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Speed loop module gives full feedback

A Control Techniques Dynamics product story

Edited by the Engineeringtalk editorial team Feb 13, 2002

Novel speed loop (SL) module technology forms the basis for a new speed and position feedback device.

Such is the success of Control Techniques Dynamics speed loop (SL) module technology, now offered to customers as part of its range of Unimotor AC brushless motors, that other motion control companies are showing interest in the product.

The only company able to offer this technology, CT Dynamics is assembling the high-performance feedback device on a full production line basis and with fully automated testing facilities.

Offered to customers as a standard option, the system is a speed and position feedback device for use with the M'Ax range of Control Techniques servo drives and Control Techniques Dynamics permanent-magnet Unimotor SL motor range.

The module is mounted directly on the motor and combines a high-precision sin-cos encoder, DSP and a high-speed two-wire RS485 serial communications interface operating with the Drivelink protocol for data transfer to and from the drive and motion controller.

The module samples the shaft speed and position every 30us to a resolution of one eight-millionth of a revolution.

The following information is then transmitted over the serial communication link: position and speed demands from motion controller; position feedback to the motion controller; current/torque demands from the drive; and parameter values.

By the factory programming the onboard memory with all relevant motor parameters, the Control Techniques Dynamics SL module offers complete "plug and play" facilities with Control Techniques M'Ax drive.

The close proximity of the encoder and electronics enables low noise interpolation resulting in its very high resolution of 8 million counts per turn.

With automatic local control of the motor now provided through the SL, CT Dynamics has been able to reduce the number of cores needed in the feedback cables.

This makes cabling quicker, simpler and easier to carry out.

Signal connections to the motor are limited to just four wires including the DC power and digital communication, and is not subject to error tolerance due to system noise.

Feedback resolution and jitter-free system synchronisation is such that acceleration feedback can be computed (double differentiation of position).

A stable response can be achieved accelerating or when a load disturbance occurs while running at a constant speed.

Extremely sensitive speed control is possible through the system's ability to detect very low levels of acceleration induced in high inertial loads combined with its associated torque variation.

There is no performance degradation in noisy environments and no loss of feedback information during fast transient disturbances.

Forming part of its ongoing commitment to new technology and product improvement, CT Dynamics expects the SL module will prove its largest growing sales option during 2002.

To meet this growing demand a dedicated production area with full electrostatic (ESD) protection has been created at CT Dynamics factory in Andover Hampshire.