In-line conveyor scale with a primary first motor to provide constant torque, a secondary servo motor to provide fine-grained variable torque in response to a closed loop torque sensor, and a processor to assertain weight of an item conveved based on the closed loop servo motor response

Abstract

Disclosed are various applications of differential torque sensing, seeking to maximize the sensing power of servo motors in applications that have a wide torque range. In one embodiment, a transmission () combines a constant, relatively larger torque provided by a primary drive motor () and a smaller, variable torque provided by a servo motor (), to form an output torque for driving a mechanical assembly (). A relatively small change in mass of the system causes a perturbation from ambient operating speed. The servo motor, under control of a servo amplifier (), quickly adjusts the secondary, variable torque to return the system to the ambient operating speed. Thus the servo motor torque accurately reflects the change in mass of the system.