adccommunitymod (AutomationDirect) asked a question.
EZ-T10C Touch Screen - Serious Problem
Created Date: September 21,2003
Created By: Sid
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I am using a T10C touch screen as part of the control on a PLC/Servo based infeed system on a Crank Pin Grinder. The various manual infeeds are activate by pressing and holding buttons on the touch screen. Unfortunately, on occasion, these have "stuck on ", allowing infeed when the operator has removed his finger. Obviously this is a very serious problem/safety issue. Is any else seeing this problem on the touch screens? (retaining signals when the "touch " is removed).
Created Date: September 21,2003
Created by: Sid
I am using a T10C touch screen as part of the control on a PLC/Servo based infeed system on a Crank Pin Grinder. The various manual infeeds are activate by pressing and holding buttons on the touch screen. Unfortunately, on occasion, these have "stuck on ", allowing infeed when the operator has removed his finger. Obviously this is a very serious problem/safety issue. Is any else seeing this problem on the touch screens? (retaining signals when the "touch " is removed).
Created Date: September 22,2003
Created by: HOSEY
Sid, yes this would be a problem, but you are putting this problem onto yourself. A touch screen no matter who produces it utilizes a protocol type scheme of either a serial protocol like directnet, k- sequence for Plcdirect or DF1 or DH+ like in an A/B product. It takes time to update these using a serial or other type of protocol and cannot be gauranteed under any circumstance. Just because a finger has been removed means nothing since you are sending data to the plc then the plc ack's or naks back. If it acknowleges it will then procced to send anouther string of data in wich the plc returns a string. This goes on until the specified data has been checked and verified using an end specifier. So if the Plc or the touchscreen is busy doing anouther task it will put the last task into a que so the task will become first in first out. I suggest that Push buttons be used directly.
The other part of this post of yours that deeply disturbs me is the fact that you are using servos and a plc but your are using a person to push the pb's on the Touch Screen. This seems like a waste.
To better use a plc and servo system would be to have a recipie do the control or a set path that is repeatable. The only time that you should have this type of control would be for jogging the part or setting the part up.
Created Date: September 22,2003
Created by: bcarlton
Please check that the bits being modified by the pushbutton are in registers reserved ONLY for writing by the display. The PLC program should not modify in any way the bits in these bit registers being used by the display. You may get a conflict even if the PLC is modifying bits not used by the display.
Created Date: September 22,2003
Created by: Sid
Reply to Hosey.
The problem is in deed caused by the signal protocol. ie. if the PLC or screen is updating while the touch is removed, the change in signal may not be registered and the system sees no change in status.
You are correct, to use a servo in such a way would be wasteful. Pushbutton infeed is used on initial manual set up only, to set the grind line. All auto motion is by canned cycle in the servo control.
We had already resigned ourselves to the fact that hard pushbuttons are by far the much safer option, in this instance.
Must advise that after updating firmware for both ECOM and EZ Ethernet today (prior to hard buttons being fitted) we have not experienced one hang up during a full day of testing (warily). Thanks for the input.