Machine Design

Servopneumatics speed beverage packaging

The system consists of three components: a high-bandwidth pneumatic servovalve, an electronic control card, and a custom-designed low-friction pneumatic cylinder with integral position feedback.

A single motion profile is necessary for a simple decision to reject containers that are all the same size. Displacing containers different distances onto different conveyor lanes requires a separate profile for each defect. Additional profiles are needed for containers of different materials and sizes. The computer determines precisely when to send a motion profile command to the rejection unit. The operator simply selects appropriate profiles before inspection.

A new high-speed servopneumaticactuator system automatically rejects defective cans and bottles from beverage-packaging lines operating at speeds from full stop to 1,200 containers/min. In addition, containers of similar weight can be sorted automatically onto different conveyor lanes at maximum line speed.

Until now, pneumatic control systems generally have relied on conventional four-way on/off solenoid valves for motion control. These systems use mechanical stops and manual flow-control valves that must be adjusted each time the motion profile changes.

Conventional systems also need adjustments on stops and valves each time a different size container runs through an inspection head. Otherwise, containers tip and spill when rejected from the line. In addition, beverage-packaging lines using solenoid valves often require two or more rejection actuators to accommodate high line speeds or sort containers of varying size.

A new rejection-actuator system, however, uses software to select motion profiles for pneumatic servovalves. The number of controlled positions along the actuator stroke is virtually unlimited, which permits precise tailoring of load position, velocity, and acceleration to a wide range of industrial applications.

In one application, the rejection-actuator system works in conjunction with X-ray and video cameras that automatically detect container imperfections, such as low liquid level, misplaced labels, cracks, or foreign objects. The rejection system mounts 1 to 2 ft downstream from the inspection station.

The system consists of three components: a high-bandwidth pneumatic servovalve, an electronic control card, and a custom-designed low-friction pneumatic cylinder with integral position feedback. The electronic controller receives an analog signal from the inspection-station computer. The controller inter-faces with the pneumatic servovalve, which mounts on the cylinder, and with a linear variable differential transformer (LVDT) that is built into the cylinder and senses position.

The cylinder mounts perpendicular to the direction of conveyor travel and extends to displace defective containers from the line. The electronic controller, in a closed feedback loop that is independent of container speed, continuously adjusts actuator motion during the rejection cycle. Rejection is smooth and consistent at speeds from full stop to 20 containers/sec, even when containers touch. Containers of varying height, diameter, material, and fill weight are rejected without tipping or spillage.

Only one rejection-actuator system is required for each installation regardless of line speed or container type. The entire assembly is just 6 X 9 X 14 in. with the actuator retracted. Installation in existing equipment takes a matter of hours and the system operates on shop air. All components are rugged and withstand washdown. The pneumatic cylinder has a rod cover and scraper to prevent internal contamination.

A key component in the rejection-actuator system is a new high-bandwidth Model 27C R-DDV rotary direct-drive servovalve from H.R. Textron. The servo-valve's frequency response exceeds 150 Hz, and high pneumatic bandwidth allows rapid flow-rate adjustments when the electronic controller receives a new motion profile. High bandwidth also enables tuning the system for maximum repeatability.

Loads, excluding the container, weigh about one lb. Maximum velocity for the combination of servovalve, load, and actuator is 100 ips. The rotary direct-drive valve controls flow in a single stage, independent of supply pressure. Single-stage flow eliminates springs, nozzles, filters, and pilot valves normally required in servovalves, which significantly reduces costs.

This information supplied by HR Textron Industrial Products, Santa Clarita, Calif.

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