Tuesday, August 19, 2008

Expanding a control system for CNC-programming

Expanding a control system for CNC-programming

Modern machines require high quality control systems to achieve the specifications desired. These control systems are quite commonly build around a Personal Computer with some sort of extension. Machine setup : This machine, an updated Colath lathe, is placed in the ‘Precision Engineering’ Laboratory of the Eindhoven University of Technology. This machine consists of 3 movable axis. The x-axis, the z-axis and the C-axis (rotation around the z-axis (spindle)). The friction-wheel actuators are controlled by a weak, analog control loop. The feedback-signal is based upon a light-sensor. To control the VC-actuators of this system for both x-axis and z-axis a Heidenhain LIP 382 linear encoder is used. This is an exposed incremental linear encoder (sealed encoders usually cause friction) with a signal period of 0.128 pm. This means that the distance between 2 lines of the encoder is 0.128 pm. The rotation of the C-axis is measured by a static Hall-sensor in combination with 18 magnetic pool-pairs on the rotating axis: by this method again a sine and a cosine-signal is achieved with 18 periodes in one rotation of the C-axis. In this chapter the PMAC (programmable multiple axis controller) control board is discussed. The PMAC is a product of Delta Tau Data Systems inc. Actually it’s a complete family of control systems and here only the PMAC-1 Lite will be discussed. A PMAC system setup can be done mostly from software. Hardware features have to be set using jumpers in hardware. The software setup can be done using the PMAC Executive Software (PEWIN32). It provides a convenient environment for writing programs, setting variables and troubleshooting PMAC. Control law, notch filter. Although not discussed in full detail, these programs form the implementation of the CNC-programming language for the Colath high-precision lathe using NC32 and the PMAC control board.


DOWNLOAD LINK: http://alexandria.tue.nl/repository/books/625485.pdf

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