The importance of inspecting sutures

Medical suture specialist, PharmSouth, have expanded their range, using maxon DC motors and controllers, with a new inspection machine, that will save labour and material costs and achieve a much higher quality product.

Their new machine inspects the sutures for defects, enabling companies to make substantial savings in both labour and material costs and achieve a much higher quality product. Defects in sutures are common as they are made up from lengths of braided or twisted polymer. The fibres can break, stick out or bunch up, which leads to suture breakages and discarded product.

PharmSouth consultant, Stuart Best has worked with maxon motor uk on numerous machines, he commented, ‘Mark Gibbons is a very useful support at maxon motor. It is great to have someone on the end of a telephone to discuss any issues. Indeed, Mark was instrumental in suggesting we use the maxon EPOS2 50/5 controller to utilise the dual encoder mode of operation, solving the issue with the elasticity of the suture.‘

The machine can inspect sutures of a diameter range from 0.2mm to 1.5mm. The suture to be inspected is placed on the off-wind spool, then threaded through an 3 axis inspection head, over a measuring encoder wheel, through a 3 axis diameter gauge, under a camera, to the Knotting Station and finally on to the take-up spool. The inspection head provides two digital signals - major flaw or minor flaw. The Knotting Station, also manufactured by PharmSouth, is used to mark the flaw position with a knot. The machine runs at speeds up to 150 metres per minute and is able to take two sizes of spools.

The off-wind and on-wind spools use RE 40 brushed DC maxon motors with maxon motor postioning controllers.The off-wind controller is an EPOS2 24/5 positoning controller, whilst the on-wind is an EPOS2 50/5 motor positioning controller. The off-wind runs in tension (current) mode, utilising a dancer arm. The dancer arm input to the EPOS2 motor controller is via an optical potentiometer. The suture is layered on to the take-up spool using a traverse which is a screw design, driven by a brushless DC maxon EC45 flat motor, with a EPOS2-P 24/5 controller. This runs in Master Encoder Mode, taking its positional ratio to the on-wind from the suture diameter, to ensure the spool collects the suture evenly. The Master Encoder Mode electrically gears the guiding traverse motor to the speed of the suture. This ratio is changed for each formula depending on the various thicknesses of suture.

All three maxon controllers are linked with CAN bus, with the traverse EPOS2-P 24/5 motion controller, which powers the axis, instructing the other nodes and containing the control program. The EPOS2-P 24/5 controller runs an IEC 61131-3 program controlling the speed / tension and sensing of flaws, utilising the EPOS “Position Marker” functionality. This functionality permits the use of digital input in order to capture the instantaneous position at the time of the input being triggered. This stored position is then used to reference the jog of the suture to different inspection/work points throughout the machine. The EPOS2-P initiates the camera to take the defect picture and also the knotter to tie a knot to mark the defect. The EPOS2-P 24/5 program also processes flaw positional data, to determine if multiple flaws are only one large flaw, by implementing a monitoring window.

The Southampton based company has revolutionised the suture processing industry over the years, with a range of manufacturing machines, from pack winding to the attaching of the needle and stiffening the ends.

© 2015 by maxon motor UK Ltd