Gearheads can solve inertial mismatches created by design updates and changes. It's interesting how improving designs can sometimes create a whole different set of challenges. For example, servo motors are putting out more torque, relative to frame size, than in the past with their use of lightweight materials, dense copper windings, and high energy magnets. Because of this, greater inertial mismatches can be present between these motors and the loads that they are trying to control. Gearheads can help.
Inertia is defined as a measure of an objects resistance to a change in velocity given the objects shape and mass. The larger an object's inertia, the greater the amount of torque that will be required to accelerate or decelerate it. In rapid start and stop applications you can significantly improve system performance by having the correct ratio of load inertia to motor inertia. If the load inertia is too great compared to the motors an application may experience overshoot and/or increased settling times which will greatly decrease a production lines throughput. In contrast, a motor too large for an application will have to use more power to accelerate its own inertia resulting in increased operating costs, in addition to the higher cost of the motor itself.
A gearhead will help to match the inertia of the motor and the load that it has to control. The reflected inertia experienced by the motor will be equal to the load inertia divided by the square of the gearhead ratio. So as an example, if you were using a Parker MPP0921B with a rotor inertia of .00039 lb-in-sec^2, and your load inertia is 1 lb-in-sec^2, your inertial mismatch is 2564:1. Using a 10:1 gearhead ratio then with a Parker PS90-010 will now create an inertial mismatch of only 25:1, a PS90-020 will get you down to 6:1 inertial mismatch between motor and load.
How you look at solving an inertial mismatch is dependent on the application requirements, and the components being used in the application. Gearheads are just one of the ways to design an efficient and productive system that will perform reliably for many years to come.
Jeff Nazzaro, Gearhead and Motor Product Manager, Parker Electromechanical Division North America
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