Piezo Controller Thermal Stability – A Comparison

Table of Contents

Introduction
Managing Thermal Effects
Aerotech Q-Series™ Piezo Controllers
Summary

Introduction

Piezo controller design can considerably influence thermal stability leading to undue errors in precision motion applications. In this article, certain techniques used for controlling thermal effects are briefly discussed and comparison is drawn between the thermal stability of Aerotech’s piezo control electronics and a competitive design.

Managing Thermal Effects

Thermal stability is of tremendous importance in any precision process. Thermal drift of electrical and mechanical components can result in errors that go beyond any tolerance stackup of components or positioning errors of motion equipment used in that process. Given below are three frequently used ways through which designers can manage thermal effects in precision instrumentation and machinery.

  1. Control the environment where the machine or instrument is placed. This is normally considered the best approach as it tackles the root of the problem, but this technique can be quite costly as environmental control requires a temperature control system, conditioning equipment, and air handling.
  2. Measure thermal variations and offset with control systems. While this technique can be effective, it often needs a sensor network and an accurate system model. The system model is characteristically a unique model that describes the machine, instrument, and the surroundings to a reasonable level of accuracy.
  3. Design the machine or instrument such that it is not sensitive to thermal changes. Usually, this technique is the most difficult to follow but when implemented properly, it can be very robust and economical.

Aerotech Q-Series™ Piezo Controllers

Thanks to their high levels of accuracy, repeatability and resolution coupled with millisecond response times, piezoelectric nanopositioning stages with capacitance sensor feedback are frequently used in precision processes. In order to attain long-term stability with capacitance sensor feedback piezo stages, it is well known that a robust mechanical design is very important. However, most users do not know that the piezo controller design can have a major effect on the thermal stability of the machine or instrument. To exacerbate things, the piezo stage electronics are usually placed in electrical cabinets or in areas that are not controlled by temperature, which causes obvious thermal drift of the process.

Aerotech has designed its A3200 and Ensemble QLAB, QDe, and QLe controllers with a sophisticated thermal stability feature that makes the capacitance sensor feedback circuit highly insensitive to fluctuations in environmental conditions. To demonstrate the effect of this feature, a test was carried out on both a leading competitive controller and an Aerotech A3200 QLe controller. To remove the differences in the stage designs, an ultra-stable, low-CTE (Coefficient of Thermal Expansion) capacitor (1.3 nm/°C effective thermal sensitivity) was connected to the feedback input of both controllers. This capacitor imitates a piezo stage with capacitance sensor feedback sitting at a constant position. The feedback capacitors and controllers were kept inside a small thermal enclosure where the air temperature was varied by approximately 7 °C with a heating cycle and a cooling cycle of 1 hour each. The position feedback and air temperature were observed over a period of 70 hours. Figure 1 shows the results of the test.

Thermal stability

Figure 1. Thermal stability comparison between an Aerotech A3200 QLe controller and a leading competitive controller.

At a 2 hour heat-cool frequency, the test results show the QLe thermal sensitivity to be about 1.4 nm/°C while the competitive controller displayed a thermal sensitivity of approximately 59 nm/°C.

Summary

Thermal management is vital in precision processes. Apart from the stage mechanical design, the electronics used in piezo stage capacitance feedback play a major role in maintaining process thermal stability. The high-performance piezo controllers by Aerotech display 40 times higher thermal stability than the leading competitive controller.

Customers can contact Aerotech to discuss their applications and discover how Aerotech’s Q-Series™ piezo controllers and nanopositioning stages can enhance the process.

Aerotech, Inc

This information has been sourced, reviewed and adapted from materials provided by Aerotech, Inc.

For more information on this source, please visit Aerotech, Inc.

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