APPARATUS FOR CONTROLLING THE SPEED OF ELECTRIC MOTORS

Abstract: In an apparatus for controlling the speed of electric motors, the servo amplifier of the speed controller is provided with at least any one of a current feedback gain switching circuit (h), a speed feedback gain switching circuit (f), a speed loop gain switching circuit (a) or a current loop amplitude, phase and table memory circuit switching circuit (b). Therefore, the apparatus is suited for switching a plurality of main shaft motors having different ratings in a machine tool.

Description: This invention relates to a motor velocity control apparatus and, more particularly, to a motor velocity control apparatus used in a changeover control circuit of a spindle motor in a machine tool. In machine tools such as machining centers, a plurality of motors are employed. These motors ordinarily have different characteristics so that they can operate as high-output and low-output motors or as high-velocity and low-velocity motors, etc. However, since these motors perform differently on account of their output and velocity characteristics, each motor requires an exclusive servoamplifier for control. Moreover, in a case where one of the motors is used, there are many instances in which the other motors are at rest, so that control circuits of the servoamplifiers belonging to these motors also are at rest. Therefore, the cost of the equipment is high and the equipment is not utilized efficiently. An object of the present invention is to lower the cost and raise the efficiency of utilization of a motor velocity control apparatus by enabling the hardware for one servoamplifier to be shared by each of the motors in an arrangement where the spindle or the like of a machine tool is driven and controlled by a plurality of motors which perform differently. EP-A-125317 discloses a prior attempt to achieve this employing an arithmetic circuit comprising a processor. The aforementioned problem is solved by the features of Claim 1. The invention therefore has the following advantages: (1) An input command voltage can be normalized to a predetermined value (e.g. 10 V). (2) The output of a speedometer can be normalized. (3) A function ensuring against excess speeds can be put to practical use. (4) The resolution of commands can be made the same for motors of both large and small output. In addition, since the apparatus can be constructed by arranging the amplifier on a single circuit chip, mass productivity can be enhanced and cost reduced. It is also easy to replace the amplifier should the amplifier malfunction. Brief Description of the Drawings Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a flowchart, Fig. 3 is a circuit diagram of a changeover signal generating circuit, Fig. 4 is a circuit diagram of a current feedback gain changeover circuit, and Fig. 5 is a velocity feedback gain changeover circuit diagram. An embodiment of the present invention will now be described in detail with reference to the drawings. Fig. 1 is an explanatory view illustrating an embodiment of a motor velocity control apparatus according to the present invention. In the Figure, spindle drive motors M₁, M₂ are for a machine tool or the like. It is assumed that one of the motors is for a higher output or higher rotational velocity in comparison with the other motor, and that the other motor has a different output or velocity characteristic. These motors are driven by a converting circuit (e) constituted by a transistor inverter or the like controlled by an output signal from a PWM circuit (c). The supply of power to the converting circuit (e) is performed by a rectifying circuit (d) connected to three-phase AC power supply R, S, T. The rotational velocities of the motors M₁, M₂ are sensed by pulse generators PG₁, PG₂, which apply signals indicative of the sensed velocities to a velocity feedback gain changeover circuit (ρ). Also provided are a velocity loop gain changeover circuit (a) and a ROM changeover circuit (b) having a changeover circuit of a current loop amplitude and phase table storage circuit. The ROM changeover circuit is provided with a plurality of memories. For example, the characteristics of the motor M₁ are stored in a ROM A, and the characteristics of the motor M₂ are stored in a ROM B. The operation of this motor velocity control apparatus will now be described. When a motor changeover signal enters the changeover signal generating circuit (g), a signal from one of the pulse generators PG₁, PG₂ is applied to the velocity feedback gain changeover circuit (f), this being decided by whether e.g. the high-velocity motor M₁ or low-velocity motor M2 is selected. Next, the gain of the velocity loop gain changeover circuit (a) is changed over in dependence upon the selection made by the velocity feedback gain changeover circuit (f). Further, ROM A or ROM B is selected depending on which of the motors M₁, M₂ has been chosen, whereby the amplitude and phase of the current loop are decided. The pulse width of the PWM circuit (c) is decided by the current feedback gain changeover circuit (h). The output signal of the PWM circuit (c) controls the conduction of the converting circuit (e) composed of the transistor inverter or the like, thereby controlling each of the motors M₁, M₂. The operation of the motor velocity control apparatus will now be described in further detail using the flowchart of Fig. 2 and the changeover signal generating circuit, current feedback gain changeover circuit and velocity feedback gain changeover circuit illustrated in detail in Figs. 3, 4 and 5, respectively. (1) It is assumed that the changeover signal in Fig. 3 is off, a switch SWo in Fig. 5 is off, and that the motor M₁ is operating with a velocity feedback gain a₁ (Fig. 5) and a current feedback gain b₁ (Fig. 4) (step S₁). (2) The changeover signal in Fig. 3 is turned on to select sub operation (step S₂). Next, motor M₁ is stopped and excitation is turned off (step S₃). (3) A ROM for sub is selected (step S₄), and the contents of a RAM, such as an amplitude pattern, phase angle pattern, slip pattern and sine wave pattern, are rewritten (step S₅). (4) The power line and signal line are changed over (contacts MCC, SW in Fig. 1 are changed over) (step S₆). (5) In accordance with Figs. 4 and 5, the velocity feedback gain is changed over to a₂, the current feedback gain is changed over to b₂ (step S₇), and the motor M₂ for sub is run (step S₈). In the above embodiment of the velocity control apparatus, two differently rated motors M₁, M₂ are controlled by a changeover operation within a single servoamplifier. However, the gain of each characteristic of the servoamplifier can be set at will. By setting at will the constants of each of the circuits provided in the hardware of one and the same servoamplifier, it is possible to construct servoamplifiers corresponding to respective ones of the motors having the different ratings. In such an embodiment, the portion A enclosed by the one-dot chain line can be composed of the same hardware. This enables cost to be reduced by mass production. Another advantage peculiar to this embodiment is that the servoamplifier can be replaced in a simple manner if it should malfunction. Industrial Applicability According to the motor velocity control apparatus of the present invention, a single servoamplifier adjusted so as to conform to the characteristic of each motor is changed over and connected when controlling a plurality of motors which differ in terms of characteristics and performance. Therefore, in a case where plural motors having different characteristics so that they can operate as high-output and low-output motors or as high-velocity and low-velocity motors are used in a machine tool or the like such as a machining center, the hardware of a single servoamplifier can be shared by each of the motors to enable a reduction in cost and more efficient utilization.

Claims: A motor velocity control apparatus for feedback control of plural types of motors (M₁,M₂) of different characteristics based on a velocity command voltage, characterised by: a servoamplifier for changing over the gain of feedback signals from the motors (M₁,M₂) to adjust and amplify said command voltage, a changeover signal generating circuit (g) for changing over and controlling said servoamplifier by a motor changeover signal, a current feedback gain changeover circuit (h) for changing over the feedback gain of an input current to each of the motors (M₁,M₂), a velocity feedback gain changeover circuit (f) for changing over the feedback gain of a rotational velocity signal of each of the motors (M₁,M₂), a velocity loop gain changeover circuit (a) for changing over the velocity loop gain of each of the motors (M₁,M₂) and a changeover circuit (b) of a current loop amplitude and phase table storage circuit. A motor velocity control apparatus according to claim 1 having a servoamplifier capable of controlling plural types of spindle motors (M₁,M₂) having different characteristics, comprising: connecting means for selectively connecting the plural motors to said servoamplifer by the motor changeover signal.

Inventors: FUJIOKA, YOSHIKI, HIROTA, MITSUHIKO
Applicants: FANUC LTD.
Application year: 1986
Main classification: H02P5
IPC codes: H02P5