Electricity: motive power systems – Positional servo systems – With compensating features
Patent
1982-07-27
1985-02-26
Dobeck, B.
Electricity: motive power systems
Positional servo systems
With compensating features
318572, 74825, G05D 23275
Patent
active
045019991
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention broadly relates to a spindle control system for use in a machine tool which automatically performs mechanical machining while making automatic exchange of tools and, more particularly, to a system incorporating a resolver and adapted to stop the spindle of the machine tool at a commanded position. Still more particularly, the invention is concerned with a system for stopping a spindle at a commanded position, improved to permit an adjustment of the stopping position.
Such machine tools are known as having automatic tool exchanging functions and are capable of automatically performing mechanical machining through automatic exchange of tools. In this type of machine tool, it is essential that the spindle be stopped precisely at a commanded position, in order that the mating portions of the spindle and the tool can smoothly engage with each other. The stopping of the spindle at the commanded position is necessary also in boring, because the boring tool cannot be correctly inserted into a bore formed in the workpiece unless the spindle is stationed precisely at the commanded position. Thus, in the field of mechanical work, there is a great demand for in the art for stopping the spindle of a machine tool precisely at a commanded position. Hitherto, a mechanical braking mechanism and a pin mechanism in combination have been used for stopping the spindle at the commanded position. This mechanical system, however, often failed to stop the spindle at the commanded position partly because of frequent breakage of the pin mechanism (stopping mechanism) due to the application of an abnormal external force or the occurrence of an extraordinary state in the machine tool and partly because of rapid wear of the braking mechanism due to friction. As a consequence, conventional machine tools often failed to perform the automatic exchange of tools and the insertion of the boring tool. In order to avoid such a failure, it has been necessary to undertake a frequent inspection of the machine tool or a renewal of worn parts.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a spindle stopping system capable of stopping a spindle at a commanded position with a high precision purely electrically, i.e. by means of a resolver.
The invention also has an object of providing a system for stopping a spindle at a commanded position, improved to permit a fine adjustment of the stopping position within a range of about .+-.5.degree..
According to the invention, the spindle of a machine tool carrying and driving various tools is driven at a commanded speed under the control of a speed control system. Then, as a spindle stopping command is given for stopping the spindle at a commanded position, the control is switched from the speed control system to a position control system to decelerate the spindle from a normal machining speed to a predetermined low speed. As the spindle is decelerated to the predetermined low speed, an output obtained through synchronous rectification of one of the output voltages from the primary coil of a resolver and an output obtained by converting the other output voltage of the primary coil into a rectangular wave are combined with each other to form a positiom offset signal which smoothly crosses the zero level when the spindle rotates across the commanded stop position. This position offset signal is used as the reference signal in the position control system to make the spindle gradually approach the commanded position. Then, as the spindle comes into a predetermined rotational region for stopping, an in-position signal is produced and, after confirming that the spindle is correctly stopped at the commanded position, an orientation completion signal is produced to start the next step for tool exchange. According to the invention, therefore, it is possible to maintain the correct positional relationship between the tool on the spindle and the workpiece to permit a smooth and safe exchange of tools.
According to another aspect of
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JP,B1, 49-47355 (Carney and Tracker Corp.), Dec. 14, 1974, (14.12.74) & USA, 3,483,767.
Fujioka Yoshiki
Kohzai Yoshinori
Ota Naoto
Dobeck B.
Fanuc Ltd
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