Integrated Temperature Compensation for Thermal Error Management
Table of Contents
Since the 19th century, thermal error management has been a key concern of precision machine designers. Even today, thermal effects and temperature changes continue to be the largest error sources in precision machines. One main reason for this is the extreme expense and difficulty associated with designing a thermally insensitive machine.
Most often, the best way to reduce thermal errors is to control the environment in which the machine works and thereby mitigating the need for thermal insensitivity. However, while this method is effective at reducing thermal effects, it proves very expensive when sustaining precise building temperature control, and always adds to production quality risks because of the inherently unreliable stability of many air-conditioning systems.
In most industrial facilities, the level of environmental stability achieved together with great expense and care taken to control the building’s air-conditioning systems, would still prove to be insufficient for a majority of high-precision manufacturing processes. Shown in Figure 1 is the temperature stability of a usual lab-grade industrial facility, demonstrating variations upwards of 0.5 °C over the duration of one hour.
This means, not only the average environment will differ with time, but considerable gradients can also take place across the volume of a production facility. In large facilities, multiple air-conditioning units are used in symphony which can cause spatially varying environmental dynamics across the production floor. This will affect the machine’s output quality with time and also impact the quality output from one machine to another.
Figure 1. Example of environmental fluctuations in a typical lab-grade production environment with a set point temperature of 20 °C. Air-conditioning cycle times can vary from minutes to hours, and significant gradients can occur across the facility.
Consequently, the accuracy of machine positioning is obstructed by the stability, or lack thereof, of a facility’s environmental control – even when relatively expensive air-conditioning hardware is employed.
Figure 2 shows the positioning effects of an above-average production environment by demonstrating measured positioning error on an actual system that undergoes a step-and-scan measurement procedure in the environment depicted in Figure 1. Owing to the duration of the test, the machine’s accuracy in the step direction (X axis) is directly tied to the abilities of the air-conditioning system and not to those of the controller and stage.
However, this level of impact would be unacceptable in any number of precision processes, but despite this fact not much effort has been made to cost-effectively lower these types of effects on precision positioning equipment, until now.
ThermoComp™, a new product feature from Aerotech, offers the much needed relief from almost all of the effects of thermal instability on the precision positioning parts of a machine when employing Aerotech equipment. ThermoComp™ offers a complete mechatronic solution to thermal errors.
By using integrated sensors and hardware, and a proprietary compensation algorithm implemented through the A3200 controller software, ThermoComp™ completely eliminates a stage’s accuracy degradation caused by thermal effects. As shown in Figures 1 and 2, one of the main sources of thermal-related error in positioning systems arises in the environment, or external to the machine.
Figure 2. Real-world measurement of positioning errors caused by environmental thermal cycling due to air-conditioning instability.
Shown in Figure 3 is the exceptional ability of the ThermoComp™ to reject external thermal impacts, even over adverse temperature ranges. More than 95% of the thermal-related errors are fully eliminated, irrespective of temperature change and stage travel.
Figure 3. Measurement data showing successful compensation of thermal-related positioning errors at several temperatures using the ThermoComp feature. Results are typical of stage performance with and without ThermoComp.
Lastly, external environmental changes are not the sole thermal influencer on positioning error. Another major source of thermal-related positioning errors is internal self-heating, especially in stages without direct feedback devices such as ball-screw-driven stages. Moreover, ThermoComp™ prevents environmental changes from impacting positioning performance and also reduces the errors caused by internal heating. Shown in Figure 4 is the successful elimination of more than 94% of the thermal-related errors induced by the self-heating of a ball-screw-driven stage.
Figure 4. Measurement data showing successful compensation of internal heating related positioning errors during prolonged operation of a ball screw stage using the ThermoComp feature. Results are typical of stage performance with and without ThermoComp.
Presently available on all PRO Series stages, ThermoComp™ operates through an intuitive and user-friendly integrated command set within the A3200 controller software. The factory handles system setup, which is standard on every ThermoComp purchase and ensures a hassle-free customer experience. System setup is available within Aerotech’s Order-to-Ship expedited delivery system.
To know more about how ThermoComp™ can make the process less susceptible to thermal-related errors and enhance the facility’s output quality, customers can contact an Aerotech Applications Engineer.
This information has been sourced, reviewed and adapted from materials provided by Aerotech, Inc.
For more information on this source, please visit Aerotech, Inc.