Product category:
Stepper and Servo Drives, Motors, Controls
News Release from: Micromech | Subject: Delta Tau PMAC
Edited by the Engineeringtalk Editorial
Team on 05 July 2006
Motion controller provides volumetric
compensation
An existing EDM machine for the manufacture of moulds for the plastic injection moulding industry had a problem - and the answer came in the form of the Delta Tau PMAC motion controller.
An existing EDM machine for the manufacture of moulds for the plastic injection moulding industry had a problem The machine is 15 metres long and 6 metres high, the canterlevered y-axis weighs 4 tonnes and carries the z and O axis to a full-extended travel of 5.5 metres
This article was originally published on Engineeringtalk on 26 Feb 2001 at 8.00am (UK)
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Due to the immense size of the machine it was not possible to get accuracy of movement required to meet the demands of the mould industry.
Uncompensated, the inherent machine accuracy was only 0.18mm and the previous Heidenhain control did not have the ability to do volumetric compensation, so Delta Tau found the solution.
The answer was to combine the EDM control board and power supply with the Delta Tau PMAC PC motion controller to control all the motion axes and spark control.
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The motion board controlled the four axis of motion (x, y, z and O) and compensated for the liner bearing and ballscrew errors.
All the EDM control board and power supply had to do was provide the precision spark control.
The linear error was measured by a laser interferometer and the data used to build the compensation table in the PMAC.
The system still used the original Heidenhain linear encoders as position feedback and also closed the velocity loop from the motor feedback.
In addition the PMAC is able to control machine logic thus allowing for the flexibility to incorporate a complex tool changer into the upgrade.
The main features of the PMAC used to solve this application were the 2D and planar linear compensation, the spline mode for motion profile, asynchronous motion and logic control, and co-ordinate system definition.
It is a PC based motion board and has a very fast CPU calculation capability.
The result of these enhancements was to provide part finish and quality goals required by industry, achieving a final accuracy of 0.025mm.
The project cost was far less than the alternative approaches but a seventy times improvement in machine accuracy was attained when compared with old NC control, and by only using an "off the shelf" technology from Delta Tau.
The part finish quality was met by the ability of the motion controller to perform on the fly calculations (4ms) for electrode position based on feedback from the EDM process controller.
Maximising the value of capital equipment these days is now a priority and being able to upgrade the performance of an existing machine thus saving the expense of a new machine and at a fraction of the cost is good news for the manufacturer and the customer.
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