Robot Details

  Lizotte has designed and built a system to pack sardines. This is a process the customer wanted to automate, because finding manual labour was becoming increasingly difficult. The Lizotte machine dredges pre-cut sardines from a hopper and places them lengthways and one-by-one on conveyor. These flow through an imaging station at a rate on the order of 7 per second, where they are graded by artificial vision. Those that are not suitable for selling to the customer (improperly cut, damaged, etc.), are graded ‘ReJect’. Those that are not properly positioned on the belt for robotic handling (badly angled to the belt axis, too close to the side, incompletely singulated, etc.), are graded ‘ReCycle’. Those that are graded as Packable are further identified by which of four orientations they lie in: tail-end leading or trailing; belly towards one or the other side of the belt. The PLC also accepts additional, trivalent, data of size (average, small, and large). After passing by the two kick-off stations (ReCycle and ReJect), the packable sardines proceed down the conveyor where there are six pick-and-place robotic stations. Operating with a cycle time of under one second, each robot is able to remove a pre-cut from the belt and manipulate it into a tin that has been staged for filling. The robot’s manipulation places the pre-cuts into tins, belly-up and in an alternating head-tail pattern. As tins are filled, they are moved out, and new tins come in.

  The PLC (programmable logic controller [Robert’s domain]) handles the overall logic: Tracking objects on the conveyor with 3-mm precision; Telling the imaging system when to take exposures, and receiving and processing the subsequent grade data; Controlling the kickers; Instructing the robots on the required manipulation, and when to initiate it; Tracking the number of fish in every tin (a fixed number for any one production run), and instructing the robot system when to index for next tin, as opposed to indexing for the next fish-position; Ensuring, where two pre-cuts are so close that the picking of the first would cause a collision with the next, that the second fish is removed from the belt before the first; Tracking the tin’s content visa vi large and small pre-cuts, and ensuring that a tin is not underweight because of two small fish, nor over-full because of two large fish (but allowing two large (or small) in a tin where there is an offsetting small (large)). The PLC also controls the level in the primary hopper from which the pre-cuts are dredged, and controls the supply of tins to each robot.

  The logic is written so that the decision of whether or not a fish is picked by a robot is made as the fish is presented to the robot. This means that minor variances in robot cycle time need not be accounted for, to the degradation of the overall cycle time. It also means that real-world problems such as interrupted supply of cans to one or more robots, and equipment breakdown, have minimal impact on production throughput.

  Robert’s additional project involvement included: The design of the fingers which do the actual picking of the pre-cuts off the belt; Overall system design; Purchasing of most components; Writing the manual; etc.