Motion control applications are now frequently to be found in automation
schemes, but they are still regarded as a 'specialist' area, which some
OEMs are reluctant to embrace. David Ramsay explains how graphics based
programming can open up motion control for all
Fifteen years ago, PLCs were viewed as specialist products - to be
installed only by dedicated control engineers who had been trained to
programme and commission them. Today, the PLC is almost a commodity item
in control engineering terms, designed into systems as readily as timers
and relays once were, but offering so much more flexibility and
functionality. Motion control is now set to follow a similar development
path in response to industry's demands for faster and more flexible
machines with reduced cycle times and higher productivity.
The coming of the micro PLC provided an affordable entry level product
which gave users greater access to the technology. Cost-effective servo
systems with absolute positioning capability are already available as an
alternative to simple systems based on, for example, stepper motors, yet
they offer so much more functionality. The only barrier to user
acceptance seems to be the preconception that such programming is
difficult.
Acknowledging that the development of graphically based ladder logic, as
a recognisable standard programming tool, opened up the potential of PLCs
to control engineers, Mitsubishi has developed 'Visual Positioning
System' (VPS). The aim of VPS is to demystify positioning control with
the aid of a user-friendly front-end, and encourage more OEMs to
incorporate this technology as an affordable solution that customers will
increasingly be prepared to specify.
Operating as a standard Windows package, the VPS front-end presents an
operating panel that is similar to an HMI displaying a SCADA system. The
user visualises the positioning control strategy by moving through a
flowchart based sequence and being led through the programming step by
step as the machine moves from one position to the next. All the familiar
point, click, drag and drop functions are available. The value of this
flowchart approach is in the graphics, which are entirely intuitive and
understood by all, from engineering apprentice to manager.
While some engineering packages customarily offer fixed menus and
monitoring elements, VPS allows the user to create a monitoring facility
by dragging and dropping switch buttons such as 'start' and 'jog', as
well as any data device or diagnostic data to read back from the
controller hardware. Clicking the switch to 'monitor' mode renders all
these buttons interactive, so in just a few mouse clicks the user can
customise a jog test panel without having to download the data, change
parameters or make hardware adjustments. This valuable feature enables
the OEM to test positioning control solutions before attempting either
wiring or programming. Moreover, motors can be set moving by the
controller in just four of five mouse clicks. At only £95, VPS software
represents a minimal investment for those wishing to improve their
engineering capability in motion control.
And if you can't wait to get into motion, a free demo disk is available
to the first 50 readers responding via the postal reader enquiry service,
using the number below. You will find the reader enquiry card opposite
the inside back cover of this issue.
David Ramsay is Motion Systems product manager at Mitsubishi
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