Servomotor/gearhead combinations are often limited by temperature -- as the torque load and/or rpm increases, so does the temperature. This presents a number of machine design issues for certain high-speed applications. To improve system performance, the temperature must be lowered -- a process which can be accomplished through better extraction of heat from the motor/gearhead combination.
Adapters used to connect servomotors to a gearhead can play a central role in the heat extraction process. These adapters are typically a solid piece of aluminum. Replacing a traditional adapter with one specially developed with an internal channel that allows circulation of fluid (air or liquid) to remove heat generated in the application can be key to temperature reduction when operating at high speeds.
This conclusion can be better explained through an application example. Take a Rockwell MPL-B540K servomotor mated to a gearhead with a traditional adapter at 50 percent torque load and 3000 rpm. In this scenario, the output bearing of the gearhead will reach a steady state temperature of 87C (189F) with natural convective cooling. Replacing the traditional adapter with a fluid-filled adapter and allowing 7C (45F) water to run through the internal adapter channel, a steady state temperature of 53C (127F) can be achieved - a reduction of 34C (62F) over the natural convective air cooling.
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As seen in the accompanying graphs (Figures 1 and 2), significant heat removal can be achieved by using a channeled adapter. The type of fluid used will depend on what is available at the location. Water at 7C (45F) provides the best solution. However, any reduction in temperature achieved through the use of a cooling fluid (e.g., use of chillers, water/glycol, etc.) would serve to improve the cooling effect.
In this example, a lowering of the motor winding temperatures can also be observed. This is accomplished because the cooling is taking place between the servomotor and the gearhead, thereby extracting heat from both pieces of equipment.
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Because the temperature is lower throughout the servomotor/gearhead, the combination can now be run at a higher torque load and/or rpm. Note, however, that published maximum values by the manufacturers must still be observed. Figure 2 shows that a unit under test that once ran at 500 rpm with a 50 percent torque load can now run at up to 2000 rpm with a 50 percent torque load without an increase in temperature. This represents a significant improvement in performance.
William Bollig is engineering manager at Wittenstein Inc.
