Machine Tool Calibration
After the alignment of a machine tool has been inspected / adjusted to the manufacturers specifications (see alignment), it is possible to benefit from axis positioning measurement / compensation. The following is in reference to a machine with X, Y and Z axes. The machine could be vertical or horizontal. There are six potential errors for each linear axis and three potential squareness errors for the interaction of the axes.
The three potential linear errors are: the linear positioning accuracy parallel to the movement of the X axis (1) and the linear movement parallel to the perpendicular axes Y (1) and Z (1) as the X axis is moving.
Three potential angular errors can occur. They are the rotational movements of the moving axis with respect to the three machine axes. The X axis will be used for discussion. As the X axis moves from one position to another, there is the potential for the axis to move in a manner that would be measured as rotation around the Y axis. That rotation is called pitch. The measurement of rotation around the Z axis as the X is moving is call yaw. The measurement of the rotation around the X axis as the X axis is moving is called roll.
The interaction of perpendicular axes to each other (squareness) increases the potential sources of error for an X, Y, Z machine by 3 (squareness X-Y, X - Z and Y - Z).
A machine with three linear axes perpendicular to each other has a total potential of 21 sources of error. This is often referred to as 21 degrees of freedom.
Almost all CNC control systems have configurable parameters and pitch error compensation tables to improve the linear positioning accuracy. Some control systems offer as an option straightness compensation capability. Angular error, if severe enough to affect the ability to produce machined parts correctly, cannot be compensated and must be corrected by machine repair.
To achieve and maintain optimum performance from a CNC machine, mechanically it must be functioning correctly. The purpose of the adjustment of compensation parameters and pitch error tables is to fine tune a machine that is mechanically functioning correctly. When compensation adjustment is done to attempt to mask or overcome mechanical problems, the problems still exist, continue to get worse (requiring more adjustment) and inevitably something gets scrapped and the machine has to be repaired to achieve proper performance. CNC Productivity checks machine performance prior to measurement and calibration so that the customer can be advised if the machine needs repair or tuning for better performance.
Unlike many companies offering measurement and compensation services, CNC Productivity has an experienced CNC Field Service Engineer providing this service. This CNC Field Service Engineer is capable of diagnosing and repairing machine problems that affect repeatability and accuracy. If there is a problem that needs to be repaired before compensation values will effectively improve the machines performance, CNC Productivity can provide the repair service.
This is a great advantage for the customer. One supplier can measure, diagnose / repair if necessary, re-measure and compensate to complete the job. Using two suppliers lengthens the downtime of the equipment and increases the total cost of the services received.
Before CNC Productivity would begin a laser measurement, there would be several checks made with conventional measuring tools (indicator, level and square). These checks are relatively quick and provide information that will indicate if the machine tool is prepared to be measured by the laser (see alignment).
laser measurement / compensation services have been provided to:
Maintenance, Machine Tool Monitoring, Retrofits
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