DRIVE CONTROL SYSTEM FOR SERVO MOTORS

Abstract: In a drive control system for servo motors, an operation processing unit (11) and a servo motor (10) are arranged being physically separated from each other, and the data are ex­ changed through a data bus (14) between the operation pro­ cessing unit (11) and a main CPU (12) which performs the input data processing and sequence processing. Therefore, drive instruction for the servo motor (10) and feedback data can be transferred at high speeds without causing any particu­ lar interface unit. Moreover, the operation circuit can be sepa­ rated from the environment where the servo motor (10) is placed.

Description: This invention relates to a drive control system of a servomotor for driving a load such as a machine tool. In order to control a multiple-axis machine tool or the like with a high degree of accuracy, use is made of a servomotor driven by a command signal from a numerical control unit (hereafter referred to as an NC unit) or the like. Conventionally, servomotors of this type are driven by analog servo systems. However, with the progress that has recently been made in the technical development of computer control, various expedients dealing with the question of how to control a plurality of servomotors efficiently by a single control unit have been devised. Fig. 2 is a block diagram illustrating the general features of such a servomotor control circuit. As shown in the Figure, a main CPU 1 of microprocessor construction, which is for reading in input data and executing predetermined processing, and a plurality of shared RAMs 2, are connected to an NC unit side by a data bus B1. A servo-control CPU 3 of microprocessor construction is connected to each of the shared RAMs 2 via a bus B2 and outputs an analog signal indicative of a velocity command to each servoamplifier 4 associated with a servomotor. The servoamplifier 4 comprises a velocity control circuit 5, a current control circuit 6 and an inverter 7 and subjects a servomotor 8 to prescribed feedback control on the basis of current, position and velocity. Each shared RAM 2 is for performing an exchange of data between the main CPU 1 and the servo-control CPU 3. For example, a signal indicative of the position of the servomotor 8 is temporarily stored in the shared RAM 2 through the servo-control CPU 3, and the main CPU 1 reads out this stored value to perform display processing and the like. Further, a position command signal from the main CPU 1 is temporarily stored in the shared RAM 2 and the servo-control CPU 3 reads out this stored value and outputs a velocity command to the servoamplifier 4. An apparatus generally of this type is disclosed in GB-A-2086085. In such a digital servomotor control system the servo-control CPU and the servoamplifier are provided on the servo side, namely close to the load, e.g. a machine tool, driven by the servomotor. With the above control system, however, the environment in which the CPU is installed is undesirable for the electronic circuitry in view of vibration and the high ambient temperature. Such an environment is a cause of failure and malfunction, especially for a CPU using an IC having a high degree of integration. Further, since complex circuitry for position, current and other control functions is provided in such an environment, the performance of adjustments and maintenance is accompanied by complications and hazards. Problems are also encountered in terms of operating efficiency. Furthermore, since the main CPU and the CPU on the servo side are remote from each other, a high-speed interface device is necessary to transfer data. A problem that results is higher cost. This is illustrated, for instance, in section 9.5 on pages 371-376 of the book 'The numerical control of machine tools', W. Simon, 1973 (1970); Edward Arnold, London. Figs. 247 and 248 in that section each show an NC machine including a processor, and a remote host computer responsible for a greater or lesser proportion of the control of the machine. This arrangement needs screened multi-core leads between the host computer and the individual machines with their NC equipment. According to the invention there is provided a servo-operated machine including a servomotor, a servoamplifier for the servomotor, and a servomotor drive control system in which a drive command signal and data fed back from a servomotor are to be processed to drive and control the servomotor, the control system comprising: a main CPU for performing input data processing and sequence processing and a numerical control unit associated with the main CPU and including a servo-control CPU for controlling the servomotor and dedicated to it; characterised in that the numerical control unit is coupled to the main CPU so as to constitute a processing section and this processing section is arranged remote from the servoamplifier and connected to it by cables for exchanging current, velocity and position command and detection data. Embodiments of the present invention thus provide a servomotor drive control system in which the servocontrol CPU is provided on the NC unit side and is connected to the main CPU by the main CPU data bus, thereby greatly reducing the control circuitry provided on the servo side and enabling data to be transferred at high speed. Since the processing section and the servomotor are arranged remote from each other it is possible to transfer servomotor drive commands and feedback data between the processing section and the servomotor at high speed without requiring a special interface device. Further, the major portion of such complex control circuitry as the servo-control CPU and the main CPU that performs the input data processing and sequence processing is arranged on the NC unit side, and only the minimum number of circuit elements need be provided on the load side. As a result, operator maintenance and control operations are simplified, and it is possible to prevent control apparatus failure and malfunction caused by such environmental conditions as vibration and heat. Brief Description of the Drawings Fig. 1 is a block diagram illustrating an embodiment of the present invention, and Fig. 2 is a block diagram illustrating an example of a conventional servomotor drive control system. An embodiment of the present invention will now be described in detail with reference to the drawings. Fig. 1 is a block diagram of an embodiment of the present invention, in which one (or a plurality of) servo-control CPU 11 for controlling the current, velocity and position of a servomotor 10 is arranged in an NC unit along with a main CPU 12 and a shared RAM 13, and is connected to the main CPU 12 by a data bus 14. An example of an application in which a plurality of servo-control CPUs 11 are provided is one where a servo circuit for driving various articulations of a robot having plural degrees of freedom is to be controlled. The servo-control CPU 11 provides a servoamplifier 15 with a PWM command in the form of a digital signal. Accordingly, an inverter 16 in the servoamplifier 15 is constructed to include only final stage driver elements such as power transistors. In other words, almost all complicated control circuit elements are disposed on the NC side, and only the minimum number of circuit elements such as the power transistors are disposed in a control panel on the load side. Numeral 17 denotes a cable for sending digital signals such as the PWM command from the NC unit side to the servoamplifier 15. Numerals 18a, 18b denote cables for feeding back current and position data, respectively, from the servomotor 10 to the NC unit side. With a servomotor control system so constructed, the main CPU 12, which reads in input data and performs predetermined sequence control, applies a drive command for each servomotor 10 to the servo-control CPU via the shared RAM 13. The servo-control CPU sends current, velocity and position control signals to the servo side via the cable 17. In response to these control signals, the servoamplifier 15 drives the servomotor 10. Signals indicative of the current and position of the servomotor 10 are fed back to the NC unit side via the cables 18a, 18b. Accordingly, the servo-control CPU 11 and the main CPU 12 are both located within the NC unit, and data are transferred between them at high speed via the shared RAM 13. If a plurality of servomotors are to be driven and controlled, this can be accomplished efficiently through an arrangement in which the main CPU is coupled to CPUs dedicated to respective ones of the servomotors. Moreover, since the arithmetic circuitry is remote from the environment in which the servomotor is installed, failures and malfunctions due to vibration and heat can be reduced and both maintenance and inspection are facilitated. The present invention is not limited to the above-described embodiment. Outstanding results can be obtained even if the invention is applied to a control system based on various data other than data relating to position and velocity. Such applications do not depart from the scope of the invention. Industrial Applicability The servomotor drive control system according to the invention enables servomotor drive commands and feedback data to be transferred at high speed without requiring a special interface device. In addition, since the major portion of the complicated control circuitry is arranged on the NC unit side and only the minimum number of circuit elements are disposed on the load side, control of a machine tool or the like is simplified and it is possible to prevent control apparatus failures and malfunctions caused by such environmental conditions as vibration and temperature.

Claims: A servo-operated machine including a servomotor (10), a servoamplifier (15) for the servomotor, and a servomotor drive control system in which a drive command signal and data fed back from a servomotor (10) are to be processed to drive and control the servomotor, the control system comprising: a main CPU (12) for performing input data processing and sequence processing and a numerical control unit (11,13) associated with the main CPU and including a servo-control CPU (11) for controlling the servomotor and dedicated to it; characterised in that the numerical control unit (11,13) is coupled to the main CPU (12) so as to constitute a processing section and this processing section is arranged remote from the servoamplifier (15) and connected to it by cables (17,18a,18b) for exchanging current, velocity and position command and detection data. A servomotor drive control system according to claim 1, in which the servoamplifier comprises an inverter (16) consisting only of final stage driver elements. A servomotor drive control system according to claim 1 or 2 and having a plurality of servo-control CPUs (11) for controlling current, velocity and position of respective servomotors (10). A servomotor drive control system according to claim 3, in which the servo-control CPUs (11) are adapted respectively for controlling a servo circuit which drives each articulation of an industrial robot.

Inventors: KURAKAKE, MITSUO
Applicants: FANUC LTD.
Application year: 1985
Main classification: G05B19
IPC codes: G05B19, H02P29, G05D3