Flesher: Technical Support

System 3 Service Bulletin 012:

"Over Travel" Theory and Use

System 3 and Premere hot foil lettering machines are capable of implementing 'overtravel' during axis moves. Overtravel is the ability of the machine to position an axis so the final movement to the desired position is always from the same direction. This may be desirable depending on the positioning accuracy required. Making the final movement to the desired position from the same direction will reduce the detrimental effects of friction or mechanical free play in the system.

On the System 3 and Premere machines, this is accomplished by adding 'overtravel' to any movement that approaches the final position from the 'wrong' direction. That is, moving past the final position and then reversing direction to approach the final position from the desired direction. There is an 'overtravel' parameter associated with each axis. Normally it is set to zero (no 'overtravel').

The disadvantage to 'overtravel' is that it takes more time to move the axis to the final position. In fact, on average and when 'overtravel' is turned on, one-half of all moves will take a little more time.

The most important use of 'overtravel' is on the Z axis (printwheel rotation) when vertical lettering is used. When lettering vertically, the position of the base line of the characters is dependent on the accuracy of the rotational positioning of the printwheel. There are a number of factors that affect the accuracy of the rotational position of the printwheel (see service bulletins "Setting System 3 Printwheel Belt Tension", "Pre-load Adjustment for System 3", "Spindle Bearing Lubrication for System 2 & System 3 Spindle Bearings"). All these factors must be in good and proper adjustment. 'Overtravel' is not a cure-all for other problems.

Some experimenting with the amount of over travel may yield better or worse results, but it's been found that an 'overtravel' value of 400 for the Z axis seems to be a good compromise between effectiveness and reasonable speed. More 'overtravel' may help some, but at the cost of additional positioning time. A velocity of at least 25,000 and acceleration of at least 150,000 is recommended.

'Overtravel' on the X axis can improve the character-to-character positioning accuracy between the first and second characters on a line especially if the material being embossed is not very stiff. About .250 inch (6mm) is suggested.

On System 3 machines, 'overtravel' on the Y axis can have the same effect on multiple line vertical lettering as with the X axis. Y axis 'overtravel' on Premere is probably not necessary, but may have some desirable effect.

'Overtravel' for wheel tilt position, foil position, or feeder position is probably not necessary on any machine.