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Hot off the press

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THE Ford Motor Company of Australia (Geelong) blanker 5 press is critical for the stamping plant. The old press control system relied on an external device to control the programmable limit switch (PLS) output, and slide adjustment was done manually.

With the incorporation of Modicon Concept Derived Function Blocks (DFBs) into the main Modicon Quantum PLC application program, PLS control and slide adjustment control are now performed automatically.

Ford was using an external device to control the PLS outputs - which is also responsible for slide angle resolver inputs, press motion detection, stoke rate and program selection. These outputs can be configured via an array of parameters, including dwell on or off, multiple dwell, simple dwell, timed dwell and speed compensation.

Schneider Electric ’s Forming Applications Business (FAB) utilises a similar approach to configurability for control of PLS outputs; however, its press control systems are PLC-based and do not use external devices for slide angle resolver inputs, motion detection, etc.

Instead, a PLC running Concept IEC-61131 programming software is responsible for all the controls related to the press.

Two separate smaller PLCs are responsible for clutch/brake control. Resolver inputs come directly into the PLCs by way of resolver input cards. The PLCs are responsible for activities such as motion detection, stroke rate and interfacing with a single HMI device. Outputs associated with the PLS functions derive from PLC output cards as opposed to an external device.

Based on comprehensive PLC-based system layout (as opposed to a press control system with sub-components like the external device), a software module in Concept IEC-61131 ladder logic is used to control the PLS outputs. This module accepts configuration parameters for the operation of the PLS outputs from a human-machine interface (HMI) computer.

These outputs may be turned on in four different modes.

The PLS software module can accommodate up to eight outputs.

The slide adjust software module has the following Concept sections: Slide-Adjust-Logic and Slide-Adjust-Faults.

Slide-Adjust-Logic contains logic that interfaces directly with a slide adjust resolver input card from AVG Autotech (SAC-TX-103-M0000). This module resides in the Quantum PLC’s local rack, and accepts a standard, multi-turn resolver input for slide adjust position.

The set-up logic for the AVG TX-103 card occurs at the beginning (top) of the Concept section.

The logic section of the module relies heavily on a slide adjust DFB, developed by Schneider Electric FAB, which hooks up to Concept variables in an array of input and output variables.

The general operation of the slide adjust module is as follows:

• The AVG TX-103 card reports the raw position of the slide adjust to the PLC.

• The software module scales the raw position based on a circular offset, scale factor and minimum position to obtain an internal working value (type DINT) scaled as inches *1000.

• The HMI reads the actual slide adjust position, scales it accordingly, and reports it on a screen.

• When a manual slide adjustment is performed (key switch input in manual position), the up and down pushbutton inputs are used to engage the up and down motor outputs, respectively, when all the required interlocks for slide adjust operation are present.

• When an automatic slide adjustment is performed (key switch input in auto position), either the up or down pushbutton inputs initiate an automatic slide adjustment when all the required interlocks for slide adjust operation are present. The control module automatically attempts to adjust the position from the current actual position to the target (in the Target register, as sent to the PLC by the HMI).

• The automatic slide adjustment will perform up to three attempts to adjust the position to within tolerance, making corrections to the glide of the slide after the motor is disengaged after each attempt.

• The tolerance is defined within the module as +/- .005 inches.

• If the automatic slide adjustment fails to adjust the position to within tolerance after three attempts, a fault coil is energised in the faults Concept section.

By automating the slide adjustment, Ford has achieved consistency on this setting, thus increasing quality of the final product.

Use of DFBs can make a Concept PLC program more modular and improve the readability of the code.

DFBs help significantly with troubleshooting problems because, in principle, once the logic in a DFB is proven, it does not need to be modified.

Without DFBs, sections can become very cluttered with logic that is unrelated to the problem being investigated. Looking at less allows a user to identify a problem more quickly, and provides a portable code module that can be used on other machines.

The PLS output software module and slide adjust software module utilise DFBs for these reasons. Sections are less cluttered because the  gcore h logic is contained in the DFB, with external inputs and output being tied to the pins on the DFBs.

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