Electricity: motive power systems – Positional servo systems – Digital or numerical systems
Patent
1988-06-28
1990-03-27
Shoop, Jr., William M.
Electricity: motive power systems
Positional servo systems
Digital or numerical systems
318632, 318571, 36447429, 3644743, G05B 1924
Patent
active
049123858
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a tapping control apparatus for controlling tapping operation of a numerically controlled machine tool, and more particularly to a tapping control apparatus for effecting high-speed, stable tapping operation by automatically determining an acceleration/deceleration constant for the rotational speed of the spindle of a machine tool.
2. Description of the Related Art
Demands for higher-speed machining operation require the tapping operation to be also carried out at higher speed. For tapping metals such as aluminum, it is necessary that the rotational speed of a spindle and the speed of feeding movement along a Z-axis accurately be in synchronism with each other. To meet this requirement, the conventional tapping process employing a floating tapper is replaced with a rigid tapping process which uses a rigid tapper and keeps the rotation of a spindle and the feeding movement along a Z-axis in synchronism through pulse distribution for tapping operation.
The applicant has filed two applications, Japanese Patent Applications Nos. 61-175868 and 61-175869 directed to the rigid tapping process. However, in the tapping disclosed in these applications only one time constant is used for acceleration/deceleration control of the rotation of the spindle and the feeding movement along the Z-axis, with the result that the problem of overshooting or the like is brought about when high-speed tapping operation is performed. If a large time constant is selected, the time required for machining is increased at low-speed operation.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a tapping control apparatus for effecting high-speed, stable tapping operation by automatically determining an acceleration/deceleration time constant for the rotational speed of the spindle of a machine tool.
In order to solve the aforesaid problems, there is provided in accordance with the present invention a tapping control apparatus for effecting tapping operation by synchronizing the rotation of a spindle and the feeding movement along a Z-axis through pulse distribution, said tapping control apparatus comprising: to a speed command for the spindle; time constant for effecting tapping operation.
Since the time constant is selected according to the command speed for the spindle, when the commanded speed of the spindle is high, the time constant is large, thereby preventing overshooting. When the commanded speed of the spindle is low, the time constant is small for high-speed tapping operation.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of an embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
An embodiment of the present invention will hereinafter be described in specific detail with reference to the drawings.
FIG. 1 is a block diagram of an embodiment according to the present invention. Denoted in FIG. 1 at 1 is a pulse distribution circuit for issuing output pulses Ps for rotating a spindle and output pulses Pz for controlling feeding movement along a Z-axis, in response to commands P (the pitch of screw threads to be formed) and S (the rotational speed of the spindle). The pulses Ps, Pz are calculated in order to synchronize the rotation of the spindle and the movement along the Z-axis for tapping operation in conformity with the lead of screw threads. Specifically, assuming that the speed of Ps is converted to the rotational speed of the spindle S (rpm), the speed of Pz is indicated as Vz (mm/min.), and the lead of screw threads is indicated by P (mm), the pulses are distributed to meet the equation:
Designated at 2 is a time constant determining means which has a time constant table 3 having time constants T corresponding to spindle rotational speeds S. When a spindle rotational speed S is commanded, a time constant T which corresponds to the commanded spingle speed is selected from the table 2. For example, time constants can be selected from the time constant table according to
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Kawamura Hideaki
Sasaki Takao
Fanuc Ltd.
Ip Paul
Shoop Jr. William M.
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