JP7593249B2 - Grinding Machine - Google Patents

Description

The present invention relates to a grinding machine.

Patent Documents 1 and 2 describe a grinding machine that uses a grinding wheel to grind the outer peripheral surface of a workpiece. In the grinding machine, the workpiece is rotated by the rotational driving force of the spindle device. The workpiece is then ground by the grinding wheel as it is rotated by the rotational driving force of the spindle device against the grinding resistance of the grinding wheel.

In addition, in Patent Documents 1 and 2, a turning member (also called an eccentric drive fitting or eccentric drive pin) provided at a position eccentric from the axis of the spindle is used as a mechanism for transmitting the rotational drive force of the spindle to the workpiece. The turning member revolves at a position eccentric from the axis of the spindle as the spindle rotates. In addition, the turning member can rotate the workpiece around the axis of the spindle by engaging with a non-circular part of the workpiece, such as a wheel attached to the workpiece or a counterweight part of the crankshaft, in one direction of rotation.

JP 2002-11658 A JP 2010-194682 A

The turning member may be configured to be able to move back and forth in the axial direction so as not to interfere with the workpiece when it is being loaded or unloaded. In such a configuration, if an abnormality occurs in the mechanism that moves the turning member forward in the axial direction and the turning member is unable to move forward properly, the rotational driving force of the spindle device may not be properly transmitted to the workpiece.

If the rotational drive force of the spindle device is not properly transmitted to the workpiece, the workpiece may rotate along with the grinding wheel due to the rotation of the grinding wheel. After the workpiece rotates along with the grinding wheel, the rotating member may move forward and engage with the workpiece.

However, if the workpiece begins to rotate along with the grinding wheel, the grinding wheel will not be able to grind the workpiece properly, and the desired shape accuracy, for example, in terms of roundness and cylindricity, will not be achieved.

In addition to the above-mentioned cases where an abnormality occurs in the mechanism that advances the turning member, the rotational drive force of the spindle device may not be properly transmitted to the workpiece. In such cases, as described above, the workpiece may rotate in unison with the grinding wheel. If the workpiece rotates in unison with the grinding wheel, as described above, it is not possible to obtain the desired shape accuracy in terms of roundness, cylindricity, etc.

The present invention was made in consideration of these problems, and aims to provide a grinding machine that can determine whether the workpiece is rotating in unison with the grinding wheel.

One aspect of the present invention is
A spindle device that supports a workpiece and rotates the workpiece;
A grinding wheel for grinding an outer peripheral surface of the workpiece, the grinding wheel being rotated and driven by a grinding wheel head;
a moving device for moving the workpiece and the grinding wheel toward and away from each other;
a control device for controlling the spindle device, the wheel head, and the moving device;
Equipped with
The spindle device is
A spindle housing;
a spindle rotatably supported in the spindle housing;
A spindle motor that rotates the spindle;
A detector for detecting a rotation angle of the spindle;
a drive circuit that drives the spindle motor based on a command value of the control device and a rotation angle of the spindle detected by the detector;
Equipped with
The control device or the drive circuit is
The grinding machine uses the difference between the actual rotation angle of the spindle detected by the detector and the ideal rotation angle of the spindle calculated from a command value to the spindle motor, and determines that the workpiece has rotated together with the grinding wheel when the difference exceeds a predetermined threshold value or when the fluctuation range of the difference exceeds a predetermined range.

The control device or drive circuit uses the difference between the actual rotation angle of the spindle and the ideal rotation angle of the spindle to determine that the workpiece has rotated in conjunction with the grinding wheel if the difference exceeds a predetermined threshold value or if the fluctuation range of the difference exceeds a predetermined range. Here, when the workpiece is not rotating in conjunction with the grinding wheel and is being ground normally by the grinding wheel, the spindle and workpiece rotate together. For example, when the spindle is controlled to rotate at a constant speed, the actual rotation angle of the spindle nearly matches the ideal rotation angle of the spindle, and the difference between the actual rotation angle and the ideal rotation angle is a very small value (almost zero).

On the other hand, when the workpiece rotates in unison with the grinding wheel, the spindle and workpiece do not rotate together. At this time, the rotation of the spindle and the rotation of the workpiece are in different states. Then, when the workpiece temporarily rotates in unison with the grinding wheel and then begins to rotate together with the spindle, the rotation of the workpiece is transmitted back to the spindle, causing the spindle to rotate in a different state than normal.

As a result, the actual rotation angle of the spindle deviates from the ideal rotation angle of the spindle. If the actual rotation angle of the spindle deviates significantly from the ideal rotation angle of the spindle, the difference between the actual rotation angle of the spindle and the ideal rotation angle of the spindle exceeds a predetermined threshold value. When this happens, it is determined that the workpiece has rotated in conjunction with the grinding wheel.

In addition, when the workpiece rotates along with the grinding wheel, if the rotation of the workpiece is transmitted back to the spindle, the actual rotation angle of the spindle will deviate from the ideal rotation angle of the spindle. If the actual rotation angle of the spindle deviates significantly from the ideal rotation angle of the spindle, the difference between the actual rotation angle of the spindle and the ideal rotation angle of the spindle will exceed a predetermined threshold value. When this condition occurs, it is determined that the workpiece has rotated along with the grinding wheel.

In addition, instead of using a predetermined threshold value, the following can be used. As described above, when the workpiece rotates together with the grinding wheel temporarily and then rotates together with the spindle, the rotation of the workpiece is transmitted back to the spindle, causing the spindle to rotate in a different state than normal. At this time, the difference between the actual rotation angle of the spindle and the ideal rotation angle of the spindle fluctuates more than normal. Therefore, the fluctuation range of the difference between the actual rotation angle of the spindle and the ideal rotation angle of the spindle exceeds a predetermined range. Even in this state, it is determined that the workpiece has rotated together with the grinding wheel.

When the workpiece rotates along with the grinding wheel, if the rotation of the workpiece is transmitted back to the spindle, the difference between the actual rotation angle of the spindle and the ideal rotation angle of the spindle will fluctuate more than normal. Therefore, the fluctuation range of the difference between the actual rotation angle of the spindle and the ideal rotation angle of the spindle will exceed a specified range. Even in such a state, it is determined that the workpiece has rotated along with the grinding wheel.

Therefore, by using the actual rotation angle of the spindle and the ideal rotation angle of the spindle, it is possible to determine whether the workpiece is rotating along with the grinding wheel, which prevents the shape accuracy of the workpiece from deteriorating and reduces the occurrence of defective products.

FIG. FIG. 2 is a functional block diagram showing a partial configuration of the grinding machine. 1A is a diagram showing the rotation directions of a workpiece and a grinding wheel during normal grinding, and FIG. 1B is a diagram showing the rotation directions of a workpiece and a grinding wheel when the workpiece rotates together with the grinding wheel. FIG. 4 is a diagram showing the configuration of a first determination process in a control device and a spindle drive circuit. (A) shows the time change (behavior) of the output value of the sizing device during normal grinding. (B) shows the time change (behavior) of the power of the grinding wheel motor during normal grinding. (C) shows the time change (behavior) of the difference between the actual rotation angle of the spindle and the ideal rotation angle of the spindle during normal grinding. (A) shows the time change (behavior) of the output value of the sizing device when entrained rotation occurs. (B) shows the time change (behavior) of the power of the grinding wheel motor when entrained rotation occurs. (C) shows the time change (behavior) of the difference between the actual rotation angle of the spindle and the ideal rotation angle of the spindle when entrained rotation occurs. FIG. 11 is a diagram showing the configuration of a second determination process in the control device and the spindle drive circuit.

(1. Configuration of Grinding Machine 1)
The configuration of the grinding machine 1 will be described with reference to Fig. 1. The grinding machine 1 rotates a workpiece W, rotates a grinding wheel T, and moves the grinding wheel T relatively close to the workpiece W in a direction intersecting the axis of the workpiece W, thereby grinding the outer circumferential surface of the workpiece W.

The grinding machine 1 can be a table traverse type grinding machine, a wheel head traverse type grinding machine, etc. The grinding machine 1 can also be a cylindrical grinding machine, a cam grinding machine, etc. In the following, a table traverse type cylindrical grinding machine will be used as an example of the grinding machine 1. In other words, the grinding machine 1 is configured to move the workpiece W in the axial direction of the workpiece W, and to move the grinding wheel T in a direction intersecting the axis of the workpiece W.

The grinding machine 1 includes a bed 10, a table 20, a spindle device 30, a tailstock device 40, a grinding wheel head 50, a sizing device 60, and a control device 70. The bed 10 is installed on an installation surface. The bed 10 is formed so that the width (length in the Z-axis direction) of the front side in the X-axis direction (lower side in Fig. 1) is long, and the width of the back side in the X-axis direction (upper side in Fig. 1) is short.

The bed 10 has a Z-axis guide surface 11 extending in the Z-axis direction on the upper surface on the front side in the X-axis direction. Furthermore, the bed 10 has a Z-axis drive mechanism 12 that drives along the Z-axis guide surface 11. In this embodiment, the Z-axis drive mechanism 12 includes a ball screw mechanism 12a and a Z-axis motor 12b. The ball screw mechanism 12a extends parallel to the Z-axis guide surface 11, and the Z-axis motor 12b drives the ball screw mechanism 12a.

A Z-axis drive circuit 12c and a Z-axis detector 12d are provided to drive the Z-axis drive mechanism 12. The Z-axis drive circuit 12c includes an amplifier circuit and drives the Z-axis motor 12b. In this embodiment, the Z-axis detector 12d is, for example, an angle detector such as an encoder, and detects the angle of the rotation shaft of the Z-axis motor 12b. Note that the Z-axis drive mechanism 12 can also use a linear motor or the like instead of the configuration including the ball screw mechanism 12a described above.

The bed 10 also has a guide surface 13 on the upper surface on the rear side in the X-axis direction, which extends in a direction intersecting the Z-axis direction. In this embodiment, the guide surface 13 is an X-axis guide surface that extends in the X-axis direction perpendicular to the Z-axis. The bed 10 also has an X-axis drive mechanism 14 that drives along the X-axis guide surface 13. In this embodiment, the X-axis drive mechanism 14 includes a ball screw mechanism 14a and an X-axis motor 14b. The ball screw mechanism 14a extends parallel to the X-axis guide surface 13, and the X-axis motor 14b drives the ball screw mechanism 14a.

To drive the X-axis drive mechanism 14, an X-axis drive circuit 14c and an X-axis detector 14d are provided. The X-axis drive circuit 14c includes an amplifier circuit and drives the X-axis motor 14b. In this embodiment, the X-axis detector 14d is, for example, an angle detector such as an encoder, and detects the angle of the rotation shaft of the X-axis motor 14b. Note that the X-axis drive mechanism 14 can also use a linear motor or the like instead of the configuration including the ball screw mechanism 14a described above.

The table 20 is formed in an elongated shape and is supported on the Z-axis guide surface 11 of the bed 10 so as to be movable in the Z-axis direction (horizontal left and right direction). The table 20 is also fixed to the ball screw nut of the Z-axis ball screw mechanism 12a, and moves in the Z-axis direction by the rotational drive of the Z-axis motor 12b.

The spindle device 30 supports the workpiece W and drives it to rotate. The spindle device 30 is disposed on one end of the table 20 in the Z-axis direction. The spindle device 30 includes a spindle housing 31, a spindle 32, a spindle motor 33, a spindle detector 34, a spindle drive circuit 35, a center member 36, and a drive force transmission mechanism 37.

The spindle housing 31 is fixed onto the table 20. The spindle 32 is rotatably supported by the spindle housing 31 via a bearing. The spindle motor 33 drives the spindle 32 to rotate. The spindle detector 34 and the spindle drive circuit 35 are provided to drive the spindle motor 33. In this embodiment, the spindle detector 34 is an angle detector such as an encoder, and detects the angle of the rotation shaft of the spindle motor 33. The spindle drive circuit 35 includes an amplifier circuit and drives the spindle motor 33.

The center member 36 supports the end face of one axial end of the workpiece W. The center member 36 may be fixed to the spindle housing 31 so as to be non-rotatable, or may be fixed to the spindle 32 so as to be rotatable relative to the spindle housing 31.

The driving force transmission mechanism 37 is provided on the end face of the main shaft 32, and transmits the rotational driving force of the main shaft 32 to the workpiece W to rotate the workpiece W. The driving force transmission mechanism 37 is, for example, a rotating member provided at a position eccentric to the axis of the main shaft 32. In other words, the rotating member serving as the driving force transmission mechanism 37 is an eccentric drive pin that extends in the axial direction of the main shaft 32 from the axial end face of the main shaft 32. The rotating member revolves around the axis of the main shaft 32 as the main shaft 32 rotates.

In this embodiment, the rotating member as the driving force transmission mechanism 37 rotates the workpiece W around the axis of the main shaft 32 by engaging with the carrier Wa attached to the workpiece W in one rotational direction. The rotating member as the driving force transmission mechanism 37 can also rotate the workpiece W around the axis of the main shaft 32 by engaging with a non-circular portion of the workpiece W, such as a counterweight portion of a crankshaft or a cam portion of a camshaft, in one rotational direction.

In this embodiment, the turning member as the driving force transmission mechanism 37 is provided so as to be movable in the axial direction of the main shaft 32. For example, a mechanism that allows the turning member to move in and out is provided so as not to interfere with the workpiece W when the workpiece W is loaded or unloaded. The turning member is retracted when the workpiece W is loaded or unloaded, and is advanced when engaging with the workpiece W.

The mechanism for moving the rotating member forward and backward is provided with, for example, a spring 37a, and the rotating member advances due to the biasing force of the spring 37a. If the rotating member gets caught on the main shaft 32, the rotating member may not advance completely. In such a case, the rotating member will be disengaged from the retainer or the like.

The tailstock device 40 is disposed on the other end side in the Z-axis direction on the table 20. The tailstock device 40 includes a center member 41. The center member 41 supports the end face of the other axial end of the workpiece W. The center member 41 may be provided so as to be non-rotatable or rotatable.

The grinding wheel head 50 is equipped with a grinding wheel T and drives the grinding wheel T to rotate. In addition to the grinding wheel T, the grinding wheel head 50 is equipped with a grinding wheel head body 51, a grinding wheel spindle 52, a grinding wheel motor 53, and a grinding wheel drive circuit 54.

The grinding wheel T is formed in a disk shape. The grinding wheel T is used to grind the outer peripheral surface of the workpiece W. The grinding wheel T is composed of multiple abrasive grains fixed with a binder. The abrasive grains used include general abrasive grains made of ceramic materials such as alumina and silicon carbide, and super abrasive grains such as diamond and CBN.

The grinding wheel head 50 is formed, for example, in a rectangular shape, and is supported on the X-axis guide surface 13 of the bed 10 so as to be movable in the X-axis direction (horizontal front-back direction). The grinding wheel head 50 is also fixed to the ball screw nut of the X-axis ball screw mechanism 14a, and moves in the X-axis direction by the rotational drive of the X-axis motor 14b.

The grinding wheel spindle 52 is rotatably supported by the wheel head body 51 via a bearing. The grinding wheel T is fixed to the tip of the grinding wheel spindle 52, and the grinding wheel T is rotated by the rotation of the grinding wheel spindle 52. The grinding wheel motor 53 rotates the grinding wheel spindle 52. For example, the grinding wheel motor 53 transmits a rotational driving force to the grinding wheel spindle 52 via a belt. However, the grinding wheel motor 53 may be arranged coaxially with the grinding wheel spindle 52. In general, the rotation speed of the grinding wheel T driven by the grinding wheel motor 53 is faster than the rotation speed of the workpiece W driven by the spindle motor 33.

The grinding wheel drive circuit 54 is provided to drive the grinding wheel motor 53. The grinding wheel drive circuit 54 includes an amplifier circuit and drives the grinding wheel motor 53.

The sizing device 60 is provided on the upper surface of the bed 10 and measures the outer diameter of the workpiece W. The sizing device 60 has, for example, a pair of contacts that can contact the outer peripheral surface of the workpiece W, and measures the outer diameter at the contact point with the workpiece W.

The control device 70 is a CNC device that executes machining control. That is, based on the machining program and the measurement results by the sizing device 60, the control device 70 drives the Z-axis drive mechanism 12 and the X-axis drive mechanism 14 as moving devices to control the positions of the table 20 and the grinding wheel head 50. That is, the control device 70 controls the positions of the table 20 and the grinding wheel head 50, etc., thereby moving the workpiece W and the grinding wheel T closer to or farther apart relative to each other. Furthermore, the control device 70 controls the spindle device 30 and the grinding wheel head 50. That is, the control device 70 controls the rotation of the spindle 32 and the grinding wheel T.

(2. Functional Block Configuration of Grinding Machine 1)
Next, functions of a part of the configuration of the grinding machine 1 will be described with reference to Fig. 2. The control device 70 generates a control command value based on the machining program and the measurement result by the sizing device 60. The control device 70 outputs the control command value to each of the drive circuits 12c, 14c, 35, 54, and each of the drive circuits 12c, 14c, 35, 54 drives each of the motors 12b, 14b, 33, 53 based on the control command value. In addition, each of the drive circuits 12c, 14c, 35, 54 acquires the detection results by each of the detectors 12d, 14d, 34, and drives each of the motors 12b, 14b, 33, 53 based on the detection results in addition to the control command value.

(3. Rotational state of workpiece W and grinding wheel T)
The rotational state of the workpiece W and the grinding wheel T will be described with reference to Fig. 3. As shown in Fig. 3A, during normal grinding, the workpiece W and the grinding wheel T rotate in the same direction. In other words, at the grinding point, the tangent vector of the rotational direction of the workpiece W and the tangent vector of the rotational direction of the grinding wheel T are in opposite directions. In addition, the rotational speed of the grinding wheel T is higher than the rotational speed of the workpiece W.

Here, as shown in FIG. 3B, the rotational driving force of the spindle 32 may not be sufficiently transmitted to the workpiece W, and the grinding resistance between the workpiece W and the grinding wheel T may cause the workpiece W to rotate along with the grinding wheel T. In this case, at the grinding point, the tangent vector in the rotational direction of the workpiece W and the tangent vector in the rotational direction of the grinding wheel T are in the same direction. Thus, the workpiece W and the grinding wheel T rotate in opposite directions.

Such co-rotation of the workpiece W can occur, for example, when there is an abnormality in the driving force transmission mechanism 37. This can occur when the turning member serving as the driving force transmission mechanism 37 does not move completely forward due to being caught on the main shaft 32. When the turning member temporarily does not move forward, the workpiece W rotates co-rotatingly.

In addition, when a driving force transmission mechanism 37 such as a rotating member is not used, the rotational driving force of the spindle 32 may be transmitted to the workpiece W, for example, by the frictional force between the center member 36 and the workpiece W. In this case, if the grinding resistance is very large, the workpiece W may rotate along with the grinding wheel T, rather than being rotated by the rotational driving force of the spindle 32.

Here, the workpiece W rotates together with the grinding wheel T when the mutual pressing force between the workpiece W and the grinding wheel T is large. In rough grinding, the feed speed of the grinding wheel T is high. Therefore, when the workpiece W is not ground during rough grinding, the mutual pressing force between the workpiece W and the grinding wheel T becomes large. And when the mutual pressing force between the workpiece W and the grinding wheel T becomes large, the frictional force between them increases, and further, the gripping force of the abrasive grains of the grinding wheel T increases. Therefore, the workpiece W is more likely to rotate together with the grinding wheel T during rough grinding than during fine grinding or fine grinding.

(4. First Determination Process Regarding Co-Rotation)
A first judgment process for judging whether or not the workpiece W is rotating together with the grinding wheel T as shown in Fig. 3(B) will be described with reference to Fig. 4. The first judgment process is a process performed by the control device 70 and the spindle drive circuit 35. In Fig. 4, judgment 70a, threshold setting 70b, and post-judgment process 70c, which are blocks shown inside the control device 70, represent functions executed by a program in the control device 70. Functional elements shown inside the spindle drive circuit 35 represent functions executed by formed circuits.

As shown in FIG. 4, the control device 70 outputs a speed command value to the spindle drive circuit 35 for rotating the spindle motor 33, and further outputs a position command value obtained by integrating the speed command value.

The spindle drive circuit 35 acquires the speed command value and position command value acquired from the control device 70, as well as the actual rotation angle of the spindle 32 detected by the spindle detector 34, and drives the spindle motor 33 based on the speed command value, position command value, and actual rotation angle. This function is a basic process that is unrelated to co-rotation.

In detail, the position counter 35f of the spindle drive circuit 35 acquires the actual rotation angle of the spindle 32 detected by the spindle detector 34, and obtains a count value that represents the position of the actual rotation angle. Then, the position deviation generating unit 35a of the spindle drive circuit 35 generates a position deviation that is the difference between the position command value acquired from the control device 70 and the output value of the position counter 35f. The position deviation corresponds to the difference between the position command value acquired from the control device 70 and the rotation angle of the spindle 32 detected by the spindle detector 34.

The position control processing unit 35b of the spindle drive circuit 35 generates an output value by multiplying the input position deviation by the position loop gain. In addition, the position speed conversion unit 35e converts the output value of the position counter 35f into a speed value.

Then, the speed deviation generating unit 35c of the spindle drive circuit 35 generates a speed deviation based on the speed control value output from the control device 70, the output value of the position control processing unit 35b, and the output value of the position speed conversion unit 35e. The speed control processing unit 35d of the spindle drive circuit 35 multiplies the input speed deviation by the speed loop gain, and outputs a drive signal for the spindle motor 33.

Here, the position command value output by the control device 70 corresponds to the ideal rotation angle of the spindle 32 calculated from the speed command value. The ideal rotation angle may be generated, for example, by successively integrating the speed command value. The spindle drive circuit 35 mainly controls speed, with position control being performed secondary. Because it is performed secondary, it is not significantly amplified by the position control processing unit 35b. Alternatively, the position control processing unit 35b may not be provided so that position control is not performed secondary.

Meanwhile, as described above, the spindle drive circuit 35 acquires the actual rotation angle of the spindle 32 detected by the spindle detector 34. Here, the resolution of the spindle detector 34 is sufficiently high because an encoder is used as the spindle detector 34. Therefore, even if the spindle 32 rotates at high speed, the actual rotation angle of the spindle 32 acquired by the spindle drive circuit 35 can be acquired.

Then, the spindle drive circuit 35 generates the difference between the ideal rotation angle of the spindle 32 and the actual rotation angle of the spindle 32. In this embodiment, as described above, the position deviation generating unit 35a generates a position deviation between the position command value output from the control device 70 and the count value indicating the position of the actual rotation angle from the actual rotation angle of the spindle 32 detected by the spindle detector 34. This position deviation is the difference between the ideal rotation angle of the spindle 32 and the actual rotation angle of the spindle 32.

The spindle drive circuit 35 then outputs the generated difference (position deviation) to the control device 70. Here, a predetermined threshold value Th is preset in the control device 70 for determining whether or not the workpiece W is rotating in association with the grinding wheel T. The control device 70 determines whether or not the workpiece W is rotating in association with the grinding wheel T based on the difference (position deviation) acquired from the spindle drive circuit 35 and the preset predetermined threshold value Th. Next, if it is determined that the workpiece W is rotating in association with the grinding wheel T, the control device 70 performs post-determination processing. The post-determination processing includes, for example, stopping the drive of the spindle device 30, stopping grinding, issuing a warning, and notifying the operator or manager.

(5. Method for Determining Co-Rotation)
In the first determination process, the control device 70 determines whether or not the workpiece W is rotating together with the grinding wheel T based on the difference between the actual rotation angle of the spindle 32 and the ideal rotation angle of the spindle 32. A method for determining whether or not the workpiece W is rotating together with the grinding wheel T will be described below with reference to Figs.

First, normal grinding will be described with reference to Figure 5. Figure 5 (A) shows the time change (behavior) of the output value of the sizing device 60 during normal grinding. Figure 5 (B) shows the time change (behavior) of the power of the grinding wheel motor 53 during normal grinding. Figure 5 (C) shows the time change (behavior) of the difference between the actual rotation angle of the spindle 32 and the ideal rotation angle of the spindle 32 during normal grinding.

In FIG. 5 (A), (B), and (C), times t1 to t6 are as follows. Time t1 is when the grinding wheel T starts to approach the workpiece W by fast forwarding. Time t2 is when rough grinding of the workpiece W starts. Time t3 is when rough grinding switches to fine grinding (first finishing process). Time t4 is when fine grinding switches to fine grinding (second finishing process). Time t5 is when fine grinding switches to spark out. Time t6 is when spark out ends, i.e., when grinding ends. The rotational speed of the spindle 32 and the rotational speed of the grinding wheel T are the same for rough grinding, fine grinding, fine grinding, and spark out. The cutting speed of the grinding wheel T in the X-axis direction relative to the workpiece W decreases in the order of rough grinding, fine grinding, and fine grinding. The cutting speed of the grinding wheel T in the X-axis direction relative to the workpiece W at the time of spark out is zero.

Here, measurements by the sizing device 60 are performed from the start of rough grinding at time t2 to the end of grinding at time t6. In addition, the process of generating the difference between the actual rotation angle of the spindle 32 and the ideal rotation angle of the spindle 32 is performed only during rough grinding.

As shown in (A) and (B) of FIG. 5, when rough grinding starts at time t2 (rough grinding feed operation starts), initially, the power of the grinding wheel motor 53 increases due to the application of coolant dynamic pressure. Next, the workpiece W is deflected and deformed, so the power of the grinding wheel motor 53 increases further. During this time, the workpiece W has not yet been ground.

Next, when grinding of the workpiece W begins, the value (sizing value) of the sizing device 60 begins to decrease. Then, rough grinding is completed at time t3. During rough grinding (t2-t3), as shown in FIG. 5C, if the workpiece W is not rotating in association with the grinding wheel T, the difference between the actual rotation angle of the spindle 32 and the ideal rotation angle of the spindle 32 is almost zero. In detail, the difference is smaller than the upper predetermined threshold value Th and larger than the lower predetermined threshold value -Th. In other words, the difference does not exceed the absolute value of the predetermined threshold value Th. Furthermore, the fluctuation range of the difference is smaller than the predetermined range ΔA.

The reason for this phenomenon is as follows. When the workpiece W is being ground normally by the grinding wheel T, without rotating along with the grinding wheel T, the spindle 32 and the workpiece W rotate together. Furthermore, the spindle 32 is controlled to rotate at a constant speed. Therefore, the actual rotation angle of the spindle 32 is almost equal to the ideal rotation angle of the spindle 32, and the difference between the actual rotation angle and the ideal rotation angle is a very small value (almost zero).

Next, when fine grinding begins at time t3, the power of the grinding wheel motor 53 decreases, and when fine grinding begins at time t4, the power decreases even further, and when spark-out ends at time t6, the power becomes almost zero. The value of the sizing device 60 (sizing value) approaches the target dimension as the process progresses in the order of rough grinding, fine grinding, fine grinding, and spark-out.

Next, a case where the workpiece W rotates together with the grinding wheel T during rough grinding will be described with reference to FIG. 6. As described above, it is highly likely that the workpiece W rotates together with the grinding wheel T during rough grinding. The following describes the case where the workpiece W rotates together with the grinding wheel T during rough grinding.

In FIG. 6, at time t2a, for example, the rotating member serving as the drive force transmission mechanism 37 becomes caught with the main shaft 32, preventing the rotating member from moving forward, and the workpiece W begins to rotate along with the grinding wheel T.

As shown in FIG. 5, from time t1 to t2a, the behavior is the same as during normal grinding. When the workpiece W starts to rotate entrained at time t2a, the workpiece W does not rotate relative to the grinding wheel T, and so is not basically ground. However, if a relative rotation that is different from the ideal state occurs, a portion of the workpiece W will be ground locally. Therefore, as shown in FIG. 6(A), the value of the sizing device 60 (sizing value) changes irregularly after time t2a, unlike the change shown in FIG. 5(A).

As shown in FIG. 6B, since grinding of the workpiece W is not performed, the power of the grinding wheel motor 53 drops sharply. It may fluctuate slightly depending on the degree of relative rotation between the workpiece W and the grinding wheel T.

After the workpiece W rotates in unison with the grinding wheel T, the engagement between the turning member and the spindle 32 may be released, causing the turning member to move forward and engage with the workpiece W. When this happens, the rotation of the workpiece W, which has been rotating in unison with the grinding wheel T, is transmitted in reverse to the spindle 32 via the turning member. Specifically, after the workpiece W rotates in unison with the grinding wheel T, the workpiece W may collide with the turning member when the turning member engages with the workpiece W. This collision causes the rotation of the workpiece W to be transmitted in reverse to the turning member, and then from the turning member to the spindle 32.

As a result, the actual rotation angle of the spindle 32 deviates from the ideal rotation angle of the spindle 32. In particular, as shown in FIG. 6C, the difference between the actual rotation angle of the spindle 32 and the ideal rotation angle of the spindle 32 fluctuates significantly after time t2a. In particular, as shown in FIG. 3A and FIG. 3B, in the entrained rotation, the workpiece W rotates in the opposite direction to normal. In this case, the collision force between the workpiece W and the turning member becomes large, and the fluctuation also becomes large.

If the actual rotation angle of the spindle 32 deviates significantly from the ideal rotation angle of the spindle 32, the difference between the actual rotation angle of the spindle 32 and the ideal rotation angle of the spindle 32 will exceed the upper predetermined threshold value Th, as shown in FIG. 6C. The difference may also exceed (fall below) the lower predetermined threshold value -Th. If this occurs, it is determined that the workpiece W has rotated in unison with the grinding wheel T.

In addition to judging whether the difference exceeds a predetermined threshold value Th, the following can also be done. As described above, the spindle 32 is affected by the co-rotation of the workpiece W, and is driven by the rotation drive of the spindle motor 33. In this case, the difference between the actual rotation angle of the spindle 32 and the ideal rotation angle of the spindle 32 fluctuates more than in a normal case. Therefore, the fluctuation range of the difference exceeds a predetermined range ΔA. Even in such a state, it can be judged that the workpiece W has rotated co-rotatingly with the grinding wheel T.

As described above, when a driving force transmission mechanism 37 such as a rotating member is not used, if the grinding resistance is very large, the workpiece W may rotate along with the grinding wheel T, rather than being rotated by the rotational driving force of the spindle 32. When the workpiece W rotates along with the grinding wheel T, the rotation of the workpiece W may be transmitted back to the spindle 32. In this case, as in the above, the actual rotation angle of the spindle 32 is deviated from the ideal rotation angle of the spindle 32. Then, by using a predetermined threshold value Th or a predetermined width ΔA, it can be determined that the workpiece W has rotated along with the grinding wheel T.

As in normal operation, the spindle motor 33 attempts to rotate the spindle 32 in one constant direction (Figure 3A). However, because the workpiece W rotates together with the grinding wheel T, the friction between the center member 36 and the workpiece W causes the spindle 32 to rotate in the direction of the workpiece W (Figure 3B). Therefore, the actual rotation angle of the spindle 32 varies greatly depending on the rotational driving force from the spindle motor 33 and the rotational driving force from the workpiece W, as shown in Figure 6C.

Even in this case, the control device 70 can determine that the workpiece W has rotated along with the grinding wheel T if the difference between the actual rotation angle of the spindle 32 and the ideal rotation angle of the spindle 32 exceeds a predetermined threshold value Th (or -Th), or if the fluctuation width of the difference exceeds a predetermined width ΔA. Note that the determination may be made based only on the predetermined threshold value Th, or only on the predetermined width ΔA, or both.

(6. Second Determination Process Regarding Co-Rotation)
A second judgment process for judging whether or not the workpiece W is rotating together with the grinding wheel T as shown in Fig. 3B will be described with reference to Fig. 7. The second judgment process is a process performed by the control device 70 and the spindle drive circuit 35, similar to the first judgment process. In Fig. 7, blocks shown inside the control device 70 indicate functions executed by the program in the control device 7. Judgment 35g and threshold setting 35h, which are blocks shown inside the spindle drive circuit 35, indicate functions executed by the program in the spindle drive circuit 35. Functional elements shown inside the spindle drive circuit 35 indicate functions executed by the formed circuits.

The second judgment process differs from the first judgment process in that the spindle drive circuit 35 judges whether or not the workpiece W is rotating together with the grinding wheel T. Only the parts related to the differences between the two processes will be described below. In the second judgment process, the position deviation generating unit 35a of the spindle drive circuit 35 generates the difference (position deviation) between the ideal rotation angle of the spindle 32 and the actual rotation angle of the spindle 32. In judgment 35g of the spindle drive circuit 35, it is judged whether or not the workpiece W is rotating together with the grinding wheel T based on the generated difference (position deviation).

Then, the result of the determination 35g of the spindle drive circuit 35 as to whether or not co-rotation has occurred is output to the control device 70. If the determination result obtained from the spindle drive circuit 35 indicates that co-rotation has occurred, the control device 70 performs post-determination processing. The post-determination processing includes, for example, stopping the drive of the spindle device 30, stopping grinding, issuing a warning, and notifying the operator or manager.

1 Grinding machine 12 Z-axis drive mechanism (moving device)
14 X-axis drive mechanism (movement device)
30 Spindle device 31 Spindle housing 32 Spindle 33 Spindle motor 34 Spindle detector 35 Spindle drive circuit 50 Grinding wheel head 70 Control device Th Predetermined threshold value T Grinding wheel W Workpiece ΔA Predetermined width

Claims (7)

A spindle device that supports a workpiece and rotates the workpiece;
A grinding wheel for grinding an outer peripheral surface of the workpiece, the grinding wheel being rotated and driven by a grinding wheel head;
a moving device for moving the workpiece and the grinding wheel toward and away from each other;
a control device for controlling the spindle device, the wheel head, and the moving device;
Equipped with
The spindle device is
A spindle housing;
a spindle rotatably supported in the spindle housing;
A spindle motor that rotates the spindle;
A detector for detecting a rotation angle of the spindle;
a drive circuit that drives the spindle motor based on a command value of the control device and a rotation angle of the spindle detected by the detector;
Equipped with
The control device or the drive circuit is
The grinding machine uses a difference between an actual rotation angle of the spindle detected by the detector and an ideal rotation angle of the spindle calculated from a command value to the spindle motor, and determines that the workpiece has rotated together with the grinding wheel when the difference exceeds a predetermined threshold value or when the fluctuation range of the difference exceeds a predetermined range. The grinding machine according to claim 1, in which the workpiece rotates together with the grinding wheel, and the rotation of the workpiece is transmitted back to the spindle, so that the actual rotation angle of the spindle deviates from the ideal rotation angle of the spindle. The drive circuit generates the difference and outputs the generated difference to the control device;
3. The grinding machine according to claim 1, wherein the control device determines whether or not the workpiece is rotating together with the grinding wheel based on the difference obtained from the drive circuit. The drive circuit generates the difference, determines whether or not the workpiece is rotating in association with the grinding wheel based on the difference, and outputs a determination result to the control device;
The grinding machine according to claim 1 , wherein the control device acquires the determination result from the drive circuit. The grinding machine according to any one of claims 1 to 4, wherein the control device stops driving the spindle device when it is determined that the workpiece has rotated in unison with the grinding wheel. The grinding machine according to any one of claims 1 to 5, wherein the control device or the drive circuit determines whether the workpiece is rotating along with the grinding wheel based on the difference during rough grinding. The grinding machine according to any one of claims 1 to 6, wherein the rotation direction of the workpiece during normal grinding is opposite to the rotation direction of the workpiece when the workpiece rotates with the grinding wheel.

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