Operating Temperature Range for Motors, Actuators and LEM's
Trilogy motors, actuators and our Linear Encoder Module occasionally must operate in applications with extreme temperature changes. One such application prompted us to perform testing on a T2S actuator with an ambient temperature range from -25oC to +75oC.
Application Description

A manufacturer of specialty sensors required an XY actuator operating inside a thermal test chamber. The temperature would range from -25oC to +75oC during the testing. Humidity would also go to 90% relative humidity, non-condensing. Testing was performed prior to undertaking the project to identify any potential design or operating problems arising from these severe conditions.

Test Setup

A standard Trilogy actuator, T2SS16-2NCTS, was selected for the testing. Trilogy doesn't have an environmental chamber so we had to create our own. We used our oven for the high temperature and ice chests filled with dry ice for the cold temperature. Dry ice temperature is -78.5oC. Measurement of the internal actuator temperature was performed every 10-15 minutes using an infrared temperature gun.
The actuator was placed in the oven and run at 30 ips over the full travel with no load for a period of 4 hours. Actuator hot temperatures ranged from +85oC to +105oC due to difficulty regulating the oven temperature. Actuator cold temperatures remain fairly constant at -25oC. Testing went from hot for 4 hours, cold for 8 hours and hot again for 8 hours. The actuator was running the entire time. Large amounts of frost built up on the actuator during the cold running but did not affect the operation. Following the cold testing, the frost thawed and covered the actuator with water. Again the actuator running was not affected. The picture below shows the actuator covered in ice and frost after it was removed from the ice chests and dry ice.

T2SS Actuator at -250C
Test Conclusions

Actuator Base Material

The base material chosen for the actuator was steel. With a 100oC temperature range, the thermal growth of the base, bearing rail, and magnet track would be substantial. Each material has its own Thermal Coefficient of Expansion. Steel has a thermal coefficient of 6.0x10-6 in/in/oF. Aluminum has a thermal coefficient of 13.3x10-6 in/in/oF, more than double that of steel. The actual change of length due to temperature may be easily calculated. Multiply the Coefficient of Thermal Expansion times the original length times the temperature range in oF. With a temperature range of 100oC or 180oF, the growth of the 16.8" length actuator steel base plate is 6.0x10-6 in/in/ oF x 16.8" x 180 oF = 0.018". Longer bases would of course growth proportionately. If the base were made of aluminum, the 16.8" base would grow 0.040". Noting that the bearing rail and magnet tracks are steel, the differential growth with an aluminum base plate would amount to 0.022". The result would be distortion or even shearing of screws as the two materials grew at different rates. Therefore, when actuators experience wide temperature swings, the base should be steel to match the thermal growth of the bearing and magnet track.

Modular Magnet Tracks Modular magnet tracks are ideal for high temperature swings even in applications using aluminum bases. Because modular tracks are short, each section only grows a small amount and doesn't apply significant stress to the base. There is also a small gap between each modular track providing some room to absorb any thermal growth that does occur.
Linear Encoder Module, LEM The LEM uses a proprietary temperature compensation scheme to prevent signal drift with temperature changes. Without excellent compensation, the accuracy, repeatability and smoothness of the actuator would be negatively impacted. Over the entire temperature range the actuator demonstrated consistent smoothness as measured by the servo following error. Accuracy and repeatability could not be measured while testing. The LEM requires an initial factory calibration step to achieve its high accuracy, repeatability and smoothness. This requires stability of the analog signals in the LEM head. By maintaining it's smoothness and following error during the wide temperature swings, the stability of the LEM head's signals was demonstrated.
High Flex Cable High flex cable is used in all Trilogy actuators. The outer jacket is constructed of flexible PVC that has a temperature rating of 105oC. The lower limit for the PVC jacket is -32oC and remained flexible inside the cable track during and after testing. The high temperature was surpassed at times in the testing with internal temperatures sometimes reaching over 125oC for short periods of time. Physical inspection of the cable showed no visible degradation after exposure to this high temperature.
Coil Assembly The coil assembly has a thermostat that triggers at about 90oC. During testing, the thermostat triggered, shutdown the actuator and had to be jumpered out for the remainder of the high temperature testing. The actual coil temperature is rated for 125oC and it reached this temperature at different times during testing. A physical inspection of the coil following testing revealed no heat damage to the epoxy encapsulant