Electricity: motive power systems – Positional servo systems – Program- or pattern-controlled systems
Patent
1991-04-15
1993-04-06
Ip, Paul
Electricity: motive power systems
Positional servo systems
Program- or pattern-controlled systems
318560, 318610, G05B 19407, G05B 1300
Patent
active
052006808
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a feed speed control method for a numerical control device, and more particularly, to a feed speed control method for a numerical control device by which a correct feed speed is automatically derived.
2. Background of the Related Art
In numerical control devices (CNC), a workpiece is machined to a desired shape by moving a tool at a commanded speed along a machining path instructed by a machining program.
To efficiently effect the machining operation at a high precision, the machining speed for each block must be determined by taking into account the shape to be machined, the maximum torque of a motor, the degree of shock to a machine, and the like. In particular, when a machining program is prepared, an exact stop command is inserted at, for example, a corner portion of an instructed path for a workpiece at which the cutting direction is greatly changed.
To create such a program, however, a relatively high level of skill, and a great deal of labor are required. Namely, a programmer must determine an optimum machining speed (feed speed) by taking the machine tool, the shape of a workpiece, and the like into consideration.
Further, if the machining speed is set to a value which is unnecessarily low in comparison with the high performance machining speed of the machine tool, when the program is prepared, a problem arises in that the performance of the machine tool cannot be fully utilized.
The inventors of this invention proposed, in Japanese Patent Application No. 63-224932, a method of deriving a feed speed which causes a speed variation of each axis at a corner portion to be smaller than a maximum permissible speed difference derived from a predetermined maximum permissible torque, for the control of the speed.
Further, as a related application, a method of controlling the acceleration/deceleration was proposed in Japanese Patent Application No. 1-15595, which method can reduce a load caused by a repetition of an acceleration/deceleration of a servomotor when blocks continue for infinitesimal distribution distances.
The method proposed in Japanese Patent Application No. 63-224932 is effective for a corner portion with a large angular variation, but a correct feed speed cannot be derived where individual speed variations are small but an actual acceleration for each axis is large, because the variations occur successively in a short time; for example, in the case of a free curve approximately represented by straight lines. In this case, the mechanical shock may be disadvantageously increased and an excessively large load may be applied to a servomotor.
SUMMARY OF THE INVENTION
This invention has been made in view of the above circumstances, and an object thereof is to provide a feed speed control method for a numerical control device by which shock to the machine can be reduced. Further, another object of this invention is to provide a feed speed control method for a numerical control device by which the occurrence of shock to a machine or an excessively large load on a servomotor can be prevented during the execution of a machining program containing successive infinitesimal distribution distances.
In this invention, to solve the above problem, there is provided a feed speed control method for a numerical control device by which a feed speed of a tool traveling along an instructed machining path is controlled in accordance with a machining program, wherein an acceleration of each axis is derived based on a variation in the speeds of adjacent blocks for each axis, and the distribution distances and speeds of the adjacent blocks. In addition, a first ratio of a permissible acceleration to the acceleration of each axis is derived when the acceleration of each axis is larger than a permissible acceleration/deceleration, the smallest of the first ratios of the respective axes is selected, and the command speed is multiplied by the square root of the smallest first ratio to derive an actual or approximated feed speed.
An acceler
REFERENCES:
patent: 4757457 (1988-07-01), Matsumoto
patent: 5107193 (1992-04-01), Iwashita
Fujibayashi Kentaro
Otsuki Toshiaki
Saito Yasuhiro
Sasaki Takao
Fanuc Ltd.
Ip Paul
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