Hypertherm PHC Sensor - Manual (Page 57)

Appendix A: Interfacing to a Custom Lifter 57
Appendix A: Interfacing to a Custom Lifter
The performance of the Sensor™ PHC is tightly coupled to the lifter and motor characteristics. The Sensor™
PHC was designed as a conventional plasma height control and the lifter does not include any position
feedback. All lifter moves are timed moves at regulated speeds. The Sensor™ PHC microprocessor uses both
the DC motor’s back generated voltage and the DC motor’s ohmic component to calculate the motor feedback
speed. The lifter screw pitch affects the lifter linear speed and the control loop gain when operating with arc
voltage. The screw pitch also affects the limited stall force sensing. The lifter friction and maximum torch
weight affect the point at which the lifter requires a brake to maintain position. For these reasons, the motor
and lifter characteristics are critical and must be tightly controlled.
Requirements
The following is a partial list of lifter and motor characteristics that are compatible with this controller.
• Lifter Ball screw pitch = 2mm/rev
• Lifter with limit switches or lifter with soft mechanical end stops
• Lifter capable of 200 in/min.
• Lifter should have low backlash and little mechanical play
• If the functions are required the lifter should provide for the electrical interface to limit switches, breakaway
switches, and torch tip sensing. Contact Hypertherm Automation Engineering for information concerning
the lifter signal interface.
• Motor should be a 24Vdc permanent magnet type
• Motor should turn 2500 RPM at 24Vdc. Alternatively, the motor RPM at 24Vdc should be matched with the
lifter ball screw pitch/ gear reduction/ pulley reduction so that the combination results in 200 in / min of lifter
linear speed.
• Motor should have 2A, 3A, 4A, or 6A max current rating.
• Motor resistance should be about 20% of full-scale rating. For example, a 3A rated motor should have an
ohmic resistance of approximately = 24 / 3 * 20% = 1.6 Ohms
• Depending on the torch weight load and lifter friction, you may need a brake to hold position.
WARNING:
The performance of the Sensor™ PHC is tightly coupled to the lifter and motor characteristics. To ensure
proper operation, a non-standard customer designed lifter should be fully tested with this controller under all
anticipated operating conditions.