Electricity: motive power systems – Positional servo systems – Program- or pattern-controlled systems
Patent
1986-06-16
1988-11-08
Shoop, Jr., William M.
Electricity: motive power systems
Positional servo systems
Program- or pattern-controlled systems
318569, 36447434, G05B 1910
Patent
active
047836172
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
TECHNICAL FIELD
This invention relates to a method of restoring a rotary axis to a reference point. More particularly, the invention relates to a rotary axis reference point restoration method for rotating the rotary table of a machine to position the table at a predetermined angular position.
BACKGROUND ART
In a machine tool having a rotary table, a rotary axis is rotated to position the table at a predetermined angular position by numerical control (NC) in the same manner that control is performed along linear axes (e.g. X, Y and Z axes) so that a workpiece placed upon the table may be subjected to boring and other machining. In numerical control, (1) a rotational direction workpiece coordinate system serving as a programming reference for a rotational direction machine coordinate system is decided, (2) data specifying an angle r between the origin of the workpiece coordinate system and a reference point in the machine coordinate system are commanded by a program (a G-function instruction for setting a coordinate system), and (3) the position of the rotary axis is controlled by NC program data created on the basis of the workpiece coordinate system, and present positions Pm, Pw in the machine and workpiece coordinate systems, respectively, are monitored. Note that Pm=0, Pw=-r will hold when the rotary axis is situated at the reference point.
When the rotary axis is to be restored to the reference point in the machine coordinate system, it is desired to perform the reference point restoration by rotation through less than one revolution in order to shorten restoration time. Conventionally, therefore, whenever the present position Pm in the machine coordinate system surpasses 360.degree., the present position Pm is reset to 0 so that the value of Pm is kept below 360.degree. at all times. As a result, when a reference point restoration command is generated, the rotary axis is rotated only by Pm degrees to be restored to the reference point, so that the amount of rotation required for the reference point restoration operation is less than one revolution.
However, when a reference point restoration is performed in a case where the present position Pw in the workpiece coordinate system is more than one revolution away from the origin of the workpiece coordinate system, the present position Pm in the machine coordinate system becomes 0.degree. in correct fashion, but the value of the present point Pw in the workpiece coordinate system does not become -r. Accordingly, the workpiece coordinate system does not return to its original attitude, thus making it necessary to reset the coordinate system after the reference point restoration. The reason why Pw does not become -r is that only Pm is reset to 0 when it exceeds 360.degree., whereas Pw is not reset to 0 when it exceeds 360.degree.. The reason why Pw cannot be reset to 0 is that since a target position is commanded in excess of 360.degree. by the NC data, correct positioning would no longer be possible if Pw were reset to 0.
SUMMARY OF THE INVENTION
Accordingly, an object of the invention is to provide a rotary axis reference point restoration method whereby a rotary axis can be restored to a reference point by rotation through less than one revolution, and in which the workpiece and machine coordinate systems can both be returned to their original attitudes (i.e. in which the relations Pm=0, Pw=-r can be established) after the reference point restoration.
A workpiece coordinate system serving as a programming reference with respect to a machine coordinate system is decided, NC program data are created including at least NC data specifying an angle r between an origin of the workpiece coordinate system and a reference point in the machine coordinate system, and rotational direction positioning data based on the workpiece coordinate system, and a rotary axis is positionally controlled based on the NC program data.
The method of the invention includes updating present positions Pm, Pw of a fixed point Q on the rotary axis i
REFERENCES:
patent: 4410951 (1983-10-01), Nakamura et al.
patent: 4556833 (1985-12-01), Kishi et al.
patent: 4604560 (1986-08-01), Inagaki et al.
Fanuc Ltd
Martin D.
Shoop Jr. William M.
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