Electricity: motive power systems – Positional servo systems – With compensating features
Patent
1994-12-20
1996-05-14
Cabeca, John W.
Electricity: motive power systems
Positional servo systems
With compensating features
318617, 36447418, G05B 1132
Patent
active
055171001
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a servo motor control method designed to apply a certain amount of offset to the velocity command during the position loop control in order to prevent an irregular machined surface from being formed when the rotation of the servo motor is reversed in the middle of machining of a circular or arc-shaped surface while the feed shaft of a machine tool or the arm of a robot is controlled using a servo motor.
2. Description of the Prior Art
In carrying out an arc-shape cutting in a X-Y plane using a machine tool driven and controlled by an X-axis servo motor and a Y-axis servo motor, irregularity of the machined surface occurs when the machining progresses from one quadrant to the next quadrant, for example, from quadrant I (x>0, y>0) to the quadrant IV (x>0, y<0), quadrant III (x<0, y<0) and quadrant II (x>0, y<0) as shown in FIG. 8.
To describe the above-mentioned phenomenon with reference to FIG. 8, the direction of drive by the X-axis servo motor is changed from positive direction (rightward direction in FIG. 8) to negative direction (leftward direction in FIG. 8), while the direction of drive by Y-axis motor remains unchanged or continues in the negative direction (downward direction in FIG. 8). Thus, the Y-axis servo motor continues to drive at the same speed and in the same direction as the previous speed and direction. However, the X-axis servo motor has an X-axis positional deviation becoming zero, and, therefore, a torque command value becomes small. Furthermore, in the speed loop control, the inversion of the sign of an integrator is delayed. The servo motor is subjected to a frictional resistance and therefore cannot immediately reverse its rotational direction. In addition, a table has backlash of a feed screw of the table; thus, the table is also unable to start shifting immediately in the opposite direction. For the reasons described above, the table cannot follow the shift command with respect to the shift movement in the direction of X axis, and this causes protrusions to be formed on a cut surface as shown by "p" in FIG. 8.
For preventing the formation of such protrusion, Japanese Patent Application Laid-Open KOKAI 4-8451 proposes a servo motor control, in which, when reversing the sign of shift command, a certain amount of offset is added to a speed command to increase the speed of the servo motor in reverse direction of rotation, thereby preventing the formation of the protrusion.
Furthermore, as disclosed in the Japanese Patent Application LAID-OPEN KOKAI 3-228106, already proposed is a method of automatically determining the amount of such an offset value for reversing the servo motor in accordance with an integral value of the integrator in the speed loop control given immediately before the servo motor reverse its direction. According to this method, the value of an integrator whose sign is reversed simultaneously with the reversal of the sign of the shift command is used as the after-reversal target value of the integrator, and the value obtained by subtracting the integral value of the integrator in each cycle of the speed loop processing from the above target value is added to the speed command so that the amount to be added is decreased gradually.
FIG. 1 is a block diagram showing a servo motor control such as the one disclosed in the Japanese Patent Application LAID-OPEN KOKAI 4-8451, wherein a certain amount of offset for reversing the servo motor is added to the speed command in order to accelerate the speed of the servo motor in its reverse direction of rotation when the sign of shift command is reversed. In the drawing, term 1 represents a position gain Kp used in the position loop control; term 2, an integral gain K1 used in the speed loop control; term 3, an integrator in the speed loop control; and term 4, a proportional gain K2 used in the speed loop control. Furthermore, term 5 is a transfer function of a servo motor, which is expressed in the simplified form of an integr
REFERENCES:
patent: 4887015 (1984-12-01), Kuakake et al.
patent: 4951208 (1990-08-01), Etoh
patent: 5027680 (1991-07-01), Kohari et al.
patent: 5083074 (1992-01-01), Suzuki et al.
patent: 5095221 (1992-03-01), Tyler
Iwashita Yasusuke
Matsubara Shunsuke
Okita Tadashi
Cabeca John W.
Fanuc Ltd.
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