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Digital Piezo Translators (DPTs) are piezo-electric translation devices capable of moving up to 70 microns with very high linearity and essentially perfect repeatability. Hysteresis is less than a nanometer. The DPT comes out of more than 100 man-years of R&D and attains accuracy 20 times higher than any other device on the market.
Overcoming Problems Associated with Ordinary Piezo-Electric Translators
Ordinary piezo-electric translators are non-linear and exhibit hysteresis and creep. To overcome these problems a position sensor is built into each DPT. The output of this sensor controls the voltage on the piezo-electric stack so as to remove the hysteresis, non-linearity and creep.
Each DPT from Queensgate Instruments is supplied with a calibration curve, which can serve as a basis to correct the very small residual non-linearity.
The Control Module for Digital Piezo-Electric Translators
The position sensing circuitry and piezo drive amplifiers have been miniaturised and packaged in a stand alone Control Module which requires only ±15 V DC to operate. This makes the DPT-C particularly suitable for volume OEM applications. The Control Module comes complete with analogue input, 14 bit parallel digital interface, status lines and position monitor.
Mounting and Interfacing the Control Module
A Control Module is required to operate a DPT-C. The Control Module can be mounted in either the AX101 (1-channel) or AX301 (3-channel) Host Unit, which provides ±15V for module(s), position display, optional IEEE-488 or RS232 interfaces, and allow manual control of the translators. A variety of accessories are available. Host units require mains supply. Alternatively the CM can be used stand alone, powered by ±15V DC supply. The CM can interface to a computer, via a digital I/O card mounted inside the computer (e.g. National InstrumentsTM PC-DIO-24 - 24 lines of digital I/O).
The Key to Accuracy and Repeatability in Queensgate’s DPT’s
The key to the outstanding positioning accuracy and repeatability achieved by the DPT-C is Queensgate’s unique capacitance sensor technology. Each DPT-C contains a capacitance position sensor, which has picometer sensitivity. Changes in the length of the DPT-C are detected by this sensor and used to control its length.
Ensuring Accuracy in the DPT-C
The DPT-C's are made of Zerodur (a low thermal expansion coefficient glass) and Invar to minimise temporal and thermal drift. The DPT-C operates in a closed servo-loop incorporating an almost perfect integrator stage - as a result the DPT-C is extremely stiff. As loads on the device change its length so the servo loop responds, changing the voltage on the piezo stack to correct for these perturbations. The DPT-C has a slew rate of 1μm.ms-1, and a noise level of less than 1 nm rms.
System Component Flexibility
The capacitance sensors developed for the DPT-C are now also available as separate units, for other applications, which demand the highest possible position sensitivity. Please contact Queensgate Instruments for further information.
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