Ruth, Robert W. (Washington, DC)
Le Bow, Bennett S. (Washington, DC)

04/814235

07/27/1971

04/08/1969

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DSI Systems, Inc. (Rockville, MD)

353/27A

355/18

G03B21/11; G06K17/00; G03B21/10; G11B13/00; G03B23/00

340/172.5 235/157 40/106.1 353/25,39,68,71

3346853

Control/display apparatus

October 1967

Koster

Henon, Paul J.

Chapuran R. F.

What I claim is

1. A microfilm viewer for automatically indexing a strip of microfilm to a desired viewing position wherein said microfilm strip includes a plurality of longitudinally spaced index markers at regular intervals to signify the location of successive film frames disposed thereon, said viewer comprising:

2. A microfilm viewer as in claim 1 including:

3. A microfilm viewer as in claim 2 further including:

4. A microfilm viewer as in claim 1 for use with microfilm strips having at least first and second index markers at predetermined relative dispositions for each of said regular intervals on the strip of film and wherein said detecting means includes:

5. A microfilm viewer as in claim 1 wherein said input means includes external automatic digital computing means for generating said digital input signals.

6. A microfilm viewer as in claim 1 wherein said input means comprises:

7. An improvement for an automatically indexable viewer which permits automatic indexing with use of only simple elementary index spots on a strip of microfilm, said improvement comprising:

This invention relates to information retrieval apparatus, and more particularly to microfilm readers of the electrically operated type.

A main object of the invention is to provide a novel and improved microfilm reader which is of relatively simple construction, which is very compact in size, and which is so arranged that it may be operated either from a self-contained page-selecting means, or alternatively, from a remote source.

A further object of the invention is to provide an improved automated microfilm reader of the cartridge type having photoelectric monitoring means responding to the movement of the film in a cartridge and having means controlling the drive mechanism of the cartridge in a manner such that the mechanism may be operated in accordance with a coded input signal corresponding to a particular film frame desired to be viewed, the signal being derived either from a keyboard on the device, or from a remote source.

A still further object of the invention is to provide an improved automated microfilm reader adapted to be employed as part of an information retrieval system wherein command signals may be generated, for example, at a computer, the microfilm reader being adapted to be controlled by such command signals to drive the film-moving mechanism of the device in such a manner as to display a corresponding desired film frame number on the viewing screen of the apparatus.

A still further object of the invention is to provide an improved automated microfilm reader having drive means for winding or rewinding the film of an associated cartridge, the microfilm reader including circuit means for controlling the direction of movement of the film and means for moving the film to a desired position wherein a selected frame is displayed; the movement of the film being monitored by photoelectric means and the driving apparatus being controlled by the photoelectric means in a manner such that the film is driven in accordance with input data corresponding to the film frame desired to be displayed.

A still further object of the invention is to provide an improved automated microfilm reader of the cartridge type having photoelectric monitoring means and drive means controlled thereby to operate in a manner in accordance with a coded input signal corresponding to a particular film frame desired to be viewed or a desired increment of frames through which the film is to be moved each time the reader drive means is activated, whereby the microfilm reader may be operated either in an absolute mode, or in an incremental mode.

A still further object of the invention is to provide an improved automated microfilm reader which is relatively inexpensive to fabricate, which is durable in construction, which is highly accurate in its operation, and which is adaptable for use in a number of different ways, for example, either to directly display a selected numbered film frame carried in a cartridge inserted there in or to provide incremental advancement of reversal of the film in the cartridge, namely, selected steps or increments of film movement, and being adapted either for operation locally by means of a keyboard or corresponding command device, or from a remote source, such as a command-generating computer system or device.

Further objects and advantages of the invention will become apparent from the following description and claims, and from the accompanying drawings, wherein:

FIG. 1 is a perspective view of an improved automated microfilm reader constructed in accordance with the present invention.

FIG. 2 is a transverse vertical cross-sectional view taken substantially on the line 2-2 of FIG. 1, and showing the microfilm reader with a film cartridge inserted therein.

FIG. 3 is an enlarged fragmentary vertical cross-sectional view taken substantially on line 3-3 of FIG. 2.

FIG. 4 is an enlarged fragmentary plan view of a portion of the keyboard employed with the microfilm reader of FIGS. 1, 2 and 3, showing various control elements associated with the device.

FIG. 5 is a schematic block diagram showing the general circuit arrangement employed in the microfilm reader of FIGS. 1 to 4.

FIG. 5a is a fragmentary view of a short section of microfilm employed in a cartridge adapted to be inserted in the microfilm reader of FIGS. 1 to 5, illustrating the location of typical monitoring spots provided on the film and cooperating with photoelectric sensing means forming part of the microfilm reader drive control mechanism controlled by the circuit shown in FIG. 5.

Referring to the drawings, 11 generally designates a typical embodiment of an automated microfilm reader employed in an information retrieval system according to the present invention. The microfilm reader 11 comprises a bottom supporting housing 12 on whose top wall 13 is secured an upstanding hollow vertical post member 14 on which is mounted the enlarged auxiliary housing 15 provided with a translucent viewing screen 16, forming part of its front wall. The housing 15 contains a folded projection system defined by respective inclined mirrors 17 and 18 oriented so as to properly direct images to the translucent viewing screen 16 from a reflecting mirror 20 provided in the bottom housing 12 subjacent the hollow post member 14, as shown in FIG. 2.

The main supporting housing 12 is provided with an inclined front wall 21 having a front-loading magazine receptacle 22 adapted to receive a conventional microfilm cartridge 23 therein in the manner shown in FIG. 2. The cartridge 23 is of conventional type having a built-in film gate 24 and having forward and reverse drive spindles 25 and 26. The receptacle 22 also includes the built-in inclined mirror 27 oriented to reflect a vertical beam of light 28 rearwardly toward the inclined mirror 20 when the cassette 23 is positioned as in FIG. 2. A projection lamp 29 is mounted in the rear portion of housing 12, located to generate the light beam 28, the light from the lamp 29 passing though a conventional condensing lens system 30 to a reflecting prism assembly 31 which acts to reflect the light from the condenser assembly 30 upwardly to form the beam 28 above-mentioned. The cassette 23 is suitably apertured to admit the beam 28 and allow it to impinge on the mirror 27, from which it is reflected through the film gate 24, passing through a section of film therein, the transmitted light then passing through a focusing lens assembly 32 mounted in the housing 12 between the position of the magazine 23 and the inclined mirror 20, as illustrated diagrammatically in FIG. 2. Thus, the image formed by the light beam 28 is focused onto the translucent projection screen 16 so as to be viewed in greatly magnified size from the front of the microfilm reader.

Mounted in the rear portion of the housing 12 is a suitable ventilating blower 33 which provides a sufficient flow of cooling air to prevent the interior of the housing from rising to an excessively high temperature.

Mounted in the forward portion of housing 12 under the region of the magazine receptacle 22 is a vertically positioned electric motor 34 employed for driving the spindles of the magazine 23 in a manner presently to be described. The spindle assemblies 25 and 26 of the film magazine 23 are adapted to become automatically coupled with respective driving shaft elements 35 and 36 and being, at times, drivingly connected to the electric motor 34 as will be presently described. The coupling of the film magazine 23 to the spindles 35 and 36 is of conventional structure, and will not be explained in detail.

Referring to FIG. 3, spindle shaft 36 constitutes the forward, or takeup spindle of the transmission assembly, and the shaft 35 constitutes the reverse, or rewind shaft element of the assembly. Shaft element 36 can be driven, at times, from a takeup drive pulley 37 mounted on suitable shaft means journaled in a generally U-shaped bracket member 38 secured to the horizontal wall portion 39 forming the bottom of the magazine-receiving receptacle 22. Between pulley 37 and shaft element 36 there is provided a conventional electrically operated clutch assembly 40 and a conventional electrically operated brake assembly 41, as shown in FIG. 3. Under normal nondriving conditions the clutch assembly 40 is deenergized and is in nondriving condition, whereas the brake assembly 41 is in an applied condition so that shaft element 36 is locked against rotation. In other words, when the microfilm reader is in a nondrive (nonsearch) condition, as will be presently explained, the main drive motor 34 is running, assuming that the device is energized, the forward drive clutch assembly 40 is disengaged and the forward brake assembly 41 is energized and prevents shaft element 36 from rotating.

In a similar manner, the rewind or reverse shaft element 35 is mounted in a U-shaped bracket 42 secured to wall 39, shaft element 35 being journaled in alignment with the shaft of a rewind pulley 43 journaled in the bracket, with an electrically operated clutch assembly 44 and an electrically operated brake assembly 45 provided between shaft element 35 and the shaft of pulley 43. As in the case of clutch assembly 40 and brake assembly 41, in a nondrive (nonsearch) condition of the apparatus, with motor 34 running, clutch assembly 44 will be disengaged and deenergized and brake assembly 45 will be in an applied condition, locking shaft element 35 against rotation.

Journaled in another bracket 46 secured to wall 39 are respective driving shafts 47 and 48, the shaft 47 being provided with a slow-speed driving pulley 49 and the shaft 48 being provided with a high-speed driving pulley 50. The pulleys 50, 49, 43 and 37 are in alignment, as shown in FIG. 3, and are intercoupled by a common drive belt 51.

Journaled in bracket 46 in axial alignment with shaft element 48 is a driving shaft element 52 having secured thereon the large pulley 53 and the relatively small pinion pulley 54. Motor 34 is provided with the drive pinion 55 which is drivingly coupled to the large pulley 53 by a drive belt 56. Also journaled in bracket 46 in alignment with shaft 47 is a shaft element 57 provided with a large pulley 58, the pulley 58 being drivingly coupled to the pinion element 54 by a drive belt 59. It will thus be seen that the motor pinion 55 drives shaft element 52 at a relatively constant speed, whereas the shaft element 57 is driven at a much slower speed, since the diameter of the pulley 58 is much greater than that of its driving pinion 54.

An electrically operated high-speed clutch assembly 60 of conventional construction is provided between shaft element 52 and shaft element 48, and a similar conventional electrically operated slow-speed clutch assembly 61 is provided between shaft element 57 and shaft element 47. In a nondrive (nonsearch) condition of the apparatus, with the main drive motor 34 running, the low speed clutch assembly 61 is in an engaged condition, whereas the high-speed clutch assembly 60 is in a disengaged, nondriving condition. Therefore, under these conditions the shaft element 47 and pulley 49 will be rotating and will be driving the pulleys 43 and 37 at a relatively slow speed. Pulley 50 will be likewise driven by belt 51, but will not be connected to shaft element 52 in view of the disengaged condition of the high-speed clutch assembly 60. Suitable conventional energizing circuits, not shown, are provided for the drive motor 34, the high-speed clutch 60, the low speed clutch 61, the reversing clutch 44, the forward drive clutch 40 and the electrically operated brake assemblies 41 and 45. As above mentioned, the circuitry is so arranged that the low speed clutch 61 is normally energized and the high-speed clutch 60 is normally deenergized. Suitable conventional means are provided for automatically deenergizing the low speed clutch when the high-speed clutch becomes energized, the arrangement being such that only one of the clutches 61 or 60 can be in an engaged condition at any one time.

FIG. 5, therefore, does not represent the specific wiring details of the various elements, but merely is a block diagram illustrating the essential elements involved in controlling the various components so as to condition them to operate, as will be presently described. FIG. 5a illustrates in an enlarged view a fragmentary portion of a film strip 62 carried in a typical magazine 23 adapted to be employed with the microfilm reader 11. As shown, at the top and bottom of each frame 63 of the strip is a spot employed for counting the number of frames. Thus, each frame has a spot 64 at the top thereof (at the right side, as viewed in FIG. 5a ) and directly opposite at its bottom side another spot 65. Respectively, suitably oriented photoelectric detection systems are provided adjacent the position of the film gate 24, said systems including the respective photocells 66 and 67 arranged to respond to interruptions of light caused by said top and bottom spots 64 and 65 as the strip moves past the film gate. Thus, the photocells 66 and 67 are located on the center line passing through the top and bottom spots 64 and 65 of the film gate, therefore, corresponding to the center of the center line of the film image projected through the gate. The spots 64 and 65 may be of any suitable nature adapted to provide an adequate response from the photoelectric devices 66 and 67, which, for example, may be photodiodes. The spots 64 and 65, for example, may be transparent spots in otherwise opaque portions of the film strip 62. The light passing through such spots may, therefore, be delivered to the photosensitive elements 66 and 67 in any suitable manner, for example, through fiber optics. The output of the photocells 66 and 67 is delivered to an amplifier and squaring circuit, designated at 68, which may comprise a conventional X10 linear amplifier and a high-gain open-loop switching circuit.

The two channels are compared to determine that images are legitimate images rather than defects in the film. This is accomplished by means of an image detector 69 which is triggered by photocell 67 (which is the reference cell at the bottom side of the film strip).

The image detector 69 provides a time delay from the response of the reference cell and at the end of the delay, automatically determines if the top photocell 66 has detected an image. If a top image has been so detected, then by definition of the detector logic, a legitimate image is determined as being present. If the photocell 66 has not yet detected an image, an error lamp, not shown, becomes energized.

Therefore, only signals representing legitimate images are forwarded to the control logic, which directs the signals to a "present position" register 70 and to run-up counters 71 and 72. These signals are hereinafter referred to as "page-indicator pulses."

The origin of all film motion after the film has been initially loaded into the magazine receptacle 22 and advanced to a position corresponding to page 1, is derived from the information placed into an input register, shown at 73. This information may be generated by either of two sources, indicated as a block 74, which may comprise either a keyboard, in the "off-line" mode of operation, or a computer in the "online" mode. The information is Binary Coded Decimal (BCD) digits which represent either the absolute page number of a frame to be displayed or incremental numbers of pages to be searched. Various selectable modes determine which of the two types of information is to be obtained and the nature of the selected performance.

Each digit of the page to be entered is incoded BCD four bits per digit, 2 ⁰ , 2 ¹ , 2 ² , 2 ³ ) at the origin (keyboard or computer) before it is entered into the input register. A stroke pulse, shown at 75, which is generated in the device 74 with each digit is delayed 5 milliseconds to insure that a digit rather than noise is to be entered. On the leading edge of the stroke pulse a four-bit shift is performed before the digit is entered (stored). This permits the page to be entered with the most significant digit first, zero's being excluded (for example, page number 0099 is entered as 99). After the four-bit shift, which is accomplished at a frequency of 1 megahertz, the entry digit is stored. After the last digit of the page of increment of pages has been shifted and stored, and "End of Entry" (search) is generated by a keyboard switch 76 or a corresponding computer command. The "End of Entry" switch is provided with means to generate a 5 millisecond delay to determine if the command origin was noise or the switch actuation. This delay is bypassed in the computer (online) mode. If the command is legitimate, it initiates the start of the calculation cycle for achieving display of the absolute page of interest. This command may be set up in conjunction with one of two modes by which the calculation logic is programmed. The first mode is the " absolute" mode which accomplished display of a specific desired page. The other mode is the "incremental search" mode. This mode is determined by the operator's selection of either of the "Up" or "Down" switches 77 or 78, (see FIG. 4) rather than the "search" switch 79.

In the logic system of the device, shown in FIG. 5, the registers 70 and 73 are of a conventional type and the register 70 is of the reversible type. Thus, register 70 can be made to count "count" in response to a signal provided at the output line 80 leading from the "present position runup counter" 71, which occurs responsive to the filling up of the counter, for example, when the counter attains a total count of 9999 in the illustrated embodiment of the invention. Similarly, the register 70 can be reversed so as to count "up" responsive to a command signal provided at the output line 81 of the "input" register runup counter" 72, which occurs responsive to the filling up of counter 72, which, in the present illustrated form of the invention, corresponds to the digital total of 9999. Thus, when counter 72 fills up, the register 70 will be placed in a state to count up, whereas, when it receives the command signal from counter 71 corresponding to the filling up of counter 71, the "present position" register will be adjusted to the state in which it counts down.

Both of the runup counters 72 and 71 can be reset to zero in the conventional manner, by the provision of a "clear" switch 83 operable at the control panel and located adjacent the digital input keyboard designated generally at 84' in FIG. 4.

As shown in FIG. 5, respective channels 84 and 85 are provided for the transfer of the contents of input register 73 to the input register runup counter 72 and from the "present position" register 70 to the "present position" runup counter 71.

It is to be noted that the calculation logic, for all practical purposes, has two possible modes or operation; the first mode is the "absolute" mode, which determines the direction, speed and the distance the film must travel, and the other mode, namely, the " incremental" mode, determines only the speed and distance. The direction in the "incremental" mode is determined by the operator (in the off-line mode of operation) by the choice of either the "up" switch 77, or the "down" switch 78. In the "incremental" mode, the calculation logic merely determines the incremental page distance the film must travel.

The absolute mode is entered into when the "end of entry" (search) line command is received. The command is checked to assure that it is legitimate, in the manner above described, and if it if found to be legitimate, it is stored in a "search" flip-flop circuit 107. The leading edge of the flip-flop signal creates two pulses from a series of two one shots, the latter pulse being generated on the trailing edge of the first. The first of the two pulses is used to reset the runup counters ("input register" and "present position") 72 and 71. The second pulse transfers the information from the "input register" 73 and the "present position" register 70, respectively, to the "input" register "runup counter" 72 and the "present position" runup counter 71. In the respective registers 70 and 73 are stored the date corresponding to the present page being projected on screen 16 and the page to be searched, respectively.

At the trailing edge of the second pulse a 1 megacycle oscillator 86 is enabled to advance both counters. Thus, as shown in FIG. 5, the oscillator has an output channel 87 connected through a gate 88 to the "present position" runup counter 71 and through a gate 89 to the "input register" runup counter 72.

Prior to the further detailed information of the operation of the logic system, a general explanation of the calculation cycle will be given.

As above-stated, the page numbers of the present page and the page-to-be-searched are stored in two separate and distinct BDC counters 71 and 72. By design, the full contents of each counter is 9999. If both counters are counted simultaneously until one of them indicates 9999, this shows that this counter contains the greater of the two page numbers. Therefore, if the device knows which is the greater number of the two, the required direction of the film can be determined.

If the "present position" is greater than the page-to-be-searched, reverse motion is required; if the page-to-be-searched is greater than the "present position," forward motion is required. With the direction determined, the speed and distance can be determined by inhibiting the oscillator 86 when the first counter indicates 9999, enabling the drive mechanism to drive the film in the determined direction at high speed, and steering the page indicator pulses to the counter which has not indicated 9999. It will be understood that when the first counter indicated 9999 the difference between the contents of the first and second counters was equal to the page distance between the page-to-be-searched and the "present page." For example, assume that the "present page" is 1000 and the page-to-to-be-searched is 2000 , whereby the difference therebetween is 1000. Runup pulses will be delivered by oscillator 86 simultaneously to both counters 71 and 72 in the amount of 7999 pulses until the contents of the input register runup counter 72 represents 9999 and the contents of the "present position" runup counter 71 represents 8999. As previously mentioned, this indicates the need for forward drive, and correspondingly conditions the "present position" register 70 to count up. As will be noted from FIG. 5, the line 81 is connected through a gate 90 and amplifier 91 to the control mechanism associated with the "forward clutch" 40, whereby the forward clutch is enabled to drive the film in the required forward direction.

Alternatively, assume that the page-to-be-searched is 1000 and the "present page" is 2000. Again, 7999 pulses from the oscillator 86 will be necessary to fill up one of the counters, and in this case the counter 71 is the first to reach 9999. This conditions the "present position" register 70 to count down, causes the "forward" clutch mechanism to become ineffective and enables the "reverse" clutch mechanism 44 to drive the film in the reverse direction, since the command line 80 of counter 71 is connected in a manner to enable clutch 44 to operate, through a gate 93 and an amplifier 94.

As will be presently explained, the high-speed clutch mechanism 60 becomes energized in either of the above cases.

Furthermore, the oscillator 86 is rendered ineffective under either of the above conditions, namely, when either counter 72 reaches 9999, or counter 71 reaches 9999 by the provision of an "inhibit connection" through gate 95 and flip-flop 107 to the oscillator from the respective lines 81 and 80.

It will be understood that command signals to enable the high-speed clutch mechanism 60 are provided through a gate 96 having one input line 97 connected to the line 98 leading to the reversing clutch mechanism 44 and having a corresponding input line 99 connected to the line 100 leading to the forward clutch mechanism 40. As above mentioned, energization of the high-speed clutch 60 automatically deenergizes the low speed clutch 61, and vice versa. Furthermore, it will be noted that when one of the reels is being driven, the opposite reel is partially braked, so as to maintain proper tension on the film. Therefore, the reverse brake 45 is energized to provide partial braking at the same time the forward clutch 40 is energized, by a connection to line 99, shown at 101, which leads to the reverse brake mechanism 45 through an amplifier 102 and a resistor 103. In a similar manner, partial braking is obtained on the takeup spindle by the partial energization of the forward brake mechanism 41 when the reverse clutch 44 is energized, by a connection from line 97 to the forward brake mechanism 41, shown by a line 104, leading to forward brake 41 through an amplifier 105 and resistor 106.

As the film moves, the film indicator pulses advance the second counter (the counter which has not previously reached 9999) until it indicates 9999. When the second 9999 occurs, all power to the film drive clutches is released and the feed and takeup spindles are braked to a stop, thus completing the calculation cycle, which additionally completes the drive cycle.

Returning now to the explanation of the calculation logic system, when the counter initially having the greater number reaches 9999, the 9999 recognition gate 95 resets the flip-flop, shown at 107, which had previously enabled the action of the 1 megacycle oscillator 86. Also, as above explained, it enables the drive logic and the "present position" register 70 to operate in the desired direction. This causes page indicator pulses to be furnished to the "present position" register 70 and to the runup counter 71, or 72, indicating less than 9999.

The primary purpose of the "present position" counter 70, is to maintain the current number of the page being projected. Therefore, the counter 70 is designed as a BCD up-and-down counter, as above mentioned. If the film is being driven to the higher number pages, the counter is enabled to count the page indicator pulses up. Conversely, if the film is being driven to the lower order pages (for example, to a page number lower than that indicated at the start on counter 70) the counter is enabled to count the pulses down, in the manner above explained It is, therefore, to be understood that the ability of the microfilm viewer 11 to maintain the present page indication or memory is derived from the sequential counting up or down of the page indicator pulses, starting on the first pulse after film loading. The film, when loaded, feeds the leader thereof until the first page indicator pulse is picked up. During the loading cycle the present position pulse counter 70 is reset to 0000 and then released to prepare it to count the first pulse.

As above-mentioned, when the counter 71 or 72 originally showing less than the number of the new page to be displayed reaches 9999, the page indicator pulses are disabled from the counters, drive power to the clutches is disabled, and the brakes are set.

As previously stated, the calculation cycle has another mode of operation, namely, the "incremental" mode. The operation of the calculation logic is similar for this latter mode, with the exception that the direction of film movement is established by the "up" or "down" switches 77, 78. With the direction of film movement established by the operation of a selected one of these switches, only the speed and the incremental distance has to be calculated.

To place the apparatus into the "incremental" mode, the input information delivered to the input register 73 comprises a number of pages the film should be moved through per increment in the selected direction, rather than the absolute page. For example, if an increment of 10 pages in the forward or reverse direction is desired, the appropriate switch 77 or 78 is actuated after the input keyboard supplies the binary coded date corresponding to the number 10 to the input register 73. Under these conditions, the present position runup counter 71 has previously been reset to 0000. The input register information is first transferred to the input register 73, as above stated, and after this has been done, the oscillator 86 is enabled to operate in the manner previously described and the remaining portion of the cycle takes place in the same manner as in the case of the absolute mode. Thus, the input register runup reaches 9999, and the film drive elements and the "present position" register 70 are enabled to operate in the direction determined by the selection of either switch 77 or 78. As in the previously described operation of the device in the absolute mode, when the input register reaches 9999 the oscillator 86 and the automatic direction logic are disabled, and the "present position" runup counter 71 is enabled to count the page indicator pulses until 9999 is indicated therein.

The system of the apparatus includes means by which the speed of the film is controlled in either mode or operation in a manner such that the film is moved at a fast rate until if approaches the page-to-be-searched, at which time the speed is reduced to a slow rate until the requested page has been reached, at which point the film is stopped. As above mentioned, the drive mechanism of the device consists of a constant-speed main drive motor 34, a high-speed clutch 60, a low speed clutch 61, a forward clutch 40, and a forward brake 41, a reverse clutch 44 and reverse brake 45, and the cooperating mechanism contained in the film cartridge 23. The status of these devices in a nondrive (nonsearch condition) is such that the main drive motor runs at a constant speed whenever alternating current power is applied to the device; the low speed clutch is engaged, the forward and reverse clutches are disengaged, whereas the forward and reverse brakes are applied.

The sequence of controlling these devices during a film drive cycle is determined by the film drive logic, which receives various commands from the calculation logic, cartridge load or unload (rewind) logic and the manual (forward and reverse) slow control structure, not shown, which may be employed, if so desired. The controlling sequence to the mechanisms is the same for any means of up-down drive. It is the function of the drive logic to determine the mode of drive the mechanisms are entering. Summarizing the previously described operating information the steps for establishing the drive until a drive cycle has been completed are as follows:

1. Release the forward or reverse brake completely or partially. If the new direction is forward, the reverse brake is only partially released to maintain drag on the film. The converse is true if the direction is reversed. The brake in the driving direction is always released completely.

2. Energize the forward or reverse clutch. This completes the drive linkage to the takeup or payoff spindles on the cartridge.

3. Energize the high-speed clutch until the slow-speed window is recognized (a spot 64) and then reduce to slow speed.

4. When a stop command is recognized, the film should be moving at slow speed, at which time the brakes are set, the forward or reverse clutches are deenergized, and the cycle is completed.

The means by which the drive logic determines the direction, speed and the stopping of the mechanisms for the calculation logic is merely the logic manipulation of the commands sent to it.

As previously stated in connection with the description of the calculation procedure involved in the absolute-page-search, the first runup counter that reaches 9999 establishes the direction, and for the "incremental" mode page, the operator depresses the proper direction switch 77 or 78 for the drive mechanisms. Therefore, the drive logic merely remembers the conditions delivered to it. If a direction switch 77 or 78 is not actuated, the logic employs the first counter runup to 9999 and sets the direction on the basis of this count of 9999. In view of the necessity for establishing a slow speed of movement of the film immediately prior to reaching the desired page, the necessity of a count which is somewhat less than 9999 arises, for example, a count arbitrarily set at 9995. The reason for this modified count is to provide a slow-speed window ahead of the stopping point to prevent override of the page of interest.

In running up the counters to establish a direction, the first 9995 count is stored. When a counter reaches 9999, four counts later, the mechanisms are directed to go at high speed, provided that the other runup counter has not indicated 9995. If it has, then the page-of-interest is within plus or minus four pages of the present page being views. Therefore, the drive mechanism will search at slow speed until both counters reach 9999, and then stop. From FIG. 5 it will be seen that this is accomplished by the provision of a 9995 recognition gate 108 having a first input line 109 from runup counter 72 providing the 9995 command therefrom and having another input line 110 from counter 71 providing the 9995 command from the latter counter. Responsive to a 9995 command from both counters 71 and 72, gate 108 furnishes an "inhibit" signal to gate 96, which results in the deenergization of the high-speed clutch 60 and the automatic substitution of the low speed clutch 61. When 9999 is reached by the counter being runup by the page indicator pulses, deenergization of the driving mechanism and application of the brakes take place in the manner previously described.

The slowdown action above described is the same for both the "absolute" mode and the "incremental" mode of operation of the microfilm viewer.

When a cartridge is inserted in the receptacle 22, it is driven to a starting position responsive to operation of the "load" switch 111 on the instrument panel, and it is driven at slow speed until the first page is recognized, at which time it stops.

The film may be rewound at any time by operating the "unload" switch 112 on the instrument panel, which causes the film to reverse at high speed until the film drive is stopped by the action of an "end of film" detector of suitable design. This may include suitable markings provided on the film near its end cooperating with associated detection means arranged to sense such markings.

As above mentioned, manual forward or reverse slow control means may be provided, and under such conditions, the operation of the "slow" window is simulated by a counter employed exclusively for this mode. This arrangement allows the operator to generate a high-speed or slow forward or reverse until the release of either one of the direction switches 77 or 78. At such release, the film then moves at slow speed until the counter indicates 4 -page indicator pulses, at which point the drive stops.

While a specific embodiment of an improved information retrieval system in a microfilm viewer has been disclosed in the foregoing description, it will be understood that various modifications within the spirit of the invention may occur to those skilled in the art. Therefore, it is intended that no limitations be placed on the invention except as defined by the scope of the appended claims.