Estimates say that only about one-third of the motion control systems in service use gearing, although there are good reasons for doing so. For example, when your motion control system must run at 1,000 rpm or less, the use of a gearhead is advantageous. It’s also wise to use gearing when designing systems that have size constraints. Pairing a gearhead with your servo motor or using an integrated gearmotor can let you employ a smaller motor, thereby reducing the system size.
Advantages of using a gearhead with your servo in a motion control system include:
Fig 1. The use of a gearhead such as this in a motion control
application can make it run at lower rpms and provide more torque.
Recall that inertia is a measure of an object’s resistance to any change in its motion and is a function of the object’s shape and mass. The greater an object’s inertia, the greater the amount of torque needed to accelerate or decelerate the object.
When the load inertia is much larger than the motor inertia, it can cause excessive overshoot or increase settling times. Both conditions decrease production line throughput.
On the other hand, when the motor inertia is larger than the load inertia, the motor will need more power than necessary for the particular application. This increases costs because you’re paying more for a motor that’s larger than necessary and the increased power consumption means higher operating costs. The solution is to use a gearhead to match the inertia of the motor to the inertia of the load. Choosing the appropriate gearhead lets you use a smaller motor as well as develop a more responsive system.
The upshot is that torque multiplication, rpm reduction, and inertia matching help cut system cost because the use of a gearhead allows the uses of a smaller size motor and drive.
For example, say an application requires 200 in-lbs of torque at a speed of 300 rpm. To drive the load with a servo motor alone (at standard performance attributes found in the industry), a servo motor with a 142 mm frame size and a drive that can supply 30 A continuous is necessary. The system costs about $6,000. But using a gearhead for the application lets you use a 90 mm servo motor and a correspondingly smaller drive. This system costs about $3,300.
This is Part 1 of a 2 Part series
Article contributed by shared by Jeff Nazzaro, Gearhead and Motor Product Manager, Parker Hannifin - Electromechanical North America Division