Hydraulic press controls

[vettedrivr 0]

I am in the process of retrofitting a 4 post 500 ton hydraulic press with a new control system. I have read the OSHA standard for press controls which states if using a PLC for press control it has to be a redundent processor system. It also goes on to say that hydraulic presses are exempt from such requirements but doesn't say much else on the subject and OSHA requirements read like a mud cake recipe. I am planning on using a SLC 5/05 and panelview 550 as the main control and LDT's as ram and cushion position sensors. Several press control manufacturers have been contacted for the safety requirements and the ones that make dual processor controls (Including Allen Bradley) have told me that dual processors are Recomended but won't come right out and say that 2 processors are not absolutely needed. I will have all the usual safety equipment such as light curtains, anti-tie down two hand controls, gate interlock switches, and probably safety feedback relays. Did I miss anything in my reading or can someone show me what else is ABSOLUTELY REQUIRED. Thanks

[BobLfoot 302]

This may be no better at answereing your question, but I worked from 2000 to 2002 in the automation of an Upset Forge Shop. While under different regulations than presses in a lot of cases, some of what I learned and saw may prove useful. Our Kentucky Labor Cabinet actually publishes an interpretation document of ANSI B11 and the OSHA press standard. The old phrasology was "self - checking" for all actuation controls. The new term is now "control reliable". We used dual SLC 5/05's on our medium and large presses and a single fail safe SLC 5/05 with dual I/O and dual i/o paths back to the processor on out small presses.

[TConnolly 13]

Why the 5/05? SLC5/05 are a great deal more expensive than a CompactLogix. AB also offers a canned system for press control that is based on dual ML1500s. Again, the ML1500 is a lot less expensive than the SLC5/05.

[BobLfoot 302]

In 2000 CompactLogix did not exist, ControlLogix Gateway had just hit the market and the ControlLogix L1 CPU was still a good six months from existing for sale. The ML 1000 had also just come out and the 1200/1500 were still on the design board. AB's canned system for presses with dual SLC's featured the SLC 5/03 and could be upgraded to Dual 5/05 if you wanted ethernet. How quickly we forget that today's great processors are just that.

[Peter Nachtwey 15]

The speed or size of the PLC doesn't make much difference if you use a hydraulic motion/force controller that can synchronize the acutators and do the force/pressure control. We have been involved with numerous presses. The presses had a PLC and a hydraulic motion/force controller that can synchronize a 4 post press and do the pressure control too. The PLC counts as one and they hydraulic motion controller counts as another. The communications between the controller and PLC were done by Ethernet or Profibus DP. Using the hydraulic motion/force controller relieves the PLC of all the fast deterministic code so even a small automation direct can do the job because all it needs to do is keep track of the safety features and turning on the HPU etc. Even if you use a hydraulic motion/force controller, a four corner press is not a simple application. The hardest part is getting the hydraulic design right and the force sensors mounted correctly.

[BobLfoot 302]

Interesting thought Peter. In our Upset Forge Press applications the PLC did everything. Safety, Motion Timing, Force Monitoring, Lubrication and Data Logging. Quite a pain and a lot of code. The production people were tired of a Trabon Lube contoller readout, A toledo pressure sensor readout, a dataliner plc readout and timing chains and gearing for moton. They wanted a "one box" control feel. I'd still be interested in who is making your motion controllers?

[gravitar 3]

I think the query was directed toward the person who started the thread, who is contemplating using a 5/05 in the present day!

[vettedrivr 0]

Thanks for the responses guys. Just to clear up a few points, we have standardized to Allen Bradley PLC's 20 years ago. In the last 9 years my plant has gone from 11 PLC's to 44 PLC's. The SLC 5/05 will be used because of the ethernet capability and the fact we are moving toward data and production number gathering as part of engineering and production management involvement although no initial data will be taken from the press production. We presently have no compact logic or control logic controllers in the plant and unless we find a specific need for them they will be slow in coming. I realize Rockwell Automation makes a packaged press control (Omega) geared more toward mechanical stamping presses and it was then shoved over into hydraulic press control packages just as a way of selling more press control units (I've spoken to their reps on this). In fact, some of their press control configurations call for a THIRD SLC 500 processor to take care of additional logic that might be needed for other options. OSHA 29 CFR 1910.217 addresses mechanical stamping presses and excludes hydraulic presses. ANSI B11 section doesn't say anything new and ANSI is only a suggested guideline anyway. If spoken to press control manufactures who provide control packages with a single processor and those that have packages with a dual processor and I'm getting the run around as far as what I have to have. Everybody gives me an opinion on what is needed based on what they have to sell me. I have retrofitted a lot of machines to PLC control but never a hydraulic press. Now, does anyone know what I ABSOLUTELY HAVE TO HAVE as far as single or dual processors to retrofit my press. Thanks in advance for your input.

[Peter Nachtwey 15]

We do! See this thread http://forums.mrplc.com/index.php?showtopic=7679 and this site http://www.deltacompsys.com/ A Rockwell PLC can use MSG blocks or Ethernet/IP to communicate with our controllers. We were at the last metal form show in St Louis. Vetteboy, you should have gone. You could have got the information you needed then and there. Hydraulic servo position and force control is what we do. We design make our own hydraulic controllers and for others like Rockwell like the 1756-M02AS, 1756-HYD02 and 1746-QS. The 1756-M02AS works well with rotoary motion applications to. Our controllers allow one to mix and match feedback devices like MDT and analog or SSI and analog. The analog is for the pressure/force feedback. Vetteboy, I am not a press OEM although we do sell hydraulic controllers to press OEMs. We have one press OEM customer that does the whole press control just using our hydraulic controller. I would not take this to mean that only one controller is required. I am just saying I have seen it done. These were smaller 25 ton C frame presses. BTW, we got designed in after they tried to do the pressure control with a PLC and failed. Frankly, I haven't seen many press manufactures that really understand the interrelationship between hydraulics, mechanics and control. This is harder yet for people that are trying to upgrade their press for the first time.

[vettedrivr 0]

Thanks, that does answer my question. I would have liked to have gone to the St.Louis trade show but I would have had to take vacation time to do it. You nailed the problem I've been running into, people with press controls to sell and not enough cross technology knowledge to carry them through. I will proceed with the retrofit using as many safety features as possible (Light curtains, gate interlocks, backup pressure control/monitoring, anti-tie down two hand operation, safety relays, and so on). If anyone has anything further to add I would appreciate your input. Thanks.

[Peter Nachtwey 15]

I know people that have the knowledge. None work for a press manufacturer. I too know a lot. How can one make a product for doing press control without the knowledge of the process? Here is a graph of a silicon rubber press that make power line isolators. This press came in two sections. Each section has 2 20 inch dia main cylinders and 1 inch jack ram. The two sections had to be synchronized. ftp://ftp.deltacompsys.com/public/jpg/LAWTON.JPG This press was made by CA Lawton in Green Bay, WI and sold to NGK, the same Japaneese company that makes spark plugs. I did the PID and control programming you see. This data was gather for the acceptance test which was passed easily in fact the NGK people couldn't believe it. What kind of press are you upgrading?