Using a simple tension sensor - such as a spring and potentiometer - Roboteq controllers can be used to create electromechanical systems that produce constant pulling or pushing force. These techniques depart from traditional motion control and enable a whole array of innovative force amplification and stabilization applications.

Theory of Operation

The proposed technique uses the controller in position mode but where the feedback sensor is measuring force or pressure, rather than position. The motor's action result in moving the origin of that force until the force is at the desired level. The animated diagram below shows the technique in action.

The example shows a wire spool attached to a motor. The pulley on the spring shaft is used to create some tension on the wire when the shaft is horizontal.

When the wire is pushed back to the spool while the motor is off, the spring will pick up the slack, causing the shaft to move up. The potentiometer at the joint detects the position error and activates the motor until the shaft returns in the horizontal position.

If the wire is pulled while the motor is off, the shaft will rotate and elongate the spring. A pot at joint senses that the shaft is off center. The controller sees a position error and activates the motor until the shaft returns to the horizontal position

In a real situation, the detection and motor activation loop is done very quickly, so the shaft moves very little.

To build such a system, the controller must be configured in position mode. It is not necessary to send commands to the controller since the destination is always 0 (center). Motor will activate automatically as soon as the shaft move the pot off the center position.

Giving the controller a destination position different than 0 (not centered) will cause the rest position of the shaft to move up or down. In this way, it is possible to control the desired wire tension at rest. Commands can be sent to the controller via RS232, RC Radio, or an Analog pot or joystick.

While while all Roboteq controller models support the necessary closed loop positron mode, it is recommended to use one with dynamic braking:

• AX1500 for two motors up to 30A each or a single motor up to 60A
• AX3500 for two motors up to 60A each or a single motor up to 120A
• AX2500 for two motors up to 120A each or a single motor up to 240A

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