Motion profile: Detail the full motion profile, including acceleration time ( t acc), continuous run time ( t cont), deceleration time ( t dec), and dwell time ( t dwell).Work with the applications engineers, sending them CAD renderings of your system and whatever other information is available. Most manufacturers offer sizing software, some of which is quite sophisticated. Load inertia: Take advantage of the skills of your vendor.Before prospecting online or picking up the phone to call a vendor, assemble a detailed description of the application, with as much technical information as possible. Specifying a gearbox for a motion control system requires much more than just application torque or speed data. Specifying a Gearbox Gather Application Requirements The latter issues can be mitigated to a large extent by properly specifying the gearbox for the application. They increase maintenance and monitoring tasks. In any case, gearboxes do add complexity and points of failure to the system. They increase cost, although the motor/gearbox combination may still be less expensive than a larger motor. They add size and weight to the system, although that can be offset, to some degree, by the accompanying reduction in the size of the motor. If the gearbox is properly sized, the noise is mitigated because you're not working the motor as hard. Especially when it's operating at higher utilization, you start getting winding noise. “However, the motor creates a lot of that noise itself. “There's a misconception that servo gearboxes are loud,” says Joe Schneider, Application Engineering team lead at Wittenstein (Bartlett, Illinois). “You have a resolution that's much finer at the output shaft at the gearhead.”Īnother less appreciated benefit to gearboxes is that they can reduce running noise in servo systems. “The steps are diminished directly by the ratio of the gearheads,” says Brien Shirey, Director of Engineering at CGI Gear (Carson City, Nevada). The gear ratio also increases the resolution of a stepper motor. However, it’s important to remember that the gearbox does contribute to overall inertia. The approach saves money, reduces the size, and enhances performance. This property equips a smaller motor to effectively control a larger load. The gearbox scales the reflected inertia by the inverse square of the reduction ratio. The inertia reflected from the load, J R, is scaled by the gear ratio as: This is where the gearbox can assist.īy multiplying motor torque, a gearbox also effectively scales the motor’s ability to control the load. If the load inertia is too much higher than that of the motor, the axis will be unable to position the load at the location and time required, and performance will suffer. It’s not enough for the motor to be able to start the load it needs to control and decelerate it as well. Gearboxes are also very useful for inertia matching. Adding the gearbox enables the servo motor to run at optimal speed from a controls standpoint while still generating a modest amount of torque, which increases to the required levels by the gear ratio. The servo system provides tight control of angular velocity, but servomotors don’t traditionally perform well or generate much torque at slow speeds. To keep the crystal as round, smooth and homogeneous as possible, the entire assembly must be rotated very gradually, at a rate of 15° per hour. Crystal growth, for example, requires the boule to be gradually raised out of a drum holding the melt. Torque multiplication makes it possible to drive a system with a much smaller motor, saving money and space.įor some applications, the role of the gearbox as a speed reducer is just as important as its function as a torque multiplier. In other words, the gearbox acts as a torque multiplier and a speed reducer. If we attach a motor with torque t 1 and input speed w 1, and the output of the gearbox will be Let’s start by considering the gear ratio G, which is given by:
Gearing can play a number of roles in motion systems. Here, we review the process of sizing and selecting a gearbox for a servo or stepper system with an eye toward achieving the required performance at a price that won’t break the bank. Properly specifying a gearbox for a servo motor or stepper motor involves taking into account machine parameters, application requirements, environmental conditions, mechanical factors, and, of course, budget.
They’re most commonly considered torque multipliers but actually serve several other functions, including speed matching, inertia reduction, and resolution increase. Gearboxes can be used to fine-tune the performance characteristics of a motion axis.