Support > Knowledge Base > XL200 Series Controllers > Parameters > Shear Dwell Down
Shear Dwell Down
Help ID: 121
Initial Version: 1.0
Appears In: All Software Models Except XL208CL
As of the publishing of this webpage (09/21/10), the assumption of the software of every XL200 Series controller is that it controls a cutoff (shear) press, regardless of whether or not the cutoff is an actual shear, slug die, saw, etc. The XL200 simply turns on a digitial output for the programmed Shear Dwell Down time.
The Shear Dwell Down parameter allows the user to define how long it takes the shear to cut, or break through, the material. In most applications, this value is set for the time required to cut through the thickest material the production line will run. Depending on the application, it might make sense to change the time based on material thickness and line speed.
Regardless of the physical requirements for the setting, it is important to note that the XL200 Series controller does not dictate the speed of the press. Some users see a correlation between the parameter setting and the amount of time the press fires. The actual press speed is a function of the mechanics of the press, itself - stroke, hydrualic or pneumatic pressure, flow, mechanical linkages, etc. What this means is the controller does not control press speed, the parameter is so the XL200 can know how long it takes for the press to do its job.
Corollary
Regardless of the type of press or any other factors (including parameter settings), the Shear Complete input to the XL200 Series controller always overrides the programmed Shear Dwell Down time. This functionality exists to help support systems that use a mechanical press. In open loop flying die applications, press consistency directly affects part length. Often, press manufacturers will use a PLC or a set of latching relays (logical flip-flop circuit) as an "anti-repeat" circuit. Used in combination with a cam sensor, this prevents the press from over/under rotating, and helps it to return to top-dead-center (TDC).
Most PLCs and mechanical relays have a timing variance of several milliseconds. This timing variance will manifest itself as a length variance that corresponds to line speed - the faster the machine runs, the worse the variance. To help minimize stopping variance on a mechanical press, the XL200 Series controller can be used to fire the clutch/brake solenoids directly, and the cam sensor can be tied to the controller's Shear Complete input for millisecond control to help stop the press more consistently at TDC.
The millisecond the XL200 Series controller receives the Shear Complete input, it turns off the Shear Down output. For software models with a Shear Up output, that output is immediately fired for the programmed Shear Dwell Up time.
Specific to Open Loop Applications
In open loop feed-to-stop applications, the Shear Dwell Down parameter can be used in conjunction with the Tolerance parameter to pre-fire a slow moving press in order to minimize wasted time stopped and increase throughput. The controller performs 2 tests as it's bringing the material to a stop to determine if it can fire the shear:
- The controller checks to see if the shear point is within the programmed Tolerance range.
- The controller checks to see if the material is "close enough to stopped". This software function calculates Tolerance/Shear Dwell Down to find a speed in inches per second. If the target is within Tolerance, and the material is at Tolerance/Dwell or lower, the Shear Down output is fired.
For presses with a long reaction time, this allows the user to pre-fire the press so the tooling is almost in contact with the material by the time the material actually stops. This minimizes the amount of time the machine must be stopped for press operations and helps maximize throughput.
Specific to Closed Loop Applications
For closed loop flying die systems, the Shear Dwell Down parameter is not only the amount of time to fire the press into the material, it is also the amount of time the cutoff die must match speed and position with the target while the press is being fired. During this time period, the XL200 Series controller will command the servo to do whatever it sees the material doing in terms of speed, direction and position. This compensation occurs in real time.