The use of LPT indexers appears to be an inexpensive way to automate a machine. Indeed the parts cost for stepper motor based systems can be competitive,
even when the additional electronic items required to implement a working control system are included. When servo motors are used any cost advantage is lost
as brushless drives compatible with step and direction signals are more expensive than those operating from + 10v.
However a major additional cost incurred when using LPT indexer based control systems is the complexity of and time taken to build the complete control
system. System interfacing and wiring is complex, it takes many hours to implement, and complicates subsequent maintenance.
A further problem in an industrial environment is the susceptibility of LPT based machine control systems to electrical noise. This is due to wiring
complexity, the use of TTL level signals, and the absence of optical isolation.
An additional problem in an industrial environment is the poor level of safety associated with Emergency STOP switches unless additional safety
components are integrated.
When you add the disadvantages of poor system performance when performing 2 and 3D engraving to the above, using an industrial quality 'standalone
controller' is a far better solution.
Upgrade
A considerable proportion of the time taken to upgrade the system was spent in disconnecting and removing redundant items. These included, three
parallel ports, two power supplies, two custom signal interface boards, an Opto 22 output board, additional contactor contacts, and a lot of electrical
cabling shown above.
The machine is now controlled using a standalone AMC B 3 axis stepper controller plus a remote graphics handpad. The machine controller was installed and interfaced to the existing drives and other
I/O devices including the Yaskawa spindle motor drive in just a few hours and the machine was soon moving reliably and rapidly.
The machine is controlled from a PC based Touchscreen by four custom control panels generated using WinAMC®.
The main control panel shows machine X, Y and Z position numerically, the spindle speed using a meter, the current part program name and run time, the
current part program feed rate, and the feed override control. Part programs can also be selected, run, stopped, continued or aborted. Part program
progress is displayed both graphically and by highlighted command lines. Keys are provided to access a Machine Setup panel, a Jog panel, and a Tool settings panel.
The Machine setup panel permits tool parameters to be set, the machine to be manually moved to precise positions and the home (park) position to be set and moved to.
Tools can be selected and automatic tool length compensation set. Accessible tool parameters include depth, clearance, tool down and up speeds.
The Jog panel permits any machine axis to be moved. The unique jog controls are elongated arrows. Jog speed increases as the pointer moves towards the arrow tip
and slows the further away the pointer is from the tip. This feature mimics AMC pressure sensitive machine jog keys enabling machines to
be precisely positioned.
The Tool settings panel enables the operator to monitor and set parameters associated with the tools.
Benefits realised
- The retrofit was carried out in 2 days
- Reliable machine operation
- Considerably increased machine productivity , especially when routing 3D parts where increases of 300% to 1000% were achieved, dependent on the part program.
- Maximum machine traverse speed increased from 900 to 1500 inches per minute
- Easy to use control system utilises PC based custom control panels in multiple languages generated using WinAMC®
- Machine is now easily maintained, standard parts are available
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