Motion control solutions are primarily mechanical in nature. If the mechanism is right for the load, the motion solution can be designed to meet the project objectives without difficulty. The starting point for this process is the selection of the motor.
In keeping with the mechanical nature of the problem, consider that across all of the possible fields of use for electric motors, very few of them occur at typical motor nameplate speeds. Even in large fan systems where you would think you need high rpm, 1200 to 1800 RPM is a rarity. 60 miles per hour in a car is really only 800 rpm at the rear tire, depending on the tire diameter. Most servo systems are designed at 4000 to 8000 rpm in order to increase the energy density of the solution. Size restrictions abound in many types of equipment, so this approach makes sense in some markets. But generally, motor speeds and load speeds do not match up very well.
This overall situation in the motor industry make the requirement for mechanical transmission of some type a necessity, and most often it includes gear reduction. Gear reducers have been engineered over the years in many forms, complex, simple, low and high accuracy, low and high efficiency. There are also belt and pulley reducers, clutch systems, and recently more exotic systems like magnetic couplings. All with the intent of matching the motor speed to the required speed of the load.
The most significant contribution of gear reducers is the multiplication of torque output of the motor, or said in reverse, the reduction of the load torque requirement by the ratio of the reducer ( minus efficiency losses ). Due to the relatively low cost of mechanical solutions, gear reduction is the most inexpensive way to gain torque. In high performance systems, a torque increase comes at a relatively high price if it has to be derived directly from the motor and drive system. This is based on the cost of power electronics and permanent magnets.
The other major effect of gear reducers is the reduction in reflected inertia of the load. The neat thing here is that the inertia is reduced by the square of the ratio. So a 10:1 gear reducer will reduce inertia by 100 times. This is a huge advantage especially when high performance velocity regulation, as in multi-control printing, or precise positioning are required.
The feature of “controllability” comes from a combination of dynamic response in the current and voltage regulation between the motor and power electronics and the position feedback device. The best way to know what “zone” of performance is required is to use the parameter “dynamic response” to gauge the behavior of the load. This is an unequivocal measure that all manufacturers are able to reference for performance. Unfortunately, dynamic response is not always the first parameter on a spec sheet, so it takes some digging to get to. But over a number of years of doing motion control projects, it is one of the key variables that can clearly distinguish where an application sits in the “performance continuum”
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