Fail-safe block control system for driverless vehicles

Driverless vehicles move in one direction along a path divided into blocks. Movement command signals are radiated from plural elongated radiators per block, arranged end-to-end, the last in each block a departure radiator wholly within the block. A receiver in each vehicle comprises a memory element established in active condition by a momentary "clear" signal and maintained in active condition by a continuous succession of movement command signals. A departure radiator emits no movement command signals while the block directly ahead of it is occupied, but it emits a "clear" signal and continuous movement command signals when that block is safe for entry. Only departure radiators emit "clear" signals; hence, a vehicle which slides into an occupied block cannot continue moving in that block.

This invention relates to systems wherein driverless vehicles move in one 
direction along a track or path that is lengthwise divided into blocks, 
each block intended to be occupied by only one vehicle at a time, and 
wherein elongated radiators that extend lengthwise along each block, in 
end-to-end relation to one another, radiate signals by which the movements 
of the vehicles are controlled; and the invention is more particularly 
concerned with means in such a system for assuring that in the event a 
vehicle, through some failure, enters an occupied block, such vehicle will 
be unable to progress any substantial distance into that block. 
The driverless vehicle control system of the present invention is similar 
in many respects to the one disclosed in U.S. Pat. No. 3,848,836, to 
Wallgard et al. In that system, as in the one herein described, an 
elongated radiating means extends the full length of a path along which 
vehicles move in one direction. Signals that are detected by the vehicles 
and utilized for their control are radiated from the radiating means. 
The path along which the vehicles move may be defined by tracks on which 
the vehicles ride; or the path may be defined by the radiating means, in 
which case the vehicles may steer themselves automatically in response to 
detection of the signal radiations from it. In either case, the radiating 
means consists of elongated radiators laid end-to-end along the path, each 
radiator comprising a cable length or an elongated antenna loop. Each 
vehicle is responsive only to signals from the radiator nearest it; hence 
the several vehicles along the path can be individually controlled by 
impressing different appropriate signals upon the several radiators. 
The apparatus is so arranged that a vehicle cannot more unless it is 
receiving movement command signals, each of which signifies a speed to be 
maintained. Normally, movement command signals are radiated continuously, 
each signal being repeated for as long as its remains valid; and thus the 
absence of movement command signals signifies movement at zero velocity. 
For purposes of vehicle control, the path is lengthwise divided into 
blocks. Each block has a front end which is defined from the rear end of 
the block next adjacent to it in the direction of vehicle travel by a 
block boundary. As explained in U.S. Pat. No. 3,848,836, vehicle detectors 
in the path, located at or near the block boundaries, produce outputs when 
a vehicle enters a block and leaves it. These outputs are employed to 
control vehicle movements in such a manner that the presence of a vehicle 
in a block sets up a condition which is intended to prevent a following 
vehicle from entering that block as long as it is occupied. 
For purposes of block control, there are plural radiators in each block. 
The radiator in the front end portion of each block is a departure 
radiator that serves for control of vehicle movements across its adjacent 
block boundary. 
Whenever a block is occupied, the departure radiator in the block directly 
behind it is prevented from radiating movement command signals, so that a 
vehicle adjacent to that departure radiator is commanded to stop before it 
can move across the adjacent block boundary and into the occupied block. 
In the known systems, a departure radiator is caused to resume radiation 
of movement command signals as soon as the block ahead of it is vacated, 
and a vehicle that has been stopped alongside the departure radiator is 
thereby enabled to resume its motion and proceed into the newly-vacated 
block. 
With such known systems it can happen that a vehicle moving along a 
departure radiator towards an occupied block fails to stop before reaching 
the adjacent block boundary, owing to defective brakes, sliding or the 
like. As it enters the occupied block, the vehicle begins to receive 
movement command signals intended for the vehicle already in that block; 
and if it responds to those signals it can move through the block and 
collide with the vehicle ahead of it. 
In general, the object of the present invention is to eliminate the risk of 
collision in a situation such as has just been described. 
Stated more specifically, it is the object of this invention to provide an 
improved system of the type wherein driverless vehicles move in response 
to radiated movement command signals that denote speeds to be maintained, 
and wherein the absence of such movement command signals denotes zero 
speed, said system being improved in that a vehicle which for any reason 
moves completely through a block control zone within which it is required 
to stop, and which thereby crosses a block boundary into a block that it 
is not authorized to enter, is prevented from continuing to move in the 
unauthorized block, even though it is receiving movement command signals 
intended for a vehicle authorized to be in that block. 
Those skilled in the art will appreciate that the term "block" is used 
wherein to denote any defined zone along a vehicle path, which zone is 
intended to be entered by a vehicle only if conditions prescribed for such 
entry have been fulfilled. In that sense, the entry to a switch can be 
regarded as a block, inasmuch as the control system should cause a vehicle 
to stop at a safe distance ahead of the switch if it is not correctly set 
for the vehicle, and should cause the vehicle to proceed through the 
switch if the switch is set correctly. 
With the foregoing in mind, it can also be said that it is a general object 
of this invention to provide a block control system for driverless 
vehicles that is fail-safe, in that if a vehicle for any reason enters a 
block when the prescribed conditions for its entry into that block have 
not been satisfied, the vehicle is prevented from moving any further into 
that block unless and until it receives a special signal which is 
transmitted to it only when the resumption of its forward movement is 
known to be safe. 
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 specific apparatus 
disclosed herein without departing from the essentials of the invention 
set forth in the appended claims.

Referring now to the accompanying drawings, the numeral 1 designates a 
transmitting unit for generating signals S.sub.o which signify movement 
commands to be issued to driverless vehicles. Through a connection 5, the 
transmitter 1 impresses the signals S.sub.o upon a radiator 2 that extends 
along a path (not shown) to which the vehicles are confined and along 
which they move in one direction. In the following explanation, it will be 
understood that the radiator 2 is a departure radiator which is located 
wholly within a block, and nearest the front boundary of the block, as in 
the above described known radiator arrangements for driverless vehicles. 
It will be understood that movement command signals that signify speed 
demand values are radiated from the radiator 2 only at times when the 
block immediately ahead of it in the direction of the vehicle travel is in 
a condition safe for entry of a vehicle into it. 
Each vehicle carries a receiver, designated generally by 3, which receives 
the movement command signals S.sub.o radiated from the radiator nearest 
which the vehicle is located. The receiver converts those signals into 
control signals S.sub.m which are fed to a control instrumentality 4 in 
the vehicle and which, in effect, constitute instructions to the control 
instrumentality by which the latter, in turn, causes the vehicle and its 
equipment to execute the various operations denoted by the radiated 
signals. It will be understood that certain of the command signals S.sub.o 
may designate vehicle functions such as operation of doors, lights and the 
like, but in the following description attention will be centered on those 
of the various possible signals S.sub.o that signify vehicle speed. 
In the system of this invention the receiver 3 comprises a memory element 6 
which controls a signal gating element 7. The memory element has two 
conditions, active and inactive. When the memory element is in its active 
condition, it causes the gating element 7 to pass control signals S.sub.m 
to the control instrumentality 4; when in its inactive condition it causes 
the gate 7 to prevent control signals from reaching the control 
instrumentality. The memory element is established in its active condition 
by a "clear" signal S.sub.k which can be transmitted only by the 
transmitter 1, that is, by a departure radiator. Once a "clear" signal is 
received, the memory element remains in its active condition only as long 
as it continues to receive movement command signals substantially 
continuously. Upon any substantial interruption in movement command 
signals, the memory element reverts to its inactive condition. 
At the beginning of operation of a vehicle, a special starting signal is 
applied to its receiver to establish its memory element 6 in the active 
condition. The vehicle then moves along the path as long as it 
continuously receives movement command signals S.sub.o from the several 
radiators along the path, its speed at any given time being controlled by 
the movement command signals which it is then receiving. If the vehicle 
now moves along a departure radiator just ahead of a block occupied by 
another vehicle, that departure radiator will not be radiating movement 
command signals, and because of the absence of such signals the memory 
element 6 will assume its inactive condition and the vehicle will come to 
a stop. When conditions in the block ahead are such that the vehicle can 
safely proceed into it, the departure radiator 2 emits a "clear" signals 
S.sub.k and also resumes emission of movement command signal S.sub.o. In 
response to the "clear" signal, the memory element 6 returns to its active 
condition and the movement command signals are effective to cause the 
vehicle to move at the speed they signify. 
If the vehicle, instead of stopping while still adjacent to the departure 
radiator, had slid across the block boundary and into the occupied block, 
the movement command signals emitted by radiators in that occupied block 
would not have affected the control instrumentality 4 of the vehicle, 
owing to the inactive condition of its memory element 6 established during 
the time that it was moving along the departure radiator and receiving no 
movement command signals. In that case the vehicle would remain stopped 
until its memory element 6 was placed in the active condition by a special 
starting signal, which could be issued by manually controlled means; and 
of course the starting signal would not be issued to the vehicle unless 
there was assurance that resumption of its forward motion would be safe. 
Referring now to FIG. 2, the receiver 3 in each vehicle receives its inputs 
from a receiving antenna 9. If the signals are emitted as electromagnetic 
radiations, the antenna 9 can be a more or less conventional loop or the 
like. If each radiator comprises a conductor in which the signals are 
manifested as pulsed currents and are radiated in the sense that they can 
be detected by contact with the conductor at any point along it, then the 
antenna 9 can comprise a trolley or the like that has sliding contact with 
the radiator. The receiver 3 comprises an amplifier 10, a detector 11, a 
series-parallel converter 12 and memory-gate unit 13 which corresponds in 
function to the memory element 6 and signal gating element 7 of FIG. 1. 
The output of the memory-gate unit 13 is fed to the control 
instrumentality 4 of the vehicle. 
The movement command signals S.sub.o may be emitted as binary coded 
signals, each appearing as a series of tones of different frequencies, 
each frequency having a binary signification. These tone frequencies are 
detected in the receiving antenna 9, and after being amplified by the 
amplifier 10, they are converted, in the detector 11, to binary signals in 
series form. Through parity control and/or control of length of characters 
and pauses between them, assurance is had that the binary signals are 
correctly received. In the series-parallel converter 12, to which the 
output of the detector is fed, the binary signals are converted from 
series to parallel form so that they can be decoded and converted to 
analogous demand values to which the control instrumentalities 4 responds. 
FIG. 3 illustrates in more detail the memory and gate instrumentalities of 
the receiver in an embodiment comprising relays. The several relays 14-18, 
all of which are normally open, have their windings so connected with the 
series-parallel converter 12 that they are respectively energized in 
accordance with the binary signal "word" appearing at that converter. The 
relay 14 is energized and closed when the "clear" signal S.sub.k is 
received. That signal can be continuously radiated by a departure radiator 
as long as the requisite conditions in the block head of it are fulfilled. 
Relay 15, which has its contacts connected in series with the contacts of 
relay 14, is energized whenever a received control command signal S.sub.o 
denotes a command for the vehicle to move along the track. For purposes of 
illustration it is assumed that the vehicle can move forward at any one of 
three different speeds, denoted by V1, V2 and V3, and therefore a movement 
command signal represents a demand value for movement at V1, V2 or V3. 
Relay 16 is energized in response to a V1 demand value signal, relay 17 is 
energized along with relay 16 in response to a V2 demand value signal, and 
relay 18 responds to V3, along with relays 16 and 17. It is to be observed 
that relay 15 is energized in response to any one of the demand value 
signals V1, V2, V3. A double pole relay 19 performs essentially the same 
function as the memory element 6 of FIG. 1, and it can be regarded as a 
memory relay. As the description proceeds, it will also be apparent that 
relay 19 cooperates with relay 15 to perform the function of the signal 
gating element 7 in FIG. 2. 
Let it be assumed that the vehicle is adjacent to a departure radiator and 
that the block immediately in front of it is occupied, so that neither 
movement command signals nor a "clear" signal is received. All of the 
relays will be open. When the block ahead assumes a condition such that 
the vehicle can safely enter it, the vehicle receives both a "clear" 
signal S.sub.k and a speed demand value signal S.sub.o from its adjacent 
departure radiator, and therefore both of the relays 14 and 15 are 
energized. Through their contacts, which are connected in series, relays 
14 and 15 complete a circuit from a positive energizing terminal 20 to the 
winding of memory relay 19, to thus close the contacts 21 and 22 of the 
memory relay and establish the same in its active condition. The contact 
21 of the memory relay, which is connected in series with the contact of 
relay 15, completes a self-holding circuit for the winding of the memory 
relay, so that the memory relay remains in its active condition so long as 
movement command signals that signify speed demand values are being 
received substantially continuously. The other contact 22 of the memory 
relay completes circuits from the energizing terminal 20 to the V1, V2 and 
V3 inputs of the control instrumentality, through the respective 
contactors of the demand value relays 16, 17 and 18. The contactors of 
relays 16, 17 and 18 are connected in series with one another and with the 
memory relay contactor 22. 
It will be apparent that if the vehicle comes alongside a departure 
radiator which is not emitting movement command signals that denote speed 
demand values, the relay 15 will open, breaking the holding circuit for 
memory relay 19 and causing the latter to open, that is, to assume its 
inactive condition. As long as the memory relay remains in its inactive 
condition no inputs can be fed to the control instrumentality input 
terminals V1, V2 and V3, owing to the open circuit at memory relay contact 
22, which breaks the connection between energizing pole 20 and the 
contacts of the several speed demand value relays 16, 17, 18. Thus, even 
if the vehicle slides beyond the departure radiator and across the block 
boundary into the occupied block, movement command signals S.sub.o emitted 
from radiators in the occupied block will not evoke a response in the 
vehicle apparatus. It will be apparent that in such a case the memory 
relay can be returned to its active condition by momentarily closing the 
relay 14, as with a special signal, at the same time that movement command 
signals S.sub.o are transmitted to the vehicle to close the relay 15. 
It should be mentioned that the memory relay 19 ought to have a 
predetermined release delay time T, so that it will not assume its 
inactive condition in case movement command signals are not received for a 
brief interval by reason of interference or the like. 
FIG. 4 illustrates a functional analogue of that part of the circuit of 
FIG. 3 that comprises relays 14, 15 and 19. In FIG. 4, an AND-gate 23 has 
two inputs, one for "clear" signals S.sub.k, the other for movement 
command signals that encode speed demand values V1, V2, V3. The output of 
the AND-gate 23 serves as the input to an OR-gate, which is in turn 
connected with a monostable flip-flop 25 that has a decay time of T. There 
is a feed-back loop from the output of the flip-flop 25 to one input of a 
second AND-gate 26, the other input of which receives movement command 
signals V1, V2, V3. It will be apparent that the flip-flop 25 is 
established in its active condition by a "clear" signal issued 
substantially concurrently with movement commands V1, V2, V3 and is 
maintained in its active condition as long as there is a substantially 
constant sequence of movement command signals. While the flip-flop remains 
in its active condition, movement commands can be impressed upon the 
control instrumentality 4; but if movement command signals are not 
received during an interval longer than the decay time T, the flip-flop 
reverts to its inactive condition in which it prevents transfer of demand 
value signals to the control instrumentality. 
In the preceding description it has been assumed that a vehicle enters an 
already occupied block by reason of a defective braking system or poor 
braking conditions, and that it has received a zero speed signal (i.e. 
absence of movement command signals) before crossing the boundary of the 
occupied block, and that it is responding to the zero speed signal to the 
extent permitted by circumstances. However, other conditions may cause a 
vehicle to cross a boundary into an occupied block. For example, a zero 
speed signal may have been issued and may have been received at the 
vehicle, but because of some failure in the vehicle control system the 
vehicle may proceed toward the boundary of the occupied block at a speed 
other than the commanded zero speed. In such a case the speed of the 
vehicle might be so high that a normal braking action could not reduce it 
to zero before the vehicle crossed the boundary into the occupied block. 
FIG. 5 illustrates a modified embodiment of the present invention whereby 
emergency braking occurs, to avoid the possibility of a collision, in the 
event a vehicle enters an occupied block. For the most part, the circuit 
of FIG. 5 is identical with that of FIG. 3, as denoted by like reference 
characters applied to like parts in the two circuit diagrams. It is to be 
observed that emergency braking should take place only when there is 
actual danger of a collision, to avoid the wear and tear on the equipment 
that emergency braking often involves. In the circuit of FIG. 5, it is 
assumed that the emergency braking device is arranged to fail safe, in 
that emergency braking occurs automatically in the absence of a brake 
inhibiting input to the emergency braking device. 
The circuit of FIG. 5 includes a normally open relay 28 which has no 
counterpart in FIG. 3 and which remains energized as long as control 
command signals are correctly received. As compared with FIG. 3, the 
memory relay 19 of the FIG. 5 circuit includes an additional normally open 
contractor 29 which is in series with the contactor of the relay 28, and 
the speed demand value relay 15 is a double pole relay, having a second 
contactor terminal 30. 
Through the contactor 29 of the memory relay 19 and the contactor of relay 
28, a circuit is completed by which current can flow from the positive 
terminal 20 to the emergency braking device, to inhibit emergency braking, 
as long as the memory relay 19 remains energized and control command 
signals are being correctly received to energize relay 28. The second 
contactor terminal 30 of relay 15 is connected in a circuit with terminal 
pole 20 that is in series with the contactor of relay 28 and in parallel 
with the contactor 29 of memory relay 19. 
It will be apparent that the brake inhibiting circuit is opened, to permit 
emergency brake actuation, whenever control command signals are not being 
correctly received so that relay 28 is de-energized. If the memory relay 
19 is de-energized, the branch of the brake inhibiting circuit that 
comprises contactor 29 of the memory will be opened; but as long as no 
control signals that denote speed demand values are received, brake 
inhibiting current will flow through the contractor terminal 30 of relay 
15 and the other branch of the brake inhibiting circuit. If, now, the 
vehicle slides across a boundary into a block occupied by another vehicle, 
the memory relay 19 will of course remain unenergized, but the relay 15 
will be energized in response to the signals denoting speed demand values 
that are being transmitted to said other vehicle. Since both branches of 
the brake inhibiting circuit will thus be broken, the emergency braking 
system will automatically go into action and stop the vehicle. 
From the foregoing description taken with the accompanying drawings it will 
be apparent that this invention provides a fail-safe control system for 
driverless vehicles whereby a vehicle will normally be stopped before it 
crosses a block boundary into a block occupied by another vehicle, and 
whereby it will be prevented from responding to movement command signals 
transmitted to said other vehicle in the event it should for some reason 
slide across the boundary of that block. 
Those skilled in the art will appreciate that the invention can be embodied 
in forms other than as herein disclosed for purposes of illustration.