Introducing a radical new method of speed control

Edited by the Engineeringtalk editorial team Nov 2, 2000

Speed/torque control methods have until now all all used the interaction of differing circumferences, but Scram employs the entirely new principle of an extendible fixed period belt

Worldwide interest has been aroused by the unveiling of Scram (simple continuous ratio adjusting machine) at BBC Tomorrows World Exhibition in June, where two working prototypes were exhibited.

The invention has been, or will be, covered in editorial by sixteen engineering journals around the world.

These include Gear Technology and Machine Design in the US and Eureka and Drives and Controls in the UK.

Prior to this invention speed/torque control methods all used the interaction of differing circumferences.

Traditional stepped automobile gears and the Variomatic and Torotrak are examples.

Scram employs the entirely new principle of an extendible fixed period belt.

For example in one embodiment a coil spring is used as the belt.

This is driven by an encircling ring from which a bearing mounted lug intervenes between two windings.

One rotation of the ring will advance the belt by one winding, whether the coil belt is slack, or fully extended.

If, say, there are 100 windings in the coil belt, 100 rotations of the ring drive will bring the same winding back to the drive ring, however much the belt is extended.

Extending the belt will make an output pulley over which the belt passes run faster.

Other belts covered by our PCT patent application no.WO0019125 include elastic belts with discrete magnetic inclusions that are driven magnetically.

The simplest form of Scram consists of a suitable belt, a ring drive, an output pulley and an extending pulley.

This is not compact for widely varying ratios.

Compact embodiments use local extension of the belt by employing two synchronous drives.

Thus a hollow drive head rotatably mounted within a drive shaft continuously releases the belt over the output pulley and an identical head recovers (pulls) it on the other side.

Moving either of the drive heads within the shafts changes the length of belt running over the output pulley in a given time and so changes it's speed.

Scram is inherently efficient and requires little lubrication.

It is very simple and cheap to build.

Useful advantages over current gears and speed changing mechanisms include: Reduction -.

Scram has an inbuilt reduction mechanism.

The reduction ratio at any moment is 2x( number of windings in contact with the output pulley).

Automation - When load increases the gap between the windings on the pull side widen and close on the feed side.

This can be exploited to provide a completely compliant automatic gear with cruise control.

Scram is an extremely cheap and efficient method of speed control and will largely replace the inefficient and expensive methods of controlling speed currently employed with electric motors.

First applications are likely to be those where a high inertia load has to be accelerated to running speed before the motor is damaged such as starting conveyor belts.

Textile and video machinery, where thread or tape is wound onto a spool have always lacked an accurate speed control mechanism to cope with the increase in speed as the spool fills.

Scram answers that requirement.

Scram's unique ability to provide two separately continuously variable outputs from one input.

enables small vehicles to be steered by powering the wheels on each side differently, or to drive the wheels and blades of lawn mowers at speeds independent of the motor speed.

In refrigeration Scram's ability to change speed/torque quickly in response to demand would enable the production of efficient, cheap piston compressors and thereby enable use of air as the refrigerant.

Washing machines, lathes, mixers, power tools.

any application where speed or load changes will be improved by Scram.