JPH0666902U - Plane accuracy correction device for chamfering with variable rotation speed - Google Patents

Abstract

(57) [Abstract] [Purpose] When a workpiece is gripped by a hydraulic chuck and the end surface is cut with a constant peripheral speed control to keep the cutting speed almost constant, the plane accuracy is poor due to the change in centrifugal force acting on the gripping claw. To obtain stable plane accuracy. [Structure] The hydraulic chuck 2 is provided with a seating pad 7 whose air nozzle 8 opens to the work contact surface, and an air sensor 13 is provided in the middle of an air supply path 12 to the air nozzle so as to change the gap between the seating pad and the workpiece. The change in the in-road pressure is detected, and the output voltage is changed by the voltage control unit 21 by this detection signal and supplied to the solenoid SOL1 of the electromagnetic proportional pressure reducing valve 17, and the change in the gripping force is changed by the change in the rotation speed under the constant peripheral speed control. By suppressing the displacement of the workpiece in the Z-axis position, good surface accuracy can be obtained.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an apparatus for correcting a plane accuracy defect that occurs when a main shaft is variably rotated in a machine tool such as an NC lathe to maintain a substantially constant cutting speed for chamfering.

[0002]

[Prior art]

 Conventionally, when a workpiece gripped by a chuck in an NC lathe is subjected to chamfering with variable rotation control (constant peripheral speed control) so that the cutting speed becomes almost constant, the machined surface is finished in medium to high. This is due to the change in centrifugal force acting on the gripping claws 102 of the chuck 101 as shown in FIG. 2, and the work W during low speed rotation floats to the front side in the Z-axis direction by the predetermined gripping force as shown by the phantom line. This is a phenomenon that occurs when the cutting point gradually moves toward the center of rotation, but the gripping force decreases due to the action of centrifugal force, and the cutting point is displaced rearward in the Z-axis direction as shown by the solid line. An example of the result of measuring the amount of this displacement by the gap sensor 104 attached to the tool rest 103 is a graph of FIG. 3. According to this, a change of 500 to 3500 rpm causes a 9 μm workpiece to be pulled in the −Z axis direction. This lack of flatness is solved by performing face plate work, but it is not commonly used because a mounting jig is required and the attachment / detachment time becomes long. Therefore, as shown in FIG. 4, a chuck with centrifugal force compensation having a counterweight 105 in the main body 106 is often used.

[0003]

[Problems to be solved by the device]

 The chuck with centrifugal force compensation described in the prior art is a small balance weight that can be stored in a limited space inside the main body, and it has no effect of correcting the reduction in gripping force and eliminates surface accuracy defects. Has the problem of being insufficient. The present invention has been made in view of the above problems of the conventional technique, and its purpose is to obtain a highly accurate flat surface even if the surface is machined by the constant peripheral speed control using an ordinary power chuck. It is intended to provide a plane accuracy correction device that can obtain

[0004]

[Means for Solving the Problems]

 In order to achieve the above-mentioned object, the flatness accuracy correction device of the present invention for face milling at variable rotation speed acts on the gripping claw when the workpiece is gripped by the power chuck and face milling is performed at variable speed. A device for correcting a planar accuracy defect caused by a change in gripping force due to a change in centrifugal force, which is provided with a seating plate for opening the air nozzle on the work contact surface of the power chuck, An air sensor is installed in the middle of the air supply path to detect a change in the inside pressure due to a change in the clearance between the seating metal and the workpiece, and means for changing the fluid pressure supplied to the power chuck by the detection signal of the air sensor is provided. It is provided to offset the centrifugal force that changes due to variable rotation by changing the chuck supply pressure.

[0005]

[Action]

 When the work is inserted into the opened gripping jaws, the rear end of the work is pressed against the work contact surface where the air nozzle of the seating plate opens and the gripping jaws are closed and the workpiece is gripped, the gripping jaws lift and the workpiece is seated. There is a slight gap between the metal and the pad. This gap amount changes depending on the spindle speed, and the centrifugal force that acts on the gripping jaws at high speed increases and the gap becomes smaller.Therefore, the air sensor detects small changes in the gap during face milling at constant peripheral speed rotation. The gripping force is kept constant by changing the power supplied to the solenoid of the solenoid proportional pressure reducing valve, and the amount of displacement of the workpiece in the Z-axis direction is suppressed to a very small width to achieve stable planar accuracy.

[0006]

【Example】

 This embodiment will be described below with reference to FIG. A hydraulic chuck 2 is concentrically fitted to the tip of a spindle 1 of an NC lathe, and a work W is gripped by a grip claw 3 of the hydraulic chuck 2. The grip claw 3 is opened / closed via a draw tube 6 by a piston 5 of a rotary cylinder 4 provided at the rear end of the main shaft 1, and a seating pad 7 is attached to the hydraulic chuck 2. An air nozzle 8 is formed at the center of the backing plate 7 and opens to the work contact surface 7a. Air is supplied to the air nozzle 8 by an air pipe 9 penetrating the inside of the draw tube 6. The air pipe 9 is in communication with an external air supply passage 12 via a rotary joint 11, and an air sensor 13 is attached in the middle of the air supply passage 12.

As the air sensor 13, a commercially available non-contact air detection device such as Pell System manufactured by CKD Co., Ltd. can be used. This is an application of Wheatstone Bridge of an electric circuit to the air circuit. If the clearance δ between the air nozzle 8 and the rear end surface of the workpiece changes and the air resistance changes, a differential pressure is generated between A and B of the pneumatic bridge circuit, which causes the float MK containing the permanent magnet to be displaced vertically. Then, the contact point of the reed switch Ca is switched. A sub-micron air filter 14 for detarring, a micro-oiler 15 for deoiling, and a pressure reducing regulator 16 are attached in series on the way of the air supply path from the air source Pa to the air sensor 13.

On the other hand, the rotary cylinder 4 is supplied with pressure oil whose pressure is adjusted from an oil pressure source Po via an electromagnetic proportional pressure reducing valve 17 via an electromagnetic switching valve 18, and a maximum pressure is provided in the middle of this adjusted pressure supply path. A limiting relief valve 19 is mounted. A voltage is supplied to the solenoid SOL1 of the electromagnetic proportional pressure reducing valve 17 via the voltage controller 21. This voltage control unit 21 maintains the voltage at that time when the voltage rises at a predetermined speed according to the detection signal of the reed switch Ca when the float MK of the air sensor 13 rises and the float MK falls and the signal is cut off. It is supposed to do. The reset unit 22 is a reset command when the constant peripheral speed control at the end face processing is finished, and the output voltage of the voltage control unit 21 is set to the normal set voltage at the constant rotation speed stored in the set pressure corresponding voltage storage unit 23. It will be returned.

Next, the operation of this embodiment will be described. The work W is inserted into the open gripping claw 3, the work rear end face is pressed against the work contact end face 7a of the pad 7, and the pressure is adjusted by the set voltage at the predetermined rotation speed output from the voltage control unit 21. The pressure oil thus supplied is supplied to the right chamber of the rotary cylinder 4 via the electromagnetic switching valve 18, the grip claws 3 are closed, and the work W is gripped. At this time, since there is a gap required for sliding between the grip claw 3 and the chuck body, the grip claw is lifted, and the work W is slightly pushed forward in the Z-axis direction as shown by the phantom line in the figure. A gap δ is formed between the pad 7 and the pad 7. Next, air is supplied to the air nozzle 8 to rotate the main shaft 1 at a rotation speed designated by a program, and the variable aperture Rv of the air sensor 13 is adjusted so that the float MK barely maintains the lower position.

When the X-axis position of the cutting edge is gradually moved to the rotation center side after entering the end face cutting and the constant peripheral velocity control is performed, the spindle rotation becomes faster and the centrifugal force acting on the gripping claws 3 increases, and the gripping force increases. Is reduced, the floating amount of the grip claw 3 is reduced, and the gap δ is reduced. A slight change in the gap, for example, in units of 0.1 μm changes the differential pressure between A and B to raise the float M K, close the reed switch Ca, and output a signal to the voltage control unit 21. When the voltage supplied to the SOL1 continuously rises while this signal is being input to the voltage controller 21, and the adjusting pressure of the electromagnetic proportional pressure reducing valve 17 rises, the gripping force increases and the gap δ increases. Then, the float MK is lowered, the reed switch Ca is opened, the signal is stopped, and the voltage supplied to the SOL1 of the voltage control unit 21 is maintained at the same potential. When the end face cutting is completed while the clearance δ is finely adjusted by repeating the above, the constant velocity control is released, and when a reset command is issued, a voltage return signal is output from the reset unit 22 and is maintained in the voltage control unit 21. The high potential voltage that had been applied is returned to the voltage corresponding to the set pressure.

[0011]

[Effect of device]

 Since the present invention is configured as described above, it has the following effects. An air sensor detects the amount of change in the gap between the seating plate provided on the power chuck and the gripping work, and changes the fluid pressure supplied to the power chuck to compensate for the decrease in gripping force due to the increase in the number of revolutions, Since the amount of lifting is suppressed to a very small width, stable flatness can be obtained even if the end face of the work is machined at a constant peripheral speed. In addition, since there is no reduction in gripping force during high-speed rotation, there is no accident of the workpiece popping out, and constant peripheral speed machining can be performed with confidence.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a plane accuracy correction device in an NC lathe according to an embodiment.

FIG. 2 is a state diagram of measurement of a movement amount of a work in the Z-axis direction due to a change in gripping force.

FIG. 3 is a graph showing the measurement results of FIG.

FIG. 4 is a cross-sectional view of a conventional chuck with centrifugal force compensation.

[Explanation of symbols]

2 Hydraulic chuck 3 Grasping claw 4 Rotating cylinder 7 Seating pad 8 Air nozzle 13 Air sensor 17 Electromagnetic proportional pressure reducing valve 21 Voltage control unit

Claims (1)

[Scope of utility model registration request] 1. A device for correcting a planar accuracy defect caused by a change in gripping force due to a change in centrifugal force acting on a gripping claw when a workpiece is gripped by a power chuck and surface-shaping is performed at a variable rotation speed. Then, the power chuck is provided with a seating pad in which the air nozzle opens to the work contact surface,
An air sensor for detecting a change in in-passage pressure due to a change in a clearance between the seating block and the work is provided in the middle of an air supply passage to the air nozzle, and a fluid pressure supplied to the power chuck is changed by a detection signal of the air sensor. A flatness accuracy correcting device at the time of chamfering with a variable rotation speed, which is provided with a means for canceling a centrifugal force that changes due to variable rotation by changing a chuck supply pressure.