WO2021214650A1

WO2021214650A1 - System for assisted guidance of a convoy

Info

Publication number: WO2021214650A1
Application number: PCT/IB2021/053242
Authority: WO
Inventors: Paolo MAGGIORE; Matteo Davide Lorenzo DALLA VEDOVA; Pier Carlo BERRI
Original assignee: Politecnico Di Torino
Priority date: 2020-04-24
Filing date: 2021-04-20
Publication date: 2021-10-28
Also published as: IT202000008995A1

Abstract

The present invention relates to a system (200) for assisted guidance of a convoy (100) comprising a tractor (101), a first trailer (102) and a second trailer (103), said tractor (101) comprising a steering system (107) adapted to steer the tractor (101) as a function of a steering angle (104). Said system (200) comprises a first sensor (108) adapted to measure a first angle (105) defined by the intersection between a longitudinal axis of the tractor (101) and a longitudinal axis of the first trailer (102); a second sensor (109) adapted to measure a second angle (106) defined by the intersection between a longitudinal axis of the first trailer (102) and a longitudinal axis of the second trailer (103); an actuator (206) adapted to actuate said steering system (107) as a function of an actuation signal (205); a directional control device (208) adapted to generate a command signal (201); a processing unit operatively connected to said actuator (206), said directional control device (207), said first sensor (108) and said second sensor (109). The processing unit is configured for acquiring a plurality of input parameters comprising the directional command (201), the first angle (105), the second angle (106) and at least one parameter relating to the motion of the convoy; computing, by means of a first PID controller (202), a first control value (203) as a function of the directional command (201), the second angle (106) and the parameter relating to the motion of the convoy; computing, by means of a second PID controller (204), the actuation signal (205) as a function of the outputted first control value (203), the first angle (105) and the parameter relating to the motion of the convoy; supplying the actuation signal (205) to said actuator (206). The present invention also relates to a computer program adapted for calibrating the system (200).

Description

SYSTEM FOR ASSISTED GUIDANCE OF A CONVOY

DESCRIPTION

The present invention relates to a system for assisted guidance of a convoy comprising a tractor and two or more trailers, according to the preamble of claim 1; in particular, the present invention falls within the field of automatic control systems applied to the directional control of a tractor comprising two or more trailers.

Controlling the direction of motion, particularly in reverse, of a convoy comprising a tractor and two or more trailers poses several difficulties in terms of manoeuvrability; such convoys are, in fact, characterized by an inherently unstable kinematic behaviour, which is difficult to estimate without using any computation tools. It follows, therefore, that the manual operations executed by a human driver for controlling the convoy, e.g., through a steering system, often turn out to be very arduous and slow, as well as scarcely intuitive. For example, controlling a convoy with two or more trailers in reverse often requires setting a steering angle opposite to the direction of the desired trajectory; because of this characteristic, manually controlling the steering system is not very intuitive and may lead to unpredictable effects. Moreover, convoy manoeuvrability becomes harder as the number of trailers increases. For example, manually controlling, particularly in reverse, a convoy comprising three or more articulations is generally considered to be virtually impossible for a human driver.

Most assisted guidance systems currently known in the art are, in general, focused on acquiring information about the position of the convoy and presenting such information to the driver. For example, such systems can estimate the position of the convoy and of any obstacles along the convoy trajectory through the use of position sensors and video cameras installed on the tractor and the trailers of the convoy. Such information is then processed and presented to the convoy driver via audible and visual signals, so as to help the driver make complex manoeuvres such as, for example, driving in reverse. For example, patent application US2019084477 describes a method of generating an overhead view of the manoeuvring area, comprising a representation of the vehicle and its trailer. While it facilitates the driver's task, such system is characterized in that the directional control of the convoy is totally entrusted to the driver.

Patent application US2014052337A1 discloses, on the other hand, a system for active and automatic control of the steering system of a vehicle towing a single trailer. Such solution has several drawbacks. First and foremost, the automatic control system described in patent application US2014052337A1 can only control the reverse trajectory of a convoy comprising a tractor and just one trailer. In fact, such system is based on a control law that comprises a kinematic mathematical model capable of modelling and predicting the movement of a given type of tractor towing a single trailer. Another disadvantage of such a solution lies in the difficult calibration of the control law of patent application US2014052337A1 when one tries to adapt the system for controlling two or more trailers; as a matter of fact, calibrating a control logic suitable for handling a multiple-trailer system implies computing optimal values of a large number of gains/ parameters. This can hardly be achieved by using a deterministic method like the one proposed in patent application US2014052337A1. Moreover, assisted guidance systems are usually based on microprocessors having low computational power; for cost reasons, it would therefore be disadvantageous to use a kinematic model like the one disclosed in patent application US2014052337A1 for controlling a convoy comprising two or more trailers. Because of the specificity of such a kinematic mathematical model, the solution disclosed in patent application US2014052337A1 would also be hardly adaptable as a retrofit solution to convoys that have not been previously prearranged for it.

In this frame, it is the main object of the present invention to provide a system for assisted guidance of a convoy comprising a tractor and at least two or more trailers, which can actively control the steering system of the tractor while manoeuvering the convoy. A further object of the present invention is to provide a software program for managing the assisted guidance system, which is based on a control law without any complex kinematic mathematical models. It is another object of the present invention to provide a system for controlling a convoy comprising two or more trailers which can be installed as a retrofit solution on convoys not specifically prearranged for assisted guidance. It is yet another object of the present invention to provide a method of calibrating the assisted guidance system of the present invention.

The assisted guidance system of the present invention is configured for use on a convoy comprising a tractor and at least a first trailer and a second trailer; said tractor comprises, in turn, a steering system adapted to steer the tractor as a function of a steering angle. The system comprises a first sensor, adapted to measure an angle defined by the intersection between a longitudinal axis of the tractor and a longitudinal axis of the first trailer (also referred to as first angle), and a second sensor, adapted to measure an angle defined by the intersection between a longitudinal axis of the first trailer and a longitudinal axis of the second trailer (also referred to as second angle).

The system further comprises a control system adapted to receive a directional command, e.g., from the driver, and a processing unit adapted to generate an actuation signal as a function of the first angle, the second angle and a parameter relating to the motion of the convoy. Lastly, the system comprises an actuator adapted to actuate said steering system as a function of the actuation signal.

In order to achieve the above-mentioned objects, the present invention provides a system for assisted guidance of a convoy, a computer program adapted for computing an actuation signal, and a computer program adapted for calibrating said assisted guidance system having the features set out in the appended claims, which are an integral part of the present description. Further objects, features and advantages of the present invention will become apparent in light of the following detailed description and of the annexed drawings, provided merely by way of non-limiting example, wherein:

Figure 1 schematically shows a convoy comprising a tractor, a first trailer and a second trailer;

Figure 2 shows a block diagram of the assisted guidance system according to the present invention;

Figure 3 shows a block diagram of a PID controller;

Figure 4 shows a flow chart of the procedure for calibrating the assisted guidance system according to the present invention.

With reference to the annexed drawings, reference numeral 100 in Figure 1 designates as a whole a convoy 100 comprising a tractor 101, a first trailer 102 and a second trailer 103. The first trailer 102 may be partially constrained, e.g., by means of a rigid bar, to the tractor 101; the second trailer 103 may be partially constrained, e.g. by means of a rigid bar, to the first trailer 102. The tractor 101 comprises a steering system 107 that allows changing the trajectory of the convoy 100 as a function of a steering angle 104. The steering system may comprise, for example, a pair of wheels configured to be steered according to a steering angle 104; said steering angle 104 may be defined as the intersection between the axis of the tractor and the axis of at least one of the wheels of the steering system, as shown in Figure 1. The steering system 107 may further comprise a steering wheel, a steering column and a steering gear adapted to move the pair of wheels, which can be steered as a function of a directional command issued by means of the steering wheel, e.g., by the driver. Reference numeral 105 in Figure 1 designates a first angle defined by the intersection between a longitudinal axis of the tractor 101 and a longitudinal axis of the first trailer 102. Reference numeral 106 in Figure 1 designates a second angle defined by the intersection between a longitudinal axis of the first trailer 102 and a longitudinal axis of the second trailer 103. In order to measure said first angle 105 and said second angle 106, the convoy 100 may comprise a first sensor 108 and a second sensor 109 suitably installed on the tractor 101 and/ or on the first trailer 102 and/ or on the second trailer 103.

Figure 2 shows, as a whole, a block diagram of the assisted guidance system 200 according to the present invention, which comprises: a first sensor 108 adapted to measure the first angle 105 defined by the intersection between a longitudinal axis of the tractor 101 and a longitudinal axis of the first trailer 102; a second sensor 109 adapted to measure the second angle 106 defined by the intersection between a longitudinal axis of the first trailer 102 and a longitudinal axis of the second trailer 103; an actuator 206 adapted to actuate said steering system 107 as a function of an actuation signal 205; a directional control device 208 adapted to generate a command signal 201; a processing unit adapted to generate the actuation signal 205 according to a control law 207.

The first sensor 108 and the second sensor 109 allow measuring, respectively, the angles between the tractor 101 and the first trailer 102 and between the first trailer 102 and the second trailer 103. The first sensor 108 and the second sensor 109 may be constrained to the convoy 100 by means of suction cups, magnets or, in general, any method known in the art and suitable for constraining the sensors 108 and 109 in a semi-permanent or permanent manner to the convoy 100. Such devices 108 and 109 may consist of a MEMS inertial platform combined with a magnetic compass. The first sensor 108 and the second sensor 109 preferably comprise a communication module capable of establishing a wireless or wired connection with, e.g., the processing unit.

The actuator 206 is operatively connected to the steering system 107 and is configured for receiving, as input, an actuation signal 205. As a function of such actuation signal 205, the actuator 206 is configured for actuating the steering system 107 in such a way as to set the steering wheels at a given steering angle 104. If the tractor 101 is equipped with an electronic power steering system, the processing unit can be connected to the actuator 205 comprised in the power steering system of the tractor without requiring any additional actuators. When the assisted guidance system is active, the steering system 107 is actuated directly by the actuator; for this reason, during the assisted guidance operations the steering wheel of the steering system 107 will also follow the movements imparted by the actuator. Alternatively, the steering wheel may be disconnected from the steering system 107 during the assisted guidance operations.

The directional control device 208 is configured for generating a command signal 201 as a function of a directional command issued by the driver. The control device 208 may be, for example, a joystick, a digital touchscreen or a directional knob. The directional control device 208 can be used by the convoy driver in order to indicate, in an intuitive manner, the desired direction in which the convoy 100 should move. For example, the driver may indicate, through the use of the control device 208, the desired direction in which the last trailer of the convoy should move during the reverse operations. In the example depicted in Figures 1 and 2, said last trailer is the second trailer 103. If the steering wheel is disconnected from the rest of the steering system 107 during the assisted guidance operations, the steering wheel itself can be used as a directional control device 208. Note that, in such a case, the direction imparted to the steering wheel by the driver will simply indicate the desired direction of the last trailer of the convoy 100; the movement and the angle of the steering wheel will not necessarily be directly reflected in the steering angle 104. During the reverse operations, in fact, the steering angle 104 may take a value which is opposite to the desired direction.

The processing unit may comprise, for example, a microcontroller operatively connected to a physical memory, a user interface, the directional control device 208, a wireless or wired communication card, the actuator device 206, the first sensor 108 and the second sensor 109. The processing unit is configured for receiving a plurality of input parameters comprising the command signal 201, the first angle 105 and the second angle 106. The processing unit is also configured for computing, or receiving as input, a parameter relating to the motion of the convoy 100; for this purpose, the processing unit may be operatively connected to, for example, an odometer aboard the tractor or, alternatively, it may comprise a GPS module adapted to compute said parameter relating to the motion of the convoy 100. Such parameter relating to the motion of the convoy 100 may be, for example, the speed of, or the distance travelled by, the convoy 100.

As a function of such input parameters and the parameter relating to the motion of the convoy 100, the processing unit is configured for generating the actuation signal 205 according to a control law 207.

Such control law 207 may be implemented through a computer program executed by the processing unit or, alternatively, it may be implemented as a hardware module comprised in the processing unit. According to one aspect of the present invention, the control law 207 is such that it can be executed in real time during the convoy guidance operations without excessive demands on computational resources.

The control law 207 comprises a first Proportional-Integral-Derivative controller 202 (also referred to as PID controller) comprising one or more gain parameters. Such first PID controller 202 is configured for computing a first control value 203 as a function of the directional command 201, the second angle 106 and a parameter relating to the motion of the convoy. Such parameter relating to the motion of the convoy may be expressed as the instantaneous speed of, or, alternatively, the distance travelled by, the convoy 100. The control law 207 further comprises a second PID controller comprising one or more gain parameters. Such second PID controller 204 is configured for computing the actuation signal 205 as a function of the outputted first control value 203, the first angle 105 and the parameter relating to the motion of the convoy. Finally, such actuation signal is inputted to the actuator 206; the actuation signal 205 is such as to allow the actuator to actuate the steering system 107 in a manner such as to cause the convoy 100 to follow a trajectory in agreement with the direction imparted by the driver through the directional control device 208.

As shown in Figure 3, the first PID controller 202 and the second PID controller 204 comprise all the functional elements of a generic PID controller known in the art. For simplicity, Figure 3 shows the reference numerals concerning both the PID controller 202 and the PID controller 204.

Reference numerals 302a, 303a and 304a designate, respectively, the gain parameters of the proportional, integral and derivative contributions of the PID controller 202, whereas reference numerals 302b, 303b and 304b designate, respectively, the gain parameters of the proportional, integral and derivative contributions of the PID controller 204.

As is known in the art, the combination of such contributions determines the output signal (i.e., 203 for the PID controller 202 and 205 for the PID controller 204) as a function of a generic input signal 301. According to one aspect of the present invention, the integral contribution 305 and the derivative contribution 306 are computed on the basis of a parameter relating to the motion of the convoy, such as, for example, its speed.

According to one aspect of the present invention, in order to ensure adequate system controllability, prior to the real-time execution of the control law 207 comprised in the processing unit it is possible to execute a step of calibrating the gain parameters 302a, 302b, 303a, 303b, 304a, 304b. Figure 4 shows a flow chart of the procedure for calibrating one or more gain parameters 302a, 302b, 303a, 303a, 303b, 304a, 304b of the first PID controller 202 and/or the second PID controller 204 comprised in the control law 207. It is important to note that, while the control law 207 executed by the processing unit must be executed in real time during the assisted guidance operations, the calibration procedure may be executed on a one-off basis during the system initialization phase. For this reason, the calibration procedure may be implemented through a computer program executed on a computing machine (e.g., a personal computer) other than the processing unit. The final gain parameters 302a, 302b, 303a, 303a, 303b, 304a, 304b may be transferred from the computing machine used for calibrating the system to the processing unit via a wireless or wired data connection at the end of the calibration procedure 400. The latter comprises generating a simulation model 401 simulating the kinematics of the convoy 100, which can compute a simulated trajectory of the convoy as a function of, for example, the actuation signal 205, the steering angle 104, the speed and/ or the initial position of the convoy. The kinematics simulation model 401 allows estimating the behaviour of the convoy 100 as a function of one or more geometric parameters that characterize the convoy, such as, for example, the maximum value of the steering angle 107, the maximum value of the first angle 105, the maximum value of the second angle 106, the length of the tractor 101, the length of the first trailer 102, the length of the second trailer 103.

The calibration procedure 400 uses a module that comprises a copy of the control law 207 comprised in the processing unit. The copy of the control law 207 is initialized with initial gain parameters 404 and is configured for receiving, as input, simulated parameters from the simulation model 401, which comprise the first angle 105, the second angle 106 and a parameter relating to the motion of the tractor 101. The calibration procedure 400 comprises generating 403 a command signal 201 as a function of a desired trajectory of the convoy 100; consequently, the control law 207 generates an actuation signal 205 as a function of the command signal 201 received as input. Such actuation signal 205 is inputted to the simulation model 401 for the purpose of generating a simulated trajectory of the convoy 100; the simulated trajectory is then compared 406 with the desired trajectory. According to one aspect of the present invention, the result of such comparison is used by the calibration procedure in order to establish if the values of the gain parameters 302a, 302b, 303a, 303a, 303b, 304a, 304b meet one or more convoy controllability criteria. For example, the comparison between the simulated trajectory and the desired trajectory may be expressed through an error parameter, such as, for example, the absolute deviation of the point of arrival of the convoy along the simulated trajectory from the point of arrival of the convoy along the desired trajectory. If said error parameter exceeds a predefined threshold, then the calibration procedure comprises a further step 402, in which one or more gain parameters 302a, 302b, 303a, 303a, 303b, 304a, 304b of the first PID controller 202 and/ or of the second PID controller 204 are appropriately modified as a function of the comparison between the simulated trajectory and the desired trajectory. According to techniques known in the art, the modification of the gain parameters 302a, 302b, 303a, 303a, 303b, 304a, 304b may be effected by means of any known optimization algorithm, such as, for example, a genetic algorithm or a pattern search algorithm. Finally, if said error parameter is below a predefined threshold, then the calibration procedure will end and the final gain parameters 302a, 302b, 303a, 303a, 303b, 304a, 304b will be sent to the processing unit of the system 200. The system for assisted guidance of a road convoy described herein by way of example may be subject to many possible variations without departing from the novelty spirit of the inventive idea; it is also clear that in the practical implementation of the invention the illustrated details may have different shapes or be replaced with other technically equivalent elements. It can therefore be easily understood that the present invention is not limited to the above-described system for assisted guidance of a road convoy, but may be subject to many modifications, improvements or replacements of equivalent parts and elements without departing from the inventive idea, as clearly specified in the following claims.

Claims

1. System (200) for assisted guidance of a convoy (100), said convoy (100) comprising a tractor (101), a first trailer (102) and a second trailer (103), said tractor (101) comprising a steering system (107) adapted to steer the tractor (101) as a function of a steering angle (104), said system (200) comprising:

- a first sensor (108) adapted to measure a first angle (105) defined by the intersection between a longitudinal axis of the tractor (101) and a longitudinal axis of the first trailer (102);

- a second sensor (109) adapted to measure a second angle (106) defined by the intersection between a longitudinal axis of the first trailer (102) and a longitudinal axis of the second trailer (103);

- an actuator (206) adapted to actuate said steering system (107) as a function of an actuation signal (205);

- a directional control device (208) adapted to generate a command signal

(201);

- a processing unit operatively connected to said actuator (206), said directional control device (207), said first sensor (108) and said second sensor (109), said assisted guidance system (200) being characterized in that said processing unit is configured for executing the following steps:

- acquiring a plurality of input parameters comprising the directional command (201), the first angle (105), the second angle (106) and at least one parameter relating to the motion of the convoy;

- computing, by means of a first PID controller (202), a first control value (203) as a function of the directional command (201), the second angle (106) and the parameter relating to the motion of the convoy;

- computing, by means of a second PID controller (204), the actuation signal (205) as a function of the outputted first control value (203), the first angle (105) and the parameter relating to the motion of the convoy;

- supplying the actuation signal (205) to said actuator (206).

2. System (200) for assisted guidance of a convoy (100) according to claim 1, wherein the first sensor (108) and the second sensor (109) are operatively connected to the processing unit via a wireless data connection.

3. System (200) for assisted guidance of a convoy (100) according to any one of the preceding claims, wherein the first sensor (108) and the second sensor (109) comprise each a MEMS inertial platform and a magnetic compass.

4. System (200) for assisted guidance of a convoy (100) according to any one of the preceding claims, wherein the control device is a joystick.

5. System (200) for assisted guidance of a convoy (100) according to any one of the preceding claims, wherein the control device is a digital touchscreen.

6. System (200) for assisted guidance of a convoy (100) according to any one of the preceding claims, wherein the parameter relating to the motion of the convoy comprises a value of the speed of the convoy (100).

7. Computer program adapted for computing an actuation signal in a system (200) for assisted guidance of a convoy (100) comprising a tractor (101), a first trailer (102) and a second trailer (103), said tractor comprising a steering system (107) adapted to steer the tractor (101) as a function of a steering angle (107), said system (200) comprising:

- a directional control device (208) adapted to generate a command signal

(201);

- a processing unit comprising a memory, said processing unit being operatively connected to said actuator (206), said directional control device (207), said first sensor (108) and said second sensor (109), said computer program being stored in said memory and being configured for executing the following steps:

- supplying the actuation signal (205) to said actuator (206).

8. Computer program adapted for calibrating the assisted guidance system of any one of claims 1-6, said program comprising the following steps:

- generating a simulation model (401) of the kinematics of a convoy (100) comprising a tractor (101), a first trailer (102) and a second trailer (103), said tractor comprising a steering system (107) adapted to steer the tractor (101) as a function of a steering angle (107);

- acquiring from the simulation model (401) a plurality of input parameters comprising:

- a first angle (105) defined by the intersection between a longitudinal axis of the tractor (101) and a longitudinal axis of the first trailer (102);

- a second angle (106) defined by the intersection between a longitudinal axis of the first trailer (102) and a longitudinal axis of the second trailer (103);

- a parameter relating to the motion of the tractor (101);

- generating a command signal (201) as a function of a desired trajectory;

- supplying to a control law (207) said first angle (105), said second angle (106), said parameter relating to the motion of the tractor (101), said command signal (201), said control law (207) comprising the following steps:

- supplying the actuation signal (205) to the simulation model (401) of the convoy (100); - acquiring from the simulation model (401) of the convoy (100) a simulated trajectory of the convoy (100);

- comparing said simulated trajectory with said desired trajectory;

- modifying one or more gain parameters (302a, 302b, 303a, 303b, 304a, 304b) of at least one of said first PID controller (202), second PID controller (203) as a function of said comparison.

9. Computer program according to claim 8, wherein said simulation model (401) comprises one or more of the following parameters:

- maximum value of the steering angle (107);

- maximum value of the first angle (105); - maximum value of the second angle (106);

- length of the tractor;

- length of the first trailer and of the second trailer.