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Swap control cards for PLC’s, reduce cycle time 20%

Blowmolding machinery manufacturer R&B Plastics Machinery, LLC (R&B; Saline, MI) has shifted to PLCs (programmable logic controllers) to manage closed loop hydraulic motions, replacing dedicated motion-control cards. The cards are inexpensive but can be difficult to coordinate with programming, leading R&B to Siemens Energy & Automation Inc. to integrate motion control functionality via PLCs for its blowmolding machines, including parison control.

to integrate motion control functionality via PLCs for its blowmolding machines, including parison control. The result, according to R&B, has been increased productivity, reduced machine-cycle times, and lower costs through component reduction.

R&B is using a standard Siemens S-7 PLC for its shuttle blowmolding machine with nine axes of servo-hydraulics (three for parison control and six for motion control). The line has two shuttles, two molds, and two blow pins, with clamp motions opening and closing the molds; blow pins moving up and down; and carriages, which hold the clamps, moving underneath the parison head, and then out to the blow station, in a standard shuttle set up.

Siemens and R&B customized the design of the function blow to reportedly achieve the same level of functionality and performance compared to a standalone controller.

The S-7 PLC’s motion control functions reportedly provide a greater coordination of the dry-cycle motions, reducing time intervals between actions and enabling multiple motions to be coordinated together so they are position based instead of time based. The companies report dry-cycle time reductions up to 20%.

In addition to positioning, the PLC is also controlling more than 30 zones of heat control from the hopper to the extruders and through to the parison head, with 12 zones for heat/cool, and 18 for heat only. 

The off-the-shelf Siemens S-7 PLC use function blocks written in standard IEC-61131 languages to control all servo hydraulic axes, without needing a different motion-control environment.

The advantages to using off-the-shelf PLC-based automation for blowmolding machines, compared to dedicated hardware for motion and parison control, are varied, according to Siemens and R&B. For one, by having all servo-functions controlled from one function block, machine cycle times are better coordinated and faster, with simplified and faster programming, as well as less equipment.

From a controls standpoint, the shift also allows the use of solidstate memory and elimination of third-party operating systems, with PLCs retaining data when they are shut off, including accidentally during power loss. In the end, one controller is managing PLC and motion-control functions, eliminating communication delays that occurred with stand-alone cards. In addition, the machines now have recipe storage for all axes, and instead of separate software packages that could only be used by a technician who understood a particular motion card, it’s all on the HMI (human machine interface).

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