JPH04289006A - Control method for gripping force of chuck - Google Patents

Abstract

PURPOSE:To always control the actual gripping force of a chuck to be optimum force by continuously changing the hydraulic pressure to operate chuck claws according to variation of rotating speed of a main spindle. CONSTITUTION:Relative characteristic between the gripping force of chuck claws 14 and the control signal of a pressure adjusting means, and relative characteristic between the centrifugal force applied on the chuck claws 13 and the rotating speed of a main spindle 11, are searched, from these characteristics, relation between the rotating speed of the main spindle 11 and the control signal of the pressure adjusting means 23 for obtaining actual gripping force suitable for machining is obtained and instituted in a control part 30. When the rotating speed of the main spindle 11 is varied, the control signal based on the relation between the rotating speed of the main spindle and the control signal is output to the pressure adjusting means 23 to change the gripping force of the chuck claws 11, and hence actual chuck gripping force is continuously controlled to be in optimum condition.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the gripping force of a chuck in a lathe, turning center, or the like.

0002

[Prior art] In lathes, turning centers, etc.,
Chucks are used to grip and rotate workpieces. With this chuck, when the rotation speed of the spindle increases,
The centrifugal force acting on the chuck jaws increases accordingly, and the force for gripping the workpiece decreases. As a result, the workpiece may come off the chuck during turning and fly out, injuring the worker or
It may damage the machine.

In order to solve this problem, the gripping force that is reduced due to centrifugal force when the spindle rotates at the highest speed is determined in advance, and this gripping force is added to the actually required gripping force to grip the workpiece. is gripped and turning is performed.

However, if a gripping force greater than the necessary gripping force is applied to the workpiece at the stage of attaching the workpiece to the chuck, problems such as deformation of the workpiece and reduction in machining accuracy occur.

Therefore, in recent years, the entire range of spindle rotation speed during turning is divided into two regions, and a pressure reducing valve is installed to generate hydraulic pressure for the chuck jaws corresponding to this divided region. A method of adjusting the gripping force in two stages has been proposed and has been implemented in some cases.

[0006]

[Problems to be Solved by the Invention] However, in the above-mentioned conventional method, since the hydraulic fluid pressure of the chuck jaws is the same from a certain rotation speed to another rotation speed, it is difficult to solve the problem that Sometimes there is still a problem that the gripping force is too strong. That is, it has not been possible to always provide the chuck jaws with an optimal gripping force depending on the rotational speed of the main shaft.

[0007] In recent years, as the workpieces to be turned have become more diverse, the opportunities for turning thin-walled workpieces or workpieces made of brittle materials have increased. When a workpiece is to be turned, the above-described conventional methods cannot sufficiently solve the problem of deformation or damage of the workpiece.

The present invention has been made in view of the above-mentioned problems.The present invention continuously changes the hydraulic pressure for operating the chuck jaws according to changes in the rotation speed of the main spindle, and The object of the present invention is to provide a chuck gripping force control method that allows the chuck to always have an optimal gripping force continuously.

[0009]

[Means for Solving the Problems] In order to achieve the above object, a chuck jaw that moves in the radial direction of the chuck body attached to the main shaft to grip a workpiece, and an operation that causes the chuck jaw to move in the radial direction. The chuck gripping force control method of the present invention, which is carried out using a device equipped with an oil pressure adjustment means and a control unit that sends a control signal to the pressure adjustment means, is based on the method of controlling the gripping force of the chuck jaws in the above device in advance. - The control signal characteristics of the pressure adjustment means and the centrifugal force acting on the chuck jaws - The spindle rotation speed characteristics are determined, and from these characteristics, the spindle rotation speed - Pressure adjustment means control signal is used to obtain the actual gripping force suitable for machining. The relationship is determined and set in the control unit, and when the rotational speed of the spindle changes, a control signal based on the relationship between the rotational speed of the spindle and the control signal is output to the pressure adjustment means to change the gripping force of the chuck jaws. , the actual gripping force is controlled. Preferably, a pressure control valve operated by a control current from a control section is used as the pressure adjustment means.

0010

[Operation] According to the above control method, when the rotational speed of the spindle increases and the gripping force of the chuck decreases due to centrifugal force, the gripping force is strengthened to compensate for this decreased gripping force, and the work is always performed with a predetermined gripping force. grasp something.

[0011]

[Embodiment] An embodiment of the present invention will be described below. First, an example of an apparatus for implementing this control method will be described with reference to FIG. The device shown in FIG.
It consists of a hydraulic device 20 that operates this chuck device 10, and a control section 30 that sends a control signal to the pressure adjustment means of this hydraulic device 20.

The chuck device 10 includes a chuck body 12 attached to the tip of a main shaft 11, and chuck claws 1 that move in a radial direction on the surface of the chuck body 12.
3, a wedge plunger 14 that transmits movement in the main axis direction of the drawbar 15 to the chuck claw 13, and a drawbar 1.
5 and a rotary hydraulic cylinder 16 that provides movement in the direction of the spindle axis. The hydraulic system 20 includes a hydraulic pump 22 that sucks hydraulic oil from a tank 21, an operation control valve as a pressure adjustment means 23 that adjusts the pressure of the hydraulic oil, and a switching valve 24 that switches the supply path of the hydraulic oil. ing. Note that the pressure adjustment means 23 may not be a pressure adjustment valve, but may be one that directly controls the rotation speed of the hydraulic motor 22 or provides a relief valve and adjusts the amount of oil returned from the relief valve. .

Further, although a numerical control device is normally used as the control section 30, it goes without saying that other control devices may be used.

[0014] A chuck gripping force control method implemented using a device having such a configuration is carried out in the following steps. (1) From the control unit 30 to the pressure adjustment means 23 of the hydraulic system 20
The relationship (characteristics) between the control signal (current) A sent to the rotary hydraulic cylinder 16 and the hydraulic pressure P supplied to the rotary hydraulic cylinder 16 is determined. In this case, the hydraulic pressure P and the control signal A are in a proportional relationship.

(2) Find the relationship (characteristics) between the gripping force F of the chuck jaws 13 in the chuck device 10 and the hydraulic pressure P supplied from the hydraulic device 20 to the rotary hydraulic cylinder 16. In this case, the gripping force F of the chuck jaws and the hydraulic pressure P are in a proportional relationship. Therefore, the gripping force F of the chuck jaws 13 and the control signal (current) A from the control unit 30 are F=C1
A
The relationship is as follows (where C1 is a proportional constant between the control current and the gripping force) (see FIG. 2).

(3) Find the relationship (characteristic) between the rotational speed N of the main shaft 11 and the centrifugal force f generated by the rotation of the main shaft 11. In this case, the centrifugal force f is proportional to the square of the spindle rotation speed N, so f=C2 N2
(here, C2 is the proportionality constant of the spindle rotation speed and centrifugal force).

(4) The above-mentioned gripping force F-control signal (current)
A relationship between spindle rotation speed N and control signal (current) A is determined from the spindle rotation speed N and gripping force characteristics. The relationship between spindle rotation speed N and control signal A is as follows: When the rotation speed increases and the gripping force decreases, how much control signal should be output in order to maintain the actual gripping force suitable for machining? It shows the modification characteristics that indicate whether it is good or not. Here, the modification characteristic is specifically determined as follows. That is, if the gripping force at the time of stopping is F0, then A0 = F0 /C1 from equation (2), and F0 at the time of stopping can be obtained from the current value of A0. (Here, A0 is the current value to obtain the initial setting gripping force.) Also, in order to keep the gripping force F reduced by the centrifugal force f constant, a gripping force f' commensurate with the centrifugal force f is supplemented and F0 + f 'It is necessary to do so. This gripping force f'
is obtained when control current A1 is added, then the relationship between the two is f'=C1 A1, that is, A1=f'/C1. Therefore, the control current A output from the control section 30 in order to keep the actual gripping force of the chuck jaws 13 constant is A=A0+A1=A0+f'/C1. Here, f' corresponds to f, so f=C2 N2 in formula ■
Therefore, A=A0 + (C1 /C2)N2 (2). As a result, by substituting the spindle rotation speed into equation (2), the corrected characteristic (the relationship between the spindle rotation speed N and the control signal A) can be obtained.

(5) Input the above modified characteristics to the control section. If the control unit is a numerical control device, create a correspondence between the rotation speed and the control signal in the program based on the correction characteristics described above, so that the control signal output command is issued at the same time as the spindle rotation speed command. . In addition, if the control unit is other than a numerical control device, the rotational speed of the spindle is detected by any means, and control is performed to output a control signal based on the above correction according to the detected spindle rotational speed. Let's do it.

(6) Operate the machine tool and control the chuck jaw gripping force by changing the output of the control signal according to the rotational speed of the main spindle.

As described above, according to the above control method, even if the rotation speed of the main shaft changes, the actual gripping force by the chuck claws 13 is always (continuously) kept constant.

[0021]Although not shown, it is possible to easily increase or decrease the gripping force to a certain degree, or to change the gripping force with an arbitrary curve or angle of inclination, by adjusting the correction characteristics. can.

[0022] Thereby, workpieces made of brittle materials or thin workpieces can always be gripped with optimum gripping force.

[0023]

[Effects of the Invention] As described above, according to the chuck gripping force control method of the present invention, the actual gripping force on the chuck can be continuously controlled to the optimum force in response to changes in the rotational speed of the main shaft. Can be done.

[Brief explanation of the drawing]

FIG. 1 shows a specific example of a chuck device for implementing the control method of the present invention.

FIG. 2 is a diagram showing the relationship between control signal A and gripping force F.

FIG. 3 is a diagram showing the relationship between the spindle rotation speed N and the centrifugal force acting on the chuck jaws.

[Figure 4] Relationship between spindle rotation speed N and control signal A (correction characteristics)
FIG.

[Explanation of symbols]

10...Chuck device 11...Main shaft 13...Chuck jaw 16...Rotating hydraulic cylinder 20...Hydraulic system 23...Pressure adjustment means 30...Control unit

Claims (2)

[Claims] 1. A chuck jaw that moves in the radial direction of a chuck body attached to a main shaft to grip a workpiece, a pressure adjustment means for hydraulic oil that causes the chuck jaw to move in the radial direction, and a pressure adjustment means for the hydraulic oil. Using a device equipped with a control unit that sends control signals to the chuck jaws, in advance, the gripping force of the chuck jaws-control signal characteristics of the pressure adjustment means and the centrifugal force acting on the chuck jaws-spindle rotation speed characteristics are determined in advance. From these characteristics, the relationship between the spindle rotation speed and the pressure adjustment means control signal to obtain an actual gripping force suitable for machining is determined and set in the control section, and when the spindle rotation speed changes, the above spindle rotation speed - A method for controlling the gripping force of a chuck, characterized in that the gripping force of the chuck jaws is changed by outputting a control signal based on the relationship between the control signals to a pressure adjusting means, and the actual gripping force is maintained at a predetermined pressure. 2. The chuck gripping force control method according to claim 1, wherein the pressure adjusting means is a pressure control valve and the control signal is a control current.