Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Patent
1997-11-26
2000-12-26
Grant, William
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
700182, 700179, 700187, 700169, 700176, 700 87, 700164, G06F 1900, G05B 1942
Patent
active
061673250
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a correction method for NC data for high-accuracy machining.
2. Background Art
After move commands for servomotors for driving individual axes of a machine tool are given to a servo system in accordance with NC data, the servo system carries out servo processing, whereupon the servomotors for the individual axes are driven to execute machining. However, a delay in the servo system can be a hindrance in executing high-accuracy machining. The delay in the servo system causes an actual tool path to deviate from the paths of machining blocks commanded by the NC data, thereby causing machining errors.
In the ordinary machining, these machining errors resulting from the follow-up delay are within an allowable range and thus are negligible. In carrying out special high-accuracy machining, however, the machining errors resulting from the follow-up delay are not negligible. In order to reduce the machining errors caused by the follow-up delay, therefore, a conventionally adopted method is such that machining is carried out at a machining speed lowered to a degree that the machining errors resulting from the follow-up delay come within the allowable range.
Reduced machining speed, however, naturally results in longer machining time, and searching for an appropriate machining speed by trial and error takes much time. Thus, it is not easy to modify data in NC programs properly in order to execute high-accuracy and high-efficiency machining.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a CNC data modification method for obtaining NC data that enable high-accuracy machining of a workpiece.
In order to achieve the above object, an NC data modification method according to the present invention comprises: (a) a step of carrying out machining by a CNC machine tool in accordance with created NC machining data to obtain actual machining position data corresponding to a command position for the starting or ending point of each block of the NC data from a CNC, and obtaining the difference between an actual machining position and the command position for the starting or ending point of each block; (b) a step of obtaining a data correction value based on the difference; and (c) a step of setting a point obtained by advancing the command position for the starting or ending point in the NC machining data oppositely from the actual machining position by a distance corresponding to the data correction value obtained in the step (b), on a straight line connecting the command position for the starting or ending point of the block and the actual machining position corresponding thereto, as a modified command position for the starting or ending point of the block of the NC machining data.
Preferably, the difference itself serves as the data correction value. Thus, the corrected command position is the position that corresponds symmetrically to the actual machining position for the starting or ending point of one block with respect to the command position therefor.
Preferably, the block by the NC machining data is composed of a series of infinitesimal straight lines constituting a curve created by utilizing a CAD, and the straight line connecting the command position for the starting or ending point in the NC data and the actual machining position corresponding thereto is a line normal to the curve at the starting or ending point.
Preferably, current positions of a move command and the actual machining position are obtained individually for each distribution cycle of the move command while the machining is carried out by means of the CNC machine tool, one of the current positions of the move command obtained individually for the distribution cycles is selected as a command position for the starting or ending point of one block of the NC data, and the actual machining position corresponding to the selected current position of the move command is used as actual machining position data for the starting or ending point of the bloc
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EP Search Report for application No. EP 97 91 4563 dated Mar. 2, 2000.
Kamiguchi Masao
Maekawa Susumu
Calcano Ivan
Fanuc Ltd.
Grant William
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