Jones and Shipman now offering high-speed adaptive control for grinding

Jones & Shipman now offering high-speed adaptive control for grinding

Keywords Grinding,Software

The advantages of simple adaptive controls have been recognised for some time and employed for metal-cutting operations, notably turning. Now, a two-year period of research and development work carried out by Jones & Shipman International in collaboration with Liverpool John Moores University has resulted in, among other innovations, the introduction of high-production adaptive control software, which is optionally available on the company's new range of Supromat and Ultramat cylindrical grinders (see Plate 4).

 Plate 4 Jones & Shipman International adaptive control power monitor screenshot, showing typical power curve.

The development programme was undertaken by two graduate engineers from Jones& Shipman International, under the Teaching Company Scheme, Andy Thomas, who won his Doctorate in the course of this work and Craig Statham, who is a registered PhD, student. The project entailed writing intelligent algorithms for Jones & Shipman developed PC software in conjunction with GE Fanuc 180 and 210i series open CNC systems, and culminated in the identification of two practical adaptive control strategies; namely, "auto dwell selection"and "feedrate update".

How auto dwell selection improves surface finish

It was found that, during the spark-out period of a cylindrical grinding cycle the forces encountered at the grinding interface decrease in a predictable fashion until the part reaches the designated diameter. Deflections in both the component being ground and in the machining system are characteristics of this decay, which is also influenced by the sharpness of the grinding wheel. A significant feature of the auto dwell strategy is the way it makes use of the basic knowledge that the amount of electrical power needed by the grinding wheel motor is proportional to the grinding forces encountered.

Additionally, by measuring the wheel power at the start of the dwell, and by applying a suitable mathematically calculated curve fit, it was possible to predict the length of time for the exponential decay curve to reach no-load power. Thus it becomes possible to make an in-cycle determination of the optimum dwell period required to bring the part to size, thereby ensuring roundness of the part and also improving the surface finish.

The feed rate update functions

A valuable by-product of the auto dwell strategy is that the maximum grinding power encountered during the cycle is recorded. Armed with this knowledge, a"feed rate override factor" can be computed, which can then be applied immediately in the production of subsequent components of the same batch and can result in a significant reduction in cycle times if, as is often the case,over-conservative feed rates have been entered into the initial program, perhaps as a play-safe precaution.

400 per cent increase in productivity

Practical tests with a lead customer, Kegworth-based Slack & Parr, have been highly successful. With a Supromat machine, which had been set up to grind a long, slender drive spindle supported by a single steady, a plunge-grind cycle time of 90 seconds was reduced to 22 seconds, thereby showing a 400 per cent increase in throughput for this particular operation.

After using the adaptive control system to grind around ten parts, an optimum power level of 40 per cent was established. The feed-factor and dwell period values were found automatically without any parts being lost throughout the entire trials process. The customer is reported to be extremely pleased with the results and, as well as fixing the optimised grinding values into the part program, is investigating the use of the system for several other applications.

For futher details contact: Jones & Shipman International, Narborough Road South, Leicester, LE3 2LF, UK. Tel: +44 (0) 116 289 6222; Fax: +44 (0) 116 289 2945; e-mail: sales@jones-shipman.co.uk