the present invention includes a cutting control device and a measurement / control device, and the cutting control device always performs a cutting retreat amount while performing the cutting in the rough grinding. Since the external input is monitored and the set retraction amount is rewritten, the retraction can be performed with the response delay of the control system minimized. In addition, a cutting control device that performs numerical control and a measurement and calculation that calculates the cutting retreat amount that is the processing condition
Since the control device is provided independently, each device can have a simple configuration and can have high versatility.

[Brief description of the drawings]

FIG. 1 is a plan view of a grinding apparatus to which a method and an apparatus for controlling grinding of a grinding machine according to an embodiment of the present invention are applied.

FIG. 2 is an explanatory diagram of a conceptual configuration of the grinding machine control device.

FIG. 3 is an explanatory diagram of a conceptual configuration showing a portion related to control of cutting retreat of the grinding machine control device.

FIG. 4 is an explanatory diagram of a conceptual configuration of a part of the grinding machine control device that calculates a sharpness of a grinding wheel (processing efficiency).

FIG. 5 is an explanatory diagram of a machining process including cut retreat.

FIG. 6 is an explanatory diagram showing a finishing grinding process.

FIG. 7 is a front view and a cross-sectional view illustrating a relationship between a grindstone and an in-process gauge.

FIG. 8 is an explanatory diagram of a processing process of a grinding process showing thermal expansion.

FIG. 9 is an explanatory diagram that emphasizes bending in grinding.

FIG. 10 is an explanatory diagram of a machining process of the grinding process, showing the presence or absence of cut retreat in comparison.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Grinding machine 29aa ... Grinding wheel sharpness calculation part 2 ... Control board 30 ... Finishing power control means 5 ... Spindle 31 ... Roughing cutting stop determination means 7 ... Cutting drive motor 32 ... Time shift amount corresponding change changing means 9 ... Grinding wheel W: Workpiece 10: Grinding wheel drive motor X: Cutting 13: In-process gauge Xbo: Cutting retreat amount 21: Cutting control device Z: Machining efficiency 22: Measurement / control device Λ: Grinding wheel sharpness (machining efficiency) 23 ... cutting control means τ ... grinding time constant 24 ... cut retreat amount rewriting means 29 ... cut retreat amount calculating means

Claims (5)

[Claims] 1. When the rough grinding process is completed, the cutting retreat is performed,
In a grinding control method of a grinding machine for controlling a cut so as to perform a finish grinding process thereafter, while performing measurement of predetermined items for a workpiece and a grinder during rough grinding, the cutback is reduced by the measured value. A grinding control method for a grinding machine that calculates a cutting retreat amount to be performed and performs the cutting retreat at the calculated cutting retreat amount when the rough grinding is completed. 2. A grinding time constant represented by the following equation: τ = α / [(grinding system rigidity) × (grinding wheel sharpnessΛ)] where α is a constant determined by the workpiece in the process of calculating the cutting retreat amount. Using τ, the sharpness Λ is a value represented by Λ = (working force) / (working efficiency), wherein the working force is a value of a grinding power or a grinding force, and the working efficiency is a unit of a working dimension. A value indicated by the product of the amount of change per hour and the processing circumference,
The grinding control method for a grinding machine according to claim 1, wherein a substantial processing dimension obtained by correcting a processing dimension of a workpiece obtained by an in-process gauge by a thermal expansion amount of the workpiece is used as the value of the processing dimension. 3. The cutting depth is determined based on a grinding time constant τ, a rough grinding speed Vr, machine response delay times t2 and t3, and a finishing cutting speed Vf or a finishing working condition obtained by a finishing grinding setting power Pf. 3. The grinding control method for a grinding machine according to claim 1, wherein the retreat amount Xbo is determined by the following equation. Xbo = δr × exp (−t2 / τ) −δ3 × exp (t3 / τ) = Vr × τ × exp (−t2 / τ) −δf × τ × exp (t3 / τ) However, the finishing cutting speed Vf When setting: δf =
Vf × τ When setting the finish grinding power Pf: δf = δr × Pf
× / Pr t2: Delay time from rough cutting to shift to cutting retreat t3: Delay time from cutting retreat to finish grinding start δr: Deflection at the end of rough grinding δf: Start of finish grinding Deflection Pr: Roughing setting power 4. A cutting control device for a grinding machine, and a measurement / control device, wherein the cutting control device performs a cutting retreat amount by a set cutting retreat amount at the time of completion of rough grinding, and thereafter finishes. Cutting control means for numerically controlling the cutting so as to perform the grinding process, and monitoring the external input of the cutting retreat amount during the coarse grinding process, and changing the external input value each time the external input value is changed. Cutting retreat amount rewriting means for rewriting the set cutting retreat amount of the cutting control means, wherein the measurement / control device measures predetermined items of the workpiece and the grinding machine during the rough machining and measures the measured value. And a cutting control device for calculating a cutting retreat amount from the cutting device, and outputting the calculated cutting retreat amount to the cutting control device. 5. A cutting control means for performing a cutting retreat by a set cutting retreat amount when the rough grinding is completed, and then numerically controlling the cutting so as to perform a finish grinding, and a cutting during the rough grinding. A cutting retreat amount rewriting means for rewriting the set retraction amount of the cutting control means to the external input value each time the external input value is changed by monitoring the external input of the cutting retraction amount. Infeed control device.