Motor Feedback

Motor feedback

More than half of all the electricity used by US industrial plants goes to power electric motors; they’re found in nearly every manufacturing plant and commercial operation. Consequently, the most common application of rotary encoders is for the control of speed and direction of electric motors, from small frame steppers to large AC induction vector-duty NEMA motors. Today’s sophisticated drives and control systems can use feedback from a single motor mount encoder to control multiple axes of motion.

Linear Measurement


Rotary encoders are widely used to provide feedback for linear measurement.  As the encoder generates pulses in response to linear displacement of the material or object to be measured, it is a matter of simple math for the receiving device to convert those pulses into distance.

Web Tensioning


The process of monitoring and adjusting the tension applied to material being wound onto a spool, reel or drum is known as web tensioning.  In industries where materials such as paper, plastic film, aluminum, fiber or wire must be wound on to a reel, web tensioning is a key portion of the manufacturing process that contributes to uniformity, quality and productivity. Rotary encoders are often applied in conjunction with other feedback devices and sensors to control web tension.



A rotary encoder is an ideal feedback device for cut-to-length applications.  A fixed number of pulses is generated as the code disc rotates.  These pulses can easily be correlated via scaling or simple counting to determine length of travel.  When the desired number of pulses has been received by the control system, the cutting device is activated.

Registration Mark Timing


For registration mark timing, a rotary encoder is used to determine the position of an object relative to a known point, referred to as a registration mark. Encoder feedback is then used to determine the speed of an axis of motion in relation to the registration mark.

Backstop gauging


In backstop gauging, a rotary encoder is used to ensure that the unit to be controlled, such as a machine tool, does not exceed a preset position or direction of travel.  Very often, this encoder function is combined with determining the speed of travel of the table, tool head, or similar component.  Other sensors may be used for backstop gauging, such as a limit switch or optical sensor; however, properly configured rotary encoders can prove to be more durable and accurate.



In many filling applications, a rotary encoder is used for table positioning. Feedback from the encoder helps ensure that the item to be filled is in the correct position prior to activation of the filling mechanism. For example, bottles, tubes, cans or cartons can be transported to a filler via a conveyor, rotary table or other delivery system.  The encoder can be mounted to a motor, drive shaft, or another suitable axis. When the proper number of counts is detected, the controller sends a command to activate the fill system. In many designs, the fill process is completed while the containers are still moving.



Because conveyors are widely used throughout almost all industries, and because they require varying degrees of control, conveyors are a very common application for rotary encoders.  Often, the encoder is applied to a motor and provides speed and direction feedback to the drive.  In other instances, the encoder is applied to another shaft, such as the head-roll, either directly or via a belt.  Finally, feedback can also be obtained by applying an encoder with a measuring wheel that rides on the conveyor belt; however, some segmented conveyor systems may not be suitable for measuring wheels.

Spooling or Level Wind


In spooling or level-wind applications, material such as cable or flat roll-stock is wound onto a spool.  It’s critical to maintain the proper relationship between the speed of the take up spool and the supply spool, since the material on both reels changes diameter as it is winding.  Also, most operations require monitoring of the length of material.  Finally, in many instances it is necessary to maintain the proper tension on the material to avoid stretching, breaking or winding too tightly or loosely.  Rotary encoders can supply the necessary feedback for all these functions.

X-Y Positioning


In X-Y positioning applications, such as automated pick-and-place, rotary encoders provide feedback on two axes of motion in order to determine X-Y coordinates.  The encoder can be attached to the shaft of a ball screw or the drive motor of an actuator. In some cases a pinion gear and rack system or measuring wheel can be used to provide position information.

Ball Screw Positioning


The principal use of ball screw assemblies is to mechanically convert rotary motion into linear motion.  They can serve for table positioning or linear actuator applications.  A rotary encoder, when attached to the end of the ball screw shaft or the drive motor, provides feedback used to determine linear speed, direction, rate and position.