134 Industrial Robotics Fundamentals Copyright Goodheart-Willcox Co., Inc. A basic three-phase synchronous motor has no starting torque. Some exter- nal means must be used to start it. A synchronous motor will rotate at the same speed as the revolving stator fi eld. At synchronous speed, rotor speed equals sta- fi tor speed, and the motor has zero slip. 6.4.3 Servo Systems Servo systems are machines that change the position or speed of a mechanical object in response to system feedback or error signals. Positioning applications include numerical control machinery, process control indicating equipment, and robotic systems. Changing the speed of a mechanical object applies to conveyor belt control units, spindle speed control in machine tool operations, and disk or magnetic tape drives for computers. In general, servo systems follow a closed-loop control path, Figure 6-16. The input of a servo system is the reference source to which the load responds. By changing the input in some way, a command is applied to the error detector.r r This device receives data from both the input source and the output device. If a correction is needed, the signal is amplified and applied to the actuator. The actua- fi tor is normally a servomotor that produces controlled shaft displacements. The output device is usually a synchro system that relays information back to the error detector for position comparison. Robotics Innovations: Edison Robot The Edison robot is a low-cost robotic solution designed for use in schools. The robot has a surface that is compatible with LEGO® blocks and allows students to build unique robot designs on top of the programmable base. Lesson plans and activities have been developed that are available for download from the Edison website. Programs can be entered with a computer or by simply printing out bar codes that the robot drives over and scans. Onboard sensors can detect light, sound, lines, and infrared signals. Standard TV and DVD remotes can be used to control the robot. The low cost and versatility of the robot make it ideal for schools with small budgets. Photo courtesy of Edison Robot Input command (reference source) Rotary actuator (servomotor) Controlled output device (synchro system) Error detector Feedback loop Amplifier Goodheart-Willcox Publisher Figure 6-16. A typical servo system uses feedback signals to adjust the position or speed of a mechanical object.