CANopen selected for carbon-fibre winding machine

The Sellers Engineering Company was founded in 1912 in Huddersfield, a town located in the heart of the Pennine Hills in northern England. By the 1930's the Sellers name was known nationally, producing an extensive range of reliable textile finishing machinery (see photo).

As an example, the Horizon model carpet-shearing machine became a household name in the industry and the accepted leader, with over 150 installations worldwide. Recent years have seen the development and introduction of the latest Excel Carpet Shear, complete integrated bitumen and PVC lines and the powder coating technology for broadloom carpets.

Sellers was approached by Tricast, a company that specialises in the manufacture of carbon-fibre tube production. Tricast was looking for a new winder machine to meet increased customer demand. Its existing mechanical machines, although capable of producing a very high standard of product, were not as versatile as Tricast wanted. Changing speeds requires manual pulley changes and other settings to be made, with the disadvantage of providing only step-changes in speed.

Speed and torque ranges

Ideally they were looking for a more automated product. One of the criteria required on this type of application is the wide range of speeds and torques required. The winder machine can be simply thought of as working similar to a lathe but instead of removing material, material is wound onto pre-selected mandrels in a controlled manner. These mandrels vary extensively in from 40mm diameter x 4500mm long to 650mm diameter x 4500mm long, with speed requirements varying from 1-1000 revolutions per minute. The mandrel design is of the hollow cylinder type, which meant that unusually high inertia loadings have to be controlled. Clearly a traditional type of motor would be unable to deal with this extreme speed range, high torque and high inertial loading with accurate speed holding, without the need for expensive and cumbersome gearboxes - which was something Tricast was looking to move away from. Adding to the complexity of this was a requirement to have a user-selectable carriage pitch; this has the effect of being able to increase or decrease the overlap of carbon-fibre tape per revolution; in essence this gives full control, providing 100 per cent profile selection, which is something a mechanical system is unable to do.

In the final machine design, two servo motors operated as a master and slave in gearing mode. However, rather than a classic servo motor being used, the design featured a high-torque direct-drive motor. These torque motors are good at producing high torque values over a speed range of zero revolutions per minute up to approximately 500 revolutions per minute. In this particular application, higher speeds were required up to 1000 revolutions/min. Torque motors have a high rotor inertia, which on this application provided an advantage by reducing the effective inertial ratio to an acceptable level without the need of a gearbox over the required speed range. A motor with hollow shaft was chosen, which simplified the mechanical integration and required fewer parts.

The HMI used in the application was the PP15, which has an integral PLC. The version chosen incorporates a dedicated numeric keypad for quicker data entry. Speeds, pitch and tension are easily entered, allowing complete repeatability time and time again. The integrated standard CANopen network was used to communicate with and control the servo amplifiers directly. No additional inputs or outputs were required because the onboard digital inputs outputs and analogue interface used for the load cell monitoring were more than sufficient.