How Piezo Controllers Have an Effect on Thermal Stability

Table of Contents

Introduction
Aerotech’s A3200 and Ensemble QLAB, QDe, and QLe Controllers
Conclusion

Introduction

Piezo controller design can have a significant effect on thermal stability resulting in extreme error in precision motion applications. This article discusses some techniques used for controlling thermal effects and also compares the thermal stability of Aerotech’s piezo control electronics with a competitive design.

Thermal stability is important in any precision process. Thermal drift of electrical and mechanical components can result in errors that far surpass any tolerance stackup of components or positioning errors of motion equipment used in that process. There are three common ways that can be used by designers to control thermal effects in precision instrumentation and machinery.

  • Control the environment where the machine or instrument is housed. This is typically the best approach as it addresses the root of the issue, but then this method can be very expensive as environmental control requires conditioning equipment, air handling, and a temperature control system.
  • Measure thermal variations and compensate with control systems: This method can be effective, but normally requires an accurate system model and a sensor network. Usually, the system model is a unique model that describes the machine, the instrument, and surroundings to a rational level of accuracy.
  • Design the instrument or machine to be insensitive to thermal changes: This method is typically the most difficult to employ, but can be robust and cost-effective if implemented correctly.
  • Piezoelectric nanopositioning stages with capacitance sensor feedback are frequently used in precision processes because of their high levels of accuracy, repeatability and resolution coupled with millisecond response times. In order to accomplish long-term stability with capacitance sensor feedback piezo stages, a robust mechanical design is required.

    However, most users do not realize that the piezo controller design can have a huge impact on the thermal stability of the machine or instrument. To make matters worse, the piezo stage electronics are usually placed in electrical cabinets or in areas that are not temperature controlled, resulting in apparent thermal drift of the process.

    Aerotech’s A3200 and Ensemble QLAB, QDe, and QLe Controllers

    A3200 and Ensemble QLAB, QDe, and QLe controllers designed by Aerotech come with an advanced thermal stability feature that makes the capacitance sensor feedback circuit largely insensitive to environmental changes. To demonstrate the effect of this feature, a test was conducted on both an Aerotech A3200 QLe controller and a top competitive controller.

    To remove the differences in the stage designs, an ultra-stable, low-Coefficient of Thermal Expansion (CTE) capacitor (1.3 nm/°C effective thermal sensitivity) was joined to the feedback input of the two controllers. This capacitor imitates a piezo stage with capacitance sensor feedback sitting at a constant position.

    The controllers and feedback capacitors were placed inside a small thermal enclosure where the air temperature was varied by about 7 °C with a cooling cycle of one hour and a heating cycle of one hour. The air temperature and position feedback were monitored over a 70–hour period. The results of this test are illustrated in Figure 1.

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

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

    Conclusion

    Thermal management is vital in precision processes. In addition to the stage mechanical design, the electronics used in piezo stage capacitance feedback play a very important role in maintaining process thermal stability.

    Aerotech’s high-performance piezo controllers exhibit thermal stability 40 times higher than over the top competitive controller. Customers can contact Aerotech to discuss their application and find out how Aerotech’s Q-Series™ piezo controllers and nanopositioning stages can improve their process.

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

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