JP2002292546A - Grinding machine provided with steady rest and its grinding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve grinding accuracy by preventing a roundness error due to a revolving motion error of a crank pin. SOLUTION: Both ends of a crankshaft W having a plurality of axially arranged crank pins P1-P4 are supported by a head stock 17 and a tail stock 18 so as to rotate about a journal axis. Therefore, the crank pins revolve around the journal axis. Both of rough grinding and finish grinding of the crank pins are carried out by controlling a wheel head 8 rotatably holding an abrasive wheel 14 in synchronization with the revolution of the crank pins around the journals. After rough grinding has been carried out by holding journals J2-J4 by a steady rest 30, finish grinding is carried out releasing the holding by the steady rest 30. Therefore, in the rough grinding, deflection of the crank shaft W due to grinding resistance of the abrasive wheel 14 is prevented, and in the finish grinding, roundness of the journals J2-J4 do not affect the revolving motion of the crank pins P1-P4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grinding machine having a touch-stop device for supporting a journal of a crankshaft and a grinding method therefor. More particularly, the present invention relates to a grinding machine provided with a steadying device for supporting a journal for grinding a crankpin by rotating a crankshaft about a journal, and a grinding method.

[0002]

2. Description of the Related Art In a grinding machine for grinding a crankpin of a crankshaft, the crankpin rotates around a journal axis of a crankshaft according to a machining program set in a numerical controller, and makes a circular motion around the journal. The advance / retreat is synchronously controlled with the rotation of the crankshaft so that the grinding wheel head is moved forward and backward following the change of the angular position in the orbital movement of the crankpin.

[0003] In general, a crankshaft has low rigidity and generates deflection when subjected to grinding resistance by a grinding wheel.
For this reason, in the above-described grinding machine that rotates the crank pin around the journal axis to grind the crank pin, the entire crank shaft is bent by the grinding resistance applied to the crank pin, and the journal axis is shifted from the rotation center. become. If grinding of the crankpin is continued in this state, errors will occur in the shape and roundness of the crankpin, and when the grinding resistance increases, the entire crankshaft will vibrate greatly, causing the crankshaft to fall off and the grinding itself. May not be possible.

Conventionally, when a workpiece is a simple cylinder, as a method for preventing deflection, a touch-stop device for pressing a crankshaft from a direction opposite to a direction in which a grinding wheel is pushed is used. However, in the above-described grinding machine that rotates the journal pin about the center of the axis to grind the crankpin, the crankshaft makes a revolving motion about the journal axis as the center of rotation. Was difficult to push. For this reason, the journal is held by a touch-stop device to prevent the crankshaft from bending so that the journal axis does not deviate from the center of rotation.

[0005]

However, when the journal is held by the steady rest device, the orbital motion accuracy of the crankpin is affected by the roundness accuracy of the journal portion. Further, when there is a coaxiality error between the two center holes or the journals at both ends, which are processing standards for the journal and the crankshaft held by the steady rest device, the crankshaft receives a bending force that fluctuates according to rotation. This force causes an error in the orbiting motion of the crankpin, causing an error in the shape and roundness. In particular, as shown in FIG. 2, a three-point support type steady rest device that maintains an angular position of approximately 120 degrees around the journal circumference has a high holding force. Can be surely matched, but on the other hand, it is susceptible to the roundness of the journal. Therefore, a main object of the present invention is to prevent a roundness error due to a rotation error of a crankpin and to improve grinding accuracy.

[0006]

SUMMARY OF THE INVENTION The present invention provides a grinding method for solving the above-mentioned problem, and its gist is that the grinding of a crankshaft in a grinding process involving a relatively large load is caused. Grinding is performed by holding the journal of the crankshaft with a steady rest so that high-efficiency grinding can be performed without causing the grinding. On the other hand, in the final finishing process with a relatively small load, the journal retention of the steady rest is released, and the crankshaft is rotated with the two center holes of the crankshaft processing reference or two points supported between the journals at both ends, and On the other hand, the grinding of the pin portion that performs the orbiting motion without error is performed.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an embodiment in which the present invention is applied to a grinding machine for processing a crankpin, and a bed 1 is shown.
A Z-axis table 6 on which a grinding wheel table 8 is mounted on a Z-axis guide rail 2 in the longitudinal left-right direction (Z-axis direction) is slidably provided by a feed screw 3. ,
A grindstone table 8 rotatably supporting the grindstone 14 is slidably provided by a feed screw 12 in a radial direction of a crankshaft W described later, more precisely, in a front-rear direction (X-axis direction) orthogonal to the Z-axis direction. ing.

A headstock 17 and a tailstock 18 are installed in front of the grinding wheel head 8 and spaced apart in the longitudinal direction, and a crankshaft W as a workpiece is supported by a pair of left and right centers therebetween. The headstock 18 is provided with a C-axis servomotor 19 for driving the rotation of the crankshaft. The shaft pin of the crankshaft W can be gripped and driven to rotate by the drive pin 20, and the rotation position is provided at the rear end of the motor 19. Detected by the encoder 19E, the tailstock 18 is configured to press and support the axis of the crankshaft W by its center.

Each of the feed screws 3 and 12 is driven to rotate by a servomotor with an encoder which is controlled by a numerical controller described later. That is, the servomotor 2 with the encoder 25E is provided at the left end of the feed screw 3 for moving the Z-axis table 6 on which the grinding wheel base 8 is mounted in the Z-axis direction.
5 are provided. A servomotor 27 with an encoder 27E is provided on the Z-axis table 6 at an end of a feed screw 12 for sliding the grindstone table 8 in the front-rear direction (X-axis direction). The grindstone table 8 supports the grindstone 14 so that it can be rotationally driven by a built-in motor (not shown).

On the bed 1, a three-point support type steady rest device 30 is arranged on the opposite side of the wheel head 8 with respect to the crankshaft W. The anti-sway device 30 includes the rest base 3
1, a feed screw 33 for indexing and moving the rest head 32 in the Z direction and a servomotor 34 with an encoder are provided. As shown in FIG. 2, the housing 35 of the rest head 32 includes a hydraulic cylinder 36 at a lower portion, and reciprocates in a direction (X direction) perpendicular to the rotation axis of the crankshaft W with respect to a base 37 moved by a feed screw 33. Moving.

A hollow hole is formed in the housing 35 at a position corresponding to the height of the rotation axis of the crankshaft W supported by the main shaft 17 at the vertical position (ie, the height of the main shaft of the grinding wheel H). A sliding body 39 is fitted to 38 so as to be slidable forward and backward. A first support arm 40 is fixed to the front end of the sliding body 39 exposed from the housing 1. At the rear end of the hollow hole 38, a drive shaft 41 is rotatably supported. The distal end side of the drive shaft 41 protrudes into the center hole 42 of the sliding body 39, and is formed with a screw portion 44 which is screwed into a female screw sleeve 43 fitted to the rear end opening side of the center hole 42 of the sliding body 39, By rotating the drive shaft 41, the sliding body 39 advances and retreats in the hollow hole 38. A gear mechanism 45 is attached to the rear end side of the drive shaft 41. The gear mechanism 45 is connected to an output shaft of a servomotor 46 mounted on a side surface of the housing 35.

A pair of a second support arm 47 and a third support arm 48 are provided on the front surface of the housing 35 and in the vertical direction of the first support arm 40.
Are provided rotatably about an axis parallel to the support shafts 49 and 50.

The second support arm 47 and the third support arm 48
Is connected to the first support arm 40 around the axis of the support shafts 49 and 50 by a hydraulic cylinder (not shown) connected to the hydraulic control device 83.
Is controlled so as to come in contact with and separate from the vehicle. In the case of a four-cylinder crankshaft illustrated during grinding, the rest head 35 moves the servo motor to the center three positions, that is, the positions facing the second to fourth journals J2, J3, and J4 from the tailstock 18 side. 34 selectively. At this indexing position, the first support arm 40 whose position has been adjusted by the servomotor 46 in advance in accordance with the sinar diameter by moving the housing 35 forward depending on the cylinder 36.
Contacts the journal. At the same time, the second support arm 47 and the third support arm 48 are closed by the hydraulic pressure from the hydraulic control device 83, so that the journal is sandwiched as shown in FIG.

The schematic configuration of the grinding machine according to the embodiment of the present invention is as described above. The crankshaft W is supported between the headstock 17 and the tailstock 18, and the left Z-axis table is used for grinding. 6 is indexed by the servo motor 25 to a position where the grindstone 14 is aligned with the crankpins P1 to P4, and the rest head is indexed by the servomotor to the position of the journal near the crankpin from which the grindstone 14 is indexed. Then, the housing 35 is advanced to bring the first support arm 40 into contact with the journal, and the second support arm 47 and the third support arm 48 are closed to sandwich the journal, thereby fixing the journal at the center of rotation. Next, the servomotor 19 of the headstock 17 is rotated to rotate the crankshaft W. At that time, since the crankshaft W is rotated on the axis of the journal, the crankpin, which is a processing portion, orbits around the journal. And
The grinding wheel base 8 is advanced by the servo motor 27 by the feed amount of the coarse grinding. At this time, since the crank pin, which is a processing portion, is revolving, the grinding is performed by the grinding wheel 14 while moving the grindstone table 8 back and forth in synchronization with the rotation of the spindle servomotor 19. The synchronous movement is superimposed on the synchronous movement to give a cutting forward movement by the servo motor 27, and the operation is performed so as to gradually grind to the rough processing size.

When the grinding pin 14 is used to grind the crankpin to the rough working dimensions, the second support arm and the third support arm are opened, and the housing is retracted to move the first support arm and the second support arm.
The journal holding by the support arm and the third support arm is released. During this time, the crank pin orbits around the journal without stopping, and the servo motor 2 of the grinding wheel head 8 is moved.
7 to advance by the feed amount of the finish grinding. At this time, since the crank pin, which is a processing portion, is revolving, the grinding is performed by the grinding wheel 14 while moving the grindstone table 8 back and forth in synchronization with the rotation of the spindle servomotor 19 by the control means. The synchronous motion is superimposed on the synchronous motion to give a cutting forward motion by the servomotor 27, and the operation is performed so as to gradually grind to the finishing completed dimension. The sizing device 51 switches the feed amount of the grindstone head 8 when the rough processing completion dimension is reached, and completes the processing after reaching the finish processing dimension. The sizing device 51 is mounted on the grindstone table 8 as shown in FIG. The sizing device 51 includes a rotating crank pin P during grinding.
A known sizing device (for example, manufactured by Marposs, Italy) of the type in which dimensional measurement is performed while continuously contacting the slab. A second arm 54 is pivotally supported at the tip of a first arm 53 that is pivotally supported by a support member 52 on the grindstone table 8 and extends forward of the grinding wheel 14, and is further provided with a measurement for measuring at a right angle to the tip of the second arm 54. The rod 55 is fixed. Measuring rod 55
Has a measuring head comprising a V-block 56 fixed to the lower end thereof and in contact with the outer periphery of the crankpin P, and a probe 57 provided at the center thereof so as to be able to move forward and backward. Is detected and output as an electric signal. A guide member 58 is fixed to the tip of the V block 56, and serves as a guide for the V block 56 to engage with the crankpin P.

On the grindstone table 8, an operation piece 59 integrated with the first arm 53 is brought into contact with the operation piece 59 to move the measuring rod 55 between a rest position (two-dot chain line position) and a measurement position (solid line position). An operating device including a hydraulic cylinder 60 is provided. Supporting piece 6 projecting forward from the lower surface of the distal end of first arm 53
The first protrusion 62 abuts on the lower surface of the second arm 54 in the rest position and serves to hold the second arm 54 horizontally. By returning the piston 60a of the hydraulic cylinder 60 from the rest position indicated by the two-dot chain line, the measuring rod 55 gradually descends, and first, the guide member 58 comes into contact with the crankpin P, and the crankpin P moves along the guide member 58 with V Block 57
, At which point the second arm 54 is free to pivot away from the projection 62 of the support piece 61.

Next, a control system for controlling the grinding machine according to the embodiment will be described with reference to FIG. The control system includes a numerical controller 70, and the numerical controller 70
Are a CPU 71, a ROM 73 as a storage device,
M74 are connected to each other. CPU 71
Is connected to the X-axis motor control circuit DUX via the interface 76, and Z
Shaft motor control circuit DUZ, S controlling rest device 30
Axis motor control circuit DUS and T axis motor control circuit DUT,
It is connected to a C-axis motor control circuit DUC that controls the spindle motor 19 and a sequence controller 79. These motor control circuits DUX, DUZ, DUS, DUT and DUC correspond to the corresponding servo motors 19, 27, 25, 3
4 and 36, and are connected to receive feedback signals from encoders 19E, 27E, 25E, 34E and 36E of these servo motors, respectively.

An operation panel 8 having a CRT, numeric keys, and the like is provided to the CPU 71 via an interface 80.
1 is connected. The ROM 73 stores a system control program and the like, and the RAM 74 stores a machining control program and the like. Further, the CPU 71 is provided with a measuring head of the sizing device 51 provided on the grinding wheel base 8 as A-
It is connected via an interface 82 including a D converter. Next, a specific grinding operation which is a feature of the present invention will be described with reference to a flowchart of FIG.

The operator mounts the crankshaft W between the centers of the headstock 17 and the tailstock 18. When the crankshaft is attached / detached, the grindstone head 8 and the rest head 32 are both at the standby position where they are retracted, and the second support arm 47 and the third support arm 48 of the rest head 32 at the standby position are in the open state. is there. After this, the operation panel 81
When a command to execute grinding is given to the numerical controller 70, the operation of the flowchart of FIG. 4 is executed, and the sequence counter N formed in the RAM 74 is set to an initial value "1" (step 90). Next, it is determined whether or not the order counter N is larger than "5" indicating that all the crank pins have been ground. (Step 92) Since the order counter N is "1" in this state, the determination is "NO", and a table index is executed as the next process (Step 94). An index position storage table IPMT shown in FIG. 5 is formed in the RAM 74, and the crankpin to be processed and the journal to be supported by the rest device 30 when the processing order N is specified are determined in advance by the operator using the operation panel 81. Specified. In this case, since the machining order is "1", the servo motor 25 is operated, and the table 6 is indexed to a position where the grindstone 14 is aligned with the crankpin P2. P2 is indexed to the horizontal processing start position closest to the grindstone side shown as the position (a) in FIG. 6 (step 9).
6).

Next, by the operation of the servo motor 34, the rest head 32 is indexed to a position aligned with the center journal J3. When the rest head is indexed to a position aligned with the journal J3, a command to advance the housing of the rest head is output from the sequence controller to the hydraulic control device 83, and the tip of the first support arm contacts the journal J3. At the same time, the servomotor 27 is operated, and the grinding wheel base 8 is rapidly advanced toward the crankshaft W. (Step 98) The forward feed amount is determined by the grinding wheel 14 having the crankpin P2 and the journal J
It is set in advance so as to be stopped at a position having a slight gap with 3.

When the rapid traverse is completed, the second support arm 4
7. A command to close the third support arm 48 is issued, and the second support arm 47 and the third
When the support arm 48 sandwiches the journal J3, the journal J3 is fixed at a position coinciding with the rotation axis of the main shaft. (Step 100).

Next, coarse grinding feed of the grinding wheel base 8 is executed (step 102). In this rough grinding, the servo motor 19 and the servo motor 27 are synchronously controlled according to the profile data. As shown in FIG. 6, the profile data indicates the position (XΘ) of the grinding wheel head 8 from the crankshaft rotation axis with respect to the rotation angle (Θn) of the crankpin P from the machining start position (a), for example, the crankshaft rotation angle. It is determined every 0.5 degrees and is registered in the RAM 74 in advance. The servo motor 27 for the grinding wheel head 8 is
The coarse grinding feed, that is, the cutting of the grinding wheel 14 with respect to the crankpin P2 is superimposed on the forward / backward movement based on the profile data, whereby the grinding wheel 14 is gradually moved forward and backward along with the orbital movement of the crankpin P2. Is done.

In the course of this rough grinding step, the cylinder 60 of the sizing device 51 shown in FIG.
And the V bevel 56 is engaged with the crankpin P2 to start measurement. This measurement start command is executed by a signal from the sequence controller 79. The operation of the sizing device to the measurement position is performed by rotating the crank pin P from the position (b) in FIG.
6 is made to track the crank pin P. In this case, the rotational speed of the crankshaft W may be reduced so that the V bevel 56 can be more accurately engaged with the crankpin P. Alternatively, the operation of moving the V bevel 56 at the measurement position may be executed with the crankpin P temporarily stopped at the phase shown in FIG. Thus, since the journal J3 is held by the steady rest device 30, the axis of the crankshaft W is maintained substantially at the rotation axis, and the bending of the crankshaft W due to grinding resistance is particularly prevented, and the three-point support steady rest is prevented. The crankshaft W in the state can perform a stable orbiting motion even when an external force acts.

In this way, the rough grinding of the crankpin P2 proceeds, and during this time, the measuring head
Monitor dimensions. (Step 104) Crank pin P
2 is coarsely ground to a predetermined size, a command to retract the housing 35 of the head 32 is output to the hydraulic controller 83 via the sequence controller 79, and the tip of the first support arm 40 is moved to the journal J3. Move away from Subsequently, a command to open the second support arm 47 and the third support arm 48 is issued, and the fixing of the journal J3 by the steadying device is released by these commands. (Step 10
6). At this time, the crankshaft W makes a revolving motion while being held only at the reference portion such as the center hole. That is, the journal performs a revolving motion that is not affected by the poor circularity of the journal that occurs when the journal is held by the steady rest. Finish grinding is performed in this state. (Step 108)

In the finish grinding, the grinding wheel base 8 is advanced by cutting at a cutting speed lower than the coarse grinding feed speed, and this cutting feed is superimposed on the forward / backward movement based on the profile data, whereby the crankpin P2 is moved at a lower grinding speed. The finish grinding is performed (step 110). Since the feed of the grinding wheel head 8 in the finish grinding is very small as compared with the rough grinding, the grinding can be performed with almost no bending of the crankshaft.

When the crankpin P2 reaches a predetermined finishing dimension (step 112), the final spark-out grinding is performed while the crankshaft W rotates a predetermined number of times (step 114), and the grinding is terminated. After the grinding is completed, "1" is added to the processing order counter N (step 116) and the process returns to step 83, and the processing of steps 94 to 112 is repeated as described above until the processing order counter becomes larger than "4". Thus, the remaining crank pins J1, J3, and J4 are ground. When the machining order counter N becomes larger than "4" at the step, the grinding is terminated, the grindstone table 8 returns to the original position (step 118), and the process is terminated.

As described above, during rough grinding, the grinding resistance of the grindstone 14 is large, so that the crankshaft bends and the grinding precision is prevented from being deteriorated by the support of the journal. In the finish grinding, the grinding resistance by the grindstone is reduced. Since the crankshaft does not bend so small, the journal support is not performed by the steadying device 30 in order to prevent the circular motion of the journal from affecting the orbital motion of the crankpin. Only the center of the headstock 17 and the tailstock 18 is supported. Thereby, the crankpin can be ground with high precision. In particular, the three-point steady rest device 3 shown in the present embodiment.
A grinder using 0 is effective because the journal retaining force of the steadying device 30 is high.

In the above-described embodiment, the journal closest to the crank pin is supported at the time of rough grinding. However, the present invention is not limited to this. ), The journal located in the center of the crankshaft is supported regardless of the position of the crankpin for grinding.
Since there is no need to move the rest head, there is no need to provide a servomotor or a ball screw, and the grinding machine can be simplified. Further, a plurality of steady rest devices may be provided. Further, without completely releasing the steady rest support during the finish grinding, the hydraulic pressure of the hydraulic control device 83 is lowered during the finish grinding to reduce the holding force of the journal by the steady rest device (for example, about 20% of the holding force during the rough grinding). You may make it grind | reduce by lowering. In the above embodiment,
Although the description has been given of only two grinding cycles, that is, rough grinding and finish grinding, finish grinding includes fine grinding and fine grinding.

[0029]

As described above, the journal is supported by the steadying device during rough grinding as in the first aspect of the present invention, and only the both ends of the crankshaft are supported at the time of finish grinding. Deflection of the crankshaft,
It is possible to perform high-efficiency grinding with a large grinding force by preventing falling off. On the other hand, during finish grinding, high precision pin grinding can be performed without being affected by shadows due to the accuracy of the journal portion. As a result, highly accurate pin grinding can be performed in a short time. Further, if the journal located closest to the pin to be ground is supported as in claim 2, deflection can be most effectively prevented. Claim 4 or claim 5
By doing so, it is possible to perform high-efficiency grinding with a large grinding force by preventing bending and falling off of the crankshaft at the time of rough grinding. A grinding machine capable of pin grinding can be provided. Further, according to the sixth aspect, it is possible to provide a grinding machine capable of preventing deflection most effectively, and a grinding machine capable of performing high-precision grinding.

[Brief description of the drawings]

FIG. 1 is a plan view of a crankpin grinding machine which is an embodiment of a grinding machine according to the present invention.

FIG. 2 is a side view showing a rest head of the steady rest device used in the crankpin grinding machine.

FIG. 3 is a side view showing a sizing device used for the crankpin grinding machine.

FIG. 4 is a flowchart of a system control program executed by the numerical control device of the crankpin grinding machine.

FIG. 5 is an explanatory diagram showing an index position storage table formed in a RAM of the numerical controller.

FIG. 6 is an explanatory diagram showing a relationship between a turning phase of a crankpin and a feed position of a grindstone.

[Explanation of symbols]

1: bed, W: crankshaft (workpiece), 17:
Headstock, 18: tailstock, 8: whetstone, 14: whetstone, 3
0: steady rest device, 32: rest head, 40: first support arm, 47: second support arm, 48: third support arm 70: numerical control device

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3C034 AA01 BB77 CB15 DD07 3C043 AC23 CC03 DD05

Claims (6)

[Claims] 1. A workpiece supporting device for supporting both ends of a crankshaft having a plurality of crankpins arranged in an axial direction on a bed so as to be rotatable around a journal axis and rotating the crankpin around the journal. A grindstone table that rotatably holds a grindstone and moves back and forth on the bed in a direction perpendicular to the axis of the crankshaft; and a revolving motion of a crankpin around a journal by the workpiece support device and reciprocation of the grindstone table. In a grinding machine equipped with a numerical control device that performs grinding by synchronizing control and a steadying device that holds the journal of the crankshaft, after performing rough grinding while holding the journal with the steadying device, A grinding method using a grinder provided with a steady rest device, wherein the finish holding is performed by releasing the holding by the steady rest device. 2. A method according to claim 1, wherein a journal closest to the position of the crankpin to be roughly ground is held by said steadying device. Grinding method using a grinder equipped with a stop device. 3. A grinding method for a grinding machine provided with a steady rest device according to claim 1, wherein the journal at the center position of the crankshaft is held by the steady rest device regardless of the position of the crankpin to be roughly ground. A grinding method using a grinder provided with a steady rest device. 4. A workpiece supporting device for supporting both ends of a crankshaft having a plurality of crankpins arranged in an axial direction on a bed so as to be rotatable around a journal axis and rotating the crankpin around the journal. A grindstone table that rotatably holds a grindstone and moves back and forth on the bed in a direction perpendicular to the axis of the crankshaft; and a revolving motion of a crankpin around a journal by the workpiece support device and reciprocation of the grindstone table. In a grinding machine having a numerical control device that performs grinding by synchronizing control and a steadying device that holds a journal of the crankshaft, the numerical control device holds a journal by the steadying device during rough grinding. Characterized by comprising a steady rest control means for controlling to release the holding by the steady rest device during finish grinding. That run-out grinding machine equipped with a stop device. 5. A workpiece supporting apparatus for supporting both ends of a crankshaft having a plurality of crankpins arranged in the axial direction on a bed so as to be rotatable around a journal axis and for making the crankpin circulate around the journal. A grindstone table that rotatably holds a grindstone and moves back and forth on the bed in a direction perpendicular to the axis of the crankshaft; and a revolving motion of a crankpin around a journal by the workpiece support device and reciprocation of the grindstone table. Force control means for switching a holding force of the steadying device for holding the journal in a grinding machine including a numerical control device for performing the grinding by synchronizing the grinding and a steadying device for holding the journal of the crankshaft The numerical control device holds the journal by the steady rest device at the time of rough grinding, and at the time of finish grinding Grinding machine provided with a steady rest characterized by comprising a holding force control means for holding by reducing the holding force than during the rough grinding the holding force by the serial steady rest by the holding force switching means. 6. A grinding machine provided with a steady rest device according to claim 4 or 5, further comprising moving means for relatively moving the steady rest device relative to the crankshaft in the axial direction thereof, wherein the control device comprises: A grinding machine provided with a steady rest device, comprising index control means for indexing the steady rest device at a position of a journal closest to a crank pin to be ground by a moving means.