Hoven, Johan Bertil (Jonkiping, SW)
Wallgard, Gunnar Alexius (Huskvarna, SW)
Svensson, Bo Herman Thorwald (Huskvarna, SW)

05/296085

05/14/1974

10/10/1972

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Saab-Scania Aktiebolag (Linkaping, SW)

340/825.640

340/825.680, 340/825.650, 180/168

B61L7/08; B61L17/00; G05D1/02; G08C19/28; G08C25/00; B61L7/00; G08C19/16; H04Q9/14

340/164R,167R,167A

Pitts, Harold I.

1. A method of remote control wherein transmitted control commands are in the form of groups of successive binary data pulses, each group signifying a discrete command and every group containing the same number of data pulses, and wherein the time required for transmission of each command is the same as for all others and spans a predetermined number of successive periods of equal duration, during each of which a data pulse is normally transmitted, said method being characterized by:

2. each received data pulse has a duration which corresponds, within predetermined limits, to the time required for generation of a predetermined number of clock pulses, and

3. The method of claim 1, further characterized by:

4. The method of claim 1, further characterized by:

5. The method of claim 1, further characterized by:

6. In remote control apparatus wherein control commands are transmitted and received in the form of binary data pulses, every control command comprising the same number of data pulses as every other, and every data pulse of a control command normally having at least a predetermined pulse duration and being normally defined from the next succeeding data pulse by a pause of not in excess of a predetermined pause duration, means for preventing control commands that are received in corrupted form from being utilized to effect responses, said means comprising:

7. a control input connected with said means for producing a control signal and whereby the counter means is caused to count when the control signal has said one signification and is reset to zero promptly upon said control signal having said other signification,

8. a counting input connected with the clock oscillator for counting clock pulses, and

9. an output upon which an "accept bit" pulse signal appears when a number of clock pulses corresponding to said predetermined pulse duration has been counted;

10. The remote control apparatus of claim 5, further characterized by:

11. a counting input connected with the clock oscillator, for counting clock pulses,

12. a control input connected with said means for producing a control signal and whereby the pause duration counter means is caused to count clock pulses when the control signal has said other signification and is reset to zero promptly upon said control signal having said one signification, and

13. an output upon which an "overlength pause" pulse signal appears when the pause duration counter means has counted a number of clock pulses which is in excess of that corresponding to said predetermined pause duration; and

14. The remote control apparatus of claim 5 wherein the last data pulse of every control command has a longer predetermined duration than the other data pulses thereof, further characterized by:

15. The remote control apparatus of claim 6, further characterized by:

16. having a counting input connected with the output of the second counter means to receive and count "accept command" pulse signals therefrom,

17. having a control input upon which it can receive pulse signals, by each of which it is reset to zero, and

18. having an output upon which it imposes an output signal when it has counted a predetermined number of "accept command" pulse signals;

19. The remote control apparatus of claim 7, further characterized by:

20. having a counting input connected with the output of the second counter means to receive and count "accept command" pulse signals therefrom,

21. having a control input upon which it can receive pulse signals, by each of which it is set to zero, and

22. having an output upon which it imposes an output signal when it has counted a predetermined number of "accept command" pulse signals;

BACKGROUND OF THE INVENTION

This invention relates generally to remote control systems of the type wherein control commands are transmitted and received in the form of groups of successive binary signals or bits, each group containing the same number of bits as all others; and the invention is more particularly concerned with a method and means for insuring that only uncorrupted control commands will be utilized for effecting responses of the controlled apparatus.

While the present invention is obviously applicable to control systems for many and widely varying types of machines and apparatus, it will facilitate understanding of the invention to consider it in relation to one specific and rather typical type of control system.

It has been proposed to cause a trackless automotive vehicle to be controlled by means of a cable laid along a road. A current at a carrier frequency is impressed upon the cable, and the vehicle carries a pair of detector coils that are employed as sensors for correcting departures of the vehicle from centering on the cable, the vehicle steering mechanism being responsive to any differences in the voltage induced in the respective coils. Insofar as the coils are utilized to sense steering deviations, their performance is relatively independent of the carrier frequency, hence alterations of the carrier frequency can be employed for transmission of commands for the control of other functions of the vehicle, such as regulation of its speed, operation of its lighting and heating system, and opening and closing of its doors.

Various systems are known for encoding, transmitting and decoding control commands in a system like that just described, but the one with which the present invention is concerned, and which has perhaps the widest application, encodes and transmits each control command in the form of a sequence of binary bit pulses, and momentarily modifies the carrier in accordance with the bit pulse being transmitted. For example, the carrier has a normal "no information" frequency, and it is momentarily raised to a predetermined higher frequency for transmission of a "one" bit, and is momentarily altered to a lower predetermined frequency for a "zero" bit.

Each control command is signified by a "telegram" (which could also be considered a word or frame) consisting of a succession of bits; and normally each different control command contains the same number of bits (say, four) as every other one.

For reliable control it is of course essential that the controlled apparatus respond only to uncorrupted control commands. Since noise and interference are ever-present possibilities, various expedients are utilized to afford control security. Several of these are described in "Remote control of radio communication systems" by J. Baguley, published in Electronic Engineering, Sept. and Oct., 1968. Many of these rely on redundancy, that is, each control command is continuously repeated until a different control command is issued, so that transmission consists of a continuous bit stream, and individual words or telegrams are defined from one another within the stream as by means of a framing code at the beginning or end of each telegram or a framing pulse consisting of a unique modulation of the carrier. Where each particular telegram is repeated several successive times, successively received telegrams may be compared, to be utilized or discarded on a majority vote principle. Also employed as an expedient for control security is synchronization of bits and/or complete telegrams to a frequency defined by a separate pilot channel or by a clock pulse oscillator that is controlled by the initiation of each bit pulse or telegram.

Obviously two or more of these several expedients for error prevention can be used in combination in a system and in fact most control systems of the general type here under consideration incorporate a combination of such security expedients.

SUMMARY OF THE INVENTION

The present invention has for its object the provision of a method and means for affording control security in a control system of the character described, whereby control commands received in corrupted form are in effect discarded to prevent the controlled apparatus from responding to them; and more specifically it is an object of this invention to provide such a control security method and means which can be embodied in equipment that is simple, inexpensive and compatible with commonly employed systems for encoding, transmitting and decoding control commands.

Another and more specific object of this invention is to provide a control security expedient that can be used both in systems wherein each control command is sent only once and in those wherein each control command is sent repetitively until superseded by a different command, and which expedient can be employed in the latter type of system either with or without a feature whereby two successive control commands must be received uncorrupted before being accepted for control purposes.

Another object of the invention is to provide a method and means for affording control security in a remote control system of the character described without interposing any significant delay between receipt of a coded control command and response of the controlled apparatus thereto.

It is also an object of this invention to provide a remote control system of the character described wherein an expedient that is employed for control security is also utilized, in a simple manner and by means of simple apparatus, for telegram framing without requiring complicated or expensive synchronization means.

In general these objects are achieved by so controlling the encoding and transmission of control command telegrams that each telegram is transmitted in the form of binary data pulses sent during an interval spanning a number of uniform-duration periods, the number of such periods being equal to the normal number of bits in the telegram, each data pulse being sent during its period and having a duration equal to a predetermined portion of its period. The duration of each received data pulse is measured by reference to clock pulses generated at a frequency high enough so that several clock pulses occur during each period. For control purposes only those telegrams are utilized in which each received data pulse has a duration substantially equal to said predetermined portion of its period. Preferably the last data pulse of each telegram has a normal duration substantially longer than that of the other data pulses, and this longer duration pulse is utilized not only for purposes of control command authentication but also for telegram framing where control commands are transmitted repeatedly in a continuous bit stream.

With these observations and objectives in mind, the manner in which the invention achieves its purpose will be appreciated from the following description and the accompanying drawings, which exemplify the invention, it being understood that changes may be made in the precise method and means of practicing the invention and in the specific apparatus disclosed herein without departing from the essentials of the invention set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWING

The accompanying drawings illustrate one complete example of an embodiment of the invention constructed according to the best mode so far devised for the practical application of the principles thereof, and in which:

FIG. 1 is a generalized block diagram of a control system embodying the principles of the present invention;

FIG 2 is a block diagram illustrating in more specific detail portions of the apparatus illustrated in FIG 1; and

FIG. 3 is a pulse-time diagram showing the relationship to one another of the various signals produced by the apparatus of FIG. 2, where a sequence of received telegrams is as indicated in the top line of FIG. 3, time is plotted horizontally, and the signal identifications on the lines correspond to the connection identifications in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now more particularly to the accompanying drawings, the numeral 4 designates generally a control input means, which can be in the nature of a known console having switches, keys or the like, by which control inputs can be delivered to a control system to cause a controlled object 5 to make any selected one of a number of different responses. Inputs to the control input means 4 are fed into transmitting apparatus which is designated generally by 6 and which comprises an encoding unit 7 that translates such inputs into binary code, a parallel-series converter 8 that translates each encoded command into a binary pulse sequence, and a modulator 9 that modulates a carrier for transmission of the pulse sequence.

For simplicity of illustration it is assumed that no more than sixteen different control commands need be available; hence these can be encoded in binary bit arrangements of four bits each, to provide sixteen different combinations of binary "ones" and "zeroes." On this assumption the encoding unit 7 is shown as having four input connections to the parallel-series converter 8. In effect the parallel-series converter scans the encoder and issues successive "one" and "zero" data pulses in accordance with the code information it finds in the encoder.

In this instance, where it is assumed that a carrier must be continuously available for steering control of a vehicle, the carrier altering means 9 is illustrated as a frequency-shift-key (FSK) modulator, whereby a carrier that has a predetermined standby or no-information frequency is altered to a different (e.g. higher) frequency during transmission oof a "one" bit and is altered to another different (e.g. lower) frequency for a "zero" bit. The FSK modulator effects "one" bit modulation whenever a pulse is delivered to it by way of a connection a _s from the converter 8, and effects "zero" modulation in response to an input from the converter through a connection b _s .

It will be understood that where a continuous carrier is not needed, the carrier could be transmitted only during transmission of each bit pulse; or in a wired system the bits could be transmitted in the form of d.c. current pulses issued directly from a suitable converter 8, the modulator 9 being then unnecessary. Those skilled in the art will also appreciate that various expedients for encoding commands and for producing and transmitting pulse signals signifying the coded commands are well known, and that the choice of the particular expedients to be used depends upon the nature of the object to be controlled. The medium by which bit pulses are transmitted can likewise take various forms, depending upon the nature and purposes of the system.

In the present case, where it is assumed that the carrier is continuously transmitted by means of a cable, for remote control of a trackless vehicle, the output of the FSK modulator 9 is applied to that cable by way of a connection 10; and at the controlled apparatus 5 the carrier is detected by coils in inductive relation to the cable, or by other detector means designated by a connection 11 and comprising part of a receiving apparatus 16.

In general, the receiving apparatus 16 is a reflection of the transmitting apparatus, in that the detected signals are fed into an FSK demodulator 12, the output of which is fed into a series-parallel converter 13 through connections a _m and b _m , the former for "one" pulses, the latter for "zero" pulses. At any time that only the basic carrier frequency is being received in the demodulator, the latter of course feeds no signal into the converter.

Cooperating with the converter 13 is a discriminator unit 14 which, in effect, evaluates received telegrams, rejects those found to be corrupted, and accepts for control purposes only those that conform to criteria inherent in the principles of the present invention. The discriminator unit 14 is described in more detail hereinafter.

The converter 13, through four connections with a decoding unit 15, feeds into the latter each received and accepted telegram, and the decoding unit translates the binary language of such telegrams into control inputs suitable for the particular servos and the like that actuate the controllable elements of the controlled apparatus or object 5.

Again, the demodulator 12, the converter 13 and the decoder 15 can be of any of several known types.

In general, the method that is embodied in the discriminator unit 14 depends upon so transmitting each telegram that its transmission spans a predetermined time interval that is divisible into a fixed number of equal periods, during each of which a data bit pulse is transmitted, with the data pulse for each period having a duration that is in a predetermined ratio to the duration of its period. For optimum control security the data pulse in a predetermined one of the periods for each telegram -- preferably the last one -- has a different duration than that of the data pulses for other periods.

In the receiving apparatus, and specifically in the discriminator unit 14, the duration of each received data pulse is measured by comparing it with reference pulses generated by a clock oscillator 24 and counting such reference pulses during the duration of the data pulse. If the data pulse for each period of a telegram is found to have a duration substantially equal to the predetermined portion of its period during which it is required to persist, and the telegram also meets other criteria described below, the entire telegram is forwarded to the decoding unit 15; otherwise the telegram is inhibited from reaching the decoding unit and is thus in effect rejected. For acceptance of a telegram it is also required that no pause between its data pulses shall continue for longer than the time required to generate a predetermined number of reference pulses, and that it shall not consist of other than the predetermined number of correct-duration data pulses. When a telegram has been rejected, it is preferred to require that two successively received telegrams -- which need not necessarily contain the same information -- shall be received in uncorrupted form before being utilized for control purposes. Where the last data bit pulse in each telegram has a longer normal duration than the other pulses of the telegram, such long pulse is preferably used for telegram framing.

A form of apparatus by means of which this method can be practiced is illustrated in FIG. 2.

The series-parallel converter 13 comprises, in general, a binary circuit 18, a shift register 19 and a gate 20, all of which cooperate with elements of the discriminator unit 14.

The binary circuit 18, in addition to forwarding accepted data bit pulses to the shift register 19 as data signals, converts the signals received from the demodulator 12 into a secondary or control binary signal c. The control signal c contains a "one" bit pulse for every received data bit pulse, whether "one" or "zero," and contains a "zero" bit pulse for every pause between data bit pulses; and of course the duration of each "one" or "zero" bit pulse of the control signal is exactly equal to the duration of the bit pulse or pause in the data signal to which it corresponds. It will be evident that the binary circuit 18 can comprise an inverter by which all data signal bits of one signification are converted to the other signification for purposes of producing the control signal c. That control signal is used in measuring the duration of received data pulses and of pauses between them.

The shift register 19 receives each data bit only upon receipt of an "accept bit" command signal d from the discriminator unit. As hereinbefore indicated, such a signal is issued only if the duration of a data pulse is substantially equal to a predetermined portion of the duration of its period. The gate 20 provides for release of a complete telegram stored in the shift register, and for its transfer to the decoding unit 15, provided the discriminator unit 14 has issued to the gate a release signal signifying that the telegram is acceptable.

The discriminator unit 14 cooperates with the clock oscillator 24 and comprises six counters 26-30 and 60, two AND-gates 32 and 33, an OR-gate 34 and a bistable flip-flop 36.

Each of the counters 26, 27 and 28 has a counting input 37 from the clock oscillator 24 and thus counts clock reference pulses.

The counter 26 has a control input 38 from the binary circuit 18 in which it receives the control signal c from the binary circuit and by which it is caused to count clock pulses whenever the c signal is binary "one" and by which it is reset to zero whenever the c signal becomes and remains binary zero for at least a predetermined but very short interval. Thus the counter 26 measures the duration of each received data bit pulse. Counter 26 has three outputs 39, 40 and 41. When it has counted a predetermined number of clock pulses, signifying that a received data bit pulse has a predetermined duration, counter 26 issues from its output 39 an "accept bit" pulse signal d that is fed to the shift register and causes the latter to receive and temporarily store that data bit.

The "accept bit" pulse signal d is simultaneously fed to the counting input 42 of the counter 29, which has a counting capacity equal to the number of bits in a normal complete telegram, and which can thus be regarded as a "bits in telegram" counter. The output 43 of counter 29 is connected with an input of each of the AND-gates 32 and 33. Hence when the number of "accept bit" pulse signals d that have been counted in counter 29 is equal to the number of data bits in a normal telegram (four in this case), that counter issues a pulse signal e to one input of each of the AND-gates 32 and 33. If other prerequisites are satisfied, as described hereinafter, the AND-gate 32, through its output 47, issues an "accept telegram" impulse i which can cooperate with another signal, as explained below, to effect opening of the gate 20.

Still assuming a normal four-bit telegram, each of the first three bits of the telegram should be signified by a data pulse having a duration of, e.g., at least 35 percent of a period (nominally 50 percent of a period); and the pause between any two successive data bit pulses should not exceed, e.g., 75 percent of the duration of a period. However, the fourth bit of each telegram, but only the fourth one, should have a duration equal to at least, e.g., 60 percent of a period (nominally 75 percent). The fourth pulse, by reason of its greater duration than the other three, can be used not only for error control but also for purposes of framing, as will now appear.

The "accept bit" pulse signal d is issued after the pulse duration counter 26 has counted a number of clock pulses signifying (in terms of the foregoing example) 35 percent of a period. If the data pulse signal continues thereafter, then at the time when the counter 26 has counted the number of clock pulses signifying 60 percent of a period, it issues from its output 40 another pulse signal f which is fed to another input of each of the AND-gates 32 and 33. The pulse signal f thus signifies that a data pulse corresponding to the normal fourth bit of a tele-gram has been received.

However, the telegram that is temporarily stored in the shift register is not passed to the decoding unit unless the "fourth bit" pulse signal f has in fact been issued for the fourth bit of an acceptable telegram. As explained above, the e signal output of the "bits in telegram" counter 29 is issued in response to four successive "accept bit" d signals. Since the fourth such d signal appears before the f signal is produced, the e signal pulse begins before the f signal pulse, but the duration of the e signal pulse is long enough (see the e and f lines in FIG. 3) so that a portion of an e signal is fed to the AND-gates 32 and 33 simultaneously with feeding of its corresponding f signal thereto. In response to this fulfillment of the "and" condition, the AND-gate 32, through its output 47, issues an "accept telegram" pulse signal i to the gate 20. The "acceptable telegram" counting apparatus hereinafter described issues a signal the cooperates with the i signal and which is likewise forwarded to the gate 20, to cause the contents of the shift register 19 to be transferred into the decoder 15. Obviously if a data pulse long enough to trigger an f signal is received as other than the fourth bit of a telegram, that f signal will not be attended by an e signal, and the condition of the AND-gate 32 will not be fulfilled.

To utilize the long final data pulse for framing synchronization, the pulse duration counter 26 cooperates with the "bits in telegram" counter 29 through the counter 28. To this end the output 41 of counter 26 is connected with the control input 44 of counter 28. Simultaneously with issuance of the "long bit" pulse signal f, the pulse duration counter 26, through its output 41, issues to counter 28 a brief control pulse, having a duration of about two clock pulses. This causes counter 28 to start counting clock pulses. When it has counted two clock pulses counter 28 issues a zero setting impulse from its output 45 to the zeroing input 46 of the "bits in telegram" counter 29, which is thus reset. The counter 28 is provided to insure that the e signal from counter 29 will persist through the duration of the f signal, to fulfill the "and" condition of gate.

The "pause duration" counter 27 cooperates with the OR-gate 34 and the flip-flop 36 to prevent acceptance of any telegram in which there is a pause between data pulses of more than a predetermined duration. The "pause duration" counter has its control input 59 connected with the c signal output from the binary circuit 18, but that counter responds to the c signal in the opposite sense from the data pulse duration counter 26; that is, the counter 27 counts clock pulses only during pauses between data pulses. When the counter 27 has counted clock pulses in number corresponding to a pause of more than a predetermined duration (in the present illustrative case, more than 75 percent of a period), it issues from its output 54 to the OR-gate 34 an "over-length pause" signal l. In response to the l signal the OR-gate issues a signal m which can have the effect of closing the gate 20 or preventing opening thereof, as explained below.

At this point it will be evident that a system embodying the principles of the present invention allows for some leeway in synchronization. Minor frequency shifts in the clock oscillator or slight discrepancies in data pulse timing will not affect either discrimination or framing.

The counter 30 provides for a requirement that two acceptable telegrams be received before received commands will be transferred to the decoding unit. The "acceptable telegram" counter 30 constitutes a desirable but optional additional feature, made possible by the principles of the present invention.

The counter 30 has its counting input 48 connected with the output 47 of AND-gate 32 and thus counts "accept telegram" i signals. The output 49 of counter 30 is connected with the "one" input 50 of the bistable flip-flop 36; and the "one" output 51 of the flip-flop is in turn connected with an input 53 of gate 20. When the counter 30 has counted two i signal pulses, it issues to the flip-flop a signal j that tends to set the flip-flop in its "one" condition. When a "one" output signal k from the flip-flop is being fed to the with an input 53 of gate 20. an "accept telegram" signal i from the AND-gate 32, the contents of the shift register are allowed to pass from the gate into the decoding unit.

The OR-gate 34 cooperates with other units, as will now be described, to prevent opening of the gate 20 unless two successive uncorrupted telegrams have been received. As explained above, the OR-gate has one input connected with the output 54 of the "pause duration" counter 27, by which the OR-gate receives l signals signifying over-length pauses. The other input to the OR-gate is connected with the output 58 of the AND-gate 33.

As already mentioned, the f signal output 40 of the pulse duration counter 26 has an input connection to the AND-gate 33, and the e signal output 43 of the "bits in telegram" counter 29 also has an input connection to that AND-gate. However, the last mentioned input connection is an inverting one. Hence whenever the AND-gate 33 receives an f signal "last bit" pulse without simultaneously receiving a "fourth digit" e signal from the "bits in telegram" counter 29, it issues a signal n from its output 58 to the OR-gate.

Thus the OR-gate issues an output signal m in response to either an "over-length pause" signal l from the "pause duration" counter 27 or an n signal from the AND-gate 33 signifying a long data pulse that is not the last bit of a telegram. The output 55 of the OR-gate is connected with the control input 57 of the "acceptable telegram" counter 30, and the issuance of an m signal from the OR-gate to that counter resets the counter to zero so that it cannot issue a onesetting j signal to the flip-flop 36 until two subsequent and successive telegrams have been found to be uncorrupted -- i.e., until two successive "accept telegram" i signals have been counted.

The m signals from the OR-gate are also fed to the counter 60, which feeds a zerosetting signal to the zeroing input 56 of the flipflop 36 after it has counted a certain number of m signal pulses -- e.g., two. With the flip-flop thus set to its "zero" condition, the gate 20 is brought to a condition in which there is no input to the decoding unit. The counter 60 prevents unnecessary zero setting of the flip-flop 36 and thus provides for temporarily holding on the gate 20 the last uncorrupted telegram received immediately before a corrupted one. As explained above, the flip-flop is reset to its "one" condition by a j signal from the "accepted telegrams" counter 30, signifying that a subsequent two consecutive telegrams have been accepted.

In summary, a telegram or control command will not be accepted unless it meets these criteria:

The duration of each data pulse, as determined by the counter 26, must be at least equal to a predetermined portion of one of the equal time periods allotted to each telegram;

The last data pulse of the telegram must have a longer predetermined duration, also as determined by the counter 26;

The long data pulse must be the last one in the telegram, as determined by the counter 29;

(Failure to meet any one or more of these criteria prevents transfer of the corrupted telegram from the shift register 19 to the decoding unit 15, by reason of the functioning of AND-gate 32);

No pause between data pulses may exceed a predetermined duration, as determined by the counter 27; and

Two acceptable telegrams must be received in succession, as determined by the counter 30;

(Failure to meet either or both of the last two mentioned criteria inhibits opening of the gate 20 through the functioning, essentially, of OR-gate 34 and the flip-flop 36, in cooperation with the counters just mentioned and AND-gate 33).

From the foregoing description taken with the accompanying drawings it will be apparent that this invention provides, in a remote control system wherein control commands are in the form of telegrams that contain a fixed number of binary bits, a method and means for insuring acceptance for control command purposes of only those received telegrams that are uncorrupted, and for simply and conveniently framing individual telegrams where particular control commands are sent repetitively in a continuous bit stream.

Those skilled in the art will appreciate that the invention can be embodied in forms other than as herein disclosed for purposes of illustration.