US2926860A - Indicating and control device - Google Patents

Description

M rch 1, 19 A. POMARICO 2,926,860

INDICATING AND CONTROL DEVICE Filed June 50, 1958 2 Sheets-Sheet 1 RAPID REWIND NTROL FIG; 1

40 E?) PHOTO CELL INVENTOR ANDREW POMARICO BY M AT ORNEY March 1, 1960 A. POMARICO INDICATING AND CONTROL DEVICE 2 Sheets-Sheet 2 Filed June 30, 1958 FIG MACHINE REEL FILE REEL United States Patent 2,926,860 INDICATING AND CONTROL DEVICE Andrew Pomarico, Fishkill, N.Y., assignor to Internal tional Business Machines Corporation, New York, N .Y., a corporation of New York Application June 30, 1958, Serial No. 745,449 4 Claims. (Cl. 24255.12)

This invention relates to indicating and control devices and more particularly to an improved circuit, using a lamp and a photocell in the indicating device in combination with a control circuit which fails safe when the lamp fails.

-It may not always be possible to arrange the device being controlled so that it operates in the preferred manner when the light is not shining at the photocell. Thus, if the light should fail, the device will continue to operate in the less preferred manner with, in some cases, damaging results. If the control device must operate so that the lamp not shining in the photocell gives the less preferred mode of operation, the invention contemplates that the'failure of the lamp causes fail safe circuitry to place the device in the preferred mode of operation.

It is therefore an object of the invention to provide an improved fail safe circuit.

Another object of the invention is to provide a fail safe feature in a control device which utilizes a lamp and photocell to indicate which of at least two conditions, the machine being controlled is in.

Still another object of the invention is to provide a fail safe feature in a control device which utilizes a lamp and photocell to indicate which mode of operation is being performed by a controlled machine, so as to place the machine in the preferred mode of operation if the lamp fails.

A further object of the invention is to provide in a control device that must operate so that thelamp not shining in the photocell gives the less preferred mode of operation, fail safe circuitry to place the device in the preferred mode of operation if the lamp should fail.

A still further object of the invention is to provide a control and indicating circuit for a two speed device wherein the lesser speed must be indicated by a blocking of. the indicating device wherein a failure of the indicating device causes the machine to operate at the lesser speed.

Another object of the invention is to provide in a tape drive unit a fail safe circuit which places the machine at its lower speed it the indicating device should fail.

Still another object of the invention is to provide a circuit which controls two modes of operation of a machine and indicates which mode is being operated and which additionally fails safe if the indicating circuit fails.

A further object of the invention is to provide a circuit under control of a lamp and photocell which fails safe if the lamp burns out.

A still further object of the invention is to provide a control circuit which is operative to control a utilization means and is also operable to energize a lamp including fail safe circuitry which is inoperative to effect the control circuit when the lamp is lit but which automatically places the control circuit in the preferred mode of operation when the lamp burns out.

Another object of the invention is to provide in a control circuit means for energizing a lamp including aiunidirectional device which does not effect the control circuit when the lamp is lit but which automatically places the control circuit in a preferred condition when the lamp burns out. t

Other objects of the invention will be pointed out in the following description and claims and illustrated in the accompanying drawings, which disclose, by way of example, the principle of the invention and the best mode, which has been contemplated, of applying that principle.

In the drawings:

Fig. l is a circuit diagram of the preferred form of the invention.

Fig. 2 is an elevation of a tape drive unit which utilizes the invention, in a backward operation and with flinch. of tape on the machine reel.

Fig. 3 is a view similar to Fig. 2, but in a rapid rewind operation and with more than /2 inch of tape on the machine reel.

In magnetic tape drive machines especially those used in present day electronic data processing machines, tape is fed from a file reel to a machine reel while information is magnetically read from or written onto the tape. Such a tape drive machine is fully described in the US. patent application, entitled Tape Feeding Machine, Serial No. 468,832, to W. S. Buslik et al. filed November 15, 1954. Due to the high cost of this equipment, it is desirable to be able to rewind the tape from the machine 1 reel back to the file reel at very high speeds, in order to be able to reprocess the magnetic tape or change file reels in a minimum of time. If the magnetic tape is to be reprocessed the tape must be stopped close to the beginning ef the tape, i.e., before the tape is completely rewound from the machine reel.

In these machines, arms bearing rollers which ride on the tape of the tape reel, usually on the machine reel, until a predetermined amount of tape remains on the reel at which time the position of the arm is such that it operates a pair of contacts which is in a circuit that deenergizcs the rewind motor and causes the file reel to stop. From this point the tape is fed slowly back to the start point which is usually detected by a photocell which senses the presence of a strip pasted to the tape, the strip having ditferent reflective characteristics than the tape.

The roller on the arm by riding on the tape produces undesirable wear on the tape. A photocell, in combina-- tion with a light, could be used to detect the end of highspeed rewind time and eliminate the Wear. However, the. following problems exist. If the photocell and light were: to detect the amount of tape on the machine reel dur-. ing a rewind operation, the light would shine at the..- photocell to indicate end of high speed rewind. Shouldi the light fail, the machine would continue in its high speed! rewind operation until all the tape is off the machine:

. reel at which time the reel would continue spinning and? spewing tape to damage it. It may be understood that in: these high cost electronic data processing machines, valuable information and time may be lost because of damaged tape.

' If the lamp and photocell are placed to cooperate with the file reel, they can be set so that if more than a certain amount of tape on the file reel will cut off the light and indicate end of high speed rewind. In this way, the failure of the light would mean end of high speed rewind area and thus the machine would fail safe. However, this arrangement cannot be utilized because these machines use file reels with a variety of lengths and it would impractical to adjust the position of the lamp with each different tape. reel.

unblocking of light by the tape on themachine reel signals the end of high speed rewind area in com bination with a fail. safe circuit which signals the end of the high speed rewind area if the light fails.

Before describing the details of the fail safe circuitry, a description of the preferred embodiment of the machine in which the invention may be used will be given first.

In Fig. 2, a tape reel 10, which shall. be designated as a file reel, is mounted on a drive spindle 12. It may be assumed that the reel has thereon acoil of tape 14 on which data has been recorded and from which the tape is to be fed through a tape reading and recording head unit 16. In its forward feed direction the tape will pass through the tape reading head unit 16 and will be coiled on a second reel 13, which may bedesignated herein as a machine reel. The machine reel 33 k; mounted on a drive spindle 20. The file reel drive spindle 12 and the machine reel drive spindle 20 maybe selectively rotated in either direction by a pair of motors.

In the hereinbefore mentioned Buslik et al. application, even the relatively low speed of tape through the tape head 16 requires very rapid acceleration (that is, starting and stopping) and so it is important thatthe tape be provided. with little load or mass thereon. To this end the driving mechanism for the reel 10 and. 18 provides a pair of tape loops 22 and 24 (only partially shown), disposed in a pair of tape control vacuum columns 26 and 28. Each of the columns 26 and 28 have therein means responsive to the position of the respective tape loops for maintaining a. relatively stable position of these loops withinthe columns. The loop sensitive means within the columns 26 and 28 control the reels and the reel drive mechanism in such" a manner that the loops, so to speak, are self compensating. The tape reel drive mechanism for each reel operates inde pendently of the other and both reels are driven independently of the feed of tape through the tape head 16. Atape fromthe loop supply in the vacuum columns 26 and 28 is driven through the tapev head 16 by a pair of normally constantly rotating tape drive capstans. In Fig. 2, a tape drive capstan 30 may be deemed to be constantly. rotated in a clockwise direction, and may consequently be designated as the backward drive capstan. A. similarly constantly rotating capstan 32 may be deemed to'be constantly driven in a counterclockwise direction and may, therefore, be designated as the forward drive capstan. 'In connection with the drive capstans 3i) and 32, there are provided a pair of tape moving. idler pulleys 34 and 36. The pulley 34 is adapted to.move a tape trained thereabout intodriving capstan 30; while the tape moving pulley 35 is adapted to move a tape, trained. thereabout into driving contact with the forward drive.v capstan 32; As described in the Buslik et al. application, thepulleys are mounted on a com-. mon linkage system (not shown) which is so designed as to impart the proper related movement for selectively driving the tape either in a forward or a backward direction through the tape head unit 16.

Another novel feature. of the. Buslik et al. application tape feed machinev is the ability to rewindv tape at aspeed' much greater than that of the normal backward operation. In order to perform this rapid rewind operation, the tape must be brought to the unloadedposition shown in Fig. 3, with the tape loops out of the columns26 and 28 and the tape running between. idlers 36 shown,-, rotates: the file; reel; 10; counterclockwise; at very high speed. The subject invention provides means to indicate when the beginning of the tape is approaching and it acts to shut off the rapid rewind motor and apply a light brake to bring the tape to a gradual stop. The machine at that point operates automatically to reload the tape into the vacuum columns and perform a normal backward operation until the beginning point is sensed at which. time the tape will stop, ready to be unloaded or ready'for a normal forward operation. This indicating means includes a lamp 38 so positioned with respect to the machine reel as to-shine into a photocell 40 mounted in a finger guard 42' between the reels.

When the tape is near the beginning point, the lamp shines into the photocell 40 because there is very little tape on the machine reel 18. During normal forward operation the tape is wound upon the machine reel and when more than /2 inch of tape, in a radial direction, is wound thereon, the light from lamp 38 is blocked so that it no longer shines at photocell40. The point at which the light is blocked is known as the transfer point and is a dividing line between a rapid rewind area.

on the tape and a backward area. That is, in a rapid rewind operation, the machine reel will be filled with tape and no light will shine at photocell 40. When the transfer point is reached the light does shine into photocell 40 and an indication of this factv is given to the machine which. then goes into a normal backward operation.

It may be understood that in any complete high speed rewind operation, the magnetic tape is fed at the high rewindspeed until a low speed area is detected. This low speed. area is predetermined as being the length-v on the tape whenthere' is inch of tape onxthe-machine reel 18, that is, a thickness'on the hub of /2 inch of tape in a radial direction.

Fig. 2 illustrates the situation where A: inchof tape is on the machine reel and the light 38 may shine into the photocell 40. In Fig. 3 more than A2 inch of tape is on the machine reel 20 and the light 38 does not shine into the photocell 40. It may be understood at this time that if light 38 should fail, the tile reel 10 would continue to rotate at very high speed and the tape 14' would completely unwind from machine reel 18 and the tape would be flung around by the file reel 10 destroying valuable information. To eliminate this possibility, and to getaway from the problems of the mechanical arm, the circuit of Fig. 1 was designed.

The circuit of Fig. 1 will be described by first describing the situation when the machine is beingrewound. and there is more than /2 inch of'tape on the machine reel. In this case-no light'from lamp 38 will shine in the photocell 40. The photocell 40 is. connected between a +1.2 volt. source 42' and a point B, which is connected through a K ohm resistor 42 to a -l2 volt source 56; In the high speed area just described with no light shining there at, the impedance of the photocell 40 approaches: the order of magnitude of hundreds'of megohms, and'therefore its resistance is high with respect to resistor 48. Therefore, almost all' of the voltage drop is across the photocell and point B is at practically -12 volts. Point B isconnected to the base'of aPNP transistor 54; With a relatively'negativevoltage on the base of transistor'54; transistor; 54'turnson and current flows through resistors 56 and 58'. to the 12 volt source 6%. This causes a positive shift at a mid-point C between resistors 56 and 58. Point C is connected to the base of an NPN transistor 62. Transistor 62, being an NPN transistor is' turned. on. by a positive shift and current fiows through.

transistor62 and its load resistors 64 and 63 to the +6 that whenever the tape is in the high speed rewind area, this fact is indicated by the contacts Rl-l being open. The contacts R1-1 of Fig. 1 performs exactly the same function as the arm switch contact 256 in Fig. 313 of the hereinbefore mentioned Buslik et al. application.

In rewinding at high speed, when less than /2 inch of tape is on the machine reel 18, the tape is in the low speed rewind area. With the tape in this low speed rewind area, the light 38 shines into the photocell 4-6. When photocell 40 has light shining thereat, its resistance goes down substantially and the current flowing through resistor 48 produces a substantial voltage drop causing point B to go positive. The positive shift of point B cuts oil transistor 54 which, in a well known manner, lowers the potential at point C. This in turn cuts off transistor 62 to raise the potential at point D and in turn cut 01f transistor 72. With transistor 72 cut off, no current flows through relay R1 and the contact Rl-l returns to its normally closed position, initiating low speed rewind; i

It can thus now be understood that if the light 38 fails during high speed rewind, the circuit would never be operated, and if no fail safe provisions were made, the circuit would never be operated to close contacts Rl-l and the machine would remain in the high speed rewind condition. It is also desirable that the machine not be able to get into a high speed rewind operation if the light fails and the circuit of Fig. 1 makes provisions for these two situations.

In order to understand what would happen if the lamp 38 failed, it is necessary to understand the circuit for energizing the lamp 38. Lamp 38 is in a circuit from +12 volts 42 through lamp 38 to a point A, a 50 ohm potentiometer 80 and a 150 ohm resistor 82 to the ---12 volts 60. With these potentials the current flowing through the lamp and resistors is of such a value that there is approximately a +4 volt drop across lamp 38. This puts point A at approximately +8 volts and back biases a diode 82 so that no current flows between point A and point C. This is true because during normal operation, point C varies from 12 volts with transistor 54 cut oflf to 6 volts with the transistor 54 conducting, both voltages applying a more negative voltage at the anode than the +8 volts of point A at the cathode of diode 84. When lamp 38 burns out, point A is no longer connected to +12 volt source 42, and even when the transistor 54 is conducting, the voltage at point C will be close to -l2 volts. Now current flows through the diode 84 and the resistors 80 and 82. Since the value of resistors 80 and 82 are small, both with respect to resistor 58 and resistor 56, the voltage drop across resistors 80 and 82 are small with respect to the voltage drop across resistor 56.

Thus, point C goes relatively negative in spite of the fact that the transistor T13 is on. It is this negative drop at point C which turns oil transistor 62 and transistor 72 de-energizing relay R1 and closing points Rl-l, placing the machine in the low speed rewind area and providing the desired safety feature.

While there have been shown and described and pointed out the fundamental novel features of the invention as applied to a preferred embodiment, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

1. In a tape feeding device, a tape reel for storing tape, a photocell associated with said reel, means for feeding tape from said reel, a light source positioned with respect to the reel so as to be sensed by said photocell when lessthan a predetermined amount of tape is on said reel,

a circuit including said photocell and operative to deactivate said ieed means when said photocell senses said light source, and fail safe means within said circuit and fidapted to deactivate said feed means when said light ails.

2. In a tape feeding device, a tape reel for storing tape, a photocell associated with said reel, means for feeding tape from said reel at a high and low speed, a light source positioned with respect to the reel so as: to be sensed by said photocell when less than a predetermined amount of tape is on said reel, a circuit for controlling said feed means including said photocell for placing said feed means in said low speed when said photocell senses said light source, said circuit comprising means for energizing said light source, fail safe means connected in the circuit and to said light source, said fail safe circuit operative when said light fails to place the feeding means in low speed.

3. An indicating device comprising in combination, a photocell having a low resistance when light shines thereat and .a high resistance when no light shines thereat, a lamp positioned to shine at said photocell when energized, moveable means placed between said light and said photocell and selectively operable to block the light from shining at said photocell, a first circuit connected to the photocell and operable to produce a first output when the photocell has high resistance and the second output when the photocell has low resistance, a lamp energizing circuit, a fail safe circuit connected to the first circuit and the lamp energizing circuit and not operative to afiect the output of said first circuit if the lamp is energized, said fail safe circuit causing the first circuit to produce the second output when current to the lamp is interrupted.

4. In a fail safe circuit comprising a transistor, 2. two condition utilization device connected to the output of said transistor, a load resistor connected to the output of said transistor, a photocell connected to the input of said transistor and adapted to cause said transistor to conduct through said load resistor to place the utilization device in a first condition when no light is shining at said photocell and to be nonconductive through said load resistor to place the control device in a second condition when light is shining at said photocell, a first source of voltage connected to said load resistor, a second source of voltage, a lamp, a second resistor, circuit means connecting said first voltage source in series with said second resistor, said lamp and said second voltage source, and a diode having its one terminal connected between the lamp and the second resistor and its other terminal connected to the output of the transistor, said lamp when energized producing a reverse bias on the diode so as to leave the output of the transistor unaliected, said lamp when unenergized producing aforward bias on the diode to bypass the load resistor and place the controlled device in the second condition.

References Cited in the file of this patent UNITED STATES PATENTS 2,108,410 Perry Feb. 15, 1938

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