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Product category: Hydraulic Components
News Release from: Bosch Rexroth - Hydraulics | Subject: HACD digital controllers
Edited by the Engineeringtalk Editorial Team on 17 October 2006

Hydraulic upgrade boosts productivity

Linear slide manufacturer Accuride is benefiting from improved manufacturing productivity, enhanced reliability, reduced chemical consumption and faster startup.

Following the upgrade of its plating line hydraulic power-pack and control system, linear slide manufacturer Accuride is benefiting from improved manufacturing productivity, enhanced reliability, reduced chemical consumption and faster startup Designed and manufactured by Bosch Rexroth Sales Partner, Kanflu, the system centres around a new generation of Rexroth HACD digital controllers

Accuride's Northampton site employs 200 people, it was here that the company decided to upgrade its plating line and used the opportunity to embrace a new generation of power-pack and control technology.

Plating quality and uniformity are critical to the performance of the finished linear slides.

In addition to providing a corrosion resistant and aesthetically pleasing surface, the plating has a direct impact on the slide's mechanical performance.

Fine rectification and process control is required to provide a smooth, precise plated bearing running surface.

Any unevenness would lead to a rough, inferior bearing movement.

In operation, three pairs of hydraulic cylinders are used to 'step' the jigs through the plating process, while a seventh cylinder vertically lowers the jigs into the baths/stations, holds them for a set period, and then raises them.

The single lift cylinder powers a series of linear chain drives which lift the individual jigs.

The decision to upgrade the hydraulic power-pack and control gear was initially driven by obsolescence issues: it was becoming increasingly difficult to source spares for the original system.

Having justified the upgrade from a maintenance perspective, Accuride then decided to capitalise on the decision by updating the technology.

At the heart of the new system lie seven Rexroth Eurocard format HACD digital controllers.

Six are used to control the three pairs of transfer cylinders via proportional valves, while the seventh is used to control the lift cylinder.

Key reasons for choosing the HACD for this application included accuracy and ease-of-use.

No programming knowledge is required because applications are built using predefined function blocks.

Each block contains command and control parameters, with blocks triggered by a variety of conditions such as digital inputs, analogue signal comparison and dwell time.

In this application the HACD controllers were configured using a laptop PC via software which can be freely downloaded.

Another important feature of this controller is its optimisation for specific valve characteristics via a predefined valve database.

Additional hydraulic features include overlap jump, spool jump and creep/residual velocity.

Accuride designed and manufactured the enclosure housing the seven HACD controllers.

The cabinet provides access to the front mounted RS232 ports.

Together, the new controllers, proportional valves, high-flow power-pack and transfer cylinders had an immediate effect on productivity.

Prior to the upgrade, the original cycle time was 20s.

Now, by improving the synchronisation of the transfer steps, the cycle time has been reduced to 17s: an improvement of 18%.

The reason the original system had difficulty synchronising the transfer steps was load variation.

For example, because each jig can carry varying numbers of differently shaped components, the force required to pull the jigs through the baths changes at every process step.

Thus, the side of the line with the lightest loaded jigs would complete its cycle first and then have to wait for the opposite side to catch up.

Now, using digital encoder feedback, the HACD controllers can sense and compensate for any imbalance between the transfer cylinders, ensuring each process step starts and finishes in synchronisation.

Lift cylinder positional feedback is provided by a wire encoder, while transverse cylinder sensing is managed by a noncontact magnetic transducer.

With the controllers compensating for varying load conditions and offering digital positioning accuracy, the likelihood of the cylinders juddering or touching their end stops has also been eliminated.

This has resulted in smoother motion, reduced maintenance and less likelihood of components jumping off the jigs.

If an emergency stop is activated the system still comes to an immediate halt.

Another unexpected productivity improvement relates to warm-up time.

With the previous control system sensitive to load variations, Accuride often needed to wait up to 30 minutes on cold mornings before the oil warmed sufficiently for the motion to synchronise.

Using the HACD controllers, the system can now compensate for oil temperature and viscosity, meaning the line is immediately ready for full production.

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