CA1060987A - Electronic dynamic braking for tape recorder devices - Google Patents

Abstract

ELECTRONIC DYNAMIC BRAKING
FOR TAPE RECORDER DEVICES
ABSTRACT OF THE DISCLOSURE
For use in a tape transport including a drive motor for transporting tape across a recording or play-back head, and a motor drive circuit for selectively applying drive current to the motor, an electrical circuit for applying a reverse drive current to the motor for rapidly reducing the speed of the drive motor upon the receipt of a stop signal. The circuit provides controlled reverse current to the drive motor over a period of time initiated by a stop signal and extending until a pre-determined reduced speed is reached after which the reverse drive signal is removed and the motor allowed to coast to a halt.

Description

106~91 37 .
The present invention relates to tape transport apparatus and specifically to a method and apparatus for reducing the ~ime required to stop the transport from a running speed.
In tape transpor~s employed with data process-ing equipment and specifically, cassette transports, the design criteria for stopping the transport from a play-back or recording mode of operation sets the limit that the tape can travel after a stop signal is received to approximately .1-.2 inches, This relatively critical stopping distance is required in order to produce inter-record gaps between recorded segments sufficiently short -~ to conform to recen~ly promulgated recording formats as well as to efficiently utilize the entire length of the tape for recording several records thereon.
In cassette tape transports, direct current permanent magnet motors are typically employed to drive a tape capstan which in turn transports tape in a cassette ;~ 20 across the recording and playback heads. In many exist-ing transports, the tape is stopped by simply removing the drive current for the motor. In such systems, however, - the inertia of the drive mechanism allows the tape to coast a distance far in excess of the a~ceptable limits. -To reduce ~he stopping time of tape transports, several approaches have been utilized including the short-ing of the armature leads during the stopping interval.
This induces a current in the armature which develops a magnetic field that opposes further rotation of the armature thereby slowing the motor and the drive mechanism of the transport. It has been found that although such an

-2-1060g~7 l approach reduccs the bra~ing time over that available by simply removing t}lc motor drive current, the braking time and, therefore, distance in cassette recordcrs remains excessive.
A sccon~ approach has becn to utilize a frictional brake apparatus WlliC]I contacts a moving portion of the drive mechanism. Frictional brake systems, however, add considerably to th~ cxpense and bulk of a transport and additionally require ~reguent adjustment as the fric~ional braking element wears during use. This adjustment is required to maintain the stopping distance rclatively constant and frequently such adjustments are rather time consuming an~ relatively dif~icult to accurately achieve.
Thus, there exists a need for an improved braking system for use with da~a processing tape transports and particularly, cassette recorders which will overcome the shortcomings of the known braking techniques employed to reduce the braking time.

The system here described solves the need for the relatively fast braking time required in cassette tape transports while not requiring expensive or bulky mechanical braking means by providing an electri-cal control circuit which, upon the receipt of a stop signal, applies a reverse current to the drive motor of the transport for a period of time sufficient to slow the transport from a running speed to a lowcr speed limit after which the transport is allowed to coast to a halt.
Such tape transport systems include means for providing signals indicating the speed of a moving element of a tape transport mechanism

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1060~37 1 which includcs a drivc mptor. Selectivcly actuated circuit mealls are coupled to tllc providill~ means for developin~ a reversing drive si~nal ~pplied to the motor in responsc to the receipt of a stol) control si~nal and applying the reversing signal to the motor until the tape speed reduces to a predetermined v~lue as indicated by the signals from the providing means.
It is an object of the present invention to provide an improved braking system for t~pe transports.
Another object of the present invention is to provide an electrical circuit for developillg a reverse drive signal which is applied to the drive motor of a tape transport for rapidly slowing thc transport speed from a running speed to a prede~ermine~ lower speed.
A further object of the present invention is to provide a method of reducing the stoppin~ time of a tape in a tape transport system.
More particularly in aceordance with the invention there is provided, in a tape transport having: means, including a drive motor, for transporting tape across a recording or playback head, the improved braking system comprising: motor drive circuit means coupled to said drive motor for applying forward drive excitation to said motor to implement a normal forward running mode of operation of the transport; and means coupled to said motor drive circuit means for selectively controlling the latter to apply reverse drive excitation to said drive motor during forward movement thereof to effect braking of such movement, said reverse drive excitation being of an opposing character with respect to said normal excitation and tending to drive said motor in an opposite direction from said normal forward movement 1060~87 thereof, to rapidly slow such forward movement; said means coupled to said motor drive circuit operating to selectively control the latter to remove said reverse drive excitation at a time subsequent to that at which the same was applied, said time subsequent occurring when said forward movement has been slowed to a speed lower than its normal level, but . greater than zero, said means includes means for determining the occurrence of such speed.
Specific embodiments of the invention will now be described with reference to the accompanying drawings in which:
Fig. 1 is a perspecti~e view of a cassette tape transport embodying the present invention shown with the case partly broken away; and Fig. 2 is an electrical circuit and mechanical diagram partially in block and schematic form showing the electrical circuit employed in the preferre~ embodiment of the invention.
DETAILED DESCRIPTION OF TllE PREFERRED E~lBODI~fENT
:
In Fig. 1 there is shown a cassette data pro-cessing recorder 10 including a hinged front door 12 -~- .

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~ 4a -1060~7 1 providing access to a cassette receiving recess 14. The recorder includes a pair of spaced spindles 15 and 16 adapted to extend through correspondingly spaced tape reel apertures 15' and 16' of a Phillips type cassette 18 when the cassette is inserted into the recorder. Tape 20 ~Fig. 2), wound on the reels of the cassette, is driven adjacent write and read-after-write heads 22 and 24, res-pectively, of the recorder which are positioned on a carriage assembly 26 as seen in Fig. 1.
A drive capstan 25, shown schematically in Fig.
2 is coupled to the shaft 28 of a drive motor 30 shown in Fig. 1. Shaft 28 is also coupled to an electro-optical tachometer 32 (Fig. 2). Tach 32 is similar to a tach described in greater detail in United States Patent No.
3,803,632 issued April 9, 1974 entitled DATA-ENTRY CLOCK
MEANS AND METHOD OF IMPLEMENTING SAME, assigned to the present assignee. Motor 30 is a conventional permanent magnet, direct current motor including an armature winding 29 which is electrically coupled to a motor drive circuit 40 for receiving drive signals as described in greater detail below.
The tape drive mechanism includes a pinch roller (not shown) opposite drive capstan 25 such that the tape is engaged therebetween and transported across the heads 22 and 24. In addition, a pair of torque motors (not shown) are coupled to the drive spindles 15 and 16 to maintain tension on a tape during its motion across the heads and between the tape reels of the cartridge. A
thumb slide 23 is mechanically coupled to ~he pinch roller to control its positioning with respect to the capstan and also engages an electrical switch for controlling 1060~87 1 actuators to move carriage 26 and shift the heads 22 and 24 into operative en~agement with the tape during play-back and record modes of operation. The thumb slide additionally serves the purpose of locking the cover door in a closed position.
In addition to the mechanical drive assembly, the recorder 10 includes a transport control circuit 35 which can be of conventional design and includes switching circuitry which responds to signals received from external sources so as to selectively conduct recording and playback data signals to and from heads 22, 24 as well as apply -control signals for actuating the motor drive circuit.
The electro-optical tachometer 32 provides a pulse train as shown by the waveform 34 accompanying lS output conductor 33 of the tach. Pulses 34 are repre-sentative of the tape speed and are applied to a speed control circuit 36 as well as to the motor stop circuit 50.
Tach 32 and circuits 36 and 40 provide a closed loop feedback system for maintaining the tape speed at desired and constant recording and playback speeds. The speed control circuit 36 can be of conventional design to respond to pulses received from the tach to apply a speed regu-lating signal to the motor drive circuit 40 via conductor 38 which maintains the record and playback speeds constant during these modes of operation.
- ~lotor drive circuit 40 is of the type which generates drive pulses having a duty cycle selected for the desired tape speed. Thus for example, if the tape speed is desired to be increased, the du~y cycle or the percentage "on time" of current applied to the armature winding 29 is increased. Circuit 35 provides control ~060~8~

l signals ~e.g., polarity-coded) for driving motor 30 in a forl~ard direction during record and playback and a reverse -~ direction during rewind and the dynamic braking employed.
Such control signals are provided at output terminal 39 of circuit 35 which is coupled to circuit 40.
The transport control circuit 35 is suitably coupled to remote interface equipment 31 for receiving tape command signals including a stop command signal to which it responds to generate a stop signal shown by waveform 42 adjacent the output conductor 37 of the circuit.
As seen by waveform 42, the signal will be at a logic high level corresponding to a running mode of operation for the motor and drops to a logic "0" level upon the receipt of a stop command signal. This transition occurs at an instant of time, indicated as t~ in Fig. 2, and after which drive motor 30 is desired to be stopped to prevent tape movement in excess of the .1-.2 inches as discussed above.
In order to provide a reduced stopping time, the conven-tional motor drive and speed control circuitry is supple-mented by the motor stop circuit 50 now described.
Circuit 50 is coupled to tach 32 by conductor 79 to receive tape speed representative signals and to circuit ; 35 by conductor 37 to receive the stop signal. The output of circuit 50 is coupled by lead 74 to a stop drive circuit 80 which applies a signal of controlled duration to circuit 40 via conductor 84 to actuate the motor drive circuit to supply a reverse drive signal to motor 30 to rapidly stop the . motor.
Circuit 50 includes NAND gate 52 having input terminals commonly coupled to output terminal 37 of circuit 35. The output of NAND gate 52 is coupled to the input `

106(~987 1 terminals of NANl) gate 5~ and to input terminal 61 of NAN~
gate 60. The output terminal of NAN~ gate 54 is coupled to an integrator circuit comprising resistor 56 and capacitor 58, the junction of which is coupled to a second input terminal 62 of gate 60.
The output terminal of gate 6n is coupled to the inverting input 63 of OR gate 64. The output terminal of OR gate 64 is coupled to the input of a retriggerable one-shot multivibrator 70 whose relaxation period is determined at least in part by the RC time constant of a resistor 72 coupled to a source of voltage +V and a capacitor 71. The retriggerable one-shot multivibrator can be a Fairchild type 9602 integrated circuit whereupon the resistor is coupled to terminal 2 while the opposite terminal of capacitor 71 is coupled to terminal 1. The ~ retriggerable one-shot multivibrator 70 includes an input - terminal 73 which receives a logic low signal thereat when signal 42 is at a logic high state. A logic low signal at terminal 73 prevents multivibrator 70 from triggering.
Terminal 73 is coupled to the output terminal of NAND gate 52 to assure that multivibrator 70 is inhibited while the drive motor 30 is in a running mode of operation thereby preventing the accidental generation of a stop pulse during the operation of the tape transport.
The retriggerable one-shot multivibrator 70 further includes an output terminal 74 at which there is developed a controlled stop pulse 75 initiated at time ts ; and terminating at a later time indicated by tL in the figure.
; Signal 75 is applied to one input terminal 77 of an AND gate 78 having its remaining input terminal 79 coupled to the tach circuit 32 for receiving pulses 34.

~06(~9~37 1 Gate 78 is enabled by the positive going pulse 75 to apply the tach pulses 34 to input terminal 65 of OR gate 64. Terminal 65 is connected to the positive voltage supply +V by a resistor 67 for bias selecting purposes.
~laving briefly described the interconnection of the circuit elements employed with the system of the present invention, a description of the operation of the system is presented.
OPE~ATION
During the running mode of operation (i.e., during playback, recording or rewind), the signal at output terminal 37 of circuit 35 will be at a logic high state (i.e., "1"). The output of gate 52 will, therefore, be at a logic low state (i.e., "0") which holds the output of gate 54 in a high state. The "1" from gate 54 is applied to terminal 62 of gate 60 while a "0" is also applied to terminal 61 of the gate from gate 52. Gate 60, therefore, will provide a logic "1" output indicated by waveform 69 adjacent the output terminal of the gate.
At this time, output terminal 74 of multivibrator 70 will be at a low state thereby inhibiting AND gate 78 ;~ from passing positive clock pulses 34 to terminal 65 of gate 64. With the input applied to inverting terminal 63 of gate 64 at a high state and the input applied to terminal 65 of the gate at a low state, the output of gate 64 remains ç 25 in a low state preventing the triggering of the multi-vibrator 70 such that the output at terminal 74 remains at a logic low state.
When the interface equipment 31 generates a stop command signal, the output terminal 37 of transport circuit 35 drops to a logic low state (indicated at time tS ) which causes the output of gate 52 to switch from a low to a g 10609~7 1 high logic state. The output of gate 54 drops to a logic low state. The inte~rator circuit formed by resistor 56 and capacitor 58 momentarily holds the terminal 62 of gate 60 in a logic high state thereby causing the output of gate 60 to switch to a low state at time tS as indicated by the ~ stop pulse 69 adjacent gate 60.
- With input terminal 63 of gate 64 at "0", the output switches to a "1" triggering multivibrator 70 to provide a logic "1" at terminal 74. After a predetermined time interval determined by the RC time constant of resistor 56 and capacitor 58, terminal 62 will drop to a low state causing the output of gate 60 to again go to a high state indicated at time tSl in waveform 69.
Once the retriggerable one-shot multivibrator is initially triggered by stop pulse tS~ its output will remain at "1" during the relaxation period determined by the RC time constant of resistor-capacitor 72, 71 res-pectively. The positive-going output signal at terminal ~ `
~' 74 is initiated at approximately the time ts, shown by the controlled stop pulse waveform 75. Signal 75 is applied ` to gate 78 via input terminal 77. With terminal 77 at a logic high state, gate 78 is enabled to apply the positive going tach pulses 34 to input terminal 65 of gate 64.
With terminal 63 returned to a high state, the output of gate 64 will be a "1" during the positive interval of each of the reoccurring tach pulses 34 applied to terminal 65.
The frequency of the tach pulses is directly related to the tape speed and when the controlled stop pulse 75 is initiated (and the transport~ therefore, is still at a running speed), pulses 34 will be of a frequency ~060~7 sufi~iciently higll to retrigger multivibrator 70 since the time duration between successive tach pulses will be shorter than the relaxation period fixed by the resistor 72 and capacitor 71. The leading edge of the controlled stop pulse 75, when applied to stop drive circuit 80, causes the motor drive circuit 40 to apply a reverse drive current to the armature winding 29.
It is noted here that circuit 80 is coupled to the speed control circuit 36 via conductor 82 to actuate, via conductor 38, the motor drive circuit 40 to remove the existing drive signal. Circuit 40 receives a polarity command signal from output terminal 39 of circuit 35 at time tS such that when the controlled stop pulse 75 is applied, circuit 40 will supply a reverse polarity current ` :
pulse to the armature winding 29. This reverse current pulse rapidly slows the drive motor and, therefore, tape 20.
As the motor speed resLuces, the frequency of tach pulses 34 will decrease until ~he time period between successive tach pulses exceeds the relaxation period of the retriggerable multivibrator ac which time the desired and presettable (by selecting the RC time constant of 72, 71) lower speed limit has been reached and the output 74 of the multivibrator will again return to a logic low state at time tL as indicated by the waveform diagram 75.
At this time, the tape speed and motor speed have been sufficiently reduced such that upon the removal of all drive current from armature winding 29 by circuits 40 and 80 in response to the crailing edge of pulse 75, the motor will come to a substantially immediate ha t without reversing direction.
Once the retriggerable one-shot multivibrator has . .. ~ .. -~ 06~9~7 returned to its steady state condition with a logic low output, terminal 74 again goes to a logic low state inhibiting gate 78 which in turn prevents tach pulses 34 from triggering multivibrator 70 until a successive stop signal is received. Gates 54 and 60 together with the RC network (56, 58) form a pulse shaping circuit which allows the initial stop pulse 69 to be of relatively short duration thereby permitting the tach pulse frequency to control the removal of the reverse drive pulse at time tL when the de-sired lower speed of the drive is approached.
Thus, by employing the retriggerable multivibrator or other suitable delay means together with the remaining circuit components discussed, a controlled stop pulse is generated which provides a reverse drive current to the armature winding for rapidly braking the tape drive and, therefore, the tape within the desired limits. In practice, it has been found that optimum braking action is achieved by selecting the lower speed limit to be one-sixth that of the normal running speed.
; It will become apparent to those skilled in the art that various modifications to the specific circuitry shown in the preferred embodiment can be made without departing from the spirit or scope of the present invention as defined by the appended claims.
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Claims (8)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a tape transport having: means, including a drive motor, for transporting tape across a recording or playback head, the improved braking system comprising: motor drive circuit means coupled to said drive motor for applying forward drive excitation to said motor to implement a normal forward running mode of operation of the transport; and means coupled to said motor drive circuit means for selectively control-ling the latter to apply reverse drive excitation to said drive motor during forward movement thereof to effect braking of such movement, said reverse drive excitation being of an opposing character with respect to said normal excitation and tending to drive said motor in an opposite direction from said normal forward movement thereof, to rapidly slow such forward movement; said means coupled to said motor drive circuit operating to selectively control the latter to remove said reverse drive excitation at a time subsequent to that at which the same was applied, said time subsequent occurring when said forward movement has been slowed to a speed lower than its normal level, but greater than zero, said means including means for determining the occurrence of such speed.

2. The improved braking system of claim 1 including, means for generating signals continuously representative of tape speeds during the forward operation of the transporting means; said motor drive circuit means coupled to said drive motor operative to selectively apply first or second drive signals to said motor, said first signals causing a forward running mode of operation of the transporting means; means for providing a stop signal; and circuit means coupled to said stop-signal providing means, to said signal generating means and to said motor drive circuit means, for initiating a controlled stop signal in response to said stop signal from said providing means and terminating said controlled stop signal at a particular reduced tape speed greater than zero in response to signals from said signal generating means repre-sentative of such reduced speed, and for applying said con-trolled stop signal to said drive circuit means; said drive circuit means being responsive to said controlled stop signal by applying said second drive signals to said drive motor, said second drive signals being of a reverse character which tends to move said motor in an opposite direction from that caused by said first drive signals.

3. The improvement as defined in claim 2, wherein said signal generating means is a tachometer means coupled to the tape transporting means for providing pulsing tach signals whose frequency represents the speed of tape being transported.

4. The improvement as defined in claim 3, wherein said circuit means includes a retriggerable circuit having a presettable relaxation period for developing a controlled stop pulse in response to said stop signal and for terminating said controlled stop pulse when the period between successive cycles of tach signals exceeds said relaxation period.

5. The improvement as defined in claim 4, wherein said retriggerable circuit comprises a retriggerable multi-vibrator having a relaxation period fixed at least in part by an RC network.

6. The improvement as defined in claim 5, wherein said means for providing a stop pulse comprises means for receiving a stop command signal and supplying a stop signal in response thereto, gate means receiving said stop signal for developing a stop pulse in response thereto and for selectively applying said stop pulse to said retriggerable multivibrator to actuate said multivibrator only when a stop command signal is received.

7. The improvement as defined in claim 6, wherein said gate means includes pulse shaping means for determining the pulse width of said stop pulse.

8. A method of reducing the braking time of tape transported by a tape transport having tape drive means including a drive motor, comprising the steps of: applying first drive signals to the drive motor to bring about forward running operation thereof; monitoring tape speed and produc-ing pulsing signals representative thereof; and using said pulsing signals in stopping said tape by removing said first drive signals, applying second drive signals to the drive motor which are of a character to drive the motor in a reverse direction, and removing said second drive signals in response to said pulsing speed-representative signals having slowed to the point where the period between successive pulses thereof exceeds a predetermined interval, occurring when the tape speed is reduced to a predetermined lower level.