US2734336A - Clock system - Google Patents

Description

Feb. 14, 1956 L. T. MCRA CLOCK SYSTEM Filed May 22, 1955 ART zr I 22 Z6 -Q l@ /I/ 1 /0 ZS/I c. 30 Afd/2,6@ 25 I N VE N T 2;? i LAWREN CE Mc FFME United States Patent O 2,134,336 CLOCK SYSTEM Lawrence T. McRae, New York, N. Y. Application May zi, 1953, serial No; esistiti s claims. (Cl. sti-*24) (Granted onder Title as, U. s. "code :(1952), sec. 266) T i'e invention described herein' may lbe manufactured and' used by or" for the Government ofthe United states of America for governmental purposes without the paynient or any royalties thereon or therefor; I o

This i'nveittior'i relates to improvements in time clocks and more particularly to improvements in time clocks that are solenoid actuated for moving the type Wheel of the tithe clock whereby when a ltinte card is inserted in the clockpthe time' is recorded thereon. n

Tirn'e cl 'lts' of the type used iny places of employment by the employees for recording starting tit'ne and finishing time a job have been widely used for a long time. Generally the use ofthe tinte clock involves a time card 'which is adapted to be inserted into a slot provided inthe tirti'e clockand withdrawn froin the slot in the `tinie cloclt with a record 'left ony the tinte card to indicate when the card inserted' into the clock. Many of the time clocks now use rely upon4 the periodic enegization and deen'erglzation of a solenoid coil Yfor advancing atratchet wheel st'epeby-step and thereby advancing the clock mech'- as'in. The energization and dee'riergi'zatioh ofthe solo noid isl controlled by a periodic switch, A synchronous motor' operates the periodic switch and generally causes the switch to close a circuit to the solenoid sixty tintes an hour. The opening of the switch and the lclosing of the switch, respectively, occur at identically spaced intervals. An armature yis associated with the soloid'ad is connected by suitable linkages to the ratchet wh'eeLMThe armature is' normally biased to one position andade'pted' to be moved to a second position upon eriejjrgration'of the solenoid throiigli the periodic switch. YIn -tinte clocks tiresently in use the solenoid controlled by the periodic switeh is'energiz'ed fora srnall fraction or theorie "innte cycle and denergii'ed for the remainder of the cycle. Dining! the fraction of the cycle that' 'the solenoid is enerized the armatore is urged into engagement withV the magn'ticcre and/or frame of the solenoid ai'ld is substantially iiiimovable relative to the'svoleiioidt D g the maiiider'f each cycle th a'rrntu is biasd toll `s other' position'by a vspring and is retainedfin that position by 'the spring only; through shock or vibration' it is'possible to canse the arniatnre toniovey against the restraint offered by e spriri'gdiiring ther latter portioi of eacli'cycle. Though t'iii'lilt wise possiblel to cause' the armature to rve r'el til/fe` tothe solenoid when th solenoid isetir'gized, 'the difference in energy level of applied shock r uired for' mo' g" the armature' ag'iiist'th biafs' of the sp' g asc'oiii-y n pared t that necessary kfor moving theaii'tur relative t' the energized solenoid is very' considerable. In th case of tlielattr, the applied shock may be ample" to effectively destroy' the time clock. i y,

o I'n use" itlis been fouhdthat time clocks are tampered with by employees wanting to advance the clock. where the" armature is retained i'none 'position by a spr'ing-nly for' substantially all of a one minute cycle those' people' who' cr to tamper with the clock 'have discovered that by strikingtheclock manually at a certain average repetition frequency they arrive at the resonant frequency of 2,734,336 Patented Feb. 14, 1956 the armature and its associated parts causing the latter to vibrate and to thereby advance the ratchet wheel several steps before the' vibration s terminated due to energization of the solenoid. Another expedient resorted to by those people who are desirous of advancing the clock is to insert a thin tool into one of the apertures of the clock such as the slot that receives the time card in order to physicallynlove the armature against the bias of the spring thereby advancingl'th clock. In this case as in case of vibration of the armature due t'o shock, movement of the armature is substantially impossible during' the period of time the solenoid is energized,

This invention improves upon time clocks known to the prior art by increasing the fraction of the cycle during which the solenoid is energized so that the fraction of the cycle during which the solenoid ,s dee'nergized s not long enough to permit vibration of the armature, if any, to have any effect on the ratchet wheel. Furthermore, use of a thin tool for moving the armature is discouraged sirice the armature is relatively immovable practically all the time. One would have to keep applying force cohtinuously on the armature to move it when the solenoid is dee'nergized. t

An object of this invention is to provide an impiovenient in time clocks. y y

A rfurther 'object is to provide an improvement in time clocks which will discourage tampering with the time clocks. Y

' A further objectis to provide an improvement in` time clocks whereby dama-ge and. maitn'il'ce are minimized.

A furtherobject is to provide an improved time clock thatI minimizes plfered time.

A further objectis t'o provide ah improvement in time clocks whereby time clock 'solenoids are energized for a period of time exceeding a predetermined critical period.

Other objects and many of the attendant advantages of this invention will be readily appreciatdvas the same becomes better understood by reference to the following etailed description when considered in connection with the Aaccompanying drawings wherein:

Fig'.l 1 is a schematic diagram of a portion of a circuit forming part of one type 'of time clock so'ld commercially by 'a'.company well-known in the time clock field.

Fig". 2 is' a` schematic diagram including the iirprvements of this invention, and l Fig.. 3and Fig. 4 illustrate in two operating conditions a'pefrliodic switch that is generally of the type used in a particular time [clock er'nbod'ying` the circuit of Fig'.l 1, and including the necessary modifications and improvements for use in the improved circuit of F'g, 2i

. In Fig. l there is shown schematically la, circuit 12.

The circuit 12A includes a solenoid 14 having a coil 16 that' is wound for C. operation and a supporting magA neticfl'ame18.'` Thkcoil 1/6 has terminals 20 and 21. An armature 22 is mounted on a supporting frame 24. The supportngl'fia'm'e 24 permits the armature y22 to f in v'e into abutting relationship with the magnetic suppoi-ting frame 18 of the lsolenoid 14. A tension spring 26'bi'a`ses the armature 22 toward a raised position which the armature 22 occupies when the solenoid 14is deen'ergized. When the solenoid 14 is energized the magnetic eld generated by the solenoid coil causes the armature 22 to be quickly drawnv into abutting relationship with the magnetic supporting frame 18 ofthe solenoid and against the bias of the spring 26. In order to insure quick movement'of thearmatur'e 22 when the solenoid 14 is eily crgized Vthe solenoid is designed to generate a magnetic fieldA which exerts a for'ce that greatly exceeds the force exerted upon' the armature 22 by the spring 26. The armature 22 is adapted to be connected to a suitable linkage mechanism, not shown, for actuating the clock 1nechanism, likewise not shown'.

The solenoid 14 is conventionally periodically energized by an A. C. lighting circuit supply 28. The circuit between the supply 28 and the solenoid coil 16 is selectively manually controllable by means of a switch 32. When the switch 32 is closed the circuit including the coil 16 and the supply 28 is cyclically completed and iuterrupted through a periodic switch 34.

The periodic switch 34 includes a rotatable support 36 for tixedly mounting a pair of disc cams 38 and 39 in fixed relationship thereto. 42 and 44 support a corresponding pair of contacts 46 and 48 respectively. The ends of the contact arms 42 and 44 opposite to those to which the contacts 46 and 48 are secured bear against the periphery of the disc cams 38 and 39. The disc cams 38 and 39 are so designed that for a small fraction of a complete revolution of the cam support 36 the contacts 46 and 48 are permitted to engage and for the remainder of the revolution the contacts 46 and 48 are separated. The contacts 46 and 48 are in series between one terminal of the solenoid coil 16 and one terminal 29 of the supply 28. The model 14 time clock produced by the Stromberg Electric Company includes the above described circuit. It further includes a rectifier 54 in series with the terminal 29 of the supply 28 and the terminal 20 of the solenoid coil 16 to permit only unidirectional current to ow through the coil 16.

The cam support 36 is continuously driven by a synchronous motor 56 at a speed of 1 R. P. M. When the manual switch 32 is in closed circuit position the energization circuit of the synchronous motor is completed and includes the lead 58 electrically connecting one side of the motor to the terminal of the supply 28 through the switch 32. The other side of the motor 56 is connected to the terminal 29 of the supply 28 by means of a lead 62. Therefore, whenever the switch 32 is closed the synchronous motor 56 rotates continuously driving the cam support 36 at a constant speed of 1 R. l. M. At precisely the same instant during each cycle or each complete revolution of cam support 36 the contacts 46 and 48 are caused to engage and at precisely the same instant during each cycle the engaged contacts 46 and 48 are permitted to disengage. Since the contacts 46 and 48 are in series in the energization circuit of the solenoid coil 16, engagement of the contacts 46 and 48 are substantially instantly followed by movement of the armature 22 into abutment with the magnetic supporting frame 18 of the solenoid 14. Conversely as soon as the contacts 46 and 48 separate the armature 22 is withdrawn by means of the tension spring 26. The periodic movement of the armature 22 is transferred by a linkage mechanism, not shown, to the ratchet of the time clock and thereby to type wheel, all of which are conventional and consequently not shown.

In use it has been found that time clocks employing this type of circuit are not entirely satisfactory. Employees in numerous places of employment have found that by manually striking the housing of the time clock at a cer tain repetition frequency, it is possible to cause the arma ture 22 to vibrate at its resonant frequency thereby advancing the clock by several minutes. Advancing the clock in this manner is achieved by causing the amplitude of vibration to equal the movement caused by energization of the solenoid. Because knowledge of this inherent weakness in this type of time clock can become common knowledge of all the employees called upon to use the time clock in a particular place of employment it can become what may be likened to an attractive nuisance. Employees coming to the time clock several minutes previous to the time that they are supposed to punch out to afford an indication of a complete days work rendered, and finding that they are a few minutes ahead of time are sorely tempted to strike the clock if they are cognizant ot the inherent weakness mentioned above. Even when practiced by a relatively small percentage of the total The pair of contact arms 4 Y number of employees this expedient resorted to by the small percentage of the employees can cause a considerable expense in damaged clocks, pilfcred time, and an increased need for maintenance service to reset the clock.

Another expedient resorted to by employees attempting to advance the clock is to insert a thin tool such as an engineers scale or a hooked wire depending upon the arrangement of the armature, in order to force the arma ture to move against the bias of the spring attached thereto.

To overcome this inherent weakness in time clocks including a circuit of the type shown in Fig. l, resort is had to increasing the fraction of each cycle during which the solenoid coil is energized. During the interval that the armature is retained in engagement with the frame of the solenoid it is substantially impossible to transfer sufcient energy to the armature to cause it to move relative to the frame of the solenoid against the influence of the magnetic field generated by the solenoid. If the clock were struck with sufficient force to cause the armature to move relative to the energized solenoid, the time clock would be seriously damaged possibly even to the degree that the individual having caused the damage could not punch out.

It has been observed through experiment that there is a critical period of time involved; it is impossible to set up sympathetic vibrations of sutlcient amplitude in the armature assembly by manually striking the clock in less than this critical period. This critical period varies in accordance with the mass of the armature. It may be readily determined by experiment. It has been found in practice that if the armature of one clock that has been tried is retained in engagement with the solenoid frame for about fifty-tive seconds or more of a sixty-second cycle that insufficient time remains for setting up vibrations in the armature of suicient amplitude to advance the clock. To insure against tampering with a time clock with a thin tool such as an engineers scale or wire hook the interval of energzation of the solenoid coil may be increased to fifty-eight seconds of a sixty-second cycle or thereabout. It is not likely that anyone would care to risk discovery by holding a tool in position for the necessary period before the solenoid is deenergized for the remaining small fraction of a cycle.

To accomplish this result the circuit of Fig. 1 has been modified as shown in Fig. 2. Substantially all of the circuit moditication is centered in the periodic switch. The switch 34 of Fig. 1 has been modified to provide switch 64 for use in the circuit of Fig. 2 and is shown in detail in Fig. 3 and Fig. 4. The only differences between the illustrations of the switch 64 in Fig. 3 and Fig. 4, respectively, are that the views are taken from ditferent directions and that the switch 64 is in open circuit position in Fig. 3 whereas it is in closed circuit position in Fig. 4.

Switch 64 includes a cam support 36. A pair of substantially identical disc cams 38 and 39 respectively are secured to opposite ends of the cam support 36. Both disc cams are formed from circular discs and have a peripheral notch. The cam support 36 is xed to the shaft of a synchronous motor 56. A pair of brackets 40 are fxedly mounted relative to the motor shaft and each include a pair of guide openings that are aligned with the cams 38 and 39, respectively. Contact arms 42 and 44 are slidably mounted in the guide openings of the brackets 40. Compression coil springs 66 and 68 are disposed around the contact arms 42 and 44, respectively. A collar 69 is secured to each contact arm whereby when the contact arm 42 or 44 is moved upwardly, the corresponding coil spring 66 or 68 is compressed between associated collar 69 and the top of the associated bracket 40. One end of each of the contact arms 42 and 44 is adapted to bear against a respective one of the cam discs 39 and 38. The opposite end of the contact arm 42 is bent to dene an angle that is somewhat greater than ninety degrees; the opposite end of the contact arm 44 is bent to dene an 5 angleftht is less than ninety degrees whereby when the lengths of the" contact arms 42 and 44 are parallel the bent" ends are parallel. Cont- acts 46 and 48 are secured tothe ends of the contactarms 42 and 44, respectively.

The structure of switch 64 described above is similar to the structure of switch 34, shown in Fig. l; the switch 34 shown in Fig. 1 corresponds tothe switch i inodel 14 time clock produced by Stromberg Electric Company and mentioned previously in this description. n In switch 34 of Fig. l, the cams are arranged to cause the contacts46 and 48 to be separated about two seconds out of every minute. In switch 64, Fig. 3 and Fig. 4, the cams are arranged to cause the` contacts 46 and 48 to be enga'gedon' the order of fftyQeight seconds out of every minute. Switch 64 includes substantially the same structure as switch 34 to produce this result. The main difference is that cam support 36 in the switch 64 is assembled on the shaft of motor 56 oppositely to the cam support 36 of switch 34. In other words, if the cam support 36 of switch 34 is disassembled from the motor shaft and then is reassembled on the motor shaft so that the positions of cam discs 38 and 39 are interchanged, the resulting arrangement would be essentially that of the switch 64. Additionally, the direction of rotation of motor 56 of switch 64 is made opposite to that of motor 56 of switch 34. Additionally, while the ends of the contact arms 42 and 44 of switch 34 are bent to define a right angle, the corresponding ends of the contact arms 42 and 44 of switch 64 are bent to define an angle other than a right angle for the reason given below.

Because the disc cams 38 and 39 are substantially identical, both being formed from circular discs having a notch for permitting a rapid inward movement of the contact arms 42 and 44 under the bias of springs 66 and 68 and a smooth outward movement of the contact arms the total result is that the order in which the contacts are permitted to move inwardly is reversed. For example, for the direction of rotation shown in Fig. 3 the contact arm 42 has been permitted to move inwardly dropping into the notch of the disc cam 39 whereas the contact arm 44 is still maintained in raised position and is just about to drop into the notch in the cam 38. Before modification it was the contact arm 44 that moved inwardly first followed by the contact arm 42. In the switch 34 as shown in Fig. 1 the contacts 46 and 48 are supported on portions of the contact arms 42 and 44 that are bent to project perpendicularly to the contact arm. When both of the contact arms 42 and 44 in the periodic switch 34 of Fig. 1 are resting on the circular portions of the disc cams 38 and 39 the contacts 46 and 48 are spaced apart.

In the modified switch 64 shown in Figs. 3 and 4 the con tact arms 42 and 44 have been bent so that the contacts 46 and 48 are in engagement when the contact arm 42 is bearing against the circular periphery of the disc cam 39 and contact arm 44 is in a raised position above periphery of disc cam 38, as shown in Fig. 4 for a period of from 55 to 58 seconds. The contacts 46 and 48 in the modified switch 64 do not separate until the disc cam 39 rotates to present the notched interruption in its periphery to the arm 42. Since the disc cam 39 presents its notch interruption to the contact arm 42 before the disc cam 38 presents its interruption to the contact arm 44 the two contact arms 42 and 44 separate momentarily until the contact arm 44 moves into the notched interruption in the periphery of the disc cam 38. During the portion of the cycle that the contact arm 42 engages the circular periphery of the disc cam 39 contact arm 44 is supported out of engagement with the disc cam 38 as may be seen in Fig. 4. This insures good continuous contact be tween the two contacts 46 and 48 during that fraction of the cycle. For substantially an entire revolution the contacts 46 and 48 are engaged as shown in Fig. 4.

The relative angular positioning of the disc cams 38 and 39 determine the fraction of a cycle during which the contacts 46 and 48 are disengaged. The time during which the contacts are disengaged is based upon the result of experiments for determining, the critical period for causing the armature to vibrate by manually strikingv the casing of the time clock. It is not necessary to be eognizant of this critical period where there is'no yconcern over the' average 'currentllowing through the solenoid coil 16. In that case the encrgization of the coil 16 need only be interrupted lon'genough to permit the armature to be completely retracted by the spring 26. Itl can then be immediately reenergized. With this mode of operation the possibility that anyone can successfully tamper with the clock is reduced to a minimum. 4

The modified circuit of Fig. 2- eliminates the rectifier 54 shown in Fig. l. Instead, the solenoid coil iswound for A. C. operation with attention given to modifications in the core and frame structure of the solenoid for minimum eddy current losses and the like.

ln operation the armature 22 associated with the solenoid coil 16 is retained in abutting relationship with the frame of the solenoid for substantially the entire cycle of the periodic switch 64. During a small fraction of the cycle the coil 16 is deenergized permitting the armature 22 to be withdrawn by the spring 26 for the purpose of actuating the mechanism of the time clock. An ancillary result of this arrangement is that the additional heat generated in the solenoid due to the increased average current flow through the coil 16 is of particular advantage where the time clock is used in low temperature environment. Grdinarily in low temperature environment an auxiliary heater is necessary for proper operation of the time clock. However, the additional heating due to the increased current through the solenoid coil 16 makes the need for an auxiliary heater unnecessary.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may b practiced otherwise than as specifically described.

I claim:

l. In combination with a time clock of the type having an armature, a solenoid for actuating said armature, an electric circuit for energizing said solenoid and a periodic switch in said circuit, said periodic switch including a pair of contacts for opening said circuit to deenergize said solenoid and for closing said circuit to energize said solenoid, the improvement comprising; means in said periodic switch for positively closing said contacts for a time extending from the beginning of a predetermined period to just prior to the end of the period and for positively opening said contacts for the remainder of the period whereby said armature is actuated for substantially all of the predeter mined period.

2. A time clock as defined in claim 1 wherein said means includes cam means.

3. A time clock as defined in claim 2 wherein said switch includes a pair of parallel reciprocative members for supporting said contacts, and said cam means includes a pair of disc cams, one for each of said members.

4. A time clock comprising an armature movable to a first position and second position, a spring biasing said armature to said first position, a solenoid for actuating said armature to said second position, an electric circuit for energizing said solenoid, a periodic switch in said circuit having a pair of parallel reciprocative members, a contact supported by each member for opening said circuit to deenergize said solenoid and for closing said circuit to energize said solenoid, a pair of disc cams, one for each of said members, biasing means for each of said members to bias said members against the respective disc cams, each of said cams being substantially circular and formed with a brief interruption, the interruptions being staggered whereby said contacts are normally engaged, but are separated during the time interval required for an angular movement of the disc cams equal to the angular staggering of the interruptions.

5. The time clock defined in claim 4 wherein the interruptions in the cams are slightly staggered to permit a short break and a long make.

6. A method of operating a time clock through periodic, substantially instantaneous, movement of a mass between 4two limits, said method comprising the steps of continuously applying a first force to normally urge the mass in one direction toward one limit of its movement and to restrain the mass at the one limit of its movement, periodically 'applying a second force to the mass exceeding the rst force plus any manual force that may be applied for purposes of tampering, said second force urging the mass in the opposite direction against the influence of said first force for moving the mass substantially instantaneously to the other limit of its movement and to restrain the mass 8 at the other limit of its movement, the length of timeof application of said second force being on the order of 58 seconds out of every 60 seconds whereby extraneous force applied for purposes of tampering will not cause the mass to move. l

References Cited in the le of this patent i UNITED STATES PATENTS 2,995,683 Watkins et a1. V. oct. 12, 1937 2,239,060 Sloan Apr. 22, 1941 FOREIGN PATENTS i Great Britain Oct. 7, 1948

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