JP4647611B2 - Work clamp device - Google Patents

Description

  The present invention relates to a workpiece clamping device of a processing machine that is controlled by a numerical control (NC) device or the like and cuts a workpiece such as a piston of an engine. The present invention relates to a device capable of clamping with a wide range of variable clamping force from clamping force to high clamping force.

  As a conventional workpiece clamping device, in a workpiece clamping device that clamps and unclamps a workpiece by moving a clamper by a clamping means including a fluid actuator, the clamper is moved in the workpiece clamping direction with a high clamping force that can withstand machining resistance. A first clamping means for clamping a workpiece; and in a stopped state of the first clamping means, the clamper is moved in a workpiece clamping direction to reduce the clamping force with a low clamping force that is smaller than the high clamping force and does not act on the workpiece. Second clamping means for clamping the workpiece, and directly acting on the first clamping means and the second clamping means, and moving the clamper in the workpiece unclamping direction until a gap is formed at least between the workpiece and the clamper. Unclamp the workpiece It is that a Nkuranpu means.

  In this work clamping device, the first clamping means moves the clamper in the workpiece clamping direction and clamps the workpiece with a high clamping force that can withstand the machining resistance, and then the unclamping means when the operation of the first clamping means is stopped. Unclamping the workpiece by moving the clamper in the workpiece unclamping direction until at least a gap is formed between the workpiece and the clamper, and then moving the clamper in the workpiece clamping direction by the second clamping means. A step of clamping the workpiece with a low clamping force which is smaller than the high clamping force and does not apply an impact force to the workpiece; and the high clamping force is applied by the first clamping means while being clamped with the low clamping force. Clamping the workpiece with force To clamp. By clamping the workpiece in this way, clamping distortion due to impact force does not occur in the workpiece (see, for example, Patent Document 1).

JP 2000-354923 A

  However, in the workpiece clamping device and the workpiece clamping method described in the above-mentioned literature, when machining a workpiece, the workpiece can be clamped only with one predetermined high clamping force value, and when machining a workpiece with low rigidity, There is a problem in that machining is performed in a state where the workpiece is distorted by the clamp, and machining accuracy is lowered.

  The present invention has been made in view of the above. From a low clamping force below a predetermined threshold value to a high clamping force above the threshold value, depending on the type of workpiece or the machining process of one workpiece. The purpose is to obtain a workpiece clamping device that can generate a wide range of variable clamping force and can perform high-precision machining even with a low-rigidity workpiece, with minimal clamping distortion during machining. It is said.

To solve the above problems and achieve the object, in the workpiece clamping device according to the present invention, the clamper for clamping the workpiece to the processing machine, variable low clamping force to the clamper according to the flexural deformation amount and applying clamp spring, said via gearing is connected to the clamping spring and the damper to deform the deflection the clamping spring, and a servo motor capable impart variable Hendaka clamping force to the clamper, machining when the clamping of the workpiece at low clamping force below a predetermined threshold value is commanded by the program, the deflection control the amount of deformation before Symbol low clamping force to the clamper of the clamping spring by position control said servo motor the grant, the clamping of the workpiece in the high clamping force over the threshold by the machining program When it is decree is characterized by and a control means for applying a pre-Symbol high clamping force to the said servo motor and current control damper.

  In the work clamping apparatus according to the next invention, the control means is an NC apparatus that numerically controls the processing machine.

  In the work clamping device according to the next invention, the current control region of the servo motor is a region where the current value of the servo motor and the clamping force output from the transmission device are proportional.

In the work clamping device according to the next invention, the controllable range of the clamping force by the crank spring and the controllable range of the clamping force by the current control of the servo motor overlap in the vicinity of the threshold value. It is characterized by that.

  In the work clamp device according to the next invention, the transmission device has a ball nut and screw mechanism, and converts the rotational force of the servo motor into the clamp force of the clamper.

  In the workpiece clamping device according to the next invention, the transmission device holds the clamper so as to be rotatable about a rotation axis of the workpiece.

  In the work clamping apparatus according to the next invention, the servo motor is a linear servo motor.

  According to the workpiece clamping device of the present invention, a wide range of variable from a low clamping force below a predetermined threshold to a high clamping force above the threshold depending on the type of workpiece or on the machining process of one workpiece. Clamping force can be generated, and even with a low-rigidity workpiece, there is an effect that high-precision machining can be performed with a clamp distortion at the time of machining being minimized.

  According to the work clamp apparatus concerning the next invention, it can control by a single NC apparatus as a work clamp apparatus of NC processing machine.

  According to the work clamping device of the next invention, the relationship between the current value of the servo motor and the clamping force can be expressed by a linear function equation, so that the servo motor can be easily controlled.

  According to the work clamping device according to the next invention, a wide range of variable clamping force can be obtained from a low clamping force to a high clamping force.

  According to the work clamping apparatus according to the next invention, a rotary servo motor normally used in an NC processing machine can be used for the work clamping apparatus.

  According to the workpiece clamping device according to the next invention, it is possible to clamp a workpiece to be processed by rotating around the rotation axis.

  According to the work clamp device of the next invention, the power transmission mechanism and the ball nut / screw mechanism are not required.

FIG. 1 is a cross-sectional view showing an example in which the workpiece clamping device according to Embodiment 1 of the present invention is applied to a piston processing machine. FIG. 2A is a partially cutaway front view of an engine piston as an example of a workpiece. FIG. 2B is a side view of the same. FIG. 3 is a characteristic diagram showing the relationship between the servo motor current and the clamping force output by the transmission. FIG. 4 is a characteristic diagram showing the relationship between the command clamping force and the clamper clamping force. FIG. 5 is an explanatory diagram of the clamping operation. FIG. 6 is a diagram showing a clamp command program format. FIG. 7 is a diagram showing a clamp skip command program format. FIG. 8 is a diagram showing an example of the NC main program. FIG. 9 is a diagram illustrating an example of the G200 macro program.

Explanation of symbols

1 Piston (work)
2 Rotating main shaft 3 Vertical axis 10 Clamp head 11 Support shaft 12 Center pin 13 Spring 14 Clamper 15 Spring seat 16 Clamp spring 20 Transmission device 21 Clamp slider 22 Bearing 23 Hollow shaft 24 Case 25 Ball nut 26 Bearing 27 Ball screw 28 Power transmission mechanism 30 Servo motor 40 NC device (control means)
100 Work clamping device

  Embodiments of a work clamp device according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a cross-sectional view showing an example in which the workpiece clamping device of Embodiment 1 is applied to a piston processing machine, FIG. 2A is a partially broken front view of an engine piston as an example of a workpiece, and FIG. FIG.

  For processing of the piston 1 as a workpiece by the piston processing machine, rough processing of the ring groove 1a, same finishing, rough processing of the pin hole 1b, same finishing, outer peripheral rough finishing turning of the skirt 1c, outer peripheral finishing turning, etc. There is. The piston 1 is made of an aluminum alloy for weight reduction, and the skirt portion 1c and the like are thinned to the limit and have low rigidity. When such a piston 1 is processed, the force applied to the piston 1 varies greatly depending on the processing site and the processing type.

  For example, at the time of rough machining of the pin hole 1b, a large cutting force is applied to the workpiece, so that it is necessary to clamp the workpiece with a large force. On the other hand, when turning the outer peripheral finish of the skirt portion 1c, in order to process the thin portion with high accuracy, it is necessary to reduce the clamping force so that the skirt portion 1c having low rigidity is not distorted and to perform processing with a light cutting force. Thus, in the processing of the piston 1, it is necessary to appropriately change so as to minimize the clamping force according to the processing site and the processing type.

  With reference to FIG. 1, the structure of the workpiece clamp apparatus 100 applied to the piston processing machine is demonstrated. The piston 1 as a workpiece is placed on a rotation main shaft 2 that rotates about a vertical axis 3 of a piston processing machine (not shown) with a clamp reference surface 1d placed thereon. The work clamp device 100 includes a clamp head 10 that clamps the piston 1 to the rotary spindle 2 of the processing machine, a servo motor 30 that drives the clamp head 10 to control the clamping force, and an NC device 40 that controls the servo motor 30. A transmission device 20 is connected to the clamp head 10 to hold it and transmit the driving force of the servo motor 30 to the clamp head 10. The servo motor 30 and the NC device 40 are used for a normal NC control processing machine.

  The clamp head 10 includes a support shaft 11 connected to the transmission device 20 and held on the clamp shaft 3, a center pin 12 slidably inserted into a hole at the tip of the support shaft 11, and a spring 13 having a small spring force. And is connected to the transmission device 20 by being slidably fitted to the tip of the support shaft 11, and slides between the circular cap-shaped clamper 14 held by the flange 11 a and the intermediate portion of the support shaft 11. A disc-shaped spring seat 15 having a boss portion 15 a that can be fitted, and a clamp spring 16 that is loosely fitted to the boss portion 15 a and is sandwiched between the clamper 14 and the spring seat 15 and connected to the transmission device 20. It is made up. The clamp spring 16 is composed of a compression coil spring that generates a reaction force proportional to the amount of compressive strain deformation.

  The circular cap-shaped clamper 14 clamps the piston 1 between the outer peripheral edge portion 14 a against the crown surface 1 e of the piston 1 and the rotation main shaft 2. The clamping force is applied between the crown surface 1e and the clamp reference surface 1d. When the piston 1 is clamped by the clamper 14, the center pin 12 is first inserted into a reference hole 1f provided in advance in the center of the crown of the piston 1 to guide the clamp position of the clamper 14. When the spring seat 15 is pressed in a state where the clamper 14 clamps the piston 1, the clamp spring 16 is bent and deformed, and a variable low clamping force is applied to the clamper 14 according to the amount of bending deformation.

  The transmission device 20 is connected to the rear end of the support shaft 11 and holds the clamp slider 21, the hollow shaft 23 that rotatably holds the clamp slider 21 around the clamp shaft 3 via bearings 22 and 22, A cylindrical case 24 that holds the hollow shaft 23 slidably up and down by the slide portion 24a, a ball nut 25 attached to the rear end of the hollow shaft 23, and bearings 26 and 26 at the rear end of the case 24. A ball screw 27 that is rotatably held around the clamp shaft 3 and connected to the ball nut 25, and a power transmission mechanism 28 that connects the ball screw 27 and the servo motor 30 to transmit the rotation of the servo motor 30 to the ball screw 27. It consists of. The power transmission mechanism 28 may employ a belt transmission mechanism or a gear transmission mechanism.

  With the clamper 14 in contact with the flange portion 11a of the support shaft 11, the clamp spring 16 having a strain deformation of 0, one end contacting the clamper 14, and the other end contacting the spring seat 15, the clamp slider 21 The position is adjusted so that the front end surface is in contact with the back surface of the spring seat 15, and the rear end of the support shaft 11 is connected to the clamp slider 21. That is, no gap in the direction of the clamp shaft 3 is provided between the clamper 14, the coil spring 16, the spring seat 15, and the clamp slider 21. Accordingly, after the clamp slider 21 is lowered and the clamper 14 hits the piston 1, if the clamp slider 21 is lowered even a little, the clamp spring 16 is immediately compressed and a variable low clamping force is applied to the clamper 14.

  Next, the operation and operation characteristics of the above-described work clamping device will be described. The hollow shaft 23 is connected to the clamp head 10 via the clamp slider 21 and clamps the piston 1 rotating around the clamp shaft 3 via the clamp head 10, so that the rotational shake of the clamp head 10 and the piston 1 does not occur. As described above, the case 24 is held by the slide portion 24a with high rigidity and high accuracy. Therefore, there is almost no fitting gap between the slide portion 24a and the hollow shaft 23, and a relatively large frictional force is generated when both slide.

  FIG. 3 is a characteristic diagram showing the relationship between the servo motor current and the clamping force output from the transmission device 20, and FIG. 4 is a characteristic diagram showing the relationship between the command clamping force of the NC device and the clamping force of the clamper 14. The actual measurement characteristic indicated by the solid line in FIG. 3 indicates the relationship between the servo motor current when the hollow shaft 23 is slid downward and the clamping force (effective clamping force) output by the transmission device 20. The servo motor current value indicates a percentage (%) value of the rated current of the servo motor 30. When the current value is from 0% to around 20%, an effective clamping force is not generated due to the frictional force between the slide portion 24a and the hollow shaft 23, and when the current value is around 20% to about 30%, nonlinear characteristics are obtained. .

  For this reason, it is almost impossible to control the clamping force with high accuracy at a current value of 30% or less. When the current value is 30% or more, the current value and the clamping force are in a proportional relationship. In this region, if the current value corresponding to the frictional force is corrected (added), as shown by the broken line in FIG. A proportional characteristic without offset of the clamping force can be obtained. Therefore, the clamping force of 120 kg or more can be controlled with high accuracy by the current control of the servo motor 30. At this time, there is no need to feedback control the clamping force using a force sensor or the like.

The relationship between the motor current limit value _IL and the clamping force F is expressed by the following equation.
I _L = p / (2πK _T ) × (F + F _F ) (1)
here,
p: Lead of the ball screw 27 (cm)
K _T : Torque constant of the servo motor 30 (kg · cm / A)
F _F : Friction force of work clamping device 100 (kg)

Further, when replacing the limit value I _L of the motor current in percentage I _LPT motor rated current I _S,
I _LPT = p / (2πK _T ) × (F + F _F ) / I _S × 100
= K _LP x F + I _LC (%) (2)
It becomes. here,
k _LP = p / (2πK _T ) / I _s × 100 (% / kg) (3)
Is a constant for converting the clamping force into a motor current value (expressed as a percentage of the rated current), and I _LC is a motor current value corresponding to the frictional force expressed as a percentage of the rated current. Calculate or measure each.

  In the following description, unless otherwise specified, the current value expressed in% relative to the rated current of the servo motor is simply referred to as “current value”.

Here, one threshold value, for example, 130 kg, is set in the vicinity of the lower limit value 120 kg of the clamping force in a region where the clamping force and the current value are in a proportional relationship. When the command clamping force F commanded by the NC device 40 exceeds this threshold, the current limit value I _LPT to be commanded is calculated by the equation (2), and the current of the servo motor 30 is limited, The commanded clamping force can be generated. Since the current control area of the servo motor 30 is thus an area where the current value of the servo motor 30 and the clamping force by the transmission device 20 are proportional, the relationship between the current value of the servo motor 30 and the clamping force is a linear function Therefore, the servo motor 30 can be easily controlled.

  Next, a description will be given of the clamping force characteristics due to the action of the clamp head 10 provided to obtain a highly accurate variable clamping force of 130 kg or less. When the clamping force of the clamper 14 is controlled by controlling the amount of deformation of the clamp spring 16, the smaller the spring constant of the clamp spring 16, the higher the precision control becomes possible. In order to obtain a clamping force, the amount of bending deformation must be increased, so an appropriate spring constant is selected in consideration of the mechanical structure. In the present embodiment, the spring constant k is 10 kg / mm, and the effective deflection amount is 14 mm. Accordingly, the maximum clamping force due to the bending deformation of the clamp spring 16 is 140 kg.

The bending deformation amount of the clamp spring 16 is controlled by operating the servo motor 30 and controlling the position of the clamp slider 21 that presses the spring seat 15 with respect to the piston 1. Based on the position where the lower surface of the outer peripheral edge portion 14a of the clamper 14 is in contact with the crown surface 1e of the piston 1, the amount of bending deformation of the clamp spring 16 is 0, and the lower surface of the clamp slider 21 is in contact with the back surface of the spring seat 15. If the clamp slider 21 is moved Lmm downward,
F = k x L (kg) ... (4)
The clamping force can be obtained. Therefore,
L = C _M × F (mm) (5)
Thus, the bending deformation amount L of the clamp spring 16 corresponding to the clamp force F can be obtained. Here, C _M = 1 / k (mm / kg) is the compliance of the clamp spring 16.

  That is, when the commanded clamping force F is equal to or less than the threshold value (130 kg), the bending deformation amount L of the clamp spring 16 is calculated by the equation (5), and the clamp slider 21 is moved downward by L mm and positioned. The commanded clamping force can be obtained. In the NC control of the servo motor 30, position control in micrometer units is possible, a high resolution of the clamping force can be obtained, and the clamp spring 16 is composed of a compression coil spring having a simple structure. Highly accurate linearity can be obtained.

  In the present embodiment, the clamping force by the clamp spring 16 can be controlled up to 140 kg (when the clamping force is 140 kg, the clamp spring 16 is completely compressed or the lower surface of the boss portion 15a of the spring seat 15 is clamped by the clamper. 14), the clamping force control by the current control of the servo motor 30 can be controlled from 120 kg, the control range of both is overlapped, and the position control and current of the servo motor 30 are separated from the threshold 130 kg. The control mode of control is switched. By overlapping, a wide range of variable clamping force can be obtained from a low clamping force to a high clamping force.

  As described above, in accordance with the command clamping force of the NC device 40, the bending deformation amount control of the clamp spring 16 by the position control of the servo motor 30 and the torque control by the current control of the servo motor 30 are switched and controlled. Thus, as shown in FIG. 4, variable clamping force characteristics over a wide range from low clamping force to high clamping force can be obtained.

  FIG. 5 is an explanatory diagram of the clamping operation of the piston 1 by the clamp head 10. When processing the piston 1, the processing portion and type of the piston 1, that is, the rough processing of the ring groove 1 a, the finishing processing, the rough processing of the pin hole 1 b, the same finishing processing, and the outer peripheral rough finishing of the skirt portion 1 c are performed. A command clamping force corresponding to turning and finishing turning is given by the NC program. In response to an NC program command, the servo motor 30 rotates at the maximum speed, the ball screw 27 is rotated via the power transmission mechanism 28, the hollow shaft 23 and the clamp slider 21 are lowered via the ball nut 25, and the clamper 14 The lower surface of the outer peripheral edge portion 14a is moved at a high speed from a predetermined clamper origin position 50 to an approach point 51 just before the crown surface 1e of the piston 1.

  Next, when the command clamping force exceeds the threshold value 130 kg, the overrun amount preset from the crown surface 1e (# 506: effective deflection deformation amount of 14 mm or more of the clamp spring 16 at a preset feed speed) The clamper 14 is lowered with the position lowered by the distance) as the control target position, the lower surface of the clamper 14 is pressed against the crown surface 1e of the piston 1, and the clamp spring 16 is further bent and compressed by 13 mm or more. In this state, it is determined by the separately provided determination means that the current of the servo motor 30 has reached the current command value obtained by the expression (2), the feed command of the servo motor 30 is stopped, and the clamping force To maintain.

  When the command clamping force is equal to or less than the threshold value 130 kg, the position of the servo motor 30 is controlled to lower the clamper 14, and the bending deformation amount L of the clamp spring 16 obtained from the equation (5) is calculated from the approach point 51 to the crown surface 1 e. The piston 1 is clamped to the rotating spindle 2 with the commanded low clamping force by feeding the distance added to the distance (# 501) and compressing the clamp spring 16 by the bending deformation amount L.

  6 is a diagram showing a clamp command program format, FIG. 7 is a diagram showing a clamp skip command program format, FIG. 8 is a diagram showing an example of an NC main program, and FIG. 9 is a G200 macro. It is a figure which shows an example of a program. With reference to these drawings, the NC control method of the servo motor 30 will be described.

First, in order to perform NC control, a clamp command program format shown in FIG. 6 and a clamp skip command program format shown in FIG. 7 are newly created and defined as follows. That is, in the clamp command program format of FIG.
G200: Preparatory word indicating a clamp command A: Command address symbol for moving the clamp 14 to the approach point 51 shown in FIG. 5 by rapid traverse (G00 command speed in the NC program). The clamper 14 is relatively separated from the piston 1 When it is in a certain place (for example, when the clamper 14 is at the origin position 50), it is used for the purpose of increasing the moving speed. In this case, “A1” is commanded. Note that this address is not designated when the clamping force is changed while the piston 1 is clamped.
Q: An address symbol representing the command clamping force, and commands “q1” in kg.
F: An address symbol representing the speed of the clamper 14 when performing clamping, and commands “f1” in mm / min units.
When “A1” is commanded, the clamper 14 is fast-forwarded to the approach point 51 shown in FIG. 5 regardless of the command speed of F.

In the clamp skip command program format of FIG.
G160: Preparatory word indicating clamp skip command A: Address symbol indicating clamp axis, “a1” is commanded in mm.
Q: An address symbol representing the skip clamp force, and “q1” commands the motor current as a percentage of the motor rated current.
F: An address symbol representing the speed of the clamper 14 when clamping, and “f1” is commanded in mm / min units.
Note that G160 is a modal G code, and is maintained until G00 or G01 commands for moving the clamp shaft are instructed.

When the clamper 14 comes into contact with the piston 1 in the process of moving the commanded distance “a1” at the command speed “f1” by the clamp skip command and reaches the motor current value commanded by “q1”, the judging means Causes a skip signal to stop the movement command and cancel the remainder of the movement command. The clamping force is maintained by the droop pulse d. If the position loop gain is Kp (1 / sec), the droop pulse d is approximately
d = f1 / (60 × Kp) + Δa (mm) (6)
It becomes the size of. Here, Δa is a distance traveled by the movement command after the skip signal is generated and before the movement command is stopped.

  After the workpiece clamping using the G160 code is completed and the machining process performed with the clamping force is completed, when the clamp shaft is driven by a movement command (G00, G01, etc.), this dwell pulse d is moved by the clamp shaft. Cancel before starting with the command, and adjust the command value to the current position (position feedback value) of the clamp shaft.

  FIG. 8 is a diagram showing an example of the NC main program. In this example, first, pin hole roughing that generates a large processing reaction force is performed, then ring groove roughing that generates a relatively large processing reaction force is performed, and then each finish processing is performed. Then, the outer periphery rough finishing turning process of the skirt part 1c is performed, and finally the outer periphery finishing turning process of the skirt part 1c is performed with the smallest clamping force. The clamping operation in this case will be described.

  Before the program operation, among the variables shown in the macro program of FIG. 9, clamp feed speed 1 (# 9), clamp feed speed 2 (# 10), workpiece crown coordinate value (# 500), approach distance ( # 501), current control and position control clamping force threshold (# 502), spring constant (# 503), force / current conversion constant (# 504), current correction value (# 505) and overrun command distance (# 506) Is input in advance.

  A new work (piston) 1 is set on the stopped rotating spindle 2, and in the machining step A of the main program shown in FIG. 8, the G200 macro program of FIG. Movement modal G code (# 4001), synchronous / asynchronous modal G code (# 4005), asynchronous feed rate F modal (# 4109), and absolute / incremental G code (# 4003) from variable addresses # 2 to # 5, respectively Remember. This storage operation is performed in order to return to the state before entering the clamping operation when the clamping operation is completed.

  In the present embodiment, since the clamping operation is performed by an absolute value command, an absolute value command G code G90 is commanded in the next block, and the clamping operation is executed asynchronously with the rotation of the rotary spindle 2, so that In addition, G98 of the asynchronous feed G code is commanded. Since the command A1 is specified in the main program of FIG. 8 and # 1 is not “empty”, it is determined as the first clamp, and the clamper 14 is separately set from the clamper origin position 50 to the approach point (# 500 + # 501). At the highest speed (NC command G00). Since the command clamping force 300 kg (# 17) exceeds the separately determined clamping force threshold 130 kg (# 502) in block N100, the process jumps to block N200 and the clamping force control by current control is selected.

  In the next block, the command clamping force (# 17) is converted into a current value (# 18). Subsequently, in the G160 code, an impact is applied to the piston 1 by setting the position below the piston crown 1e as a control target position by an overrun command distance (# 506) obtained by adding several millimeters to the effective deflection amount 14mm of the clamp spring 16. The clamper 14 is brought into contact with the crown surface 1e of the piston 1 at a clamp feed speed 1 (# 9: for example, 100 mm / min). The clamper 14 is pressed against the piston 1 until the current value determined by the expression (2) is reached, and when the current value is reached, a skip signal is issued by a separately configured determination means, and the movement command is stopped and the remaining movement command is Cancel. The clamping force is maintained by the droop pulse d.

  Subsequently, the various modal values stored in # 2 to # 5 are restored. This completes the 300 kg clamping process, and the M99 command returns the program to the beginning of the machining process A of the main program shown in FIG. 8, and the piston shown in FIG. The position of 1 pin hole 1b is positioned at the drill center of a drilling unit (not shown), and rough processing of the pin hole 1b is performed.

  After the rough machining of the pin hole 1b, the command clamping force is changed to 150 kg (# 17) in the next block N020 of the main program shown in FIG. 8, and the process proceeds to the ring groove rough machining process. Jumping to the macro program shown in FIG. 9, various modal values # 4001, # 4005, # 4109 and # 4003 are stored in # 2 to # 5, respectively, and then G90 and G98 commands are executed. In this clamp command, since the first command A is not commanded, the first IF statement of the macro program jumps to the block N100.

  That is, from the 300 kg clamp state, the next clamping operation is performed without unclamping. Since the command clamping force exceeds the threshold value 130 kg (# 502), the process jumps to block N200, the clamping force control by current control is selected, and the motor current value obtained by equation (2) for the new command clamping force The piston 1 is clamped at 150 kg by the same sequence as the above-mentioned 300 kg clamp. Subsequently, after the various modal values stored in # 2 to # 5 are used, the program returns to the top part of the machining step B of the main program shown in FIG. In response to the rotation command, the piston 1 is rotated in a state of being clamped at 150 kg, and the ring groove 1a of the piston 1 shown in FIG.

  After finishing the rough machining of the ring groove 1a, the command clamping force is reduced to 60kg in the next block N030 of the main program, the distortion of the piston 1 due to the clamping force is reduced, and the finishing of the ring groove 1a and the pin hole 1b is lightly cut. Proceed to processing steps C and D to be performed. Jumping to the macro program, various modal values # 4001, # 4005, # 4109 and # 4003 are stored in # 2 to # 5, respectively, and subsequently G90 and G98 commands are executed. Even in this clamp command, since the first command A is not commanded, the first IF statement of the macro program jumps to the block N100, and the command clamp force (# 17) is equal to or less than the threshold 130 kg (# 502). The clamping force control by is selected.

  In the next block, since the movement command G01 of the clamp shaft is specified, as described in the specification of the G160 code, the droop pulse generated in the 150 kg clamp using the G160 code in the previous step is canceled here. Match the command value with the current position (position feedback value) of the clamp shaft. After the droop pulse cancellation, the position below the crown surface 1e coordinate value (# 500) of the piston 1 by the distortion deformation amount L (# 503 × # 17) of the clamp spring 16 calculated from the equation (5) Positioning is performed at a clamp feed speed f2 (# 10: for example, 50 mm / min).

  Thereby, the piston 1 is clamped with a force of 60 kg. Here, the G160 modal is canceled by the G1 code. Subsequently, the various modal values stored in # 2 to # 5 are restored. As a result, the clamping process of 60 kg is completed, the program returns to the top part of the machining process C shown in FIG. 8 by the M99 command, and the piston 1 is rotated in a state of being clamped by 60 kg by the spindle command to be separately commanded. One ring groove 1a is finished.

  Next, the process proceeds to the machining step D, and the position of the pin hole 1b of the piston 1 is positioned at the center of the drill of the drilling unit (not shown) by the spindle positioning command that is separately commanded to finish the pin hole 1b.

  After finishing the ring groove 1a and the pin hole 1b, the command clamping force (# 17) is changed to 90 kg in the next block N040 of the main program, and the process proceeds to the rough machining step of the skirt portion 1c of the piston 1. Jump to the macro program, store various modal values # 4001, # 4005, # 4109 and # 4003 in # 2 to # 5, respectively, and then execute G90 and G98 commands. Even in this clamp command, since the first command A is not commanded, the first IF statement of the macro program jumps to the block N100, and the command clamp force (# 17) is equal to or less than the threshold value (# 502). Clamping force control by control is selected.

  In this case, since the G160 modal is canceled at the time of clamping by the position control in the previous process, the droop pulse cancellation is not performed. By the next G01 command, the piston 1 is clamped at 90 kg by the same sequence as the 60 kg clamp described above. Subsequently, based on the various modal values stored in # 2 to # 5, the program returns to the top part of the machining step E of the main program by the M99 command, and the piston 1 is moved by the spindle rotation command separately commanded. It is rotated in a state clamped at 90 kg, and the profile of the skirt portion 1c is roughly processed with a tool (not shown).

  After the rough machining of the skirt portion 1c is completed, the command clamping force (# 17) is lowered to 30 kg in the next block N050 of the main program, and the process proceeds to finishing the skirt portion 1c, which is the thin portion of the piston 1. Jump to the macro program, store various modal values # 4001, # 4005, # 4109 and # 4003 in # 2 to # 5, respectively, and then execute G90 and G98 commands. Even in this clamping command, since the first command A is not commanded, the first IF statement of the macro program jumps to the block N100, and the command clamping force (# 17) is less than the threshold value (# 502). The piston 1 is clamped to 30 kg, which minimizes the distortion of the skirt portion 1c and withstands light cutting of finishing, by the same sequence as the 90 kg clamp.

  Subsequently, based on the various modal values stored in # 2 to # 5, the program returns to the top part of the machining process F of the main program by the M99 command, and the piston 1 is moved by the spindle rotation command separately commanded. It is rotated in a state of being clamped at 30 kg, and finish processing of the profile of the skirt portion 1c is performed using a tool (not shown). After the machining is completed, the spindle rotation is stopped by a spindle stop command that is separately commanded, and the clamper 14 is returned to the origin position by fast-forwarding by a clamp axis origin return command of block N070, and a series of steps is completed.

Embodiment 2. FIG.
In the first embodiment, the rotary servo motor 30 and the ball nut / screw mechanism including the ball nut 25 and the ball screw 27 are used, but a linear servo motor may be used instead. This eliminates the need for a ball nut / screw mechanism. Moreover, although Embodiment 1 is a workpiece clamping device of a processing machine in which the workpiece 1 rotates around the clamp shaft 3, the workpiece clamping device of the present invention can also be applied to a processing machine in which the workpiece does not rotate. Further, a control device other than the NC device may be used as the servo motor control device. Moreover, although the clamp axis | shaft 3 is made into the vertical axis | shaft, it is good also as a horizontal axis.

  As described above, the work clamping device according to the present invention is useful for a processing machine that processes a work having low rigidity, and is particularly suitable for a processing machine that processes an engine piston or the like.

Claims (7)

A clamper for clamping the workpiece to the processing machine;
A clamp spring which can impart variable low clamping force to the clamper according to the flexural deformation amount,
Via said transmission is connected to the clamping spring and the damper to deform the deflection the clamping spring, and a servo motor capable impart variable Hendaka clamping force to the clamper,
When the clamping of the workpiece at a predetermined threshold or lower clamping force is commanded by the machining program, the pre-Symbol lower clamping said clamper by controlling the flexural deformation amount of said clamping spring by position control of the servo motor and applying a force, when the clamping of the workpiece in the high clamping force of more than the threshold value is commanded by the machining program, and a control means for applying a pre-Symbol high clamping force the servo motor current control to the clamper ,
Work clamp device with   The workpiece clamping device according to claim 1, wherein the control unit is an NC device that numerically controls the processing machine.   2. The work clamping device according to claim 1, wherein the current control region of the servo motor is a region where a current value of the servo motor and a clamping force output from the transmission device are proportional to each other. 2. The work clamp according to claim 1, wherein a controllable range of the clamping force by the crank spring and a controllable range of the clamping force by current control of the servo motor overlap in the vicinity of the threshold value. apparatus.   2. The work clamping device according to claim 1, wherein the transmission device has a ball nut and screw mechanism, and converts a rotational force of the servo motor into a clamping force of the clamper.   The work clamping apparatus according to claim 1, wherein the transmission device holds the clamper so as to be rotatable around a rotation axis of the work.   The work clamp device according to claim 1, wherein the servo motor is a linear servo motor.

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