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Servomotors in Robotics

By Edited Sep 6, 2016 0 0

Some of the particular characteristics of servomotors are feedback looping and the storage of torque, even at zero RPM. These qualities make servomotors ideal for robotics applications. These applications range from toys that walk, to sophisticated aerospace components.

Servo control systems utilize a feedback loop employing a position sensor, the motor itself and a controller. The controller uses data from the position sensor to determine when to start and stop the motor. This controller is often a computer specifically designed for the task of running the servo controls in that apparatus or component.

The process of developing a robotic arm or walker that mimics human movement is a surprisingly challenging task. Human walking or arm movement involves a vastly complex series of incremental steps, not the least of which is constant feedback to the controlling mechanism—the brain—to tell the muscles where and how to reposition themselves—how and when to contract, expand, or do nothing, all in the space of no more than a few milliseconds. In a true robot, this process must be duplicated by servomotors and computer controllers. In this application, speed is not an issue, but programming is; as a computer servo control system has no intuitive understanding of walking or grasping an object, the process has to be broken down into thousands of tiny, discrete, incremental steps.

The brushless servomotor is an advance that has great potential for robotics. The lack of a rotating armature means that a brushless motor offers more torque than its brushed equivalent. The fact that it does not rotate also reduces wear on the motor, means the unit is not susceptible to centrifugal force, and can be cooled in an entirely enclosed case (by conduction). The brushless motor servo is usually a computer chip or, in the case of complex applications, a dedicated computer. In the early days of brushless motors, the need for computing power to drive the servomotor meant that applications for this technology were limited. However, the advent of powerful microchips has made brushless servomotors both more practical and far less expensive.

The greater torqueing capabilities of a brushless servomotor make it ideal for robotics applications; almost every moving part of a robotic machine either generates torque or requires torque to move. Also, the “micro stepping” capabilities of a computer-controlled brushless servomotor are ideal for the many incremental motions and feedback-driven commands necessary to drive a human-movement-mimicking robot.

The use of micromotors, the ultimate extension of which is the “nanobot,” is the next great leap forward in robotics technology. The two limiting factors up, until this point, have been engineering and computational power; it is difficult to make anything of very small size that has the computational power a robotic servomotor requires. However, since computer chip technology has improved exponentially in both miniaturization and power, it can be confidently predicted that, unless some absolute limit is reached, continued advances will make highly miniaturized robotic components possible.

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