US3820777A

US3820777A - Elevator assembly positioning control

Info

Publication number: US3820777A
Application number: US00270577A
Authority: US
Inventors: E Reehil
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1972-07-11
Filing date: 1972-07-11
Publication date: 1974-06-28
Anticipated expiration: 1991-06-28
Also published as: JPS5240984B2; DE2335295A1; NL7309687A; BE802196A; GB1416470A; JPS4965236A; CA1015395A

Abstract

Apparatus for regulating the position of an auxiliary elevator assembly included in an electrostatic reproduction machine wherein sheets of material are stacked upon the auxiliary elevator assembly is disclosed in accordance with the teachings of the present invention. Selecting means responsive to the manual operation of switch means is provided for selectively producing a first signal to enable the sheets stacked upon the auxiliary elevator assembly to be transported to the electrostatic reproduction machine and for producing a second signal to enable sheets stacked upon a main elevator assembly to be transported to the electrostatic reproduction machine. A reversible electric motor is mechanically coupled to the auxiliary elevator assembly for imparting bi-directional motion to the auxiliary elevator assembly. Drive control means for controlling the direction of rotation of the electric motor is coupled to the selecting means and drives the electric motor in a first direction in response to the first signal whereby the auxiliary elevator assembly is driven to a proper sheet feeding position; said drive control means serving to drive the electric motor in a second direction in response to the termination of the first signal whereby the auxiliary elevator assembly is driven to a quiescent position.

Description

United States Patent 1191 Reehil ELEVATOR ASSEMBLY POSITIONING CONTROL Edward G. Reehil, Henrietta, NY.

Xerox Corporation, Stamford, Conn.

Filed: July 11, 1972 Appl. No; 270,577

Inventor:

Assignee:

References Cited UNITED STATES PATENTS 5/l97l Mallory et al. 271/39 8/l97] Del Vecchio et al. 271/62 R Primary Examiner-Even C. Blunk Assistant ExaminerBruce H. Stoner, Jr.

[ ABSTRACT Apparatus for regulating the position of an auxiliary Machine 0 AND Print Mode I23 Time 1 OR Out I June 28, 1974 elevator assembly included in an electrostatic reproduction machine wherein sheets of material are stacked upon the auxiliary elevator assembly is disclosed in accordance with the teachings of the present invention. Selecting means responsive to the manual operation of switch means is provided for selectively producing a first signal to enable the sheets stacked upon the auxiliary elevator assembly to be transported to the electrostatic reproduction machine and for pro ducing a second signal to enable sheets stacked upon a main elevator assembly to be transported to the electrostatic reproduction machine. A reversible electric motor is mechanically coupled to the auxiliary elevator assembly for imparting bi-directional motion to the auxiliary elevator assembly. Drive control means for controlling the direction of rotation of the electric motor is coupled to the selecting means and drives the electric motor in a first direction in response to the first signal whereby the auxiliary elevator assembly is driven to a proper sheet feeding position; said drive control means serving to drive the electric motor in a second direction in response to the termination of the first signal whereby the auxiliary elevator assembly is driven to a quiescent position.

10 Claims, 2 Drawing Figures ill 122 V I ,J INV Main Elev. H4

Not in Food Position Platform AND AND

AND

D Motor N Control UP ELEVATOR ASSEMBLY POSITIONING CONTROL This invention relates to apparatus for regulating the movement of an elevator assembly, and more particularly, to apparatus for regulating the movement of an auxiliary elevator assembly upon which sheets of material are stacked, which sheets are adapted to be fed through an electrostatic reproduction machine.

In the practice of xerography as described in US. Pat. No. 2,297,691 to Chester F. Carlson, a xerographic surface comprising a layer of photoconductive insulating material affixed to a conductive backing is used to support electrostatic images. In the usual method of carrying out the process, the xerographic plate is elctrostatically charged uniformly over its surface and then exposed to a light pattern of the image being produced to selectively dissipate the charge in the areas where light strikes the layer. The undischarged areas of the layer thus form an electrostatic charge pattern in conformity with the configuration of the original light pattern.

The electrostatic latent image may then be developed by contacting it with a finely divided electrostatically attractable material, such as a resinous powder. The powder is held in the image areas by the electrostatic fields on the layer. Where the field is greatest, the greatest amount of material is deposited; and where the field is least, little or no material is deposited. Thus, a viewable powder image isproduc'ed in conformity with the light image of the copy being reproduced. The powder is subsequently transferred to a piece of paper or other support surface and suitably fused to thereby form a permanent print.

It is contemplated that the sheets of material to which the powder image is transferred be fed through the electrostatic reproduction machine in timed relation to the movement of the xerographic plate. Typical sheet feeding apparatus is disclosed in US. Patent Application Ser. No. 225,5l3 filed on Feb. 4, 1972 now US. Pat. No. 3,768,803 and assigned to Xerox Corporation, the assignee of the present invention. lt has been suggested that such sheet feeding apparatus be supplied with sheets of material that are supported in a stacklike configuration on a movable platform. The platform is preferably driven in first and second directions by suitable drive means such that a first extreme position may be assumed and a proper sheet feeding position may be assumed. In the latter position, the sheets stacked on the platform may be fed in a successive manner to the sheet transport mechanism. The platform is adapted to be driven through positions intermediate the first extreme position and the proper sheet feeding position.

In the electrostatic reproduction machine with which the aforementioned platform finds ready application, use is made of the first extreme position to resupply the platform with sheets of material, to vary the nature of such sheets of material or to effect other desired operator initiated functions. When the platform assumes its first extreme position, normal operation of the electrostatic reproduction machine is impeded because the sheets of material cannot be properly supplied to the sheet transfer mechanism. Accordingly, it is now proposed to provide in cooperation with the electrostatic reproduction machine an auxiliary movable platform. The auxiliary platform may utilized to supply the electrostatic reproduction machine with sheets of material during the period that the aforementioned main platform is resupplied. Since such periods of resupply are assumed to admit of relatively small time durations, the capacity of the auxiliary platform may be limited, thereby simplifying the mechanical construction thereof. Additionally, the auxiliary platform may be employed to supply to the electrostatic reproduction machine sheets of material having dimensions that are not frequently utilizedfThus, if copies are normally reproduced on 8% X 11 inch paper, for example, and

only infrequently reproduced on 8% X 13 inch paper, the main platform may have stacked thereon the 8 /2 X 11- inch paper while the auxiliary platform may have stacked thereon the 8 /2 X 13 inch paper. Hence, during those infrequent instances wherein the 8% X 13 inch paper is to be utilized, the time expended in resupplying and then using the main platform may be avoided merely be using the auxiliary platform. It may, therefore, be readily appreciated that a principle function of the auxiliary platform is to reduce the periods during which the electrostatic reproduction machine might otherwise not be operated because the main platform sheet supply has been either exhausted or must be changed.

Therefore, it is an object of the present invention to provide apparatus for regulating the position of an auxiliary elevator assembly upon which sheets of material are stacked.

It is another object of the present invention to provide apparatus for use in an electrostatic reproduction machine wherein a main elevator assembly and an auxiliary elevator assembly are each capable of supplying sheets of material to the machine.

A further object of this invention is to provide elevator assembly movement control apparatus requiring a specific and intentional manual operation to effect the movement of the elevator assembly to a sheet feeding position.

Yet another object of the present invention is to provide control apparatus for returning an elevator assembly to a quiescent position when the operating cycle of the electrostatic reproduction machine with which the elevator assembly operates terminates.

Various other objects and advantages of the invention will become clear from the following detailed description of an exemplary embodiment thereof, and the novel features will be particularly pointed out in connection with the appended claims.

In accordance with the invention, there is disclosed apparatus for regulating the position of an elevator assembly upon which sheets of material are stacked, including selecting means for selectively producing a first signal to enable the elevator assembly to assume a proper sheet feeding position in response to the manual operation of switch means and for terminating the first signal to enable the elevator assembly to assume a quiescent position in response to signals representing predetermined operating conditions of the electrostatic reproduction machine with which the elevator assembly cooperates; a reversible electric motor coupled to the elevator assembly for imparting bi-directional mo tion thereto; and drive means coupled to the selecting means and including a source of energy adapted to be coupled to the electric motor in a first sense in response to the first signal whereby the elevator assembly is driven to the proper sheet feeding position, the source of energy being adapted to be coupled to the electric motor in a second sense in response to the termination of the first signal whereby the elevator assembly is driven to a quiescent position.

The invention will be more clearly understood by reference to the following detailed description by an ex emplary embodiment thereof in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic sectional view of an electrostatic reproduction machine embodying the principles of the invention; and

FIG. 2 schematically illustrates an elevator assembly upon which sheets of material to be utilized by the electrostatic reproduction machine are stacked, and the control means therefor.

For a general understanding of the illustrated copier reproduction machine in which the invention may be incorporated, reference is had to FIG. 1 in which the various system components for the machine are schematically illustrated. As in all electrostatic systems, such as xerographic machine of the type illustrated, a light image of a document to be reproduced is projected onto the sensitized surface of a xerographic plate to form an electrostatic latent image thereon. Thereafter, the latent image is developed with an oppositely charged developing material to form a xerographic powder image, corresponding to the latent image on the plate surface. The powder image is then electrostatically transferred to a support surface and fixed by a fusing device to cause the powder image to adhere permanently to the support surface.

in the illustrated machine, a document D to be copied is placed upon a transparent support platen P fixedly arranged in an illumination assembly, generally indicated by the eference numeral 10, positioned at the left end of the machine. Light rays from an illumination system are flashed upon the document to produce image rays corresponding to the informational areas. The image rays are projected by means of an optical system onto the photosensitive surface of a xerographic plate in the form of a flexible photoconductive belt 12 arranged on a belt assembly, generally indicated by the reference numeral 14.

The belt 12 comprises a photoconductive layer of selenium, which is the light receiving surface and imaging medium for the apparatus, on a conductive backing. The surface of the photoconductive belt is made photosensitive by a previous step of uniformly charging the same by means of a corona generating device or corotron 13.

The belt is joumaled for continuous movement upon three

rollers

20, 21 and 22 positioned with their axes in parallel. The photoconductive belt assembly 14 is slidably mounted upon two support shafts 23 and 24 with the roller 22 rotatably supported on the shaft 23 which is secured to the frame of the apparatus and is rotatably driven by a suitable motor and drive assembly (not shown) in the direction of the arrow at a constant rate. During exposure of the belt 12, the portion exposed is that portion of the belt running between rollers 20 and 21. During such movement of the belt 12, the reflected light image of such original document positioned on the platen is flashed on the surface of the belt to produce an electrostatic latent image thereon at exposure station A.

As the belt surface continues its movement, the electrostatic image passes through a developing station B in which there is positioned a developer assembly generally indicated by the reference numeral 15, and which provides development of the electrostatic image by means of multiple brushes 16 as the image moves through the development zone.

The developed electrostatic image is transported by the belt to a transfer station C whereat a sheet of copy paper is moved between a transfer roller and the belt at a speed in synchronism with the moving belt in order to accomplish transfer of the developed image by an electrical bias on the transfer roller. There is provided at this station a sheet transport mechanism generally indicated at 17 adapted to transport sheets of paper from a movable platform included in a paper handling mechanism, generally indicated by the reference numeral 18, to the developed image on the belt at the station C.

After the sheet is stripped from the belt 12, it is conveyed into a fuser assembly, generally indicated by the reference numeral 19, wherein the developed and transferred xerographic powder image 'on the sheet material is permanently affixed thereto. After fusing, the finished copy is discharged from the apparatus at a suitable point for collection externally of the apparatus.

Further details regarding the structure of the belt assembly 14 and its relationship with the machine and support therefore may be found in copending Application Ser. No. l02,3l2 now US. Pat. No. 3,730,623, assignedto Xerox Corporation, the assignee of the present invention.

As indicated in FIG. 1, a paper handing mechanism 18 is comprised of first and second movable platforms designated as the main elevator assembly 31 and the auxiliary elevator assembly 32. Sheets stacked upon the main elevator assembly 31 are transported to the transfer station C by endless belt conveyer means 30. Sheets stacked upon the auxiliary elevator assembly 32 are transported to the transfer station C by endless belt conveyer means 29. A more detailed explanation of the manner in which the main elevator assembly 31 operates to receive, store and present sheets of material to the endless belt conveyer means 30 is described in copending Application Ser. No. 214,299 filed on Dec. 30, 1971 now US. Pat. No. 3,768,806 and assigned to the assignee of the instant invention. The electrostatic reproduction machine with which the present invention cooperates is adapted for high speed and high volume operation. Accordingly, it is desirable to provide a minimufn interruption in the operating time of the electrostatic reproduction machine during these periods when the main elevator assembly must be resupplied with sheets of material or alternatively, when differently dimensioned sheets of'material must be substituted for the sheets presently stacked upon the main elevator assembly.

it may be observed from copending Application Ser. No. 214,299 that the supply of sheets of material may be replenished when the movable platform included in the main elevator assembly 31 admits of an extreme downward position. When this extreme downward position is assumed, the operating cycle of the electrostatic reproduction machine is terminated. Resumption of the operation of the machine is delayed until sheets of material are capable of being readily transported by the sheet transport mechanism 17 to the transfer station C.

In Accordance with the present invention, the auxiliary elevator assembly 32 is provided to supply sheets of material to the transfer station via endless conveyer belt means 29 during those intervals that the main elevator assembly is not adapted to transport sheets stacked thereon. Thus, when the supply stacked upon the main elevator assembly is exhausted, an operator may select the auxiliary elevator assembly 32 to assume a proper sheet feeding position whereby the sheets of material stacked thereon may be transported to the transfer station C while the main elevator assembly is resupplied. It is evident that this procedure minimizes the idle time during which the electrostatic reproduction machine remains non-productive.

Although the electrostatic reproduction machine illustrated herein is designed to produce the final copies on sheets of material admitting of any of a wide variety of dimensions, it is expected that, during many reproducing operations, multiple copies will be formed on a particularly dimensioned sheet. For example, if a number of high volume production runs are to be performed on 8 /2 X ll inch paper, such paper will be stacked in the main elevator assembly 31.

Nevertheless, an operator may desire to reproduce a single copy or a small number of copies of an original document on, for example, 8 /2 X 13 inch paper. To obviate the necessity of replacing the 8% X 11 inch paper with 8 X 13 inch paper and then to resupply the main elevator assembly once again with the 8% X l 1 inch paper, the occasionally used paper, i.e., the 8 /2 X 13 inch paper, may be stacked on the auxiliary elevator assembly 32. Thus, when an operator elects to produce a final copy on the differently dimensioned paper, the auxiliary elevator assembly 32 may be selected to assume a proper sheet feeding position whereby the differently dimensioned sheets of material stacked thereon are adapted to be transported to the transfer station. At this time, the main elevator assembly 31 is disabled from supplying the sheets stacked thereon to the transfer station. Accordingly, main elevator assembly 31 and auxiliary elevator assembly 32 are seen to be mutually exclusive in their selection and operation.

Referring now to H0. 2, there is schematically illustrated an embodiment of the auxiliary elevator assembly upon which sheets of copy paper are stacked and adapted to be fed to endless conveyor belt means 29. Apparatus for selecting and regulating the operation of the auxiliary elevator assembly is also illustrated. More particularly, the auxiliary elevator assembly is comprised of platform 101 and driving means 104. The platform 101 is adapted for bi-directional movement and serves as a support for sheets of material 102. Each of the sheets is capable of receiving a developed electrostatic image transferred thereto and, therefore, may comprise any suitable support surface such as plastic, glass, paper, or the like, and may assume any convenient dimensions. It will be assumed, for the purpose of the present explanation, that each sheet is comprised of paper.

The platform 101 is adapted to be driven in an upward and downward direction for supplying the sheets 102 to a position whereby they may be individually transported by endless conveyer belt means 29. The platform is coupled to driving means 104 by any conventional positioning means, generally indicated at 103. Driving means 104 may comprise an electric motor, such as a synchronous motor, coupled via a conventional coupling device 105 to positioning means 103. The latter is here illustrated as an expandable frame whereby rotation of coupling device in a first direction results in an expansion of the expandable frame, and rotation of coupling device 105 in an opposite direction results in a contraction of the expandable frame. It is observed that platform 101 is appropriately displaced in accordance with the expansion and contraction of the expandable frame. Moreover, the rotation of coupling device 105 is a function of the direction of rotation of motor 104. Alternatively, the rotation of motor 104 may effect upward and downward displacement of platform 101 by a pulley and wire arrangement, such as that illustrated in aforementioned copending Application Ser. No. 214,299, now US. Pat. No. 3,768,806, a rack and pinion arrangement, or the like. In a still further embodiment, it is contemplated that platform 101 be pivoted about an axis located at the rear thereof. The platform may thus be rotated into what is described hereinbelow as a proper sheet feeding position in accordance with the direction of rotation of motor 104. Accordingly, it may be appreciated that motor 104 is capable of reversible rotation.

When platform 101 assumes a proper sheet feeding position, the topmost sheet stacked thereon admits of a position whereby it may be fed directly to the endless conveyer belt means 29 illustrated in FIG. 1. After a predetermined number of sheets have been thus fed, the platform 101 must be indexed upward to now allow the topmost sheet to be conveyed to the sheet transfer mechanism. A suitable sensing transducer 119 is provided to ascertain when the topmost sheet is in a proper position for feeding to the sheet transport mechanism, and to produce a signal representative thereof. The transducer may comprise a spring biased lever arm coupled to a mechanical switch disposed in a relatively fixed position whereby the angular rotation of the lever arm is a function of the position of the topmost sheet stacked upon platform 101. Thus, if the topmost sheet is not in position to be fed to the sheet transport mechanism, the lever arm will rotate under the influence of the bias spring, to a position effecting the closure of the switch. The signal produced by transducer 119 is utilized by the elevator assembly control apparatus to be described below.

In the preferred embodiment of the present invention, it is desirable to enable an operator to perform the various operations upon the sheets of material 102, i.e., replenish the supply, when platform 101 obtains an extreme downward position. A suitable transducer 120 is, therefore, provided to sense when platform 1.01 obtains this position, hereinafter the quiescent position. Transducer 120 may comprisea conventional switch disposed in a fixed location and adapted to be contacted by platform 101 such that a representative signal is produced when the platform assumes its quiescent position.

An exemplary embodiment of the illustrated apparatus that serves to control the positioning of the auxiliary elevator assembly comprises selecting means, driving control means and

transducers

119 and 120. The drive control means includes motor control means 106 responsive to first and second input signals applied thereto for regulating the operation of motor 104 coupled thereto. Hence, drive control means 106 is adapted to energize motor 104 in response to a first input signal applied thereto whereby motor 104 rotates in a first direction. Conversely, drive control means 106 is adapted to energize motor 104 in response to a second input signal applied thereto whereby motor 104 rotates in a second direction. If motor 104 comprises a synchronous motor, it is understood that motor control means 106 may supply the synchronous motor with alternating current admitting of a first or second phase in accordance with the application of a first or second input signal thereto; the first and second phases exhibiting a 180 phase relationship. Alternatively, if motor 104 comprises a DC motor it should be recognized that motor control means 106 may supply the DC motor with direct current admitting of a first or second polarity in accordance with the application of a first or second input signal thereto. It is, therefore, appreciated that motor control means 106 may include a suitable source of energy for motor 104 wherein the energy may be supplied to the motor in a first or second sense, such as, for example, by employing first and second conventional gating circuits.

The drive control means further includes first directional drive means 115 and second directional drive means 116. The first directional drive means 115 is coupled to the first input terminal of motor control means 106 and is adapted to supply a signal to the motor control means to effect the positioning of the auxiliary elevator assembly to a proper sheet feeding position. The second directional drive means 116 is coupled to the second input terminal of motor control means 106 and is adapted to produce a signal effective to position the auxiliary elevator assembly to a quiescent position. The first and second directional drive means are coupled to the selecting means and in addition are coupled to

transducers

119 and 120, respectively. More particularly, first and second directional drive means 115 and 116 each comprise coincidence means adapted to produce an output signal in response to the application of a predetermined signal at each .input terminal thereof. Accordingly, coincidence means 115 and 116 may comprise conventional AND gates whereby a binary l is produced at the output terminal thereof when a binary l is supplied to each input terminal thereof. For the purpose of the present discussion, it will be assumed that a binary 1 is represented by a positive DC potential and a binary O is represented by ground potential. It is, of course, understood thatthe foregoing binary signals may be represented by any suitable voltage potentials. Similarly, coincidence means 115 and 116 may each comprise a conventional .NAND gate wherein a binary is produced at the output terminal thereof when a binary l is supplied to each input terminal thereof. As illustrated herein, coincidence means 115 includes a first input terminal coupled to the selecting means and a second input terminal coupled to transducer 119. Likewise, coincidence means 116 includes a first input terminal coupled to the selecting means via inverter means 117 and a second input terminal coupled to transducer 120. The inverter means 117 is adapted to perform a logic negation on a signal supplied thereto wherein a binary l is produced in response to a binary 0 supplied thereto and conversely, a binary 0 is produced in response to a binary l supplied thereto.

The selecting means is adapted to selectively produce a first signal in response to the manual operation of switch means, to terminate the first signal in response to signals representing predetermined operating conditions of the electrostatic reproduction machine with which the present invention finds ready utilization and to produce a second signal which is capable of enabling the sheets of material stacked upon the main elevator assembly to be transported to the electrostatic reproduction machine. More particularly, the selecting means includes coincidence means 109 having a first input terminal coupled to a source of energizing potential +V through the manually operable switch means 107 and a second input terminal coupled to terminal 108. Switch means 107 is adapted to be manually operated by an operator when it is desired to select the auxiliary elevator assembly as a source of supply of the sheets of material for the electrostatic reproduction machine. Switch means 107 may be a simple switch adapted to be opened and closed or, alternatively, may comprise a suitable two-state selecting switch whereby an operator may select the auxiliary elevator assembly or the main elevator assembly in accordance with the selection, and therefore the selective state, of the switch means 107. The switch means may comprise a conventional toggle switch, a push-button switch, a latching switch or the like, well known to those of ordinary skill in the art.

Of the predetermined operating conditions which may be represented by signals applied to terminal 108, an adequate understanding of the present invention may be obtained by referring to a preselected operating condition. For the purpose of explanation, it will be assumed that when the electrostatic reproduction machine admits of the preselected operating condition a binary l is provided at terminal 108. More particularly, it may be observed that the second input terminal of coincidence means 109 is supplied with a binary l when the electrostatic reproduction machine does not admit of its print mode of operation. Accordingly, terminal 108 may be coupled to further means, not shown, such as flip-flop means 127 illustrated in FIG. 2 of copending Application Ser. No. 214,297 filed on Dec. 30, 1971 now abandoned and assigned to Xerox Corporation, the assignee of the present invention, whereby terminal 108 is adapted to receive a suitable enable signal.

Coincidence means 109, which may be similar to aforedescribed coincidence means 115, includes an output terminal coupled to bistate means 110. Bistate means 110 may comprise a conventional bistable device, such as a conventional flip-flop means, including set and reset input terminals and 1 and 0 output terminals. The bistate means may, typically, be a conventional R-S flip-flop, a J-K flip-flop, or the like. Alternatively, the bistate means may comprise cross-coupled NOR-gates, or NAND gates as is well-known to those of ordinary skill in the art. As is appreciated, bistate means 110 is adapted to assume its first state when a binary 1 is applied to the set input terminal thereof and to assume its second state when a binary l is applied to the reset input terminal thereof. The reset input terminal of bistate means 110 is coupled to terminal 118 via OR circuit 123; terminal 118 being adapted to receive signals representing predetermined operating conditions of the electrostatic reproduction machine include a signal representing the termination of an operating cycle by the machine or when the machine admits of a stand-by or ready mode. More particularly, terminal 118 may be coupled to terminal 125 illustrated in FIG. 2 of the aforementioned copending Application Ser. No. 214,297 now abandoned whereby a binary l is supplied thereto at a predetermined time subsequent to the transition of a binary to a binary l at terminal 108. OR circuit 123 is adapted to produce a binary l at the output terminal thereof when a binary l is applied to either input terminal thereof. The second input terminal of the OR cir cuit is coupled to a suitable source of energizing potential +V through manually operable switch means 122. The latter switch means is adapted to be manually operated by an operator when it is desired to select the main elevator assembly as a source of the supply of sheets of material for the electrostatic reproduction machine. Switch means 122 may be similar to aforedescribed switch means 107 and capable of mutually complementary operation therewith. Consequently, a closing of switch means 107 requires the opening of switch means 122. Conversely, a closing of switch means 122 requires the opening of switch means 107. It should be apparent that the combination of switch means 107 and 122 comprises the aforementioned two-state selecting switch whereby suitable operation thereof results in a corresponding selection of the auxiliary or main elevator assembly.

The 1 output terminal of bistate means 110 is coupled to the aforedescribed drive control means by coincidence means 113. Coincidence means 113, which may be similar to coincidence means 115, includes a first input terminal coupled to the 1 output terminal of bistate means 110 and a second input terminal coupled to terminal 108 via inverter means 114. The inverter means 114 may be similar to aforementioned inverter means 117 and is capable of supplying coincidence means 113 with a predetermined binary signal when the electrostatic reproduction machine admits of an operating condition other than the aforementioned preselected operating condition. Although not illustrated herein, if switch means 107 comprises a conventional two-state selecting switch, the switch means may be coupled to the reset input terminal of bistate means 110 to supply an appropriate signal thereto when an operator has positioned the two-state selecting switch to manifest a selection of the main elevator assembly.

The 1 output terminal of bistate means 110 is further coupled to suitable indicating means to provide a visual indication when an operator has selected the auxiliary elevator assembly to supply sheets of material to the electrostatic reproduction machine. As illustrated herein, the 1 output terminal of the bistate means is coupled to an indicating lamp 112 via conventional lamp driving means 111. Lamp 112 is connected in series with lamp driving means 111 and is included in a series circuit between a source of suitable energizing potential +V and ground. In the exemplary embodiment, the lamp driving means is comprised of transistor means 111 adapted to assume a saturation state in response to a suitable voltage potential applied to the base electrode thereof, whereupon current may flow from the source +V, through lamp 112, through the collector-emitter junction of the saturated transistor means to ground. If desired, alternative lamp driving means may be employed to effect the energization of lamp 112 in response to the application of a suitable voltage. Hence, conventional relay switch means may be provided, triac devices may be provided, or the like.

The operation of the auxiliary elevator assembly, its cooperation and interaction with the main elevator assembly and the control means therefor, will now be described. It will soon become readily apparent that the quiescent position assumed by the auxiliary elevator assembly is such wherein the topmost sheet stacked thereon is removed from a proper sheet feeding position and, in addition, the selecting means illustrated and described herein is biased such that the main elevator assembly is normally adapted to supply the sheets of material stacked thereon to the electrostatic reproduction machine. Accordingly, an operator must initiate positive action to position the auxiliary elevator assembly in a proper sheet feeding position whereby sheets of material stacked thereon are enabled to be transported to the electrostatic reproduction machine. Let it be assumed that the supply of sheets stacked upon the main elevator assembly has been exhausted during an operating cycle of the electrostatic reproduction machine. The conditions resulting therefrom are particularly described in copending Application Ser. No. 214,297, now abandoned. It is recognized therefrom that the operating cycle of the electrostatic reproduction machine is thus terminated and the machine is driven out of its print mode of operation. Consequently, a binary l is applied to terminal 108 and a suitable pulse signal is then applied to terminal 118. Bistate means 1 10 responds to the signal applied to terminal 118 to assume its second state. The exhausting of the supply of sheets of material in the main elevator assembly will prompt an operator to effect the resupply of the main elevator assembly. Should the operation of the electrostatic reproduction machine be continued during this period of resupply, the operator may choose to select the auxiliary elevator assembly to supply the sheets stacked thereon to the electrostatic reproduction machine. It is appreciated that the mutual exclusiveness of the main and auxiliary elevator assemblies permit the utilization of one while resupplying the other. Accordingly, the manual operation of switch means 107 supplies a binary l to the input terminal of coincidence means 109 coupled thereto. It is understood that, if switch means 107 comprises a two-state selecting switch, the proper positioning thereof is effective to supply a binary 1 to coincidence means 109. In addition, switch means 122 now supplies a binary 0 to the reset input terminal of bistate means 110 via OR circuit 123. Thebinary l applied to terminal 108 when the electrostatic reproduction machine assumes a preselected operating condition, e. g., the termination of its print mode of operation, is supplied to the second input terminal of coincidence means 109. Consequently, the coincidence means applies a binary l to the set input terminal of bistate means 1 10, thereby setting the bistate means to its first state.

The assumption of its first state by the bistate means indicates that the auxiliary elevator assembly has been selected to supply sheets of material to the electrostatic reproduction machine and that the main elevator assembly is to be inhibited from executing a similar operation. A binary l is thus produced at the 1 output of bistate means 110. This signal is applied to the base electrode of transistor means 111 thereby driving the transistor means into a saturation state, whereupon lamp 112 is illuminated. In addition, the selection of the auxiliary elevator assembly is effective to drive platform 101 to a proper sheet feeding position. This is achieved by coupling the binary I from the 1 output terminal of bistate means 110 to coincidence means It is recalled that bistate means 110 assumes its first state when switch means 107 is manually operated and when the electrostatic reproduction machine assumes a preselected operating condition, e.g., the machine does not admit of its print mode. In the exemplary embodiment illustrated herein, the signal provided at the 1 output terminal of bistate means 110 is coupled to coincidence means 115 in response to the manual operation of'an initiating switch as, for example, a print switch. Accordingly, coincidence means 113 includes an input terminal adapted to be supplied with a signal representing a manual operation of such initiating switch. It may be appreciated that when the initiating switch is operated, the electrostatic reproduction machine is activated to assume a print mode of operation, resulting in the application of a binary to terminal 108. The signal applied to terminal 108 is inverted by inverter means 114 and applied to coincidence means 113 as a binary l Thus, when an operator selects the auxiliary elevator assembly, and in addition, operates the machine operation initiating switch, coincidence means 113 supplies a binary 1 to coincidence means 115.

It is recalled that platform 101 initially assumes its quiescent position. Accordingly, the topmost sheet of the stack sheets of 102 does not assume a proper sheet feeding position. Transducer means 119 therefore supplies the other input terminal of coincidence means 1 with a binary l It is recognized that a binary l is now supplied to each input terminal of coincidence means 115 and, therefore, a binary l is applied to a corresponding input of motor control means 106. The source of energy included in the motor control means 106 is thus supplied to energize electric motor 104 in a first sense whereupon platform 101 is driven man upward direction to assume a proper sheet feeding position. The energization of motor 104 is thus maintained until transducer 119 senses the proper positioning of the sheets of material stacked upon the auxiliary elevator assembly. At that time, a binary 0 is supplied to coincidence .means 115 by transducer 119 and the binary 1 previously applied to motor control means 106 is removedtherefrom. Consequently, energy is no longer supplied from motor control means 106 to motor 104 and the driving of platform 101 is an upward direction is terminated. Sheets 102 stacked upon the platform are thus enabled to be successively removed therefrom and transported via the endless conveyer belt means 29 to the transfer station C of FIG. 1. If a plurality of copies are to be produced, transducer 119 produces a binary l after a predetermined number of sheets 102 are removed and fed to the sheet transport mechanism, representing that the topmost sheet is no longer in proper position. Coincidence means 115 thus applies a binary l to motor control means 106 and platform 101 is indexed upward until the transducer again produces a binary O. In this manner, the auxiliary elevator assembly is maintained in a proper sheet feeding position.

When the electrostatic reproduction machine resumcs its preselected operating condition, a binary l is applied to terminal 108. It is apparent that this condition may correspond to that assumed when the electrostatic reproduction machine does not admit of its print mode of operation. More particularly, if a selected number of copies have been produced by the machine or, in the alternative, if the last sheet stacked upon the auxiliary elevator assembly has been transported therefrom, the machine will adopt a non-print mode. A more detailed explanation as to the manner in which the print mode is terminated in response to the feeding of the last sheet of material stacked upon the auxiliary elevator assembly is set forth in copending Application Ser. No. 214,297 now abandoned. A supply of sheets of material need not be provided to the electrostatic reproduction machine when the non-print mode of operation is assumed. Accordingly, this condition enables the auxiliary elevator assembly to be driven downward to its quiescent position. More particularly, the binary l now applied to terminal 108 is inverted by inverting means 114 and is applied as a binary O to coincidence means 113. Consequently, coincidence means 113 applies a binary 0 to coincidence means and to inverter means 117. It is apparent that the logic negation performed by inverter means 117 is effective to provide coincidence means 116 with a binary l at a first input terminal thereof. Since platform 101 is not at this time in its quiescent position, transducer applies a binary 1 to the other input terminal of coincidence means 116. Thus, a binary l is applied to a corresponding input terminal of motor control means 106 whereby the source of energy included therein is supplied to electric motor 104 in a second sense to effect the return of the auxiliary elevator assembly to its quiescent position. Once transducer 120 senses the auxiliary elevator assembly has assumed its quiescent position, a binary 0 is applied thereby to coincidence means 116 to effect a termination in the supply of energy to electric motor 104 from motor control means 106. The motor thus ceases its operation.

At a predetermined time subsequent to the transition at terminal 108 from a binary 0 to a binary l a signal is applied to terminal 118 if the aforementioned initiating switch is not once again operated, said signal representing that the electrostatic reproduction machine has obtained one of a plurality of predetermined operating conditions. Accordingly, a binary l is applied to terminal 118 when the operating cycle of the machine has terminated, for example, or when the machineadmits of its stand-by or ready mode. As illustrated in FIG. 2, the signal applied to terminal 118 is effective via OR circuit 123 to reset bistate means 110 to assume its second state. The signal provided at the 1 output terminal of the bistate means is thus terminated and lamp 112 is extinguished. Moreover, a signal is now provided at the 0 output terminal of the bistate means to thereby enable the main elevator assembly to be operated such that the sheets stacked thereon may be transported via the sheet transport mechanism to the transfer station. One of ordinary skill in the art will appreciate that if switch means 107 comprises a conventional latching switch, the signal applied to terminal 118 may be additionally applied to the latching switch to reset the switch to its normally unoperated condition. This, of course, may be omitted if the switch means comprises a conventional spring biased pushbutton switch. Hence, the operation of an initiating switch by an operator will result in the feeding of sheets from the main elevator assembly, the auxiliary elevator assembly being disabled at this time.

Alternatively, if the operator wishes to return to the main elevator assembly as a source of sheets of material for the electrostatic reproduction machine, operation of switch means 122 serves to reset bistate means 110 to assume its second state. This, of course, may be accomplished at any time, provided, the main elevator assembly is properly supplied with sheets of material. The signal now provided by the bistate means 110 enables the main elevator assembly to be operated and, in addition, causes lamp 112 to be extinguished. It is recognized that the closing of switch means 122 results in the opening of switch means 107, as has been described hereinabove.

If the auxiliary elevator assembly is utilized by an operator to augment the supply of sheets stacked upon the main elevator assembly, the apparatus illustrated herein functions in the aforedescribed manner. Thus, after a selected number of copies have been produced on sheets supplied to the electrostatic reproduction machine from the main elevator assembly, a signal is applied to terminal 108 representing that the machine admits of its preselected operating condition. If an operator now wishes to produce copies upon the sheets of material supplied from the auxiliary elevator assembly, switch means 107 may be manually operated to thereby set bistate means 110 to assume its first state. It is recalled that the auxiliary elevator assembly is driven to assume a proper sheet feeding position when the operator then operates a suitable initiating switch. Furthermore, the binary provided at the 0 output terminal of bistate means 110 may be applied to further means, not shown, to inhibit the main elevator assembly from supplying sheets of material to the sheet transport mechanism when the auxiliary elevator assembly has been selected. Since the auxiliary elevator assembly may be utilized to complement the main elevator assembly, the capacity of the former may, if desired, be equal to or less than the sheet capacity of the latter.

Although the auxiliary elevator assembly has been specifically described as movable in upward and downward directions, it is recognized that platform 101 is bidirectionally movable and may, if desired, be displaced in lateral directions. Moreover, the control apparatus illustrated in FIG. 2 is intended to be merely exemplary and should not be construed as unnecessarily limiting the present invention to the specific embodiment depicted therein. [t is, therefore, appreciated that bistate means 110 and coincidence means 113 may be omitted whereby the output terminal of coincidence means 109 is coupled directly to the first input terminal of coincidence means 115 and terminal 118 is coupled directly to the input terminal of coincidence means 116. Alternatively, if it is desired to drive the auxiliary elevator assembly to its proper sheet feeding position immediately upon the operation of switch means 107 without requiring the additional operation of the initiating switch, switch means 107 may be coupled directly to 'the first input terminal of coincidence means 115.

Thus, alternative embodiments are contemplated wherein platform 101 is driven to its proper sheet feeding position when switch means 107 is operated; when the auxiliary elevator assembly is selected by the proper operation of switch means 107 and an initiating switch is subsequently operated; or when switch means 107 is operated and the electrostatic reproduction machine admits of a stand-by or ready" mode. Similarly, alternative embodiments are contemplated for the driving of platform 101 to a quiescent position when the main elevator assembly is selected by the appropriate operation of switch means 122; when a signal is applied to terminal 118; or when switch means 107 is not operated and the electrostatic reproduction machine admits of its stand-by or ready mode. Hence, the selective operation of switch means 107 is effective to supply a first signal to coincidence means whereby the auxiliary elevator assembly is driven to assume its proper sheet feeding position. The appli cation of a signal to terminal 118 as well as the selective operation of switch means 122 is effective to supply a second signal to coincidence means 116 whereby the auxiliary elevator assembly is driven to assume its quiescent position.

It is noted that if the instant invention is utilized in conjunction with apparatus described in copending Application Ser. No. 214,297 now abandoned and in copending Application Ser. No. 214,299 the exhausting of the supply of sheets of material stacked upon the main elevator assembly will normally prevent the electrostatic reproduction machine from assuming its print mode of operation until the supply is replenished. However, in accordance with the foregoing description hereof, the present invention enables the continued use of the electrostatic reproduction machine by supplying sheets of material thereto from the auxiliary elevator assembly during those periods of resupplying the main elevator assembly. Consequently, the inhibit signal provided on conductor 1 16 in FIG. 2 of copending Application Ser. No. 214,297 now abandoned may be removed therefrom when the auxiliary elevator assembly has been selected by the operator. This may be readily accomplished by inverting the binary 1 provided at the 1 output terminal of bistate means 110 and then gating the inverted signal with the signal provided on conductor 116. The electrostatic reproduction machine may thus assume its print mode in response to the operation of the initiating switch. With reference to the apparatus of the instant invention as depicted in FIG. 2, it should be appreciated that the signals produced by each of

transducers

119 and 120 are reversible. Hence, a binary 1 may be produced by transducer 1 19 when the auxiliary elevator assembly assumes its proper sheet feeding position and a binary l may be produced by transducer 120 when the auxiliary elevator assembly assumes its quiescent position. Moreover, one of ordinary skill in the art will recognize that thevarious logic gating circuits and functions performed thereby may, alternatively, be implemented by conventional OR circuits, NOR circuits, NAND circuits and other conventional logic components. It is now apparent that the foregoing and various other changes and modifications in form and details may be made without departing from the spirit and scope of the invention. It is, therefore, intended that the appended claims be interpreted as including all such changes and modifications.

What is claimed is:

1. In an electrostatic reproduction machine wherein a viewable image is formed on sheets of material and including a main elevator assembly and an auxiliary elevator assembly upon which sheets are stacked, apparatus for regulating the operation of said auxiliary elevator assembly, comprising:

a selecting switch;

first means responsive to the selective manual operation of said selecting switch to enable the sheets stacked upon said auxiliary elevator assembly to be transported to said electrostatic reproduction machine, said first means comprising first gate means having a plurality of inputs and an output for producing an output signal when each input thereof is supplied with an input signal, said first gate means having one input coupled to said selecting switch for receiving an input signal upon the selective manual operation of said selecting switch and another input for receiving an input signal when said electrostatic reproduction machine assumes a preselected operating condition;

second means responsive to the selective manual operation of said selecting switch to prevent the sheets stacked upon said auxiliary elevator assembly from being transported to said electrostatic re production machine, said second means comprising bistate means for assuming a first state and a second state, said bistate means having a first input terminal coupled to the output of said first gate means for assuming the first state thereof in response to said first gate means output signal and a second input terminal for receivingsignals representing predetermined operating conditions of said electrostatic reproduction machine, said last mentioned signals including a signal representing the termination of an operating cycle, said bistate means assuming the second state thereof when said second input terminal receives a signal, a first signal being produced when said bistate means asv sumes the first state thereof and a second signal being produced when said bistate means assumes the second state thereof;

sheet feed position sensing means for sensing when said auxiliary elevator assembly assumes a proper sheet feeding position and for generating a signal representative thereof;

quiescent position sensing means for sensing when said auxiliary elevator assembly assumes a quiescent position and for generating a signal representative thereof;

first directional drive means responsive to said first signal and to a signal representing that said auxiliary elevator assembly is not in a proper position for supplying the sheets stacked thereon to drive the auxiliary elevator assembly to said proper sheet feeding position; and

second directional drive means responsive to the absence of said first signal and to a signal representing that said auxiliary elevator assembly is not in a quiescent position to drive said auxiliary elevator assembly to said quiescent position.

2. The apparatus of claim 1 including second gate means having a plurality of inputs and an output for producing an output signal when each input thereof is supplied with an input signal, said second gate means having one input coupled to said bistate means for receiving an input signal when said bistate means assumes the first state thereof and another input for receiving a signal when said electrostatic reproduction machine assumes an operating condition other than said preselected operating condition.

3. The apparatus of claim 2 wherein said first directional drive means comprises third gate means having a plurality of inputs and an output for producing an output signal when each input thereof is supplied with an input signal, said third gate means having one input coupled to the output of said second gate means for receiving said second gate means output signal and another input coupled to said sheet feed position sensing means for receiving a signal representing that said auxilia ry elevator assembly is not in said proper sheet feeding position.

4. The apparatus of claim 3 wherein said second directional drive means comprises fourth gate means having a plurality of inputs and an output for producing an output signal when each input thereof is supplied with an input signal, said fourth gate means having one input coupled to the output of said second gate means for receiving a signal representing that said second gate means is not producing an output signal and another input coupled to said quiescent position sensing means for receiving a signal representing that said auxiliary elevator assembly is not in said quiesent position.

5. The apparatus of claim 4 wherein said drive means further comprises:

a reversible electric motor mechanically coupled to said auxiliary elevator assembly for imparting bidirectional motion to said auxiliary elevator assembly; and

a source of energy for said electric motor coupled to said third and fourth gate means and adapted to supply energy to said electric motor in a first sense in response to said third gate means output signal and in a second sense in response to said fourth gate means output signal, whereby said auxiliary elevator assembly is driven to said proper sheet feeding position and to said quiescent position, respectively 6. In an electrostatic reproduction machine wherein a viewable image is formed on sheets of material supplied by an elevator assembly upon which said sheets are stacked, apparatus for regulating the position of said elevator assembly, comprising:

selecting means for selectively producing a first signal in response to the manual operation of switch means and for terminating said first signal in response to signals representing predetermined operating conditions of said electrostatic reproduction machine, said selecting means comprising bistate means for assuming a first state in response to said manual operation of said switch means and for assuming a second state in response to the termination of an operating cycle by said electrostatic reproduction machine, said first signal being produced when said bistate means assumes said first state;

A reversible electric motor mechanically coupled to said elevator assembly for imparting bi-directional motion to said elevator assembly; and

drive control means coupled to said selecting means and including a source of energy adapted to be t coupled to said electric motor in a first sense in response to said first signal whereby said elevator assembly is driven to a proper sheet feeding position such that the sheets of material stacked thereon are fed to said electrostatic reproduction machine, said source of energy being adapted to be coupled to said electric motor in a second sense in response to the termination of said first signal whereby said elevator assembly is driven to a quiescent position.

7. The apparatus of claim 6 wherein said selecting means further comprises first coincidence means having a first input coupled to said switch means, a second input for receiving an input signal when said electrostatic reproduction machine assumes a preselected operating condition and an output coupled to said bistate means for activating said bistate means to assume its first state when said switch means is operated and said electrostatic reproduction machine assumes said preselected operating condition.

8. The apparatus of claim 7 wherein said drive control means comprises:

second coincidence means having a first input coupled to said bistate means, a second input indica tive of a position of said elevator assembly, said second coincidence means having an output coupled to said drive control means for enabling said source of energy to be coupled to said electric motor in said first sense when said bistate means assumes its first state; third coincidence means having a first input coupled to said bistate means, a second input indicative of a second position of said elevator assembly, said third coincidence means having an output coupled to said drive control means for enabling said source of energy to be coupled to said electric motor in said second sense when said bistate means assumes its second state; and means for coupling said bistate means to said respective first inputs of said second and third coincidence means.

9. The apparatus of claim 8 further including: sheet feed position sensing means coupled to said second coincidence means second input for sensing when said elevator assembly assumes a proper sheet feeding position to disable said second coincidence means; and

quiescent position sensing means coupled to said third coincidence means second input for sensing when said elevator assembly assumes a quiescent position to disable said third coincidence means.

10. The apparatus of claim 9 wherein said means forv coupling comprises:

fourth coincidence means having a first input coulogic negation means for coupling said fourth coincidence means output to said third coincidence means first input.

Claims

1. In an electrostatic reproduction machine wherein a viewable image is formed on sheets of material and including a main elevator assembly and an auxiliary elevator assembly upon which sheets are stacked, apparatus for regulating the operation of said auxiliary elevator assembly, comprising: a selecting switch; first means responsive to the selective manual operation of said selecting switch to enable the sheets stacked upon said auxiliary elevator assembly to be transported to said electrostatic reproduction machine, said first means comprising first gate means having a plurality of inputs and an output for producing an output signal when each input thereof is supplied with an input signal, said first gate means having one input coupled to said selecting switch for Receiving an input signal upon the selective manual operation of said selecting switch and another input for receiving an input signal when said electrostatic reproduction machine assumes a preselected operating condition; second means responsive to the selective manual operation of said selecting switch to prevent the sheets stacked upon said auxiliary elevator assembly from being transported to said electrostatic reproduction machine, said second means comprising bistate means for assuming a first state and a second state, said bistate means having a first input terminal coupled to the output of said first gate means for assuming the first state thereof in response to said first gate means output signal and a second input terminal for receiving signals representing predetermined operating conditions of said electrostatic reproduction machine, said last mentioned signals including a signal representing the termination of an operating cycle, said bistate means assuming the second state thereof when said second input terminal receives a signal, a first signal being produced when said bistate means assumes the first state thereof and a second signal being produced when said bistate means assumes the second state thereof; sheet feed position sensing means for sensing when said auxiliary elevator assembly assumes a proper sheet feeding position and for generating a signal representative thereof; quiescent position sensing means for sensing when said auxiliary elevator assembly assumes a quiescent position and for generating a signal representative thereof; first directional drive means responsive to said first signal and to a signal representing that said auxiliary elevator assembly is not in a proper position for supplying the sheets stacked thereon to drive the auxiliary elevator assembly to said proper sheet feeding position; and second directional drive means responsive to the absence of said first signal and to a signal representing that said auxiliary elevator assembly is not in a quiescent position to drive said auxiliary elevator assembly to said quiescent position.

3. The apparatus of claim 2 wherein said first directional drive means comprises third gate means having a plurality of inputs and an output for producing an output signal when each input thereof is supplied with an input signal, said third gate means having one input coupled to the output of said second gate means for receiving said second gate means output signal and another input coupled to said sheet feed position sensing means for receiving a signal representing that said auxiliary elevator assembly is not in said proper sheet feeding position.

5. The apparatus of claim 4 wherein said drive means further comprises: a reversible electric motor mechanically coupled to said auxiliary elevator assembly for imparting bi-directional motion to said auxiliary elevator assemblY; and a source of energy for said electric motor coupled to said third and fourth gate means and adapted to supply energy to said electric motor in a first sense in response to said third gate means output signal and in a second sense in response to said fourth gate means output signal, whereby said auxiliary elevator assembly is driven to said proper sheet feeding position and to said quiescent position, respectively.

6. In an electrostatic reproduction machine wherein a viewable image is formed on sheets of material supplied by an elevator assembly upon which said sheets are stacked, apparatus for regulating the position of said elevator assembly, comprising: selecting means for selectively producing a first signal in response to the manual operation of switch means and for terminating said first signal in response to signals representing predetermined operating conditions of said electrostatic reproduction machine, said selecting means comprising bistate means for assuming a first state in response to said manual operation of said switch means and for assuming a second state in response to the termination of an operating cycle by said electrostatic reproduction machine, said first signal being produced when said bistate means assumes said first state; A reversible electric motor mechanically coupled to said elevator assembly for imparting bi-directional motion to said elevator assembly; and drive control means coupled to said selecting means and including a source of energy adapted to be coupled to said electric motor in a first sense in response to said first signal whereby said elevator assembly is driven to a proper sheet feeding position such that the sheets of material stacked thereon are fed to said electrostatic reproduction machine, said source of energy being adapted to be coupled to said electric motor in a second sense in response to the termination of said first signal whereby said elevator assembly is driven to a quiescent position.

8. The apparatus of claim 7 wherein said drive control means comprises: second coincidence means having a first input coupled to said bistate means, a second input indicative of a position of said elevator assembly, said second coincidence means having an output coupled to said drive control means for enabling said source of energy to be coupled to said electric motor in said first sense when said bistate means assumes its first state; third coincidence means having a first input coupled to said bistate means, a second input indicative of a second position of said elevator assembly, said third coincidence means having an output coupled to said drive control means for enabling said source of energy to be coupled to said electric motor in said second sense when said bistate means assumes its second state; and means for coupling said bistate means to said respective first inputs of said second and third coincidence means.

9. The apparatus of claim 8 further including: sheet feed position sensing means coupled to said second coincidence means second input for sensing when said elevator assembly assumes a proper sheet feeding position to disable said second coincidence means; and quiescent position sensing means coupled to said third coincidence means second input for sensing when said elevator assembly assumes a quiescent position to disable said third coincidence means.

10. The apparatus of claim 9 wherein said means for coupling comprises: fourth coincidence means having a first input coupled to said bistate means, a second input for receiving an input signal when said electrostatic reproduction machine assumes an operating condition other than said preselected operating condition and an output coupled to said second coincidence means first input; and logic negation means for coupling said fourth coincidence means output to said third coincidence means first input.