• In our last Block and Tackle posting, we touched on operating a motor in a hotter ambient temperature.  For this posting, we take a look at the Root Mean Square (RMS) Torque and why it is important. Typically an axes’ motion profile is broken up into multiple segments, each segment is found to require a specific torque for a specific amount of time to complete the desired motion.  For example this can include torque required to accelerate, traverse (against an external force and/or friction),  decelerate, and dwell.  Each of these segments affects the amount of heating the motor experiences and thus the equivalent steady state continuous requirement utilized to select the correct motor.

  • How do I calculate a motor’s continuous torque when it is operating in an environment above its rated temperature? Since the motor’s continuous torque (Tc) is rated in a 40°C ambient, how can I estimate the motor’s continuous torque during my worst-case ambient temperature of 55°C?  

  • Horsepower (hp) is a measure of power, which can be further described as the rate at which work is performed.  There are slightly different definitions for its conversion to the unit watts depending on the mechanism being described: mechanical, electric, boiler, metric, etc..   Our focus here will be on servo motor systems.

  • Question: I need to operate a servo motor in a vacuum, what are some considerations? 

    Answer: In a word?  Outgassing.  You might think that proper motor sizing is a big issue, it always is, however if you can't conform to the other process requirements, there is no point to attempting to size the motor.  The biggest issue for any given motor selection to be run in a given vacuum for a specific process is the outgassing requirement, or rather, the avoidance of materials that would affect the process being performed and/or the life of the motor.

  • If you have been following along on our Evolution of Kollmorgen posts, you realize Hugo Unruh was one of the first to successfully commercialize frameless motor technology. What most people don't realize is that Kollmorgen's motor-drive phase identification standards (A, B, C) were based on these frameless motors. Now the issue at hand is both sides of a frameless motor typically look the same, except for the side where the wire leads exit.

  • Cogging and Torque Ripple questions are common and many times, difficult to answer.

    Cogging torque is defined as the attraction/interaction of the magnetic poles to the teeth (steel structure) of the laminations within an un-energized motor.

    Torque ripple is defined as the variance of the torque of the energized motor with a constant current. They are related in position independent of magnitude or direction, but cogging torque is generally not presented as a specification for servo motors.

  • There are challenges for a servo motor's protection against overheating by the manufacturer, machine designer/OEM, and user, because there is no thermal device that can protect a motor against a fast transient event.  For just as there is a time lag between the final steady-state temp rise of a coil of wire with a given current going through it, there is a time lag for the thermal device to achieve its trip resistance once that trip/application temperature has been presented to the thermal device.

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