This invention relates to sheet transport apparatus for picking up and conveying successively sheets out of a stack.
Utilization of information reading devices to recognize the information contained in sheet-like materials, such as, for example data cards, stacked one upon another, needs each card to be fed successively to information reading devices in card-by-card manner. One type of prior art apparatus for feeding cards to information reading devices utilizes a continuously rotating suction drum which includes a rotating cylindrical member with an apertured curved surface portion. Provided within the cylindrical member is a stationary suction chamber extending axially along the curved surface and having a curved opening to face the inner surface of the cylindrical member with a certain clearance. The rotating suction drum functions to suck air near to the opening of the suction chamber but outside of the cylindrical member through apertures thereof when the apertured portion of the cylindrical member passes by the opening of the suction chamber.
Such a rotating suction drum is positioned near the leading edge portion of the top-positioned card or sheet of the stack of the sheets with a certain clearance so as to pull up the top-positioned sheet in the direction of movement of the periphery of the suction drum by the sucking operation thereof. Each top-positioned sheet is pulled up at the passing of the apertured curved surface portion of the suction drum. Thus, individual sheets are intended to be pulled up in a precise rhythm in one-by-one manner as the suction drum rotates, and fed to belt conveying systems which convey the sheets in the form of sheet train with a given distance between adjacent sheets.
The information reading device reads the information contained in such transported sheets and then sheets are stacked again in a predetermined position. It is necessary for reading the information from the stack of sheets that the sheets are transported successively in one-by-one manner. It is also usually required that the distance between leading edges of adjacent sheets during transportion is approximately uniform.
The conventional suction drum, however, tends to pull up not only the top-positioned sheet but also additional sheet or sheets lying just thereunder. According to one prior art approach attempting to solve this problem, air blowing nozzles are provided for separating the additional sheet or sheets, if any, from the top-positioned sheet by air flow in the direction reverse to that pulling the top-positioned sheet. It has been found, however, that the nozzles do not provide a sufficient measure for separation. Further, the distance between the leading edges of adjacent sheets during transport hereof tends to vary.
A thin slit capable of passing only a single sheet may be employed for improved separation of the additional sheet or sheets from the top-positioned sheet. This tends to cause a jam or wrinkle of the sheets by choking of sheets within the slit. Furthermore, it is very difficult to adjust precisely the width of the slit in a practical operation.
Another prior art approach to a single sheet feed relates to a bottom feed type apparatus wherein the bottom sheet of the stack is meant to be attached by a similar first suction drum positioned under a plane defined by such sheet and ahead of the leading edge of the stack in the transport direction. Several sheets in the bottom portion of the stack are advanced in the transport direction by a second suction drum positioned under the stack of sheets at their trailing edge portion so that the bottom-positioned sheet of the thus advanced several sheets may be directly attracted by the first suction drum. Any undesired additional sheet is pushed back by still a third suction drum having peripheral movement reverse to the transport direction for retaining the additional sheet. The third suction drum generally faces the first suction drum with a clearance for passage of sheets but is positioned slightly ahead of the first suction drum in the transport direction.
The retaining suction drum includes a rotating cylindrical member which has multiple rows of apertures along the entire curved surface, and a suction chamber with an opening cooperable with a single row of the apertures facing the additional sheet, if any, along the axis of the cylindrical member. Thus, one of the apertures in the suction chamber functions to suck air while the rows of apertures in the drum generally move in the direction reverse to the direction of the sheet transport whereby the additional sheet, if any, is forced to be retained slightly or pushed back. It is noted that the push back force is given to the additional sheet at the rear end portion thereof with respect to the push back direction. There is further provided a vibration means to give vibration to the stack of the sheets to assist forward movement of the attracted sheet being fed as well as backward movement of pushed back sheet. Such apparatus is disclosed in German Patent Disclosure (Offenlegungsschrift) No. 24 54 082.
This approach, however, has disadvantages in that the pushing back operation tends to cause jamming and wrinkling of the sheets. Since only a single row of apertures of the third suction drum is effective to separate any additional sheet from the sheet being fed, and further such single row of apertures is moving generally backwardly, it is very difficult to adjust the timing of the system for obtaining expected or intended operation in practice. The numerous parts of the system and the coordination of their timing becomes very complicated in manufacture and use.