What they are and how they work
Intelligent actuators have been developed for use in a wide range of applications, in particular repetitive, multi-position tasks, such as single axis robotic automation, for drilling, packaging and materials handling. They typically combine long term, high accuracy stopping of a piston in mid-stroke, even from high speeds, with programmable flexibility.
Although there are various methods of building intelligence into pneumatic actuators, those developed by SMC represent two of the most cost effective and reliable and are therefore worth describing in greater detail. It is important to note, however, that each technology will not necessarily be appropriate in every application and SMC’s technical department should be consulted at an early stage of system design or construction.
One of the simplest methods of introducing intelligence is demonstrated by the Series CE1 cylinder. This uses a special cylinder rod, manufactured from stainless steel, solution heat treated to 1100¾C and then drawn to reduce the original sectional area by thirty per cent; this has the effect of magnetising the rod. This is subsequently heat treated locally using a laser, to create a series of narrow bands of regular width along the length of the rod; these are alternately magnetised and non-magnetised. The rod also incorporates opposing flats, to prevent it rotating.
In operation, the 0.1mm wide bands are read by a sensor as the rod extends and retracts, enabling its exact position, with reference to a datum point, to be established. The sensor has two pick-up points, mounted one behind the other, both of which detect the presence or absence of the magnetic field and give two outputs A and B.
The use of twin outputs, when analysed by a suitable counter, enable a finer resolution that the 0.1mm pitch of the bands to be achieved while, by examining the sequence of waveforms, the counter can determine the direction in which the piston rod is moving.
Taking these developments a stage further, SMC has more recently introduced the Series CE2, which has a carbon steel piston rod, etched with grooves of regular pitch. The grooves are plated with nickel and then hard chromed to again produce alternate magnetic and non-magnetic rings which, in this instance, run completely around the rod, eliminating the need for flats to maintain suitable alignment.
The Series CE2 cylinder is then paired with an application specific controller, the Series CEU2, to give accurate local control of the cylinder and interact with a system PLC to give multi-position sequences.
The Series CEU2 controller ensures excellent repeatability, even over long periods with extended cycles. Stop positions are automatically corrected by a ‘try again’ (repeat) function, while a continuous learning function compensates for changing loads and other conditions.
Series CE2 cylinders are available in bore sizes from 40mm to 100mm in diameter and can operate at piston speeds of up to 500mm/sec, with positional accuracy being 0.5mm, independent of load and speed.
The controller can store up to 16 programs of 32 position sequences and is programmed via a simple keypad. This ability to store programs can help to significantly reduce set-up or change over times where the cylinder is being used, for example, on a flexible automation system handling more than one product.