However, when the engine inertia is bigger than the load inertia, the motor will need more power than is otherwise necessary for this application. This increases costs since it requires paying more for a engine that’s larger than necessary, and because the increased power intake requires higher working costs. The solution is by using a gearhead to match the inertia of the motor to the inertia of the load.
Recall that inertia is a measure of an object’s level of resistance to improve in its motion and is a function of the object’s mass and shape. The higher an object’s inertia, the more torque is needed to accelerate or decelerate the thing. This means that when the load inertia is much larger than the electric motor inertia, sometimes it could cause extreme overshoot or enhance settling times. Both conditions can decrease production line throughput.
Inertia Matching: Today’s servo motors are producing more torque relative to frame size. That’s because of dense copper windings, light-weight materials, and high-energy magnets. This creates greater inertial mismatches between servo motors and the loads they are trying to move. Utilizing a gearhead to better match the inertia of the electric motor to the inertia of the load allows for using a smaller engine and results in a far more responsive system that is simpler to tune. Again, this is accomplished through the gearhead’s ratio, where the reflected inertia of the load to the electric motor is decreased by 1/ratio^2.
As servo technology has evolved, with manufacturers producing smaller, yet more powerful motors, gearheads are becoming increasingly essential partners in motion control. Locating the optimal pairing must consider many engineering considerations.
So how does a gearhead start providing the power required by today’s more demanding applications? Well, that all goes back again to the fundamentals of gears and their capability to change the magnitude or direction of an applied force.
The gears and number of teeth on each gear create a ratio. If a motor can generate 20 in-lbs. of torque, and a 10:1 ratio gearhead is mounted on its result, the resulting torque can be near to 200 in-lbs. With the ongoing focus on developing smaller footprints for motors and the equipment that they drive, the ability to pair a smaller motor with a gearhead to attain the desired torque output is invaluable.
A motor could be rated at 2,000 rpm, but your application may only require 50 rpm. Trying to run the motor at 50 rpm may not be optimal based on the following;
If you are operating at an extremely low velocity, such as 50 rpm, and your motor feedback quality is not high enough, the update price of the electronic drive could cause a velocity ripple in the application. For example, with a motor feedback resolution of just one 1,000 counts/rev you have a measurable count at every 0.357 degree of shaft rotation. If the electronic drive you are using to control the motor has a velocity loop of 0.125 milliseconds, it will search for that measurable count at every 0.0375 degree of shaft rotation at 50 rpm (300 deg/sec). When it generally does not find that count it’ll speed up the electric motor rotation to find it. At the rate that it finds another measurable count the rpm will end up being too fast for the application form and then the drive will slow the engine rpm back off to 50 rpm and then the complete process starts all over again. This continuous increase and reduction in rpm is what will trigger velocity ripple within an application.
A servo motor operating at low rpm operates inefficiently. Eddy currents are loops of electric current that are induced within the motor during operation. The eddy currents actually produce a drag drive within the motor and will have a greater negative impact on motor overall performance at lower rpms.
An off-the-shelf motor’s parameters might not be ideally suited to run at a minimal rpm. When an application runs the aforementioned motor at 50 rpm, essentially it isn’t using all of its obtainable rpm. As the voltage constant (V/Krpm) of the engine is set for an increased rpm, the torque continuous (Nm/amp), which is usually directly linked to it-is usually lower than it needs to be. Consequently the application needs more current to operate a vehicle it than if the application form had a motor specifically created for 50 rpm.
A gearheads ratio reduces the motor rpm, which is why gearheads are occasionally called gear reducers. Using a gearhead with a 40:1 ratio, the engine rpm at the input of the gearhead will end up being 2,000 rpm and the rpm at the result of the gearhead will be 50 rpm. Working the motor at the bigger rpm will permit you to avoid the issues mentioned in bullets 1 and 2. For bullet 3, it enables the design to use much less torque and current from the motor based on the mechanical servo gearhead advantage of the gearhead.