FR2474714A1 - Automatic steering control for driverless vehicle - maintains rotational axis of vehicle at required point along reference horizontal axis - Google Patents

Abstract

The vehicle has a chassis mounted on at least three wheels with an integral drive unit and a transmission coupling the drive to at least one of the wheels. One wheel mounting for one or two of the wheels maintains the latter so that theri geometric axis extends in a given horizontal direction relative to the chassis, while a second mounting for the remaining wheels is pivoted to the chassis and allows the wheels to be positioned so that the vehicle can rotate about a vertical axis intersecting the previous geometric axis under direction of a steering control. At least one measuring wheel monitors the position of the rotational axis and contacts the ground beneath the vehicle. The measuring wheel lies in the same vertical plane as the horizontal axis and is coupled to a signal generator providing a signal representing its rate of rotation. An output signal is obtained from this representing the forwards direction and the velocity of the horizontal axis relative to the ground at a point denoting the required position of the rotational axis, the steering control used to maintain the axis in this position.

Description

 The present invention relates to transport vehicles which it is agreed to call "driverless carriages" and that is to say, to vehicles on wheels which do not travel on rails or the like and which do not require 'a driver. Vehicles and gender have been used more and more for internal transport in workshops, warehouses, etc.

 The driverless trucks currently in use are designed to automatically follow a path or circuit defined by fixed steering elements called "directors". The directors can, for example, be made up of electric cables sunk or buried in the ground or the floor and whose magnetic field actuates a receiver installed on a trolley, or else by optical reflectors cooperating with optical path finders equipped with photocells mounted on the trolley, or by steel strips placed in or on the floor or the floor and which cooperate with electromagnetic detectors mounted on the trolleys. Thus, when the trolley deviates laterally from the defined path by the director, the path finder activates the trolley's steering device in the direction necessary to bring it back on the predetermined path. The carriage can be driven, for example, by means of one or more steering wheels which can be adjusted angularly around a vertical axis, or by means of an individual control of the rotation of two driving wheels. not angularly adjustable having a common geometric axis (differential direction).

 In current systems, it sometimes happens that the carriage, by automatically executing a turn or a change of direction, arrives at a position which deviates from the determined trajectory to such an extent that its detector or its receiver is out of contact or range of fixed or directing steering elements, an accident that can be compared to the derailment of a carriage on rails. This type of accident is particularly likely to occur in slippery areas where the grip of the wheels on the ground or floor is insufficient to prevent them from skating.

 The present invention mainly relates to a device for automatically controlling the rotation or the change of direction of a driverless trolley and mainly aims to eliminate or significantly reduce accidents or incidents of the type of those mentioned above, by means of a device which monitors the angular movement of the carriage relative to the ground or to the floor and which, when it detects that the carriage tends to deviate from the desired path, involves the steering means thereof in order to oppose this deviation.

 A more specific aim of the invention is to make possible the use of a steering system for driverless carriages defining a route or a circuit composed exclusively of straight, parallel and / or intersecting lines, that is that is to say a path which does not include any curved line between the different parts which compose it.

 Another object of the invention is to provide a control device for a driverless carriage which allows the latter to describe a predetermined trajectory or route with satisfactory precision, without the aid of fixed directors.

Other characteristics and advantages of the invention will emerge from the description which follows, given solely by way of nonlimiting example, with reference to the appended drawings, in which
- Figure 1 is a schematic view of a carriage comprising a control unit according to the invention, this control unit being shown in the form of a block diagram
- Figure 2 shows schematically a carriage according to the invention in a number of successive positions, along a path composed of several rectilinear sections
- Figures 3 and 4 each show an alternative embodiment of the carriage of Figure 1;
- Figure 5 is a schematic view of a carriage of a different type from that of Figure 1
- Figure 6 shows a modified form of the carriage of Figure 1; and,
- Figure 7 shows yet another type of trolley equipped with a device according to the invention for controlling its rotational movements.

 The carriage shown in Figure 1 has a chassis) -, of which only the outline has been sketched, chassis which is supported by four wheels 2, 3, 4 and 5. The front wheels 2, 3 have a fixed direction relative to the chassis and a common geometric axis 10. Each of the front wheels 2, 3 is driven by a drive unit 8 or 9, respectively by means of a transmission 6 and 7. Each of the rear wheels4, -5 is supported by a fork 13 , 14 can pivot about a vertical axis 11 and 12 respectively, so that these wheels can freely adapt to changes in direction of the carriage. The chassis is provided respectively at the front and at the rear with a path finder device 15 and 16, device which cooperates with fixed steering means which may, for example, be an electric cable 17 embedded in the floor. The front finder device 15 is designed to operate during the forward movements of the carriage, while the rear finder device 16 is intended to perform the same function while the carriage is reversing. Two measuring wheels 18, 19, which can rotate independently one of the other being in contact with the ground or the floor, are provided between the driving wheels 2, 3, said measuring wheels having a common geometric axis parallel to, and located in the same vertical plane, as the 'geometric axis 10, of the driving wheels 2 and 3. The measuring wheels 18, 19 each drive a generator for producing measurement signals, respectively 20, 21.

 The truck is equipped with a control unit designated in its entirety by the reference 22. This unit comprises an operating signal transmitter E, F, respectively for each of the drive units 8, 9 as well as the electrical equipment necessary for the control of said transmitters.

The signal transmitters E, F each have two respective input terminals, é2 and f1, f2. The presence of a signal at the input terminals el and f1 has the effect that the transmitter E, F respectively transmits the signal forward "to the motor unit 8, 9. Likewise the presence of a signal to the other input terminal e2, f2 causes the transmitter E, F to transmit the signal "backward" respectively to the driving unit 8 or 9. The driving units 8, 9 are designed to rotate their respective wheels 2, 3 to a speed which is a function of the level or the amplitude of the signal transmitted by the transmitter E, F. The control equipment of the transmitters E, F comprises four control units
A, B, C, D, whose input terminals a4, b4, c4, dk are connected to the output terminals k2, k3, k4, k5 of a command unit K designed to make the control units A , B, C, D active, one at a time, by transmitting a signal through the corresponding output terminal. Each of said control units is provided with two output terminals a1, a2; b1, b2; ci, c2; dl, d2, which supply the input terminals el, e2 and T1, f2 with transmitters of operating signals E, F, the combinations of control signals necessary for these transmitters to deliver the signals corresponding to the "advance forward" operations , (control unit A), "backward progression", (control unit B), "clockwise rotation" or "dextrorsum" (control unit C) and "counterclockwise rotation" clockwise "or" sinistrorsum "(control unit D). When, for example, the control unit is activated by a signal from the output terminal k2 of the order unit K, the control unit A produces a signal at its two output terminals a1, a2. Said terminals are respectively connected to the input terminals el, fl of the transmitters of actuation signals E and F, and causes each of said transmitters to supply a "forward" signal to the corresponding motor unit 8 or 9, so that these units direct the wheels 2, 3 forwards. A fifth output terminal k1 of the order unit K carries a signal corresponding to the desired speed.

This signal is supplied to the input terminals a3, b3, c3, d3 of the control units A, B, C, D and determines the level of the signals transmitted by the output terminals of the active control unit and therefore the level of the signals transmitted by the active signal transmitters E, F to the motor units 8, 9, so that the latter rotate the wheels 2, 3 at the desired speed.

 Each of the control units A, B, C, D has an additional input terminal a5, b5, c5, d5, which receive a correction signal intended to modify the level of the signals transmitted respectively by the output terminals al, a2; b1, b2; cl, c2; dl, d2 of the control units. More specifically, the presence of a positive voltage at the input terminal a5 of the control unit A, when this is activated by a signal from the output terminal k2 of the order unit K, results in decreasing the level of the signal emitted by the output terminal ai-of the control unit A to a uniform extent corresponding to the level of said positive voltage, but does not cause any change in the level of the output signal emitted by the output terminal a2 of the control unit. The presence of a negative voltage I the input terminal a5 of the control unit A results in decreasing the level dru output signal from the output terminal a2, but does not cause any change in the level of the output signal from the output terminal al of the control unit. The other control units B, C and D are designed to be controlled in a similar manner, respectively by their inputs b5, c5, d5.

 We will now describe the means provided for producing said correction signals and for applying them to the input terminals a5 to d5 of the control units A to D.

The path finder device 15 is connected to an amplifier 24 by a line 23. The output terminal 2a of this amplifier delivers a correction signal whose polarity and level are a function of the difference detected by the path finder device 15 , on either side of the route determined by the director 17. During the inactive state of a relay
X, the switching contact x3 thereof connects the output terminal 24a to the input terminal a5 of the control unit A. The relay X is designed to operate when a signal is present on one of the terminals of-- output k4, - k5 of the order unit K or on a sixth output terminal k6 whose function will be explained below.

 The other path finder device 16 is connected to an amplifier 26 by a line 25. At the output 26a of this smplifier appears a correction signal whose polarity and level are a function of the difference detected by the element 16 on one side or the other of the path determined by the director 17. When the relay X is in its being inactive, its switching contact x2 connects the output terminal 26a to the input terminal b5 of the control B by a polarity reverser 27.

 The measurement signal generator 20 is connected to the input ml of a comparator M. During the inactive state of a relay V, the switching contact v1 thereof connects the generator 21 to the second terminal d input m2 of the comparator M through a polarity reverser 29. When the relay V (whose function will be specified below) has been activated, the contact vl directly connects the generator for producing measurement signals 21 to the second terminal entry m2. When the relay X has been activated, the switching contact xi connects the output terminal m3 of the comparator M to a signal conductor bb.

This conductor can be connected to the input a5 of the control unit A by the switching contact x3, when it has been actuated and can be connected, in series with the polarity reverser 27, to the input b5 of the control unit
B, via contact x2, when this has been activated. In addition, the conductor bb is permanently connected to the input c5 of the control unit
C and in series with a polarity reverser 28 at the input terminal d5 of the control unit D.

 Each of the measurement signal generators 20, 21 is designed to produce a signal proportional to the speed of the corresponding measurement wheel 18 or 19, said signal being positive when the wheel rolls forward and negative when it rolls backwards.

 Relay V is designed to be activated when a signal is transmitted by one of the output terminals k4 or k5 of the order unit K, that is to say, when the carriage must execute a turn (a dextrorsum turn for a signal on terminal k4 and sinistrorsum turn for a signal on terminal k5). The comparator is designed to produce a proportional signal I the difference between the measurement signals applied to the input terminals m2, and ml, the resulting signal, which is applied to the output terminal m3, being positive when the positive measurement signal applied to the comparator exceeds the negative measurement signal. In addition, each of the two measurement signal generators 20, 21 is connected to one of the input terminals nl, n2 of an integrator N designed to produce an output signal proportional to the sum of the distances traveled by the wheels. 18 and 19. By means of control pulses from the address unit L, the integrator N can be adapted either to calculate the distance traveled by the carriage (when the latter moves forwards or rear), or to calculate the angle of rotation described by the carriage (when the carriage turns) and it can be reset to zero before the start of an operation. The output signal is applied by the output terminal n3 of the device N to the address unit L. The address unit L is provided with a comparator to compare the output signals using predetermined values of the length of the path and angle of rotation, values previously entered in the address unit. The address unit also comprises means controlled by said controller to ensure that - the order unit stops any subsequent movement or any rotation of the carriage as soon as the actual value of the signal supplied by the device N agrees with the prescribed value.

We will now describe the operation of the above equipment
Forward movements controlled by a director
The order unit displays the signal at its output terminals kl and k2. The signal from the output terminal k2 activates the control unit A, so that there appears at each of the output terminals ai, a2 of the latter a control signal the level of which is determined by the adjustment signal speed supplied by the output terminal kl of the order unit K to the input terminal a3 of the control unit A. The control signals of the output terminals a1, a2 are supplied respectively to the terminals d input el, fi of the operating signal transmitters E, F. The operating signal transmitters E, F are thus brought to transmit a "forward" operating signal which is applied to the motor units 8, 9, which means that - the latter rotate their respective wheels 2, 3 forward at a speed corresponding to the speed setting signal. The path finder device 15 produces no signal as long as its position is correct relative to the cable 17.

On the other hand, when a loss occurs with respect to the correct position, the device 15 produces a signal which is applied to the input terminal a5 of the control unit A by the output terminal 24a of the amplifier 24 and by the switching contact x3 in its rest position. A deviation to the right results in a positive signal, a deviation to the left, a negative signal to the input terminal a5. We now assume that a deviation to the right has occurred, -with- result a positive correction signal at the input terminal a5. As explained above, this signal results in a reduction in the level of the signal applied to the output terminal al of the control unit A in a measurement corresponding to the level of the correction signal, while the level of the signal at the output terminal a2 remains unchanged. The decrease in the level of the control signal, supplied to the operating signal transmitter E by its input terminal el, results in a corresponding change in the operating signal transmitted by the operator signal transmitter, ~, so that the drive unit 8 is caused to rotate the wheel 2 at a slower speed than that of the wheel 3. This is for consequence that the front end of the carriage and the dispositi f path finder 15 move to the left towards the correct position. Consequently, the signal produced by the path finder device 15 gradually decreases and returns to zero when this device has returned to its correct lateral position relative to the cable 17.

Reverse movements controlled because a director
The control unit K develops a signal at its output terminals ki and k3. The signal from the output terminal k3 activates the control unit B, so that this unit develops at each of its output terminals bl, b2, a signal whose level is determined by the speed control signal supplied by the output terminal k1 of the order unit K to the input terminal b3 of the control unit B. The control signals of the output terminals bl, b2 are applied respectively to the input terminals e2, f2 operating signal transmitters E, F. The signal transmitters E, F are thus brought to transmit the "rear" operating signal respectively to the driving units 8, 9 so that these units rotate their respective wheels 2, 3 backward at a speed corresponding to the speed setting signal. Any deviation from the correct position relative to the cable 17 causes the path finder device 16 to produce a signal which is applied to the input terminal b5 of the control unit B by the output terminal 26a of the amplifier 26 , by the switching contact x2 in its rest position and by the inverter 27. The track or path finder device 16 is designed so that any deviation to the right (according to FIG. 1) produces a negative signal and so that a deviation to the left produces a positive signal at the output terminal? 6a. The inverter 27 causes the application of the signals to the input terminal b5 with reverse polarity. Thus, for example, a deviation to the right, according to the figure, results in a positive correction signal being applied to the input terminal b5. This signal results in a decrease in the level of the signal applied to the output terminal b1 of the control unit B to an extent corresponding to the level of the correction signal, while the signal from the output terminal b2 is unchanged. The drop in the level of the control signal supplied to the operating or operating signal transmitter E by its input terminal e2, results in a corresponding change in the signal transmitted by the operating signal transmitter E, so that l The drive unit 8 is caused to rotate the wheel 2 at a reduced speed. This results in the rear end of the carriage and the path finder device 16 moving to the left towards the correct position. Consequently, the signal produced by the path finder device 16 gradually decreases and returns to zero when this device is again correctly centered relative to the cable 17,
Forward movements without the help of a director
The order unit K develops a signal at its output terminals kl, k2 and k6. The signal from the output terminal k6 activates the relay X which actuates its switching contacts x1, x2 and x3. The signal from the terminal k2 has the effect, as described above, that the run signal " before "is transmitted by the two transmitters E, F, so that the two drive units 8, 9 are caused to rotate their respective wheels 2, 3 having, so that the two generators of measurement signals, entralé par said wheels, generate a positive signal. The inverter 29 causes the signal from the measurement signal generator 21 to be applied to the comparator M with negative polarity. As long as the ehariot moves in a straight line; the measuring wheels 18 and 19 roll at the same speed. Thus, the signals applied to the input terminals ml and m2 of the comparator are equal and opposite and no signal is transmitted by the output terminal m3 of the comparator. ' On the other hand, when the carriage moves along a curved trajectory, one of the measuring wheels rotates faster than the other, which results in the algebraic sum of the input signals of the comparator M being different from zero. Consequently, a correction signal appears at the output terminal m3 of the comparator. This correction signal is applied to the input a5 of the control unit A by the switching contacts x1, x3. It is assumed, for example, that while it is moving in forward direction, the carriage moves towards the right of its initial direction, thus rotating the measuring wheel 18 faster than the measuring wheel 19, with the result that the amplitude of the positive signal applied to the input terminal ml of the comparator is greater than the amplitude of the negative signal applied to its input terminal m2. Under these conditions, the comparator produces a positive correction signal whose amplitude corresponds to the difference of the amplitudes of the input signals. The application of this correction signal to the input terminal a5 of the control unit A has the result, as described above, of reducing the level of the operating signal transmitted by the transmitter E, so that the drive unit 8 is caused to rotate the wheel 2 at a reduced speed. This reduction in speed is maintained until the two measuring wheels turn again at the same speed.

Reverse movements without the help of a director
The order unit K develops a signal at each of its output terminals kl, k3 and k. The signal from terminal kS excites relay X which actuates its switching contacts xi, x2 and x3. The signal from the output terminal k3 has the effect, as described above, that each of the two transmitters of operating signals E, F supplies the reverse signal "respectively to the motor units 8, i, of so that these units rotate their respective wheels backwards, at a speed corresponding to the speed control signal transmitted by the output terminal ki of the order unit K.

The corresponding backward rotation of the two measuring wheels 18, 19 causes the two measuring signal generators to produce negative signals. The inverter 29 causes the signal produced by the measurement signal generator 21 to be applied to the input terminal m2 of the comparator in the form of a positive signal. It is assumed, for example, that during its backward movement, the carriage tends to turn to the right, according to the figure, that is to say, to describe an unrevealed trajectory whose concave side is oriented to the right of the Under these conditions, the measuring wheel 18 rotates faster than the wheel 19, so that the amplitude of the negative signal appearing at the input terminal mî of the comparator M is greater than that of the positive signal from the terminal entry m2. Consequently, the comparator produces a negative correction signal which is transmitted from the input terminal m3, by the contacts xl and x2 and the inverter 27, to the input terminal b5 of the control unit B. L the inverter 27 causes the signal applied to the terminal b5 to have an inverted, that is to say, positive, polarity. This positive correction signal produces, in the same manner as that already described above, a reduction in the speed at which the wheel 2 is driven by the drive unit 8. This reduction in speed equalizes the speeds of the two measuring wheels, thus making the comparator output signal return to zero.

Dextrorsum shift
The order unit K develops a signal at each of its output terminals kl, k4 and k6. Relays X and V are energized. Relay X operates its switching contacts xl, x2 and x3. The relay V actuates its contact vl, which means that the signal generator 21 is directly connected to the input terminal m2 of the comparator M. The signal from the output terminal k4 is supplied to the input terminal e4 of the control unit C. The output terminal cl of the control unit C, thus activated, applies a control signal to the input terminal e1 of the operation signal transmitter E, thereby causing the transmission of a forward signal to the drive unit 8. This signal results in the drive unit turning the wheel 2 forward at a speed determined by the speed control signal supplied by the output terminal kl the command unit K. The output terminal c2 of the control unit C applies a control signal to the input terminal f2 of the operation signal transmitter F, which results in the transmission of a reverse signal to the drive unit 9. This signal causes the drive unit 9 to rotate the wheel 3 by a at a speed determined by the speed control signal supplied by the output terminal k7. Thus the carriage rotates clockwise. The measuring wheels 18, 19, due to their contact with the ground or with the floor, are thus caused to rotate respectively forwards and backwards. Consequently, the measurement signal generator 20 produces a positive signal and the generator 21 a negative signal, said signals being applied respectively to the input terminals mi and m2 of the comparator. As long as the vertical axis of rotation of the carriage remains placed in the center 0, between the measuring wheels 18, 19, these signals have the same amplitude, so that no signal appears on the output terminal m3 of the comparator M On the other hand, when the speeds of the wheels 2, 3 with respect to the ground are not equal, one of the wheels slipping, for example, or having a diameter smaller than the other, the axis of rotation of the carriage is located closer to the slow wheel than to the fast wheel Consequently, the speeds of the measurement wheels 18, 19 and the amplitudes of the signals generated by the measurement signal generators 20, 21 differ, thus making a difference signal appear at the output terminal m3 of the comparator M. It is assumed, for example, that the drive wheel 2 rotates more slowly along the ground than the drive wheel 3 and that, consequently, the measurement wheel 18 rotates more slowly than the drive wheel measurement 19. Thus, the amplitude of the negative signal produced by the generator 21 is larger nde that that of the positive signal generates by the generator 20, with the result that it appears at the output terminal m3 of the comparator M a negative correction signal. This signal is applied to the input terminal c5 of the control unit C by the contact in working position xl and the conductor bb. This correction signal reduces the amplitude of the signal transmitted by the output terminal c2 by The control unit C and applied to the: input terminal f2 of the operating signal transmitter F. - The resulting modification of the operating signal transmitted by the transmitter F has the effect that the power unit 9 rotates the wheel 3 at a reduced speed, thus bringing the axis of rotation of the carriage relative to the ground to the correct position 0, halfway between the measuring wheels.

Sinister rotation
The order unit K develops a signal at its output terminals kl, k5 and k6. Relays X and V are energized and activate their switching contacts xl, x2, x3 and vl. The signal appearing at the output terminal is applied to the input terminal d4 of the control unit D and activates the latter. The output terminal dl of the control unit D applies a control signal to the terminal d input e2 of the operation signal transmitter E, thereby causing this transmitter to send the "reverse" signal to the drive unit 8, which is thus caused to rotate the wheel 2 backwards, at a speed determined by the speed control signal, supplied by the output terminal k1 of the control unit K. The output terminal d2 of the control unit D applies a control signal to the input terminal fl of the transmitter of operating signals F, so that the latter transmits the running signal "forward" to the drive unit 9 which is thus caused to rotate the wheel 3 forward, at a speed determined by the adjustment signal of speed, supplied by the output terminal k7 of the order unit K. The operating conditions of the wheels which just described result in a counterclockwise rotation movement of the carriage on the ground. Contact of the measuring wheels 18 19 with the ground causes them to rotate back and forth respectively. If, for any reason, the vertical axis of rotation of the carriage relative to the ground should deviate from the correct position 0, located midway between the measuring wheels, the speeds of these measuring wheels and, consequently, the amplitudes of the signals generated by the measuring signal generators 20, 21 would be different, so that a differential signal would appear at the comparator output terminal m3. It is assumed, for example, that wheel 2, for whatever reason, for example, because it slips, progresses more slowly along the ground than wheel 3, with the result that the axis of rotation of the carriage shifts towards the wheel 2. Under these conditions, the measuring wheel 18 rotates more slowly than the wheel 19. Consequently, the positive signal generated by the generator 21 is larger than the negative signal developed by the generator 20. Consequently, the comparator M produces a positive correction signal, the level of which corresponds to the difference between the amplitudes of the signals applied to its input terminals. This positive correction signal is applied, from the output terminal m3, by the contact in working position xl and by the conductor bb, to the inverter 28 which transmits this signal, as a negative signal having the same amplitude, to the input terminal d5 of the control unit D. This negative signal produces a reduction in the level of the signal applied to the output terminal d2 of the control unit D, and is transmitted to the input terminal fl of the operation signal transmitter F. The resulting modification of the operation or operation signal transmitted by this transmitter causes the drive unit to rotate wheel 3 at a reduced speed. As a result, the axis of rotation of the carriage with respect to the ground is brought back to the correct position 0 located midway between the measuring wheels.

 The advantage of the system described above resides in the fact that the carriage, at the end of a change of direction, has a well-defined position relative to the starting position, that is to say, I the position before the change of direction. This facilitates handling or treatment of the transported products, which can be programmed to take place at the new position of the carriage; moreover, the improvement of the accuracy reduces the risks for the trolley path finder device of ceasing to be in contact with the planned director, for the subsequent movement of the trolley, which would result in the latter moving away Another advantage is the ability of the trolley to follow one or more predetermined straight paths without the help of managers.

 FIG. 2 illustrates an example of a route of the cart made up of several journeys equipped with a control installation that conforms to the invention. It can be seen that the carriage travels on a floor comprising four rectilinear steering cables, three of which, referenced 30, 31 and 32 are parallel, while the fourth cable 33 extends perpendicular to the other three. In position a, the carriage moves forward along the director cable 30. When it meets the director cable -33, the carriage stops, turns clockwise, by means of its wheels drive, at an angle of 900 to place in position b.- The carriage then continues its path along the cable 33 until it meets the cable 31 '; it then stops and turns anti-clockwise to place it in position c. From position c, the carriage advances by a predetermined distance along the guide cable 31 to the position d where it turns anticlockwise, by an angle of about 1200 before continuing its path in a straight line towards the director cable 32; when reaching it it stops in position e, turns anti-clockwise by an angle of about 600, then continues its path-along the cable 32 to the intersection of it with the director cable 33 where the carriage stops in position f to turn anti-clockwise by 900. Then the carriage continues its path along along the director cable 33 until position g, then turns clockwise by 900, and ~ goes back, perpendicular to the director cable 33, until it arrives in position h from where it returns to the director cable 33, then turning counterclockwise 900 to position g to finally move away along the director cable 33. This sequence of movements is controlled by signals appearing at the output terminals of the unit of order K, as described above. The control unit K is, for its part , controlled by an address unit L which determines the choice, the instant of generation and the duration of the successive signals transmitted by the order unit, this address unit being designed to be governed by data stored in that -this, as well as by control pulses received, while the carriage is running, control members disposed at certain points in the path of the carriage. According to another advantageous development of the invention, the measuring wheels 18, 19 and their signal generators 20, 21 are also used for the retro-application to the address unit of signals indicating the distance traveled and the angle rotation performed, said signals being compared with predetermined quantities stored in the memory of the address unit.

these signals are produced by the integrator N to which it was mentioned previously. This integrator N calculates a quantity equal or proportional to the sum of the distances covered during a movement or during a turn by the measuring wheels 18 and 19. This quantity is successively applied to the address unit L and compared, in a comparator provided therein at a predetermined quantity representative of the length of the journey or the angle of turn kept in the address unit. As soon as the values or the graders thus compared are found to be equal, the order unit K is actuated in such a way that the movement or rotation of the carriage is interrupted.

 The measurement of the distance traveled and the angle of rotation can also be measured by an integrator N which receives the output signals from only one of the measurement signal generators 20, 21. However, the use of the two signal generators The advantage of measurement is that it improves accuracy to some extent, because the errors of the two measurement wheels compensate each other to some degree.

By proceeding according to FIG. 2, the carriage moves from position S to position h and returns without the aid of a fixed director. Because the starting position of this movement is very precise and that the straightness of the trajectory during the movement is controlled by means of the device according to the invention described above, it can be seen that the precision of the movement of the carriage is good, despite the absence of a permanent director. It is even possible that the truck operates without any fixed director. The driving program, including the distances of the successive straight sections and the angles of rotation (if any) to be executed at selected points on the trajectory or circuit, is in the form of input data, stored in the address unit and successively compared with the actual values or quantities entered in the address unit by the integrator
NOT.

During the description of the embodiment of the invention shown in FIG. 1, it has been assumed that the desired position of the vertical axis of rotation is the point 0 located halfway between the driving wheels 2, 3 and also that the measuring wheels 18, 19 were arranged symmetrically with respect to point 0. However, the arrangement described can also be used to command and control the rotations of the carriage around other vertical axes of rotation. In FIG. 3, where the references 2, 3 and 18, 19 denote the same components as in FIG. 1, it is assumed that the desired vertical axis of rotation of the carriage intersects the geometric axis of the drive wheels 2, 3 in one point P located to the left of the drive wheel 2.To keep the axis of rotation stationary at point P, the drive wheels 2 and 3 must rotate in the same direction and at speeds proportional to their horizontal distance from point P. If we designate by v1 and v2, the speeds with which the measuring wheels 18, 19 roll on the ground - and by r1 and r2, their distances from point P, the following condition must be established
v1 = r
v2 r2
When the speeds of the drive wheels do not meet the condition specified above, for example, because one of them slips, the axis of rotation will deviate from point P, so that the speeds v1 and v2 of the measuring wheels will no longer correspond to the above equation. Between the displacement speed w of the real axis of rotation and the speeds v1, v2 of the measuring wheels 18, 19 there is the following relationship:
v r2 - V2 r1
w = r2 - r1
2
Consequently, the. comparator M (figure 1) must, in such a case, be designed to calculate an output signal whose magnitude is proportion
vv nelle unlike v1r2 - v2r1 (or unlike - 2 or even
r1 r2 difference v1 - v2. r1). This result can be obtained, for example, by multi r2 bending the output signal from one of the measurement signal generators by a corresponding factor before applying it to the comparator.

 The device shown in FIG. 4 differs from that of FIG. 1 in that the carriage is provided with only one measurement wheel 35: This wheel drives a generator of measurement signals 36 which, via an amplifier 37 applies a positive signal to a conductor 38 when the wheel 35 rotates forward and a negative signal when the wheel 35 rolls back. When the measuring wheel is stationary, no signal is transmitted. The conductor 38 is connected to the control units C and D (FIG. 1) instead of arriving at the output terminal m3 of the comparator M. This device tends to keep the vertical axis of rotation of the carriage stationary relative to the ground or on the floor, this fixed position coinciding with the point R by which the measuring wheel is in contact with the ground or the floor. The corrective action is similar to that of the device in FIG. 1. It is quite obvious that the wheel of measure 35 cannot, as the two wheels in FIG. 1, be used to measure the angle of rotation of the carriage or to correct the deviation of the latter from a re-straight path.

FIG. 5 schematically represents a carriage 40 comprising two support wheels 41, 42 which can rotate freely, independently of one another, these wheels having a common geometric axis 52 and a drive wheel 43. The drive wheel, together with its actuation mechanism (not shown), can pivot around an axis 44
and can be rotated around said axis by means of a helical wheel 45 and a worm 45b forming part of a steering or orientation mechanism 45, designed to be actuated by signals from a control unit 48. Each of the two support wheels 41, 42 is connected to a measurement signal generator 46, 47. Each of said generators is connected to one of the input terminals 49, 50 of the control unit command 48.

In the case shown, the drive wheel occupies a position in which its geometric axis 51 forms a right angle with the geometric axis 52 of the support wheels 41, 42 and crosses this axis 52 at a point S located at ml-distance between the support wheels. The driving wheel 43 thus tends to rotate the carriage 40 about a vertical axis passing through the point
S, in which case the wheels 41 and 42 rotate in opposite directions at equal angular speeds and the measurement signal generators 46, 47 driven by these wheels produce signals having equal amplitudes. These signals are applied to a comparator provided in the control unit, which is designed to produce an output signal corresponding to the difference between its input signals. This output signal controls the steering mechanism. When the carriage turns around the vertical axis passing through point S, the input signals are equal and there is no output signal. On the other hand, when it happens that the axis of rotation shifts from point S towards one or the other of the support wheels 41, 42, this wheel turns more slowly than the other, so that it There is a difference between the input signals from the control unit 48. The output signal from the comparator of the control unit 48 causes the steering mechanism 45 to change the orientation of the wheel 43 in the desired direction to return the axis of rotation to its correct position. It is assumed, for example, that the axis of rotation has moved towards the wheel 41, from which it follows that this wheel rotates more slowly than the wheel 42. The resulting difference in the signals transmitted by the control unit 48 causes the steering mechanism to rotate the drive wheel 43 clockwise around the vertical axis. This angular movement of adjustment of the driving wheel temporarily shifts the point of intersection of the geometric axis of the wheel 43 and the geometric axis 52 of the support wheels 41, 42, for example, - at point S '.

Thus, the wheel 43 tends to rotate the support wheel 41 faster than the support wheel 42. The angular offset of the drive wheel 43 relative to the normal rotational position remains until the wheels 41 and 42 rotate at the same speed, thereby restoring the legality of the corresponding measurement signals.

In FIG. 5, the circuits necessary to orient the carriage during forward or reverse travel, as well as the address and order units which operate in the same way as in the embodiment of FIG. 1, do not have not been shown, their presence not being necessary to explain the system provided for controlling the rotation operation
In FIG. 5, the wheels 41 and 42 serve both as support wheels for the carriage and as measurement wheels. It is possible, in addition to the support wheels 41, 42 to provide a separate pair of measuring wheels, each of which would be associated with a generator of measurement signals, as in the device according to FIG. 1. This may offer the advantage of a slightly better measurement preetion.

 In the device of FIG. 6, the mounting and the operation of the support wheels 2a, 3a and of the measurement wheels 18a, 19a correspond to those of the wheels 2, 3, 18 and 19 of FIG. 1. The support wheels 4 , 5 of Figure 1, which can pivot individually, have been replaced by two support wheels -54, 55 mounted on a common support 56 designed to be able to pivot freely around a vertical axis 57. It is also possible to replace the two wheels pivotally supported by a single swivel wheel.

 In the device shown in FIG. 7, the carriage is equipped with three support wheels 59, 60, 61. The wheel 59 is mounted at one end of the carriage and the wheels 60, 61 at the other end of the latter. The wheel 59 has a fixed orientation, its geometry axis c2 extending perpendicular to the longitudinal axis of the carriage. The wheels 60, 61, which are driven by separate motors, not shown, can pivot respectively around a vertical axis 53 or 64. Each of the wheels can be adjusted angularly around said axis by means of a helical wheel sector 65 , 66 and an endless screw 57, 68. The endless screws are entralnées by a steering mechanism 69 designed to automatically maintain between the steering angles of the wheels 60, 61 a relationship such as the point of intersection T between the extensions Y, Z of the axes of the wheels, that is to say always situated in the vertical plane passing through the geometric axis of the wheel 59. Two measuring wheels 70, 71 are provided on either side of the support wheel 59. The axes of the measurement wheels coincide with or are situated in the vertical plane passing through the geometric axis 62 of the support wheel 59. Each of the measurement wheels drives a respective generator of measurement signals 72, 73. The signals of said generators are applied to a compara tor U which serves the control unit for the steering mechanism 69, that is to say, which generates control signals necessary for the operation of the latter. The operation of the comparator U corresponds to that described above with regard to FIG. 3. When the axis of rotation of the carriage deviates from a predetermined point T, the comparator produces a control signal (positive or negative) under the action of which the steering mechanism 69 orients the wheels 60, 61 in the desired direction to return the axis of rotation of the carriage to the predetermined position.

Claims (6)

 1. Automatic steering device for a driverless trolley which comprises a chassis (1); at least three wheels (2,3,4,5) to support the chassis (1); a motor (8,9) and a transmission (6,7) for driving at least one of the wheels; first support means for at most two (2,3) wheels, these first support means being designed to define a single geometric axis (10) of the wheel or wheels, being in a horizontal direction fixed relative to the chassis (1); second support means (13,14) for the remaining wheel (s) (4,5), these second support means being pivotally connected to the chassis in order to allow the direction of the remaining support wheel (s) to be adjusted with respect to to the chassis (1) and thus to allow the carriage to rotate around a vertical axis of rotation (0) intersecting the geometric axis - (10) and steering means (EF) for adjusting the position of the axis of pivoting (0) relative to the chassis (1), device characterized in that it further comprises means for controlling the position of the pivoting axis which comprise at least one measuring wheel (18,19) designed to coming into contact with the surface on which the carriage moves, the measurement wheel or wheels having a horizontal geometric axis extending in the same vertical plane as the single geometric axis (10); signal generating means (20,21), designed to be actuated by the measuring wheel or wheels (18,19) in order to generate a signal representative of the speed of rotation of the measuring wheel or wheels, the means control system producing an output signal obtained from the signal generated by the generation means (20,21), a signal whose sign represents the direction of progression and whose amplitude represents speed, relative to the surface supporting the carriage, from a predetermined point on said single geometric axis, this point defining a given position of said pivot axis; and means (A-D) controlled by said output signal for actuating the steering means (E-F) so that these place the pivot axis (0) in the desired position.  2. Trolley according to claim 1, equipped with two measuring wheels (18) and (19), characterized in that it comprises a recording device (N) intended to receive the signals (nl, n2) tra: nsmis during a rotation operation by the signal generation means (20) - (21) associated with at least one of the measuring wheels (18) (19) and calculating therefrom a quantity representing the angle of rotation of the carriage resulting from said rotation operation; and means (L) for comparing the quantity thus calculated with a predetermined quantity, representing a predetermined change of direction of the chassis (1).  3. Trolley according to claim 1, characterized in that it comprises recording means (N) for receiving the signals (nl, n2) transmitted, during the passage of the trolley from one location to another, by said means generating signals (20,213 and for calculating therefrom an amount representing the distance traveled by the carriage during this passage; and means (L) for comparing the amount thus calculated with a preset amount representing a predetermined distance.  4. Trolley according to claim 2, characterized in that it comprises recording means (N) for receiving the transmitted signals (nl, n2), during the passage of the trolley from one location to another, by the means generating signals (20,21) associated with at least one of the measuring wheels (18,19) and for calculating therefrom an amount representing the distance traveled by the carriage during this passage; and means (L) for comparing the quantity thus calculated with a predetermined quantity representing a predetermined distance.  5. Trolley according to claim 2, characterized in that said measuring wheels (41,42) also constitute two of the three support wheels.  6. Driverless trolley which comprises a chassis (1), at least three wheels (2,3,4,5) to support the chassis, a motor (8,9) and a transmission (6,7) to drive the at least one of the wheels; first support means for at most two (2,3) wheels, these first support means being designed to define a single geometric axis (10) of the wheel or wheels (2,3), extending in a fixed horizontal direction relative to the frame (1); second support means (13,14) for the remaining support wheel or wheels (4,5), these second support means being pivotally connected to the chassis (1) so as to allow the direction of the wheel or wheels to be adjusted of support remaining with respect to the chassis and thus allowing the carriage to rotate about a vertical axis of rotation (O) intersecting said geometric axis (10) and steering means (EF) for adjusting the position of the axis of pivoting (0) relative to the chassis (1), characterized in that it comprises two measuring wheels (18,19) of the same diameter having a common horizontal geometric axis extending in the vertical plane passing through said single geometric axis (10); two signal generators (20,21) respectively actuated by one of the measuring wheels (18 or 19) in order to produce a signal (ml, m2) representing the speed of rotation of this measuring wheel; means (M) for comparing the signals (ml, m2) and for producing an output signal (m3) representing the difference between the rotational speeds of the measuring wheels (18,19) and means (A, B, C , D) controlled by the output signal (m3) to adjust the steering means (EF) to a position tending to equalize the rotational speeds of the measuring wheels (18,19).