Despite the great amount of engineering attention given in the past to the problem of high speed feeding or sheets and other more or less flat articles, there is a continuing need for improved machines to overcome deficiencies which limit continuous, error free, high speed feeding. In particular, improvements are needed in reliably singulating sheets and other articles which vary in thickness or character, and for singulating them in a manner which does not adversely affect their surface character.
When singulating paper sheets and other articles using typical prior art technology, for example--feed rollers in combination with retarder rollers or belts, double feeding or other problems such as blocking or curling can occur. One contribution to problems in even carefully configured equipment is that there is variation in the characteristics of articles being fed, even when they are of the same supposed character. Too frequently, operator intervention is required to adjust machines during operation. Similarly, extensive and careful set up is often required when changing a machine from processing one type article to another. Articles which have in the past caused feeding problems include articles having step change in thickness or varied surface texture, such as envelopes with flaps fed first, articles with body joints, window envelopes, plastic credit cards affixed to paper sheets, and heavily coated or printed articles, etc.
Another area where improvement is needed is in the retarders of singulators. Retarders wear if made of elastomer or plastic, or scrape unacceptable amounts of material from the sheet surfaces if made of abrasive ceramic. They tend to loose their effectiveness when debris, such as toner from photocopied pages, accretes on their operational surfaces. Thus, there is a need for conveniently and automatically presenting clean retard surfaces at singulator nips. Still another deficiency is that when sheets are taken away from a singulator at an increased speed, there is a tendency for slipping and rubbing on the surface of articles, either at the take-away rollers or the singulator feed rollers.