Now there's an easier way to add closed-loop control to blow molding.

Increasingly sophisticated injection and blow molding processes are requiring more and more machine movements to be regulated in closed-loop fashion. A new add-on acceleration/deceleration card for Barber-Colman MACO 4000, 5000, and 6000 series controllers makes this easier than ever before, according to spokesmen for Barber-Colman Co., Loves Park, Ill. That firm and Bekum America Corp., Williamston, Mich., jointly developed the new cards to control movements of blow pins, molds, carriages, and simple robotics on shuttle blow molding machines. The cards are also applicable to other machines such as wheel blow molders and injection molding presses.

Although closed-loop control of some machine functions is already available on MACO controllers, molders' growing appetite for closed-loop control has tended to add cost and complexity. One solution, explains Barber-Colman product manager Bart Polizotto, has been to install an auxiliary motion-control module for each additional closed-loop function. However, this typically adds wiring expense and requires the user to manually enter motion information at multiple places on the machine. An alternative is direct closed-loop control from the central machine control, now made possible with the EZ PRO card, which eliminates the need for manual set up.

DIRECT CLOSED-LOOP CONTROL

EZ PRO offers quality advantages in blow molding when applied to shuttle movements, clamp opening/closing, and raising and lowering the blow pins. Barber-Colman says EZ PRO provides precise and consistent motions with loop closure rates of 0.1 millisec.

Faster and more consistent movements cut cycle times and improve part orientation, says Polizotto. Open-loop control of shuttle movement cannot compensate for process changes such as oil-temperature variations, and thus requires some reduction in speed to avoid hitting the mechanical stop. Closed-loop shuttle movement provided by EZ PRO results in smoother motion, avoiding sudden jolts and ultimately resulting in longer machinery life. Smoother shuttle movement also results in less parison swing and better alignment during mold closing. Also, greater consistency of clamp timing means that the clamp closes on the same profile point every cycle, says Polizotto.

The same factors apply to blow-pin positions and speeds. Precise stopping allows the blow pins to meet the mold more exactly and eliminates the need for mechanical stops.

EZ SET-UP

Centralizing control of all auxiliary machine motions in the MACO controller means that set-ups are included in the part recipe. Without EZ PRO, explains Polizotto, "If you were changing from a gas can to a sprayer bottle, your blow pins might stop in different positions, and you would have to adjust the mechanical track. With EZ PRO, you would just pull up a different recipe and it will load the proper setpoints."

An added benefit is that both velocity and position profiles are shown graphically on the MACO's operator screen - not an option when adjusting external control modules. Also, the MACO automatically develops multi-step velocity and position profiles, without the user having to understand complex inter-dependencies between variables.

EZ PRO incorporates several safety functions. One feature defines the fastest deceleration possible without harming the machine. Alarms can be programmed to terminate halted or delayed motions or ones that are not following the proper position/velocity curve. Alarms for "open excitation" and "out of calibration range" detect sensor problems.

EZ PRO is available with two or four channels, and up to two EZ PRO cards can be added per MACO chassis. Each card has four digital discrete I/Os. EZ PRO is priced at $3140 for the two-channel version and $4700 for four channels.

Barber-Colman offers the card to OEMs and to the aftermarket. Bekum has adopted the card for its BM-505D and BM-704DS shuttle blow molders, which will be exhibited at NPE next month.