EP0576422B1

EP0576422B1 - Constant gap document feeder and method of operation thereof

Info

Publication number: EP0576422B1
Application number: EP91907358A
Authority: EP
Inventors: Rodney Guthmueller; Walter Hosiner; Jimmy Ogles; Ganesh Rajagopal
Original assignee: Bell & Howell Documail Systems Co
Current assignee: BELL & HOWELL DOCUMAIL SYSTEMS COMPANY
Priority date: 1991-03-21
Filing date: 1991-03-21
Publication date: 1998-01-21
Anticipated expiration: 2011-03-21
Also published as: EP0576422A4; JPH07508253A; CA2106684A1; CA2106684C; EP0576422A1

Description

BACKGROUND BACKGROUND 1. Field of Invention

This invention pertains to document feeders, and particularly to a type of feeder that maintains a constant gap spacing between documents regardless of varying document sizes.

2. Prior Art and Other Considerations

In many applications the speed or throughput for feeding documents is a significant, if not critical, operating parameter. Considerable emphasis has been placed upon optimizing document feeding speed, particularly in connection with the transport of postal documents.

Examples of document feeders purportedly designed for postal transport purposes are shown in the following United States Patents: 3,503,603 to Dvorak; 3,847,383 to Wojtowicz et al.; 3,944,214 to Fallos; 4,295,645 to Nahar et al.; 4,318,540 to Paanenen et al.; 4,346,876 to Guenther et al.; 4,431,175 to Smith; 4,451,027 to Alper; 4,573,675 to Svyatsky et al.; and, 4,607,833 to Svyatsky et al.

Some prior art feeders operate in a manner to provide a constant distance interval between leading edges of consecutively-fed documents. The practice of providing a constant distance interval between leading edges of consecutively-fed documents may be adequate in a case wherein all documents are of the same size. However, this practice is not necessarily efficient when handling documents of differing sizes.

Consider, for example, a scenario wherein a constant distance interval of eighteen inches (45.72 cm) is required between leading edges to accommodate 14 (35.56 cm) inch envelopes. A gap of 4 inches (10.16 cm) exists between a trailing edge of a first 14 inch (35.56 cm) envelope and a leading edge of a next 14 inch (35.56 cm) envelope. (As used herein, the term "gap" refers to a distance between a trailing edge of a first document and a leading edge of the subsequent document). Consider further that the size of the gap would be 9.5 inches (23.13 cm) should a 14 inch (35.56 cm) envelope follow a 5.5 inch (13.97 cm) envelope. Hence, with respect to 5.5 inch (13.97 cm) envelopes, the throughput speed is reduced by almost a factor of two.

Various prior art feeders have attempted to provide a constant gap between documents, with varying degrees of throughput efficiency. One example of a constant gap feeder is shown in United States Patent 4,331,328 to Fasig. The feeder of United States Patent 4,331,328, which discloses the features of the preamble of independent claim 1, requires three pluralities of pairs of rollers, with the first and second pluralities of pairs of rollers being driven at different speeds by servo means and the third plurality of pairs of rollers being driven at a constant speed. Further, the feeder of United States Patent 4,331,328 demands, after a required gap is obtained, that the speed of the servo means be changed to a speed which will impart the constant transport speed to the document for entry into control by the constant speed third plurality of rollers.

Heretofore the maximum throughput for documents using a constant gap feeder has been in the neighborhood of about forty six thousand (46,000) per hour. A constant gap feeder having a significantly increased feeding speed would greatly enhance document handling capabilities.

Accordingly, it is an object of the present invention to provide an efficient constant gap feeder that achieves high throughput.

An advantage of the present invention is the provision of a constant gap feeder having a simplified mechanical transport structure.

A further advantage of the present invention is the provision of a constant gap feeder that does not require the large number of rollers involved with the prior art.

SUMMARY

The present invention is defined in the independent claims 1 and 5.

A document feeder comprises servo-controlled feeder transport means positioned to receive documents from a hopper and take-away transport means positioned downstream from the Servo-controlled feeder transport means to receive documents from the servo-controlled feeder transport means. The take-away transport means is driven at a desired constant take-away transport speed to transport the documents received therein at the constant take-away transport speed.

The controller ensures a desired constant gap between a trailing edge of a first document and a leading edge of a subsequent document. The controller decreases the speed of the feeder transport upon the detection of a leading edge of a first document at an entrance to the take-away transport. The controller then linearly increases the speed of the feed transport along a speed ramp until a trailing edge of the first document is detected. Upon the detection of the trailing edge of the first document, the controller sets the speed of the feeder transport (22) to a constant value. Thereafter the controller detects a leading edge of the subsequent document. The controller determines the magnitude of an initial gap between the trailing edge of the first document and the leading edge of the subsequent document. The controller then uses the magnitude of the initial gap and the magnitude of the desired constant gap to adjust the speed of the feeder transport to an adjusted speed whereby the desired constant gap will be provided between the trailing edge of the first document and the leading edge of the subsequent document by the time that the leading edge of the subsequent document reaches the entrance to the take-away transport.

The detection of a leading edge of a first document at an entrance to the take-away transport means is accomplished using a take-away sensor means positioned proximate an entrance to the take-away transport means.

In one embodiment, the controller receives an interrupt upon the detection of the trailing edge of the first document from either a gap sensor or an early sensor. The gap sensor is positioned a first predetermined distance upstream from the take-away transport means. The early sensor is positioned at a second predetermined distance upstream from the entrance to the take-away transport means. In this embodiment, the early sensor detects the formation of a gap between documents at positions more upstream than otherwise expected, thereby requiring the controller to make an early pre-adjustment to the speed of the feeder transport.

In another embodiment, the early sensor is not provided, with the trailing edge of the first document being detected exclusively by the gap sensor.

Adjusted speeds of the feeder transport are determined by reference to look-up tables stored in a memory of the controller. A Ramp Table is consulted for determining the speed of the feeder transport during a RAMP STATE. A Gap Table is consulted for determining the speed of the feeder transport during a NORMAL ADJUSTMENT STATE. An Early Table is consulted for determining the speed of the feeder transport during an EARLY ADJUSTMENT STATE. The Gap Table and the Early Table are constructed using the formula V2 = V1(XX+D-I ) where V1 is the speed of the take-away transport; I is the magnitude of the initial gap; D is the magnitude of the desired gap; and where X is the distance from a sensor which detects the trailing edge of the first document to the entrance to the take-away transport.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of preferred embodiments as illustrated in the accompanying drawings in which reference characters refer to the same parts throughout the various views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.

Fig. 1 is a schematic plan view of a constant gap feeder system according to an embodiment of the invention.

Fig. 2 is a schematic view showing circuitry included in the constant gap feeder system of the embodiment of Fig. 1.

Fig. 3 is a graph showing amplitudes of a signal applied by a controller to a feeder belt servo of the constant gap feeder system of the embodiment of Fig. 1.

Fig. 4 is a schematic view illustrating states and steps executed by a processor included in the controller of the constant gap feeder system of the embodiment of Fig. 1.

Fig. 5 is a schematic plan view of a constant gap feeder system according to a second embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a constant gap feeder system 20 suitable for handling documents, including postal documents such as envelopes. The constant gap feeder system 20 includes feeder transport means, such as feeder transport 22; take-away transport means, such as take-away transport 24; control means such as controller 25; and, servo means 26.

The feeder transport 22 is positioned to receive documents on-edge from a hopper 27 and to transport the documents in a direction of conveyance denoted by arrow 28. The take-away transport 24 is positioned downstream from the feeder transport 22 with respect to the direction of conveyance.

The feeder transport 22 includes a pair of right pulleys 30 and a pair of left pulleys 32, with the right pulleys 30 being situated to the right of a path travelled by on-edge documents and the left pulleys 32 being situated to the left of that path. The right pulleys 30 have an a belt 34 entrained thereabout. The left pulleys 32 similarly have a belt 36 entrained thereabout.

The right pulleys 30 and left pulleys 32 are rotatably driven by an unillustrated motor included in the servo means 26. In this respect, one or more of the pulleys in each pair are coupled to an output drive shaft of a motor, with the motor being governed by the servo means 26 for adjusting the rotational speed of the

pulleys

30, 32, and hence the transport speed of the

belts

34, 36.

The take-away transport 24 similarly comprises a pair of left pulleys 40 and a pair of right pulleys 42, only one pulley in each pair being illustrated in Fig. 1.

The belts 40, 42 of the take-away transport 24 are wider and closer together than are the

belts

34, 36 of the feeder transport 22, so that documents are more tightly engaged therebetween. The pulleys 40, 42 of the take-away transport 24 are driven by an unillustrated motor at a speed whereby documents engaged between the belts 44, 46 travel at a constant speed. In the illustrated embodiment, the constant speed at which documents engaged between the belts 44, 46 travel is on the order of 160 inches per second (406.4 cm per second).

The constant gap feeder system 20 includes four sensors, particularly take-away sensor 50; gap sensor 52; early sensor 54; and hopper-empty sensor 56. The take-away sensor is positioned at an entrance to the take-away transport 24, e.g. to detect the leading edge of a document as it is introduced between the pulleys 40, 42 shown in Fig. 1.

The gap sensor 52 is positioned just upstream of the downstream ones of the

pulleys

30, 32 comprising the feeder transport 22. More particularly, the gap sensor 52 is positioned a first predetermined distance 60 upstream from the entrance to the take-away transport 24, and specifically from an axis 51 of detection of the take-away sensor 50. In the preferred embodiment, the first predetermined distance 60 is on the order of about 4 inches (10.16 cm).

The early sensor is positioned just downstream from the upstream ones of the

pulleys

30, 32 comprising the feeder transport 22. More particularly, the early sensor 54 is positioned a second predetermined distance 62 upstream from the entrance to the take-away transport 24, and specifically from the axis 51 of detection of the take-away sensor 50. In the preferred embodiment, the second predetermined distance 62 is on the order of about 6 inches (15.24 cm).

The hopper-empty sensor 56 is positioned to generate a signal when the hopper 27 is empty.

As used herein, the terms "upstream" and "downstream" are understood with respect to the direction of conveyance depicted by arrow 28.

The

sensors

50, 52, 54, and 56 can be of any suitable type, including reflective-type sensors or interrupt-type sensors. In embodiments wherein the

sensors

50, 52, and 54 are optical sensors, rays from the optical sensors are directed across the path of transport beneath the belts of the respective transport.

Fig. 2 shows the controller 25 in more detail. As seen in Fig. 2, the controller 25 includes a processor 70 having a memory 71 connected thereto; a clock 72; a digital-to-analog converter (DAC) 74; and, an operational amplifier 76. In the illustrated embodiment, the processor 70 is a 68705U3 microcomputer.

Although not shown as such in Fig. 2, it should be understood that the processor 70 is connected to an unillustrated host computer. The host computer communicates with the processor 70 to tell the processor 70 when the constant gap feeder system 20 is to commence feeding and to stop feeding. In addition, the host computer tells the processor 70 what is the length of the desired constant gap, whereby the processor 70 stores in its memory 71 a value indicative of the length of the desired constant gap as downloaded from the host computer.

As further shown in Fig. 2, the processor 70 is also connected to receive interrupts from the

sensors

50, 52, 54, and 56, as well as a clock signal from the clock 72.

A data output port of the processor 70 is connected by an eight-bit data bus 78 to an input port of the DAC 74. An analog output terminal of the DAC 74 is connected to the operational amplifier (OA) 76, which in turn is connected to apply an analog signal to the feeder transport 26.

The operation of the constant gap feeder system 20 of the present invention is facilitated by the execution of a set of coded instructions resident in the processor 70 of the controller 25. The operation is understood with respect to the steps of Fig. 4 and the timing diagram depicted in Fig. 3.

The operation of the constant gap feeder system 20 of the present invention will now be described with respect to a first document, a second document, and a third document. It should be understood that the second document is a subsequent document for the first document, and that the third document is a subsequent document for the second document.

For the purpose of illustration, the first document will be presumed to be a long document. In Fig. 3 and the ensuing discussion, the notation T1₁, T2₁, and T3₁ is employed to refer to a time frame wherein the first document enters the take-away transport 24 while the second document is in the feeder transport 22. The notation T1₂, T2₂, and T3₂ is employed to refer to a time frame wherein the second document enters the take-away transport 24 while the third document is in the feeder transport 22.

Moreover, as used herein, the terminology "the speed" shall be understood to refer to both the speed of the servo 26 and the speed of the feeder transport 22, with the speed of the servo 26 and the speed of the feeder transport 22 being used interchangeably.

The description of the operation of Fig. 4 arbitrarily commences with the processor 70 being in a WAIT STATE. At step 100, corresponding to time T1₁ in Fig. 3, the processor 70 receives an interrupt as the take-away sensor 50 detects the leading edge of a first document at the entrance of the take-away transport 24. As a result of this interrupt, at step 102 the processor 70 directs the servo 26 (via the data bus 78, DAC 74, and OP AMP 76) to decrease the speed of the feeder transport 22 to speed S1 (see Fig. 3), which reduction occurs essentially immediately thereafter. In the illustrated embodiment, the speed S1 is on the order of 127.0 cm per second 50 inches per second.

In the ensuing discussion, statements to the effect of the processor 70 changing the speed of the servo 26 refer to the processor 70 outputting a value (via the data bus 78, DAC 74, and OP AMP 76) to control the speed of the servo 26. As will be seen hereinafter, on some occasions the output value is a predetermined constant value; on other occasions the value(s) are obtained from one of a plurality of look-up tables stored in the memory 71.

Immediately after the feeder transport 22 has been decreased to speed S1 at step 102, the processor 70 enters a RAMP STATE. In the RAMP STATE, at step 104 the processor 70 consults a look-up table (called the "Ramp Table") stored in the memory 71 to determine what the speed should be. At every 0,32 cm (1/8 inch) interval that the leading edge of the first document travels into the take-away transport 24 during the RAMP STATE, the processor 70 checks the Ramp Table to determine a new speed for the servo 26. In this respect, the Ramp Table has stored therein a set of order pairs, with each pair consisting of a distance (in cm) and a corresponding new servo speed (in cm per second).

As shown in Fig. 3, the Ramp Table initially causes the speed of the servo 26 to linearly increase (e.g., "ramp up"), as indicated by reference letter R in Fig. 3. A linear increase of the speed is implemented to facilitate the development of a gap between the first document and the subsequent document at a low speed, but also to prevent the formation of too large a gap as might occur when the first document is a very long document.

As shown in Fig. 3, for a long document such as the first document of the present illustration, the ramp R may continue until the speed of the servo 26 reaches a predetermined maximum ramp speed S2. In the illustrated embodiment, the predetermined maximum ramp speed S2 is on the order of 508.0 cm per second 200 inches per second.

The speed may remain at the predetermined maximum ramp speed as the document travels another 0,95 cm (3/8 inch) into the take-away transport 24. In Fig. 3, the letters RP designate a ramp plateau RP during which the speed remains at the predetermined maximum speed for a long document. If the trailing edge of the document is not seen by the gap sensor 52 by the end of the ramp plateau RP, the processor 70 realizes that the document is more than 15.24 cm 6 inches long, and the speed is linearly decreased as indicated by letter D in Fig. 3. Thereafter, the speed is held constant at a predetermined minimum ramp state speed S3. In the illustrated embodiment, the minimum ramp state speed S3 is on the order of 228.6 cm per second 90 inches per second. The decrease and minimum ramp speed adjustment is a precaution in the event that two documents are overlapped, giving the impression of an ultra-long document.

Except for rather long documents, the speed may normally not reach the predetermined maximum ramp speed, or travel on the ramp plateau RP, or decrease in region D as shown in Fig. 3. In this respect, before the ramp plateau RP is reached, the processor 70 may switch to an EARLY ADJUSTMENT STATE or to a GAP DETECT STATE, as described below.

During the RAMP STATE, at step 106 the processor 70 continually monitors for an interrupt from the early sensor 54. If an interrupt is received by the processor 70 during the RAMP STATE, the processor 70 realizes that the trailing edge of the first document has been sensed by the early sensor 54, and accordingly that a gap is starting to develop relatively early upstream between the first document and the second document (which previously may have been slightly overlapped or essentially contiguous). When such an interrupt is sensed at step 106, the execution of the processor 70 jumps into an EARLY ADJUSTMENT STATE. In the example of the first document being a long document, however, an interrupt is not received from the early sensor 54.

During the RAMP STATE, at step 108 the processor 70 monitors for an interrupt from the gap sensor 54. When an interrupt is received by the processor 70 during the RAMP STATE, the processor 70 realizes that the trailing edge of the first document has been sensed by the gap sensor 52, and accordingly that a gap is starting to develop between the first document and the second document. When such an interrupt is sensed at step 108, the execution of the processor 70 jumps into the GAP DETECT STATE.

In the case of the first document of the present illustration, as seen in Fig. 3 the interrupt from gap sensor 52 occurs at time T2₁. That is, at time T2₁ the gap sensor 52 sees the trailing edge of the first document, which signals the beginning of the detection of a gap between the first document and the subsequent document.

Detection of the trailing edge of the first document at step 110 causes the execution of the processor 70 to jump into the GAP DETECT STATE. At step 110 of the GAP DETECT STATE, the processor 70 immediately sets the speed of the servo 26 at a predetermined speed S4. In the illustrated embodiment, the predetermined speed S4 is on the order of about 150 inches per second (381 cm per second).

While in the GAP DETECT STATE with a servo speed of S4, at step 112 the processor 70 awaits an interrupt from the gap sensor 52 caused by the detection of the leading edge of the subsequent (e.g., next) document. When the interrupt from gap sensor 52 is detected, the processor jumps to step 114 in a NORMAL ADJUSTMENT STATE. Should an interrupt not be received from the gap sensor 52 within a predetermined time interval, at step 118 the processor 70 sets the servo to a very fast speed, such as 212 inches per second (538.5 cm per second), for example, before again entering the WAIT STATE.

At the point in time (T2) at which the processor 70 enters the NORMAL ADJUSTMENT STATE, an initial gap has just been detected by the gap detector 52 between the trailing edge of the first document and the leading edge of the subsequent document. At step 114 the processor 70 calculates the length I of the initial gap, knowing the speed V1 of the first document (160 inches per second = 40,64 cm per second) and the time elapsed between subsequent interrupts of the gap detect sensor 52.

At step 116 of the NORMAL ADJUSTMENT STATE the processor 70 consults another look-up table (called the "Gap Table") stored in the memory 71. The processor 70 obtains an adjusted speed V2 from the Gap Table. The adjusted speed V2 is the speed at which the servo 26 must be set in order for a desired gap of length D to be provided between the trailing edge of the first document and the leading edge of the subsequent document by the time the subsequent document reaches the entrance to the take-away transport 24. Recall that the magnitude of the desired constant gap was downloaded from the host computer and stored in the memory of the processor 70.

The Gap Table stored in the memory 71 is composed using the following formula: V2 = V1(XX+D-I ) where V1, I, and D are as before defined, and where X is the distance from the gap sensor 52 to the entrance to the take-away transport 24 (i.e., the first predetermined distance 60). The Gap Table is comprised of a set of ordered pairs, with the first member of each ordered pair being a gap differential (D - I) between the desired gap and the initial gap distances, and the second member of each ordered pair being the adjusted speed V2 required for the associated gap differential.

Upon executing step 116, at time T3¹ the processor 70 sets the speed at the adjusted speed V2 determined at step 116. The particular adjusted speed V2₁ shown in Fig. 3 is 120 inches per second (304.8 cm per second).

Upon executing step 116, the processor has determined an adjusted speed V2 for the servo 26 which will enable the first document to reach the entrance to the take-away transport 24 with a desired gap D being provided between the leading edge of the first document and the preceding document. Thereafter, the processor 70 returns to the WAIT STATE to await (at step 100) an interrupt from the take-away sensor 50. Such an interrupt (occurring at time T1₂) indicates that the second document has been detected at the entrance to the take-away transport 24.

After the second document enters the take-away transport 24 (e.g., just after time T1₂), the processor 70 executes steps 102 and 104 as previously described to respectively decrease and then ramp-up the speed of the servo 26.

As indicated above, under some circumstances during the RAMP STATE the early sensor 54 may detect (step 106) the formation of a gap early upstream. That is, the early sensor 54 may see the trailing edge of a preceding document separating from the leading edge of the subsequent document. (Such a gap would not occur if the two documents were essentially contiguous or overlapped). Assuming such to be the case with respect to the second and third documents involved in the present discussion, at time T2₂ the processor 70 enters the EARLY ADJUSTMENT STATE as indicated in Fig. 4.

At step 120 of the EARLY ADJUSTMENT STATE, the processor 70 sets the speed of the servo 26 to the predetermined speed S4. Thereafter the processor 70 waits (at step 122) for another interrupt from the early sensor 54, indicating that the leading edge of the third document has been detected. Immediately after detection of the leading edge of the third document at step 122, the processor 70 adjusts the speed at step 124 by consulting another look-up table (called the "Early Table") stored in the memory 71. The Early Table is composed in the same manner (e.g., according to the same formula) as was the Gap Table, but the distance X utilized in the formula is the second predetermined distance 62 rather than the first predetermined distance 60. As shown in Fig. 3, an adjusted speed V2E² is set for the servo 26.

The early sensor 54 and the Early Table are not used to increase the speed of the servo 26 to close up a gap that is too large. Instead, the sensor 54 and Early Table are used to open up a gap that is too small. The only occasion upon which the early sensor 54 is used to increase the speed of the servo 26 above 160 inches per second, for example, is if there is a very large gap at the gap sensor 52 and if the early sensor 54 is still not covered. Under such conditions, the servo 26 is set to an ultra-fast speed.

After the processor 70 has executed step 124 of the EARLY ADJUSTMENT STATE, the processor 70 jumps back to step 108 of the RAMP STATE. Thereafter the processor 70 executes the steps of the GAP DETECT STATE and the NORMAL ADJUSTMENT STATE in a manner understood with respect to the previous discussion of the first and second documents.

The embodiment of Fig. 5 is identical to the embodiment of Fig. 1, except that the embodiment of Fig. 5 does not include the early sensor 54. Accordingly, the controller of the embodiment of Fig. 5 does not execute steps the EARLY ADJUSTMENT STATE, but instead executes step 108 after step 106.

Claims

A document feeder apparatus comprising:

variable-speed servo-controlled feeder transport means (22) positioned to receive documents from a hopper;

take-away transport means (24) positioned downstream from the servo-controlled feeder transport means (22) with respect to a direction of conveyance, the take-away transport means (24) receiving documents from the feeder transport means (22), the take-away transport means (24) being driven at a desired constant take-away transport speed to transport the documents received therein at the constant take-away transport speed;

first sensor means (50) positioned at the entrance to the take-away transport means (24) for sensing the leading edge of a first document received by the take-away transport means (24);

second sensor means (52) positioned a first predetermined distance (60) upstream from the entrance to the take-away transport means (24) for sensing the trailing edge of the first document and the leading edge of a subsequent document; and

control means (25) for controlling the speed of transport of documents in the feeder transport means (22), said control means (25) comprising processor means (70) for calculating the magnitude of an initial gap (I) between the trailing edge of the first document and the leading edge of the subsequent document as sensed by said second sensor means (52) and for thereafter comparing the calculated magnitude of the initial gap with the magnitude of a prestored desired constant gap, and using the result of that comparison to determine an adjusted speed for the feeder transport means (22) whereby the desired constant gap will be provided between the trailing edge of the first document and the leading edge of the subsequent document by the time that the leading edge of the subsequent document reaches the entrance to the take-away transport means (24);
characterized in that
said control means (25) are configured for at least initially decreasing the speed of the feeder transport means (22) upon the entrance of the leading edge of the first document into the take-away transport means (24) as sensed by said first sensor means (50); for then linearly increasing the speed of the feeder transport means (22).
The apparatus of claim 1, characterized in that third sensor means (54) are positioned a second predetermined distance (62) upstream from the entrance to the take-away transport means (24), the second predetermined distance being greater than the first predetermined distance, said third sensor means (54) being connected to the processor means (70) for positioning the processor means (70) in a gap calculating state before the second sensor means (52) sense the leading edge of the susequent document.
The apparatus of claim 1 or 2, characterized in that the processor means (70) is programmed for determining an adjusted speed for the feeder transport means (22) by using the relationship V2 = V1 (XX+D-I ) where V1 is the speed of the take-away transport means (24); I is the magnitude of the initial gap; D is the magnitude of the desired gap; and X is the distance from the second sensor means (52) and the entrance to the take-away transport means (24).
The apparatus of claim 1 or 2, characterized in that the processor means (70) is programmed so that the speed of the feeder transport means (22) is linearly increased until a predetermined maximum ramp speed is reached, and thereafter the speed of the feeder transport means (22) is decreased until the initial gap is detected.
A method for operating a feeder apparatus of the type having variable-speed servo-controlled feeder transport means (22) positioned to receive documents from a hopper; take-away transport means (24) positioned downstream from the servo-controlled feeder transport means (22) with respect to a direction of conveyance, the take-away transport means (24) receiving documents from the feeder transport means (22), the take-away transport means (24) being driven at a desired constant take-away transport speed to transport the documents received therein at the constant take-away transport speed; the method comprising the steps of:

(1) sensing the entrance of a leading edge of a first document into the take-away transport means (24) and at the same time decreasing the speed of the feeder transport means (22);

(2) sensing the trailing edge of the first document and the leading edge of the subsequent document and determining the magnitude of the initial gap (I) between said trailing and leading edges as a function of the time distance therebetween;

(3) comparing the magnitude of the initial gap to the magnitude of a desired constant gap and using the result of that comparison to determine an adjusted speed for the feeder transport means (24) whereby a desired constant gap (D) will be provided between the trailing edge of the first document and the leading edge of the subsequent document by the time that the leading edge of the subsequent document reaches the entrance to the take-away transport means (24);

(4) using said determined adjusted speed to adjust the speed of said feeder transport means (22).
The method of claim 5, wherein the magnitude of the initial gap (I) between the trailing edge of the first document and the leading edge of the subsequent document is determined by using gap sensor means (52) positioned a first predetermined distance (60) upstream from the entrance to the take-away transport means (24).
The method of claim 5, wherein the magnitude of the initial gap (I) between the trailing edge of the first document and the leading edge of the subsequent document is preliminarly determined by using early sensor means (54) positioned a second predetermined distance (62) upstream from the entrance to the take-away transport means (24).
The method of claim 5, wherein the speed of the feeder transport means (22) is linearly increased until an initial gap is detected between the trailing edge of the first document and the leading edge of the subsequent document, and wherein the magnitude of the initial gap and the magnitude of the desired constant gap are thereafter used to determine an adjusted speed for the feeder transport means (22).
The method of claim 5 or 8, wherein the adjusted speed for the feeder transport means (22) is determined by using the relationship V2 = V1 (XX+D-I ) where V1 is the speed of the take-away transport means (24); I is the magnitude of the initial gap; D is the magnitude of the desired gap; and X is the distance from a sensor (52) which detects the trailing edge of the first document to the entrance to the take-away transport means (24).
The method of claim 5, wherein the speed of the feeder transport means (22) is at least initially decreased upon the entrance of the leading edge of the first document into the take-away transport means (24); then is linearly increased until a predetermined maximum ramp speed is reached; and thereafter is decreased until an initial gap is detected.