March 14, 1967 _ A. GABOR ETAL I 3,309,597 MOTOR ACCELERATION CONTROL SYSTEM. l Filed April 20, T1.l _. ,57m/Az.

Transcription

1 March 14, 1967 _ A. GABOR ETAL I 3,309,597 MOTOR ACCELERATION CONTROL SYSTEM Fied Apri 20, 1964 T1. _,57m/Az. SVGA/,QL ATTORNEY

2 United States Patent O 1 3,309,597 MOTOR ACCELERATION CONTRGL SYSTEM Andrew Gabor, Huntington, Ivan 0. Fiedgate, Haesite, and Eeuthcre Poumatis, East Isip, N.Y., assignors to Potter Instrument Company, Inc., Painview, N.Y., a corporation of New York Fied Apr. 20, 1964 Ser. No. 361,179 6 Caims. (C. S18-393) This invention reates to motor speed contro systems 10 and, more particuary, to a system for controing the ac ceeration of a capstan drive on a tape transport when the drive motor is started up from zero speed. In digita tape transports, it is desirabe that the capstan and the tape driven thereby reach their high operating 15 or running speed in a very short time without overshoot ing the desired speed. For exampe, the operating speed may be 150 inches per second, which must be maintained with an accuracy of 1%, and when the capstan is started up from zero speed, it may be required to reach its op 20 erating speed within two miiseconds. The time required for the'capstan to reach its operating speed is referred to as the rise time. The requirement of the 1% accuracy means that the capstan must not overshoot the desired speed of 150 inches per second by more than 1.5 inches per second. To achieve these objectives, the acceeration of the capstan must be controed very accuratey when started and particuary when it approaches the desired operating speed. The acceeration of the capstan coud be con troed in response to the capstan zor tape speed, and this contro Woud be achieved normay by marks on a tone whee driven by the capstan. In order to achieve a two miisecond rise time to an operating speed of 150 inches per second without over >shooting by more than 1.5 inches per second, the marks von the tone whee in a veocity responsive contro sys tem woud have to be 3><0 3 inches apart, and the marks woud have to be paced on the tone whee with an accuracy or toerance of 3><10 5 inches, assuming that the tone whee marks are at the radius of the capstan. The difiicuty of achieving such a toerance is apparent. The present invention greaty aeviates these cose toerance requirements. According to the present inven tion, the acceeration is controed in response to the tota distance traveed and the eapsed time rather than in response to veocity. With the acceeration controed in this manner, the marks on the tone whee need be po sitioned with an accuracy of ony 1.S><10 3. Thus, the toerance requirement is aeviated by factor 50. A system in accordance with the present invention, ñrst, energizes the capstan drive motor to appy a high torque to the capstan and, then, automaticay reduces the torque to a ower vaue when the tone whee and the capstan reach a desired speed. The ower torque, when achieved, is controed in a conventiona manner to main tain constant speed. Eventhough the switch from vthe high torque to the ow torque is made at the time that the tone whee and the capstan reach the desired operating speed, it is not made directy in response to the tone whee speed. In stead, the switch is in response to the count in a counter dropping to zero, which count is increased ineary with time and decreased ineary with distance traveed. When a start signa is given, the counter wi begin to count the puses from a cock puse generator which in creases the count in the counter. The motor is controed to appy a high torque to the capstan when the count `in the counter is above zero. As a resut, the motor,driving the capstan wi begin t0 acceerate. A count of the marks on the tone whee driven by the capstan is fed to the counter aso, and the tota ce 3,309,597 Patented Mar. 14, registered by the counter now decreases by one in re sponse to each puse received from the tone whee. Thus, the count in the counter wi be proportiona to the eapsed time minus the distance traveed by the tape. At ñrst, the count in the counter wi increase due to the fact that the cock puses are produced at a faster rate than the tone whee puses. As the capstan and the tone whee acceerate, the tone Whee puse rate wi in crease unti the tone whee puse rate exceeds the cock puse rate. When this condition occurs, the count in the counter wi start to decrease and wi decrease at an in creasing rate due to the continued acceeration of the capstan and the tone whee, unti the count in the counter reaches zero. In response to the count in the counter becoming zero, the system automaticay changes the energization of the motor to appy a ow torque to the capstan, which ow torque is controed in a conventiona manner then to maintain a constant speed. The parameters of the sys tem, such as the cock puse rate, the distance between marks on the tone whee, and the vaue of the high torque appied to the motor during the acceeration period, are seected so that the count in the counter drops to zero just when the capstan has acceerated to the desired op erating speed. Because the contro of the acceeration is in response to the distance traveed rather than speed, the toerance requirements are greaty aeviated as described above. Accordingy, an object of the present invention is to provide an improved motor speed contro system. Another object of the invention is to provide an irri proved speed contro system for the capstan drive of a tape transport. Sti another object ofthe invention is to provide an improved system for controing the acceeration of the motor as it starts up from Zero speed. A further object of the present invention is to provide an improved system for controing the energization of a motor when it is started up so as to bring the motor up to the desired operating speed quicky without overshoot ing the desired operating speed. A sti further object of this invention is to provide an improved system for controing the capstan drive of a tape transport when the capstan drive is started up so as to bring the capstan and magnetic tape driven thereby quicky up to the operating speed without overshooting. Yet another object of this invention is to reduce the toerance requirements in the tone whee used for con troing the speed»of the capstan drive. Sti a further object of this invention is to reduce the probem of overshooting in a capstan drive system for tape transports. One of the important objects of this invention is to faciitate the bringing of the magnetic tape capstan drive quicky up to the desired operating speed without sub stantia overshoot. Further objects and advantages of the present invention wi become readiy apparent as the foowing detaied description of the invention unfods when taken in con junction with the drawings, wherein: FIG. 1 is a graph of an exampe of a desired speed pro [ie for a magnetic tape drive system; and FIG. 2 is a schematic bock diagram of a speed con tro system in accordance with the present invention. The graph shown in FIG. 1 is an exampe of a desirabe speed profie for a capstan and magnetic tape driven thereby upon starting up from zero speed. In the exam pe iustrated, the tape reaches a speed of 150 inches per second in two miiseconds, and then, the speed is main tained constant at 150 inches per second. This constant speed shoud be maintained with a 1% accuracy, which means that the tape, upon acceerating to 150 inches per

3 3,309,597 3 second, shoud not overshoot the speed of 150 inches per rising to the desired operating speed, the motor 21 ap second by more than 1.5 inches per second. An acceer pies a high torque to the capstan, and after the motor 21 ation to 150 inches per second in two miiseconds is an and the capstan 23 reach the desired operating speed, the acceeration of 7.5 >< 104 in./sec.2. motor 21 appies a ow torque to the capstan 23 and main If the acceeration is controed in response to the cap tains a constant speed. The high torque starting circuit stan speed, then, in order to ensure that the speed does 19 may comprise any suitabe circuit known to those not yovershoot by more than 1.5 inches per second, speed skied in the art such as a constant current or, ater information must be obtained every 20 microseconds. nativey, a constant votage source, depending upon the This interva can be determined by dividing the permis characteristics of the motor 21. Simiary, the ow torque sibe overshoot of 1.5 in./sec. by the required acceer running circuit 20 may comprise any suitabe circuit ation of 7.5>< 104 in./sec.2. known to those skied in the art such as a contro circuit If the speed information is suppied by a tone whee empoying the output of a tachometer couped to the driven by the capstan and having the same radius as the motor `shaft to provide a feed back signa that varies the capstan, then the maximum distance between the marks energization of the motor to maintain the speed of the can be determined by mutipying the operating or run 15 motor constant. ning speed by the 20 microsecond interva. Thus, the The motor 21, in addition to driving the capstan 23, marks woud have to be paced 3><10 3 inches apart. directy drives a tone whee 25 so that the tone whee ro In order for the speed information to have a 1% accuracy, tates at the exact same speed as the capstan. The tone the position error of each mark woud have to be not whee 25 is provided with marks around its outer circum more than 0.01 >< 3 ><10r3=3 ><10 5 inches. 20 ferentia edge, which are converted into puses by a read However, if the acceeration is constant during the 2 head 27, one puse being produced for each mark on the miisecond rise time, the speed can be determined by tone whee. These marks on the tone Whee may be mag di-viding twice the distance of tota tape trave by the netic, optica, or of any other convenient form which wi time. In this equation, the absoute vaue of acceeration generate output puses. is of no consequence since it does not appear in the 25 The output puses from the tone whee produced by the equation. read head 27 are ampified by an ampifier 31, then are If the fina tape speed is to be obtained with a 1% ac appied to the input 17 of the binary counter 15, and are curacy, it is necessary to measure the tota distance trav counted by the counter 15 in the reverse direction. The eed ony Within 1%. Since with constant acceeration quantity estabished by the counter 15 thus is a function the tota tape trave is equa to the speed times the time 30 having a positive term, the magnitude of which increases divided by 2., the distance traveed during the 2 miisec with time, and a negative term, the magnitude of which ond rise time wi be equa to increases with the distance through which the capstan 23 and tone Whee 25 have rotated. When the motor 21 and the capstan 23 driven thereby are at rest and it is desired to bring the motor and capstan up to operating speed, a start signa is appied to an input 33. This start signa sets a fip-hop 35 in its A state and sets the count registered by the binary counter 1S to Accordingy, to know this distance with a 1% accu racy, the marks on the tone Whee need to be positioned with a toerance of ony 1.5)(.10-3 inches. Hence, the toerance requirement is aeviated by a factor of Zero This means that if the.acceeration is maintained constant during the 2 miisecond rise time up to the speed of 150 inches per second and, then, is stopped by a signa oper 45 ating in response to the distance that the tape has traveed, the toerance requirements on the marks on the tone Whee are 50 times ess stringent than they are when the acce eration is controed in response to speed. This concept can be extended to acceeration functions 50 other than a constant acceeration, provided the form of the acceeration function is known. In the present in vention, the acceeration is controed in response to the distance of tape trave and the eapsed time, and thus, the invention Igreaty aeviates the toerance requirements as 55 described above. As rshown in FIG. 2, the system of the present inven tion incudes a cock puse generator 11, which is con troed internay by a crysta osciator. The cock puse generator 11 appies puses at a constant frequency to 60 an input 13 of a binary counter 15. The binary counter 15 counts in the forward direction in response to the puses received from the cock puse generator 11 and wi count in the reverse direction in response to puses appied to another input The counter 15 functions to estabish a quantity which is changed in one direction in response to puses appied to the input 13 and is changed in the opposite direction in response to puses appied to the input 17. In addi tion, the binary counter 15 operates in conjunction with 70 a high torque starting circuit 19 and a ow torque running contro circuit 20 to contro the ener-gizati-on of a printed circuit motor 21, which drives a capstan 23 of a mag netic tape transport, so that during the time the capstan and the motor 21 are starting up from zero speed and are 75 On being set in its A state, the fip-fop 35 en abes the high torque starting circuit 19, which ener gizes the motor 21 to appy a high torque to the cap stan 23. Since the motor 21 and the capstan 23 wi be at rest when the start signa is appied, no puses wi be appied initiay to the input 17 of the binary counter 15. How ever, the cock puse generator 11 which produces puses at a constant rate wi be appying puses to the input 13 of the binary counter so the count registered by the binary counter 15 wi buid up rapidy. As a resut of the high torque appied by the motor 21, the capstan 23 and the tone whee 25 Áwi start to rotate, and the rate of rotation wi acceerate rapidy. When the tone whee 25 starts to rotate, it wi cause puses to be generated yby the read head 27. These puses, after >being ampified by the ampifier 31, wi be appied to the input 17 of the binary counter 15, which wi count these puses and subtract the count from the tota counted at the input 13. Thus, the puses produced by the read head 27 wi have the effect of reducing the count regis tered by the counter 15. As the speed of the tone whee 25 increases, the read head 27 Wi produce puses at a faster and faster rate unti the puses appied to the input 17 occur at a greater rate than the puses produced by the cock puse gener ator 11. Unti this time, the count registered by the bi nary counter 15 wi have been increasing, but when the rate that the puses are being produced by the tone whee 25 surpasses the rate that the puses are being produced by the cock puse generator 11, the count registered by the counter 15 wi start to decrease. Signas representing the count registered by the counter 15 are appied to a count responsive circuit 37, which wi produce an output signa in response to the count regis tered in the counter 15 becoming zero. Count respon sive circuit 37 may convenienty comprise an AND gate

4 ' 5 3,309,5 97 with one input couped to the ogica zero (0) of each sired operating speed of the capstan driving surface, and Hip-fop of the counter 15. This output signa of the z r is the time interva in which the capstan must be ac count responsive circuit 37 is appied through an OR ceerated to the desired operating speed. gate 38 to reset the fip-dop 35 back to its B state. Therefore, in order for the capstan to reach a speed When the fip-fop 35 is reset to its B state, the high of 150 inches per second in two miiseconds, it must ac torque starting circuit 19 wi be disabed, and the fip ceerate at a rate of fop 35 wi appy an enabing signa to the ow torque running contro circuit 20 through a gate 40, which wi 5% in./sec.2=7.5><104 in./sec.2 be enabed at this time. ì The pu-se rate produced by the cock puse generator 0 The starting circuit 19, therefore, must be set to energize 11, the spacing between marks on»the tone whee 25, and the motor 21 to produce an acceeration of 7.5 ><104 the torque appied by the motor 21 when energized by in./sec.2. the starting circuit 19 are seected so that the count The spacing between the marks on the tone whee registered by Ithe counter 15 wi drop to zero» just when can be determined from the foowing formua: the capstan reaches the desired operating speed. Thus, 15 the high torque starting circuit 19 wi be disabed and ds the ow torque running contro circuit 20 wi be en abed just when the capstan 23 reaches the desired op in which ds is the mark spacing on the tone whee erating speed. When the ow torque running contro and dvo is the permissibe overshoot in veocity. There circuit 20 is enabed, it wi energize the motor 21 to fore, in order to obtain 'the veocity profie iustrated by appy a ow torque to the capstan 23 and wi contro the graph of FIG. 1 with an overshoot of not more than the energization of the motor 21 to operate at constant 1.5 inches per second, the spacing of the marks on the tone whee must be speed in a convention manner. Before the start signa is appied t-o the system, a re set signa is appied to the system at an input 41. This 25 reset signa is appied to the iiip-fop 35 through the OR gate 38 to ensure that it is in its B s-tate before the start signa is appied, and aso, this reset signa sets a fip-fop 42 in its B state. Then when the start signa is appied at the input 33, it sets the fip-fop 42 in its A state. The fip-fop 42 wi enabe the gate 40 whenever it is in its A state. The gate 40 and the Hip-fop 42 serve to prevent the ow torque running contro circuit from being enabed when the fip-fop 35 is in its B state prior to the appication of the start signa to the input 33. After the start signa is appied, the dip-fop 42 wi be switched to its A state so that the gate 40 wi be enabed when the ñip-ñop 35 switches back to its B state in response to the count registered in the counter 15 dropping down to zero. The mark spacing on the tone whee 25, the output puse frequency of the cock puse generator 11, and the torque to be appied by the motor 21 when energized by the starting circuit 19 can be determined by making the assumption that the appied torque and the acce eration produced thereby is constant. This assumption wi be sutiicienty vaid with a`conventiona energizing circuit so as to cause ony a very sma error in cacua tion. Any error in cacuation due to a non-constant acceeration may be compensated for by atering the osciator frequency as required. In fact, an acceera tion which is far from constant can be accommodated by an appropriate change of frequency so ong as the shape of the acceeration function is consistent. The exact vaue of the frequency can be determined by experiment. For acceeration functions which are ap proximatey constant, the frequency is approximatey: f 2, r ne) V0 For a inear acceeration function, the frequency is: OIVO 31h-(î If the acceeration is substantiay constant, the re quired acceeration of the capstan driving surface can be determined from the foowing formua: Vo if in which a is the required acceeration, Vo is the de äâé inohes=3 X 10*3 inches The cock puse generator output puse frequency can be determined from the foowing formua: Fm r Vo in which is the unknown frequency. Therefore, to obtain the exempary profie of FIG. 1 with an overshoot of not more than 1.5 inches per second, the puse` fre quency shoud be 1 ï 150 The above description is of a preferred embodiment of vthe invention and many modifications may be made there to with-out departing from the spirit and scope of the in vention, which is defined in the appended caims. What is caimed is: Y 1. A speed contro system comprising, a motor, and means to contro the energization of said motor to initiay generate a high torque and then to auto maticay reduce the torque generated by said motor to a ower vaue in response to a predetermined func tion reaching a predetermined vaue, said function having a first term increasing in magnitude ineary with time and ya second.term increasing in magnitude ineary with the distance through which the output of said motor has rotated, said first and second terms being of opposite signs, increases in the magnitude of said second term tending to change the vaue of said function t-oward said predetermined vaue. 2. A magnetic tape speed contro system comprising, `a capstan adapted to drive a magnetic tape, a motor connected to drive said capstan, and means to contro the energization of said motor to initiay appy a high torque to said capstan and then to automaticay reduce the torque appied by said motor to said capstan to a ower vaue and to maintain the speed of said capstan constant in re spouse to a predetermined -function reaching a pre determined kvaue, said function having a first term 'having a magnitude increasing ineary with time and a second term having a magnitude increasing ineary with the distance through which said capstan has rotated, said iirst and second terms being of opposite signs, increases in the magnitude of said second term

5 3,309, tending to change the vaue of said function toward tain vaue that is a function of the interva of high said predetermined vaue. torque energization and the incrementa distance rep 3. A system for acceerating a capstan `from rest to a resented by each puse counted. predetermined speed comprising, in combination, 4. A system as in caim 3 wherein said puse producing a motor for driving said capstan, 5 means is a tone whee. means couping said motor to said capstan, 5. A system as in caim 4 wherein said predetermined means for producing a puse in response to the rota= incrementa distance is a function of a permissibe varia tion of the capstan through a predetermined incre- tion in speed from said predetermined speed. menta distance, 6. A system as in caim 5 wherein the output puse a counter, 10 frequency of said cock puse generator is a function of a cock puse generator and means for couping an outa said permissibe variation in speed from said predetermined put from said cock puse generator to said counter for estabishing a time interva, speed. References Cited by the Examiner means for couping an output from said puse produc- UNITED STATES PATENTS ing means to an mput of said counter, 15 means to energize said motor, 2,878,434 3/1959 B'rowr? means couping an output of said counter to said motor 3,007,098 10/1961 Skrobsch ~ X energizing means, 3,064,173 1/1962 Breen et a X said motor energizing means responding to the count 3,206,665 9/1965 Burhngham in said counter to energizing said motor to initiay /1965 Hoy generate a high torque and then to automaticay /1965 Toscano change the energization of said moto-r to reduce said ORIS L RADAR Prima Examiner torque generated thereby to a ower vaue when the ` _ y _ ' count accumuated by said counter reaches a cer«g- SIMMONS, ASSISÍL UU Examiner