A one-and-a-half axis controller
Original article date: October 1999
By only having to control one axis at a time, this new controller benefits from exceptional performance, as David Norris has been finding out
Some clever technology has gone into the new PM600 digiloop motion controller which Mclennan Servo Supplies is launching. In particular, a new development of Mclennan’s control algorithm enables high positional accuracy to be achieved, but with zero deadband, even if remotely-mounted encoders are used for the positional feedback.
To enhance system stability, a dual encoder feedback technique has been used. Furthermore, the PM600 is equipped with three encoder inputs so as to allow this feedback technique to be used when one axis is to be slaved to another. In order to give the PM600 good repeatability, high-speed registration hardware has been used so that reference signals can be detected with zero error.
For cost-sensitive applications where motion is required in two axes, but not simultaneously, a single PM600 can be used to control both – hence the reference to a one-and-a-half axis controller. Nevertheless, with the PM600 priced at around (UK pounds)400, there will be many applications where it will be very cost-effective simply to install one unit per axis. Also, because the units are compact, there is not a significant requirement for cabinet space if multiple controllers are installed.
Despite its low price, the new controller is an extremely versatile device. For example, it provides both analogue and digital output signals, so it is suitable for use with either servo or stepper motors. And, in addition to bi-directional limit and datum inputs, there are 16 user-definable digital I/O and analogue inputs are provided to enable interfacing with other machine functions. Meanwhile, with operating speeds of up to one million counts per second and a positioning range of +/-2billion counts, the PM600 is a truly high performance motion controller. In many respects the exceptional performance and smooth motion result from the fact that the PM600 is a single-axis controller and the processor therefore does not have to supervise multiple axes. Loop control is therefore tighter, which results in zero error.
Apart from straightforward positioning, other standard control functions include electronic gearbox, flying shears and electronic cams.
- McLennan
October 1999