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Product category: Industrial Drives/Controls
News Release from: Precision Motion (Cofil) | Subject: Cam devices
Edited by the Engineeringtalk Editorial Team on 11 September 2001

Reduce power consumption for positioning

A demonstrably reduced power consumption will improve the sales prospects of those who use the opportunity to use cam devices, instead of servo motors.

A demonstrably reduced power consumption will improve the sales prospects of those who use the opportunity - other things being equal Many machines in automation positioning; packaging; machine tools etc., use drives which we may collectively descibe as intermittentor oscillating motions

Generally, a cam driven device is more efficient than a servo drive, and very much more efficient overall than an air driven device.

(See below some reasons why this is true).

Therefore, forward thinking designers will want to give this advantage to the end user, and should consider a cam solution to problems of intermittent motion, wherever possible and convenient.

Where is it possible to use a cam device and where is it impossible ? To answer this question, it is necessary to distinguish between 2 types of required intermittent output motion; they are:- 1 -- those that call for defined output stroke(s) (rotary or linear),which will never change, e.g 90 degrees of rotation, when required.

2 -- those that call for a variable output stroke according to desire or automatic instruction.

The first strongly suggests a cam device as the best solution; the second must have some other electrically or electronically controlled variable system if it is to have fast accurate results without shocks.

There is no escape from the laws of physics! The required intermittent motions within the machine, inevitably, will call for a net input of energy at certains moments, in order to accelerate the machine masses.

Conversely, at other moments in the motion cycle, those same parts are required to decelerate and thus they must dissipate energy.

If there be several such motions in the machine, out of phase with one another, then clearly the opportunity arises to transfer the energy from the decelerating mass to the mass which requires acceleration.

This is usually achieved automatically by a mechanical linkage between those parts, e.g a drive shaft.

result is that the nett energy requirement can be very small - largely to overcome friction.

This is usually of a much smaller order than the energy requirement to accel/decel masses.

contrast this fundamental idea with the idea promoted by servo suppliers, where one is encouraged (often for doubtful reasons) to drive each intermittent component by a servomotor.

In such case, there must be an energy input to accelerate and an energy input to decelerate.

The stored energy of each moving mass is "destroyed" (not transferred) and is given off as heat at the motor.

There is another aspect in which a cam device is frequently more energy efficient, even for those machines in which only one main part is in intermittent motion, and thus where parts linkage is not an option.

By definition, intermittent motion involves accelerations and decelerations.

Other things being equal, the peak input torque required will be a direct function of the peak accel.

or decel.

cams commonly use more sophisticated mathematics of motion "law" than are normally used by servomotors.

Net result: significantly lower peak accel/decel = lower peak torque = smaller motors (to say nothing of the fact of reduced shocks and smoother more gentle operation for exactly the same cycle time).

Our experience shows that where our cam devices have replaced servomotors and other electronically controlled devices; the motor power required and used is usually lower and sometimes embarrassingly lower.

We suggest that to use a servomotor for fixed output stroke intermittent motion, is a poor solution and expensive to run.

To use air or hydraulics, usually gives much worse results, and is dramatically more expensive to run even than electronically controlled motors.

There are many other benefits from cam systems which therefore result in a superior combination of: speed; accuracy; reliability; first cost and running cost.

Morover, in the unlikely event of a disaster, staff of ordinary qualification can easily analyse the problem - meaning that a cam system can be used in wider market than esoteric electronic systems.

Conclusion: Precise intermittent drives, run for the lowest cost, use cam Mechanisms.

IF output stroke is defined and fixed; you can use cams.

IF output stroke is undefined/variable; you cannot.

The biggest range of types of cam devices on the market is from the biggest such specialist cam device firm in Europe; who in GB are known as Precision Motion (Cofil) based at Preston and Oxford.

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