49 www.drivesncontrols.com April 2023 delivering diminishing returns. When fast-moving items are stopped using a conventional pneumatic stopper cylinder, a significant settling time is needed before the workpiece can be retrieved from the conveyor and loaded into the process. The car-parts maker found that increasing the speed of the process machinery to achieve faster cycle times resulted in frequent line stoppages to fix equipment errors. As a pilot project, the company redesigned one production line, replacing conventional conveyors with linear conveyor modules. It achieved a substantial reduction in transfer times. This saving, in turn, helped to shorten the cycle times of various processes on the line. As a result, the production volume exceeded the team’s original target and the number of errors leading to stoppages fell so far that the line came to be regarded as a model. The second manufacturer, which produces small electric motors, was looking to build orders for small runs of specific product variants more efficiently by reducing line changeover times. Optimising the changeover procedures allowed it to halve this time, from 10 to 5 minutes. The cumulative effect of these five-minute changeovers, typically performed several times each day, equated to about 16 hours of lost production every month. The team needed to manage production carefully, prioritising the products built in the highest volume, to optimise productivity. To avoid those lost hours, the company devised a special tooling jig to produce multiple product variants without reconfiguring the line. This custom jig, which holds three components of differing sizes, enabled the line to handle up to nine different product variants without needing to be changed. However, a two-axis robot being used to remove pieces from the appropriate position in the jig required the conveyor stop position to be changed depending on the product variant being built. Replacing the two-axis robot with a threeaxis type would allow the robot to move along the jig to pick up items. But either approach incurred extra costs and sacrificed some of the desired time savings. The motor manufacturer therefore turned to linear conveyor modules to boost its output by increasing the flexibility of the production line (see diagrams, opposite page). The ability to change the module stop positions by reprogramming has saved the company considerable manual setup work. The engineering team subsequently introduced a QR-code reader to identify each item at the start of production to allow all the linear modules to reconfigure their settings automatically. This has eliminated any need for human interaction with machines or equipment, resulting in full endto-end automation of the assembly process. The company can now handle short production runs as efficiently as its biggest orders. n Using linear modules to transfer workpieces Linear conveyor modules are high-speed direct-drive systems designed to replace free-flow and belt conveyors. Driven by linear motors, they are ideal for high-mix, lowvolume production because they allow users to alter the configuration and motion of production lines flexibly. The reversible modules provide accurate high-speed motion from one point to another, resulting in high throughputs. Yamaha says that, compared to conventional conveyors, its LCMR200 linear conveyor modules offer much more flexibility to adapt and improve line performance. Parameters such as acceleration, deceleration, speed, and stop positions are set electronically and can be adjusted easily by writing new values to a controller. In addition, the linear motors allow bidirectional movement. The modules’ controller eliminates the need to write ladder logic codes, allowing users to specify direct values and simple point-to-point moves. A single controller can coordinate up to 64 carrier modules connected together as part of a complete production cell. No additional sensors are needed for extra stop positions, allowing users to reconfigure production lines without affecting reliability. The linear motors accelerate and stop quickly and smoothly, with a short settling time after reaching the desired position. This settling time can be optimised by allowing wider positioning tolerance. Users can increase conveyor speeds without needing to insert extra buffering, because each module can stop, restart, and reverse independently to deliver each workpiece at the optimum time. The carriers can be programmed to stop at any desired point, with a ±5μm (maximum) positional repeatability. Transfer speeds are set electronically at up to 2.5m/s. Operating times depend on the payload and the transfer distance: a 2kg load takes 0.47s to move 250mm; while a 10kg load takes 1.121s to move 1m. The carriers can move loads of up to 30kg and their rigidity allows processes to be performed on-board, without needing to remove the workpieces. This ensures short cycle times and also saves the engineering effort and cost to develop a mechanism to transfer the workpiece to and from a separate jig for each process. Linear conveyor modules present workpieces to each process in sequence, accelerating and decelerating smoothly. They can move payloads of up to 30kg at speeds of up to 2.5m/s. Up to 64 individually controllable carriers can operate on a line up to 25m long.
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