Precision Ring and Track is key to Smart Cart success

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HepcoMotion's Precision Ring and Track system is being used by John P Waterhouse Co Ltd on its Smart Cart track-based weighing system that automatically fills bags with the correct quantities of various products.

Precision Ring and Track is key to Smart Cart successSmart Cart is a system designed by John P Waterhouse Co Ltd that delivers intelligent and mobile weighing carts to a succession of product feed stations in accordance with a pre-specified recipe. It enables a broad choice of ingredients – often in small quantities – to be dosed automatically and accurately into a single weighing cart.

One of the main merits of this system is its ability to accommodate as many weighing carriages as the application requires, while extensions to the circuit allow for the inclusion of additional material feed stations. This benefit is provided by the HepcoMotion Precision Ring and Track system (PRT).

Chris Waterhouse, Sales and Marketing Manager at John P Waterhouse Co, explains: "It offered the most adaptable and flexible solution, and also provided the high load carrying capacity that we needed." The system is designed for direct loads up to 3800N and moment loads of 210Nm.

The HepcoMotion Precision Ring Track System (PRT) provides an unlimited variation for curved and linear movement. Its individual elements of ring slides, ring segments and tracks can be mixed and matched to provide total flexibility; straight slides can be specified up to 4m in length and, if necessary, can be butted together for unlimited travel.

How Smart Carts work

Smart Carts are fixed to the HepcoMotion carriage plates, which are mounted on the PRT circuit. Low-melt bags or other receptacles are automatically or manually loaded onto the carriage that proceeds around the track collecting specific quantities of material. On completion of the batch, the bag is printed, sealed and ejected onto an accumulation system.

Force motion platform scales ensure the Smart Carts provide a weighing accuracy of +/- 2 to 3 grams and the system is powered by variable speed drives that ensure smooth speed changes and good carriage stability. Chris Waterhouse states: "The ability of the HepcoMotion PRT system to maintain a stable orientation at the increased travelling speeds of the Mark II was another reason for our choice."

Each PRT carriage features opposing concentric and eccentric bearings that enable play and friction to be optimised with simple hand adjustments. As the Smart Cart System uses ring segments and uni-directional track, HepcoMotion recommended the use of its fixed-centre carriage in preference to the bogie carriage that is best suited for configurations containing 'S' bends or bends of differing radii.

Location and low-friction

Precise positioning is clearly a requirement of this system. It employs track-mounted flags and carriage-mounted sensors to determine the carriage location. Friction-free linear movement is an important element in this regard too. To ensure smooth running, all PRT elements are manufactured from high-quality steel, zone hardened on the vee-edges and precision ground all over with datum register faces provided both internally and externally for ease of location.

The HepcoMotion bearing assemblies incorporate high-precision ball races for durability, rigidity and friction-free running. They are greased for life and supplied dust-shielded as standard. This is important in a system that does have close-coupled extraction but is nevertheless often required to handle aggressive materials.

PRT also uses the HepcoMotion lubricating system to prevent the ingress of dirt and to provide positive lubrication; lubrication increases the load carrying capability of the system by a factor of four and life by a factor of 25 typically.

Chris Waterhouse concludes: "We considered other motion systems and in particular linear motor drives, but felt HepcoMotion PRT gave us the flexibility and performance we needed. And the company gave us a lot of technical support to ensure we had the optimum system for the job."

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