Numerical controller having function of switching position control gain during synchronous control

Abstract

A numerical controller outputs a position command corresponding to a synchronous position in consideration of a servo delay of a slave axis, to the slave axis from a real position of a master axis, in order to perform position control of the slave axis, thereby making a real position of the slave axis synchronously follow the real position of the master axis. A position control gain of the slave axis is changed based on a predetermined physical quantity during the synchronous control and a compensation value for the position command for the slave axis is varied depending on the amount of change of the position control gain of the slave axis.

Claims

1. A numerical controller that outputs a position command corresponding to a synchronous position in consideration of a servo delay of a slave axis, to the slave axis from a real position of a master axis, in order to perform position control of the slave axis, thereby making a real position of the slave axis synchronously follow the real position of the master axis, wherein a position control gain of the slave axis is changed based on a predetermined physical quantity during the synchronous control and a compensation value for the position command for the slave axis is varied depending on the amount of change of the position control gain of the slave axis.

2. The numerical controller according to claim 1, wherein the position control gain is gradually increased and the compensation value is gradually reduced correspondingly.

3. The numerical controller according to claim 2, wherein the predetermined physical quantity is data on a synchronization error, an external input signal, a time elapsed since the start of synchronization, a master axis position, a slave axis position, a master axis speed, a slave axis speed, or a servo delay of the slave axis.

4. The numerical controller according to claim 1, wherein the position control gain is gradually reduced and the compensation value is gradually increased correspondingly.

5. The numerical controller according to claim 4, wherein the predetermined physical quantity is data on a synchronization error, an external input signal, a time elapsed since the start of synchronization, a master axis position, a slave axis position, a master axis speed, a slave axis speed, or a servo delay of the slave axis.

6. The numerical controller according to claim 1, wherein the predetermined physical quantity is data on a synchronization error, an external input signal, a time elapsed since the start of synchronization, a master axis position, a slave axis position, a master axis speed, a slave axis speed, or a servo delay of the slave axis.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and other objects and features of the present invention will be obvious from the ensuing description of embodiments with reference to the accompanying drawings, in which:

(2) FIG. 1 is a diagram showing a packing machine device configured to pack a bottle into a box conveyed by a conveyor;

(3) FIG. 2 is a diagram showing a case where a synchronization error occurs in synchronization based on an expected compensation when a speed of a master axis is changed;

(4) FIG. 3 is a diagram illustrating a second embodiment of a numerical controller according to the present invention;

(5) FIG. 4 is a diagram illustrating a third embodiment of the numerical controller according to the present invention; and

(6) FIG. 5 is a flowchart showing synchronous control processing performed by the numerical controller according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(7) FIG. 1 is a diagram showing a packing machine device configured so that a bottle 4 conveyed by a second conveyor S is packed by insertion means 6 into a box 2 conveyed by a first conveyor M.

(8) In the packing machine device of FIG. 1, the first conveyor M is driven by a drive unit (not shown) different from that of the second conveyor S, which is driven by a servomotor Ms controlled by a numerical controller NC. An axis that drives the first conveyor M is assumed to be a master axis, while an axis that drives the second conveyor S is assumed to be a slave axis. The slave axis is synchronously controlled by the numerical controller NC so that it synchronizes with the master axis. The position and speed of the master axis can be detected by a position/speed detector 8 attached to the first conveyor M. Further, the position and speed of the slave axis can be detected by a position/speed detector (not shown) attached to the slave axis.

(9) The numerical controller NC comprises a processor (CPU), memories such as a ROM and a RAM, input/output circuit, communication interface, and the like. The numerical controller NC performs position feedback control in response to a feedback signal from a sensor (not shown) attached to the servomotor Ms or the second conveyor S that is driven by the servomotor Ms.

(10) In the packing machine of FIG. 1 configured so that the bottle conveyed by the second conveyor S driven by the slave axis (servomotor Ms) is packed into the box conveyed by the first conveyor M, for example, the position and speed of the first conveyor M are obtained by the sensor 8 or the like. Synchronous control of the slave axis is performed so as to align the position of the bottle conveyed by the second conveyor S with the position of the box on the first conveyor M. The packing machine can accurately pack the bottle by fetching an actual position (real position) of the first conveyor M as the position of the master axis and correctly synchronizing the position of the second conveyor S (slave axis) with the fetched position.

(11) The following is a description of some embodiments of the numerical controller having a function of switching a position control gain during synchronous control to solve problems of the present invention.

First Embodiment of Numerical Controller

(12) In a first embodiment of the numerical controller according to the present invention, position control gains individually suited for a vibration section of the master axis and an area outside the vibration section are set to switch the position control gain of the slave axis during synchronous control and change a compensation value correspondingly. By making a compensation according to the set position control gain, the numerical controller can improve tracking performance for a speed change while suppressing an influence on disturbance, thereby suppressing an increase in synchronization error. The start of the position control gain switching for the slave axis can be determined based on the synchronization error.

Second Embodiment of Numerical Controller

(13) FIG. 2 is a diagram illustrating an operation in synchronization with the movement of the master axis, starting from a state where the slave axis is stopped. In FIG. 2, the abscissa and ordinate represent time and position, respectively. Further, a full line (thick line) 10 represents the real position of the master axis, dotted line 12 represents a slave axis command position, full line (thin line) 14 represents a slave axis real position, and arrow 16 represents a servo delay. Furthermore, a square area 18 and an elliptical area 20 represent areas for a speed change and a synchronization error, respectively.

(14) As indicated by the full line (thick line) 10 that represents the master axis real position, the master axis moves at a constant speed and slows down at a flexion point in the area 18. On the other hand, the slave axis starts synchronization with a low gain in order to reduce mechanical shock attributable to sudden acceleration at the start of synchronous operation. Thus, the servo delay represented by the arrow 16 occurs between the dotted line 12 that represents the slave axis command position and the full line (thin line) 14 that represents the slave axis real position.

(15) If the speed of the master axis is changed during the synchronous control, as indicated by the square area 18 (representative of a speed change) in FIG. 2, the slave axis command position 12 of which expectation time is corrected cannot respond to the speed change of the master axis because of a long expectation time. Thus, the synchronization error 20 inevitably occurs between the slave axis real position 14 and the master axis real position 10. The larger the expected amount, the greater the synchronous error 20 is.

(16) As shown in FIG. 3, in this second embodiment, a position control gain is increased during synchronous control and a compensation based on expectation is reduced correspondingly. In this way, synchronous tracking performance can be increased to suppress the synchronization error even when the speed of the master axis is changed. In FIG. 3, an elliptical area 22 represents an area in which synchronization is smoothly started because of the low gain. Further, a circular area 24 represents an area in which the gain is increased to reduce the compensation for servo delay (i.e., to bring the command position close to the real position).

(17) According to this embodiment, the start of movement is made smooth by suppressing the position control gain of the slave axis at the start of synchronization, the position control gain is gradually increased when the synchronization error is, for example, reduced to a predetermined value or less during the synchronous control (area 24), and the compensation based on expectation is reduced correspondingly. In this way, the synchronous tracking performance for the motion of the master axis can also be increased.

Third Embodiment of Numerical Controller

(18) If an attempt is made to terminate synchronization with the position control gain remaining high while the master axis is moving, the slave axis suddenly stops, thereby causing mechanical shock.

(19) As shown in FIG. 4, in this embodiment, therefore, the position control gain is gradually reduced before the end of synchronous control, and compensation for servo delay is gradually increased correspondingly. In this way, the slave axis can be smoothly stopped even if synchronization is stopped while the master axis is moving. In FIG. 4, a circular area 26 represents an area in which the gain is reduced to increase the compensation for servo delay (i.e., to separate the command position from the real position). Further, an elliptical area 28 represents an area in which the slave axis smoothly stops because of the low gain.

Fourth Embodiment of Numerical Controller

(20) In this embodiment, the start of position control gain switching for the slave axis is determined based on any one of information including an external input signal, time elapsed since the start of synchronization, master axis position, slave axis position, master axis speed, slave axis speed, and servo delay of the slave axis, in place of the synchronization error.

(21) FIG. 5 is a flowchart showing synchronous control processing performed by the numerical controller according to the present invention. The following is a sequential description of steps.

(22) [Step sa01] It is determined whether or not to switch the position control gain. If the position control gain is to be switched (YES), the processing proceeds to Step sa02. If not (NO), the processing proceeds to Step sa04. Whether or not to switch the position control gain can be determined based on the synchronization error, external input signal, time elapsed since the start of synchronization, master axis position, slave axis position, master axis speed, slave axis speed, or servo delay of the slave axis.

(23) [Step sa02] The position control gain is changed by a predetermined amount.

(24) [Step sa03] A compensation value for the slave axis, e.g., compensation for the time delayed by the gain, is calculated based on the position control gain.

(25) [Step sa04] The synchronization command position of the slave axis is calculated in consideration of the compensation value for the slave axis, based on the real position of the master axis.

(26) [Step sa05] An output amount of movement of the slave axis is obtained by calculating the difference between the synchronization command position and the command position of the slave axis.

(27) [Step sa06] The output amount of movement obtained in Step sa05 is added to the command position of the slave axis, and the result of the addition is used as the command position of the slave axis.

(28) [Step sa07] The output amount of movement obtained in Step sa05 is output.

(29) [Step sa08] It is determined whether or not to continue the synchronous control. If the synchronous control is to be continued (YES), the processing proceeds to Step sa01. If not (NO), the processing ends. Whether or not to continue the synchronous control can be determined based on, for example, a programmed command or an external command.

(30) In the processing of the flowchart described above, clamp control or acceleration and deceleration control may be performed as required for the synchronous control of the slave axis.

(31) As described above, the numerical controller according to the present invention may have the function of switching the position control gain during synchronous control. Further, the servo delay of the slave axis is reduced by increasing the position control gain, so that the expected amount is reduced. Thus, the synchronization error is small even when the master axis speed varies. At the start of synchronization, the start of movement can be made smooth by suppressing the position control gain. After a synchronization state is stabilized, the movement of the master axis can be promptly followed to improve the synchronization performance by increasing the position control gain. When the master-slave synchronization state is stabilized, e.g., when the master axis is in a constant-speed state, the position control gain is gradually increased, while the compensation based on expectation from a synchronization command is gradually reduced.