US3362013A

US3362013A - Sequential switching device

Info

Publication number: US3362013A
Application number: US360894A
Authority: US
Inventors: Abramson Paul; Richard W Bennett; Jr George R Stilwell
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 1964-04-20
Filing date: 1964-04-20
Publication date: 1968-01-02
Anticipated expiration: 1985-01-02
Also published as: SE325945B; BE662578A; NL6504951A; NL148735B; DE1437699A1; DE1437699B2; GB1073054A; CH429839A

Description

Jan. 2, 1968 P. ABRAMSON ETAL 3,362,013

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United States Patent M 3,362,013 SEQUENTIAL SWHTCHING DEVICE Paul Abramson and Richard W. Bennett, Yorktown Heights, and George R. Stilwell, In, Nyack, N.Y., assignors to International Business Machines Corporation, New York, N.Y., a corporation of New York Filed Apr. 263, 1964, Ser. No. 360,894 8 Claims. (Cl. 340-147) ABSTRACT OF THE DISCLQSURE A sequential switching device capable of sampling a plurality of remote switches to determine their status. A reed relay commutator operating in conjunction with a signal genertaor such that groups of sampling signals are either physically separated before or logically separated after passing through remote switches and the reed relays,

thus, enabling the status of the remote switches to be determined.

bing friction which is incident to any such device causes a variety of problems. First of all, it causes wear of the terminals, which, to some extent, reduces the precision of the instrument and leads to a continuous maintenance problem. The replacement cost of the terminals increases the overall cost of operating such a commutator. Secondly, the friction of the rubbing terminals increases the load on the motor driving the rotating arm. A motor having high torque and using more power is therefore required and the operating cost of the commutator is therefore increased. Another disadvantage is that, since it is extremely difiicult to hermetically seal a rotating arm commutator, such a commutator cannot be used in a contaminated atmosphere because the terminals would become dirty and useless after a short period of time. Also, the commutator cannot be used in an explosive atmosphere because the sparks generated by arcing as the terminals make and break and from friction as the terminals rub against each other could be potentially dangerous. Finally, the impossibility of preventing ordinary dirt from accumulaitng on the terminals even in a non-contaminated atmosphere prevents such a commutator from being used effectively in a dry circuit (i.e., in a circuit having very low voltage and current requirements). In such a circuit, even the slightest dirt on the terminals could prevent the low power signal from setting through.

Problems such as those indicated above can be solved by using hermetically-sealed switching elements rather than rubbing terminals in the commutator. An ideal switching element of this type is a hermetically-sealed reed switch. However, switching devices such as reed switches are not precision elements. Even for high quality reed switches, the minimum and maximum magnetic flux required to initially close the reed and to maintain it closed varies considerably from switch to switch. A commutator using these switches is generally constructed by mounting a magnet on the end of a rotating arm and causing the arm to pass in succession over a group of reed switches. With such a commutator, it is desired that a reed be closed only when the magnet is directly over it. However, the magnetic lines of force generated by the 3,362,013 Patented Jan. 2, 1968 magnet are not confined in a thin band, but in fact radiate over a small area, so that it is possible that a sufficient number of lines of force will link the next reed to be energized to cause this reed to close while the magnet is still over the preceding reed or, in the more likely situation, that sufficient lines of force will link the last reed energized to maintain this reed closed after the magnet has passed on to the next reed. The non-precision nature of the reeds further complicates this problem. A similar problem might arise where electronic pulses were being applied to successively energize relays in a chain, the overlap being due to the fact that there is a time lag between the time that energy is removed from a relay and the time that the contacts of the relay actually open. Therefore, in spite of the superior characteristics of hermetically-sealed elements as the switching elements in a commutator, it has not heretofore been possible to use such elements in a precision commutator due to the nonprecision nature of these elements.

It is therefore an object of this invention to provide an improved sequential switching device.

More specifically, it is an object of this invention to sample and identify a plurality of remote switches in an improved manner.

A primary object of this invention is to sample a plurality of switches using a frictionless reed relay commutator.

A more specific object of this invention is to obtain precision sampling of a plurality of remote switches using non-precision elements.

Another object of this invention is to sample a plu rality of remote switches with a commutator in an explosive atmosphere.

In accordance with these objects, this invention provides a sequential switching device, such as a commutator, which is made up of a plurality of switching elements and a means, for example a rotating arm, for sequentially energizing these switching elements. The novel feature of this invention which allows non-precision switching elements to be used is a means which is operable during the time period that a given switching element is being energized for deactivating the adjacent switching elements, regardless of whether these elements are open or closed at that time. In one embodiment of the invention, this means comes into play at the input to the switching elements and is operative during the time period that a given switching element is to be energized to prevent input signals from being applied to the switching elements which are adjacent to the energized switching element. Therefore, even if one of the adjacent switching elements is energized during that time period, no input signals are applied to it and there are therefore no outputs from it. Stating it another way, even if one of the adjacent switching elements is energized during the wrong time period, it is deactivated and therefore no outputs are derived from it.

In a second embodiment of the invention, the means for preventing an output from a switching element during undesired periods takes the form of a gate in the output circuit of the switching element, which gate is energized only during time periods when an output signal is desired from the element. Therefore, even if the switching element does generate an output signal during undesired periods, this signal is blocked by the gate. Since in either of the embodiments described above the signals applied to the switching elements are effectively divided into two or more groups, the number of switching elements required in the commutator is increased.

The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings.

In the drawings:

FIG. 1 is a schematic diagram of one embodiment of the invention.

FIG. 2 is a schematic diagram of a second embodiment of the invention. 1

FIG. 3A is a timing chart illustrating the minimum and maximum reed closure times permissible with prior art reed commutators.

FIG. 3B is a timing chart illustrating the minimum and maximum reed closure times for the embodiments of the invention shown in FIGS. 1 and 2.

General circuit description, FIG. 1

FIG. 1 shows one embodiment of the precision commutator of this invention being used to multiplex informationas to the location of a plurality of switches which may be positioned at one or more remote stations and to detect the open or closed condition of these switches.

Referring now to FIG. 1, it is seen that an arm having a magnet 12 mounted on the end thereof is rotated in a counter-clockwise direction around a hub 14 past a plurality of coils 21-26. As the magnet 12 rotates past each of the coils 21-26, a dipulse having a generally sine wave shape is induced in the coil. A second arm 30 having a magnet 32 mounted on the end thereof is rotated in a counter-clockwise direction around a hub 34 past a plurality of reed switches 41-48. Reed switches 41-48 are hermetically sealed and are normally open. A reed switch is closed by placing it in a magnetic field of sufiicient energy. Magnet 32 is of suflicient strength so that a reed switch is closed when the magnet is adjacent to it.

Rotating arms 10 and 30 are connected to rotating drive shaft 50 through gear box 52. The gear ratios in gear box 52 are such that arm 11 is rotating at four times the speed of arm 30. Therefore, for each complete revolution of arm 10, arm 30 moves past two reed switches 41-48.

One end of each coil 21-26 is connected to common line 54. One terminal of each reed switch 41-48 is connected through a line 61-68 respectively to an input of OR circuit 70. Output line 72 from OR circuit 70 is the information output from the circuit.

Output line 81 from coil 21 is connected through diodes 91A-91D to one terminal of switches 101A-101D respectively. Output line 82 from coil 22 is connected through diodes 92A-92D to one terminal of switches 102A-102D respectively. Similarly, output line 83 from coil 23 is connected through diodes 93A-93D to one terminal of switches 103A-103D respectively. Switches 101A-103A may, for example, be located at one remote station, switches 101B-103B at a second remote station, and so on. The other terminal of each switch 101A-103A is connected through line 111 to the other terminal of reed switch 41. The other terminal of each switch NIB-103B is connected through line 113 to the other terminal of reed switch 43. Similarly, the other terminal of each switch 101C-103C is connected through line 115 to the other terminal of reed switch 45 and the other terminal of eachswitch 101D-103D is connected through line 117 to the other terminal of reed switch 47.

Output line 84 from coil 24 is connected through

diodes

122 and 124 and

lines

112 and 116 respectively to the other terminal of

reed switches

42 and 46. Output line 85 from coil 25 is connected through

diodes

126 and 128 and

lines

114 and 116 respectively to the other terminal of

reed switches

44 and 46. Finally, output line 86 from coil 26 is connected through diode 130 and line 118 to the other terminal of reed switch 48. All of the diodes shown in FIG. 1 are connected so that only the positive half of the dipulse generated in coils 21-26 is allowed to pass.

Operation of embodiment shown in FIG. 1

In the circuit of FIG. 1, the signals generated in coils 21-23 are applied to sample successive contacts 101-103 at remote stations A-D. The particular remote station which is being sampled at any given time is determined by the position of arm 30 over reed switches 41-48. The outputs from coils 24-26 are used to provide a binary code representation of the particular one of the remote stations being sampled at any given time with the signal from coil 24 being the lowest order digit of this number. The outputs are therefore applied to output line 72 in groups of six possible pulses, the first three of which indicate the closed condition of the switches being sampled, and the last three of which indicate the remote station at which the switches are being sampled. FIGS. 3A and 3B show the sets of six possible pulses which may appear on line 72 when any remote station is sampled.

In an ordinary commutator, there would be only four reed switches, the arm 30 would be rotating at one-fourth the speed of the arm 10, and both the switch status information and the location information for a given remote station would be applied through the same line to a reed switch. Referring to FIG. 3A, it is seen that when this procedure is followed, a reed must be closed for at least the period of time required for the six possible pulses to pass through it. However, the reed must not close before the last pulse of the preceding set has expired or after the beginning of the first pulse of the following set. The tolerance between minimum and maximum reed closure times is therefore very small and highprecision reeds must be used if spurious outputs are to be avoided. Since reeds are inherently non-precision elements, the tolerances indicated by FIG. 3A are extremely difficult to meet and in many applications impossible.

However, by dividing the information relating to each remote station and applying only the switch status information to one reed and only the location information to another reed, the minimum and maximum reed closure times are decreased and increased respectively (reference to FIG. 3B). The minimum and maximum reed closure times shown in FIG. 3B allow rather wide tolerances for the reed which are easy to meet and make a device such as that shown in FIG. 1 both possible and practical.

To briefly describe the operation of the circuit shown in FIG. 1, the first time that magnet 12 is adjacent to coil 21, magnet32 is adjacent to reed 41. The resulting positive pulse on line 81 is therefore passed through diode 91A to sample switch 101A. If this switch is closed, the pulse passes through line 111, now closed reed switch 41, line 61, and OR circuit to output line 72. Magnet 32 remains adjacent to reed 41 as magnet 12 moves past

coils

22 and 23.

Contacts

102A and 103A are in this manner sampled.

As magnet 12 moves adjacent to coil 24, magnet 32 is moved adjacent to reed 42. The signal generated in coil 24 is passed through diode 122, line 112, now closed reed switch 42, line 62, and OR circuit 70 to output line 72. It is quite possible that at this time reed switch 41 is still closed; however, this does not cause an erroneous indication at the output since no input signals are being applied to this reed at this time.

Magnet 12 proceeds past coils 25 and 26. When magnet 12 has completed its cycle so that it is again adjacent to coil 21, magnet 32 has advanced to a position adjacent to reed 43. It remains substantially adjacent to this reed as magnet 12 passes coils 21, 22 and 23. During this period, contacts NIB-103B are sampled in a manner similar to that previously described. It is quite possible that reed 42 will be closed during the early part of this sampling and that reed 44 may close while magnet 12 is still adjacent to 'coil 23; however, since no signals are applied to either

reed

42 or 44 during the period that switches 101B-103B are being sampled, no erroneous indication is received. The circuit proceeds to sample the remaining switches in the circuit of FIG. 1 and to apply the binary location code for each of these switches to output line 72 in a manner similar to that previously described.

Alternate embodiment, FIG. 2

The embodiment of the invention shown in FIG. 2 is quite similar to that shown in FIG. 1 and like elements have been given the same number in both figures to assist in correlating them. One difference between the two figures is that there are now six contacts 101-106 being sampled at each of the remote stations, and the pulses in all six of the coils 21-26 are being used for sampling purposes. A second difference is that all the switches at a given remote station are connected through a single line to one terminal of two reed switches. Therefore, line 111v is connected to one terminal of reed switches 41 and 42, line 113 to one terminal of

reed switches

43 and 44, line 115 to one terminal of

reed switches

45 and 46, and line 117 to one terminal of

reed switches

47 and 48.

Lines

61, 63, 65, and 67 from the other terminal of

reed switches

41, 43, 45, and 47 respectively are commoned and connected as one input to an AND gate 134.

Output lines

62, 64, 66, and 68 from the other terminal of

reed switches

42, 44, 46, and 48 respectively are commoned and connected as one input to AND gate 136.

Output lines

81, 82, and 83 from

coils

21, 22, and 23 respectively are connected through

diodes

141, 142, and 143 respectively and line 150 as the other input to AND gate 134.

Output lines

84, 85, and 86 from

coils

24, 25, and 26 respectively are connected through

diodes

144, 145, and 146 respectively and line 152 to the other input of AND gate 136.

Output lines

154 and 156 from AND gates 134 and 136 respectively are connected as the two inputs to OR gate 158. Output line 160 from OR gate 158 is the circuit output line.

.As with the embodiment of the invention shown in FIG. 1, magnet 12 is initially positioned adjacent to coil 21' and magnet 32 is initially positioned adjacent to reed 41. As magnet 12 rotates

past coils

21, 22, and 23, pulses are applied through

lines

81, 82, and 83 respectively to sample

switches

101A, 102A, and 103A respectively. If the first of these switches is closed, a signal is applied through line 111 to one terminal of reed switches 41 and 42. Since magnet 32 is adjacent to reed switch 41 at this time, the vpulses pass through reed switch 41, and line 61 to one input of AND gate 134. The signals applied to lines 81-83 are also applied through a corresponding diode 141-143 and line 150 to the other input of AND gate 134. The signal applied to line 61 is therefore passed through AND gate 134, line 154, and OR gate 158 to output line 160. Assume, for example, that when the signal is applied to line 83, magnet 32 had moved Sllfi'lciently close to reed switch 42 as to cause this switch to close. If contact 103A had been closed, the resulting signal on line 111 would therefore find both reeds 41 and 42 closed, resulting in the signal being applied to both

lines

61 and 62. The signal on line 61 would be passed to output line 160 in a manner previously described. However, a signal on line 62 is applied to one input of AND gate 136. Since the signal on line 83 is not one of the conditioning inputs to AND gate 136, the spurious signal on line 62 is ineffective to cause an output from the circuit.

By the time magnet 12 is adjacent to coil 24, magnet 32 has been advanced to a position adjacent to reed switch 42. Magnet 32 remains substantially adjacent to reed 42 as magnet 12 rotates past coils 24-26. Switches 104A- 106A are in this manner sampled. During this period, conditioning signals are being applied through diodes 144-146 and line 152 to AND gate 136. Therefore, any signal passing through reed switch 42 to line 62 is passed to output line 160. However, if reed switch 41 should stick so that it does not open immediately after reed switch 42 closes or reed switch 43 should prematurely close, the resulting spurious signals on

line

61 or 63 would be applied to AND gate 134 which is, at this time, not conditioned. These spurious signals would therefore be blocked from appearing on output line 160. The circuit operates in a manner identical to that just described to sample the remaining switches 101-106 shown in FIG. 2.

Referring now to the operation of both FIGS. 1 and 2, it is seen that the energizing of the reed switches 41-48 in the commutator by magnet 32 determines the sequence in which switches at the remote stations are sampled. However, the time period during which an output is derived from a given reed is determined not by the reed energizing circuit but by the reed activating circuit which includes the pulse generator coils 21-26, the sampled switches, the diodes, and lines 111-118 in FIG. 1 and these elements plus diodes 141-146 and AND gates 134 and 136 in FIG. 2. Therefore, even though a reed may be energized during an incorrect time period either due to premature energization or due to a reed remaining closed too long, the reed activating circuit prevents spurious outputs from being derived from a reed during these incorrect time periods.

The main advantage of using the technique shown in FIG. 1 is that it reduces the number of logical components which must be employed at the central station. The advantage of using the embodiment of the invention shown in FIG. 2 is that it reduces the number of wires which are run between the central station and the various remote stations. The technique employed will depend on these and other considerations.

While the embodiments of FIGS. 1 and 2 show the commutators of this invention being used as part of a switch sampling mechanism, and this is one preferred use of such commutators, it is by no means the only way in which these commutators may be used. The teachings of this invention may be employed in any situation where it is desired to obtain a precision commutator while obtaining the benefits inherent in non-precision elements such as reed switches. Again, while reed switches have been shown in the preferred embodiments of the invention, and these switches are energized by rotating a magnet past them, the invention may be practiced with any suitable switching device which is sequentially energized in any suitable fashion. Also, while in FIGS. 1 and 2, each set of pulses has been divided into two groups, the circuits may be easily modified by providing additional reeds to divide each set of pulses into as many groups as is required to achieve the desired tolerances. Finally, the number of pulse generating coils and reeds in the embodiments of FIGS. 1 and !2 has been arbitrarily selected for the purpose of illustrating the invention, and it is to be understood that the number of coils and reeds employed in any application of the invention would depend on the particular design problem presented.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A switching device comprising:

a commutator having mounted thereon a plurality of switching elements, said switching elements being divided into N groups, each switching element being in the same group as the switching element N positions advanced from it;

a plurality of signal generating means, each having an output, said signal generating means being divided into N groups;

commutator energizing means for sequentially energizing said switching elements and said signal generating means, said energizing means energizing one of said groups of signal generating means during the time period in which one of said switching elements is energized, N groups of said signal generating means being energized during the time period in which reed switches, each having an input and an output, divided into two groups with alternate reed switches being in each group;

means for connecting the outputs of each sampled reed switches divided into two groups with alternate reed switches being in each of said groups; means for connecting the output of each sampled switch in a given group of sampled switches to two adjacent one of said switching elements in each group of r ed switches, each of said adjacent reed swit h s switching elements are being energized; and belng 1n dlfiereni groups; connecting means selectively connecting the outputs PP F enirglzlllg means for 9 3 1 from each of said groups of signal generating means glZlng salfl feed svlfltchfi, feed C 111 tud fi t to a different one of said groups of switching elegrouRbemg energlzed fhmng the tune 'penod that ments 10 sampling pulses are being generated on one-half of 2 A switching device comprising: said sampling lines and a reed switch in said second a commutator having mounted thereon a plurality of groupjbemg energlzed, dunng,the Penod that switching elements, said switching elements being di- Sampling pulsFs f apphed to the second half vided into N groups with each switching element of Sald Sampling hnes being in the same group as the switching element N means for @PPlYmg the Samphng pulseis on Said first half positions advanced from of the lines to gate signals passing through reed a plurality of signal generating means, said signal genswatches m Sald first group of sand reed swltches;

crating means being divided into N groups; an f 1 h commutator energizing means for sequentially energizj z ymg m 1mg pulses sald secqnd ing said switch elements and said signal generating O Sal Sal-lip mg gate slgnals passnig means, one of Said groups of said Sig n a1 generating through reed switches in said second group of said means being energized during the time period in 5 2 g g d which one of said switching elements is being ener- 5 z 2 Comprising gized, all of said signal generating means being enera dsecon swlfc mg element each havmg an gized during the time period in which N of said mpu an i Output Switching elements are being energized; signal generating means for producing a first and secmeans for selectively applying the signals from said 0nd slgnali signal generating means to the switching elements in means elierglzm'g Sald first and second switching said commutator; ments m seiquencq; Output means from said commutatorand means operating said signal generating means, said means for applying the signals from each of said groups i ii gq dunng. the Penod of signal generating means gating signals from a difi Sal d swltc i element 18 elier'glzed {and ferent one of said groups of switching elements to Secon Slgnal being P F dunng h said output means period that sald second switching element 1s ener- 3. A circuit for sampling a plurality of switches, each fi glzed; having an input and an output, arranged in a plurality rst Cqnnectmg t for P i Sald first slgnal to of groups and for identifying the group which a sami Sand. first swltchm'g. element; p d Switch is in comprising: swrtc means in said iirst connecting means for intera plurality of p g lines; ruptrng sald connecting means; Pulse generating means for generating pulses on each 40 second conne ctmg mealis for applylpg f Second one of Said Samp1ing1ines nal to the input of said second switchlng element; means for connecting some of said sampling lines to i g gfi gggi g g for pp y g Signals p g l i h of said gi uii i s irfit hzssald Switches m we through said first and second switching elements to a commutator having mounted thereon a plurality of sald Output whereby an output slgnal p duced representing the status of said switch means. 6. A circuit to provide a switch status and identification signal comprising:

a plurality of switching elements each having an outswitch in a group of sampled switches through a put and an input, said elements being divided into wo groups of N elements each; common line to the input of a reed switch in a first Signal generafin means roduci U fi t d d of said groups of reed 1fwitches; d f d 1 set of signals P rs an sewn a fig g gg ggi g 23 gf j jfif i enellgizing means sequent ally energizing said switchin in said commutator, said network supplying a coded e ements first swl tchmg element m the first P f combination of pulses to each reed switch in said groups f finerglzed fonfjwed by fir st swltchnfg other group of rzed switches; element in the second of said groups until all of sald energizing means sequentially energizing a reed switch swltfihmg elements have been energlzed;

in said first group during the time period that sam- Operating means sequentially Operating Said Signal g pling pulses are being applied to the sampling lines g means, Said first Set of Signals being generated connected to switches and then'energizing a reed during thfi time Period in which one Switching switch in said second group during the time period Inent of said first group 0f Switching elements is that sampling pulses are being applied to th remainbeing energized and all of said second set of signals ing sampling lines. being energized during the time period in which one 4. A device for sampling a plurality of switches, each switching element of said second group is being enerhaving an input and an output arranged in a plurality gized; of groups comprising: a plurality of switch means divided into N groups, each a plurality of sampling lines; switch means having an output and an input;

means for generating a plurality of separate sampling a plurality of first connecting means, each of said first pulses each on adifferent sampling line; connecting means applying one signal of said first means for connecting each of said sampling lines to the set of signals to the input of one of said switch means input of one of said switches in each of said groups in each of said N groups of switch means; of switches; a plurality of second connecting means connecting a commutator having mounted thereon a plurality of 7 the outputs of each of said N groups of switch means to the input of a difierent one of said switching elements in said first group of switching elements;

third connecting means for applying said second set of signals to the inputs of said second group of switching elements, said third connecting means providing a binary code signal for each of said switch means;

an output line; and

fourth connecting means connecting the outputs of said switching elements to said output line, whereby said switch status and identification signal is produced on said output line.

7. A circuit to provide a switch status signal comprising:

a switching element, having an output and an input;

signal generating means for producing a signal;

energizing means energizing said switching element; operating means operating said signal generating means, said signal being generated during the time period in which said switching element is energized; switch means having an input and an output;

an AND gate having two inputs and one output;

first connecting means for applying said signal to the input of said switch means;

second connecting means for applying said signal to one of the inputs of said AND gate;

third connecting means connecting the output of said switch means to the input of said switching element; and

fourth connecting means connecting the output of said switching element to the other input of said AND gate, whereby said switch status signal is produced.

8. A circuit for providing a plurality of switch status signals comprising:

a plurality of switching elements, each having an input and an output, said switching elements comprising a first and second group of N elements each;

signal generating means for producing a plurality of signals divided into a first and second set of signals;

energizing means sequentially energizing said switching elements, a first one of said switching elements in said first group being energized followed by a first one of said switching elements in said second group until the N element in said second group is energized;

operating means operating said signal generating means, all of said first set of signals being generated during the time period in which one of said first group of switching elements is energized and all of said second set of signals being generated during the time period in which one of said second group of switching elements is energized;

N groups of switch means, each having an input and an output;

a first and second AND gate, each having a first and second input and an output;

an OR gate having inputs and an output;

first and second connecting means applying each of said signals produced to the input of a diiferent one of said switch means in each group of switch means;

said first connecting means further applying said first set of signals to a first input of said first AND gate, and said second connecting means further applying said second set of signals to a first input of said second AND gate;

third connecting means connecting all of the outputs of each group of switch means to the inputs of corresponding switching elements in each of said first and second groups of switching elements;

fourth connecting means connecting the outputs of said first group of switching elements to the second input of said first AND gate;

fifth connecting means connecting the outputs of said second group of switching elements to the second input of said second AND gate; and

sixth connecting means connecting the outputs of said AN.D gates to the inputs of said OR gate.

References Cited UNITED STATES PATENTS 2,162,170 6/1939 Hicks et al. 340364 2,701,357 2/1955 Newby 340-364 3,105,232 9/ 1963 Boots 340-345 3,174,081 3/1965 Burnett 317-440 3,222,646 12/1965 Hammer 340-482 3,264,529 8/1966 Lowry 317- 3,275,896 9/1966 Deeg 317155.5

THOMAS B. HABECKER, Acting Primary Examiner. NEIL C. READ, Examiner.

A. J. KASPER, Assistant Examiner.