CONTROL METHOD FOR CONTROLLING THE MOVEMENT OF AN AUTONOMOUS MOTOR VEHICLE

Description

[Domaine technique

[0001] The present invention relates to a control method for controlling the movement of an autonomous motor vehicle, a control device for controlling such movement, a computer program product comprising program instructions operable by said control device, and an autonomous motor vehicle comprising said control device. Technique antérieure

[0002] In recent years, advances in equipping motor vehicles with driver assistance systems have contributed to a significant improvement in road safety. The challenge for the future is to design autonomous vehicles. An autonomous vehicle is a vehicle adapted to drive on an open road with little or no driver intervention. The concept aims to develop and produce such a vehicle that can eventually operate safely on public roads, regardless of traffic generated by other vehicles or obstacles (humans, animals, trees, etc.) present on the road. The term "autonomous vehicle" here encompasses a fully autonomous vehicle in which human operator intervention is not required for driving.This concept also covers a so-called "semi-autonomous" motor vehicle equipped with automated driving assistance systems, but in which the intervention of the human operator remains generally important.

[0003] The operation of an autonomous vehicle is generally governed jointly by an onboard navigation system and a system for defining a reference trajectory. The onboard navigation system is designed to program a large-scale route, that is, one covering an entire road network. This route comprises a series of consecutive road segments adapted to connect a starting point to a destination. This series of road segments may vary dynamically depending on detected traffic conditions or predefined constraints on the road network (such as the closure of certain sections for ongoing roadworks).

[0004] The reference trajectory definition device is designed to automatically process vehicle movement trajectories on a local scale, on the order of several tens or hundreds of meters. This reference trajectory definition device is adapted to implement the route programmed by the navigation system. This implementation is achieved by determining the vehicle's position, direction, and speed over time based on movement constraints, such as dynamic constraints of the vehicle (maximum speed, longitudinal acceleration, steering angle, etc.), environmental constraints (obstacles on the road, etc.), or optimization constraints (minimizing the vehicle's lateral acceleration, for example).

[0005] In an autonomous driving context, a vehicle is configured to follow a predefined urban or extra-urban route by traversing a series of road segments determined by the onboard navigation system. The reference trajectory is defined by a set of time-varying Cartesian coordinates calculated in real time based on the road segment at which the predefined route is reached and environmental parameters. This calculation can be performed using a road marking recognition system, radar or laser detection systems, an obstacle detection system, etc. During driving, the vehicle follows an actual trajectory that may differ from the reference trajectory.Indeed, during driving, the vehicle is subjected to a number of constraints (tire pressure, road gradient, wind force, etc.) that may not have been taken into account by the system defining the reference trajectory. Consequently, a lateral offset may exist between the actual trajectory and the reference trajectory, which must be minimized. Lateral offset refers to a non-zero distance between the actual trajectory and the reference trajectory, measured along an axis normal to the reference trajectory. This offset can be corrected by appropriately controlling a lateral control system to modify the vehicle's steering angle.

[0006] Patent US2016107682 discloses a method for controlling the direction of an autonomous vehicle. In this method, a point on the reference path is selected in advance. A reference distance is determined, at a given time t, between the autonomous vehicle and the selected point on the reference path. The vehicle's direction is then controlled from this reference distance.

[0007] Although the method disclosed in document US2016107682 improves vehicle steering control, it does not prevent passenger comfort issues related to oscillations of the actual trajectory around the reference trajectory, or even instability problems. These issues are particularly significant at high speeds and / or when faults occur in the control system (sensor failure, map initialization).

[0008] The documents "Three look-ahead distance scheme for lateral control of vision-based vehicles" and "Design of a High-Performance Automatic Steering Controller for Bus Revenue Service Based on How Drivers Steer" describe trajectory determinations for motor vehicles.

[0009] Therefore, there is a need to propose a control method for controlling the direction of an autonomous motor vehicle, which is simple and practical to implement and which improves the perception of comfort by the passengers of this autonomous vehicle.

[0010] The document "Three look ahead distance scheme for lateral control of vision-based vehicles" Katsumi Hasegawa and Eiji Konaka describe a method for lateral vehicle control that uses the error in the vehicle's position relative to a reference trajectory, measured with respect to three reference points located upstream of the vehicle. However, the distance to these three points is fixed. The paper "Design of high-performance automatic steering controller for bus revenue service based on how driver steer," by Tan Hua-Shue et al., IEEE Transactions on Robotics, IEEE Service Center, Piscataway, NJ, US, Vol. 30 No. 5, describes a method in which a reference point taken upstream of the vehicle is used as a target, and the vehicle's lateral control is adjusted to reach that target. Description of the invention

[0011] The present invention aims to address at least partially this need.

[0012] More specifically, the present invention aims to improve the passenger experience in an autonomous vehicle.

[0013] A first object of the invention relates to a control method for controlling the movement of an autonomous motor vehicle along a reference trajectory according to claim 1.

[0014] Thus, the invention requires the autonomous vehicle to maintain a low yaw error. More specifically, the control method selects, at a given time t, an ideal point within the polynomial of points on the reference trajectory to minimize this yaw error. More precisely, the method selects a reference distance between the vehicle's position and this ideal point to minimize the yaw error. Consequently, the risk of jerking during the implementation of actual trajectory tracking is greatly reduced, regardless of the autonomous vehicle's speed or any potential malfunctions in the vehicle. The passenger experience is therefore improved.

[0015] In a particular embodiment, the yaw error is kept less than or equal to said yaw error threshold when a lateral error y L is greater than a certain lateral error threshold, said lateral error y L being determined at the reference distance L from the reference trajectory and a vehicle position.

[0016] In a particular embodiment, the yaw error is kept less than or equal to said yaw error threshold when the speed of the autonomous vehicle is greater than a certain speed.

[0017] In a particular embodiment, the desired yaw rate is determined according to the equation: w des = 2 × y L L 2 × v x , with y L the lateral error at the reference distance L and vx the speed of the autonomous motor vehicle.

[0018] According to the invention, the reference distance is determined according to the equation: L = K LAS ( ρ ) × δ̈ , with K LAS a control function, with p a parameter depending on the vehicle speed vx, the lateral error y L and a reference distance L' determined at a time t-1, and with δ°° a steering acceleration.

[0019] In a particular embodiment, the control method is adapted to control the lateral movement of the motor vehicle.

[0020] Another object of the invention relates to a control device for controlling, via an actuator, the movement of an autonomous motor vehicle along a reference trajectory according to claim 6.

[0021] The control system is adapted to the dynamic model of the autonomous vehicle and to any type of lateral controller used. The autonomous vehicle thus automatically adapts to the various situations it encounters.

[0022] Another object of the invention relates to a computer program product comprising program instructions that can be used by the control device of a previous object, which, when executed or interpreted by said control device, trigger the implementation of the control method of another previous object in an autonomous motor vehicle.

[0023] The present invention will be better understood upon reading the detailed description of embodiments taken by way of non-limiting examples and illustrated by the accompanying drawings, in which: There figure 1 is a schematic view illustrating an autonomous motor vehicle according to the invention; The figure 2 illustrates an autonomous automobile vehicle of the figure 1 on a road. The figure 3 illustrates a control device for controlling the movement of the autonomous motor vehicle figures 1 et 2 ; There figure 4 details the contents of an intelligent reference optimization module of the control device figure 3 ; There figure 5 details the lateral control module of the control device figure 3 ; There figure 6 is a diagram illustrating the different stages of a control device for controlling the movement of the motor vehicle figures 1 et 2 ; There figure 7 allows for comparison of a response from the autonomous motor vehicle to figures 1 et 2 compared to a component of a vehicle of the prior art.

[0024] The invention is not limited to the embodiments and variants shown, and other embodiments and variants will be obvious to a person skilled in the art.

[0025] In the different figures, identical or similar elements bear the same references.

[0026] There figure 1 The diagram schematically represents a top view of a motor vehicle 10 according to the present invention. This motor vehicle 10 comprises a front section, a rear section, a roof, an interior, and steering means (not shown). The motor vehicle also comprises a chassis and one or more body panels mounted or fixed to said chassis.

[0027] Vehicle 10 is an autonomous vehicle. By autonomous vehicle, we mean a fully or semi-autonomous vehicle. There are, in fact, several levels of autonomy in a vehicle.

[0028] In the first level, known as level 1, the vehicle is responsible for a limited number of driving operations associated with that vehicle. The driver remains responsible for most driving control operations. In level 1, acceleration and / or braking (cruise control, etc.) are controlled by the vehicle. This level 1 corresponds to a level of driver assistance.

[0029] In a second level, known as Level 2, the vehicle is adapted to collect information (for example, via one or more driver assistance systems, sensors, etc.) about the external environment (the road around the vehicle, the road surface, traffic, ambient conditions). At this Level 2, the autonomous vehicle is adapted to use the collected information to control certain driving operations (for example, steering, acceleration, and / or braking). This Level 2 represents a level of partial automation for the vehicle. It is important to note that for both Level 1 and Level 2, the driver must retain full control over the driving operations performed by the autonomous vehicle.

[0030] In a third level, called level 3, the driver delegates all driving operations to the motor vehicle except when the motor vehicle requests the driver to act or intervene to control one or more of these driving operations. This level 3 is a level of conditional automation.

[0031] In a fourth level, known as level 4, the driver no longer manages any driving operations. The vehicle then controls all driving operations, including when the driver does not respond to a request for intervention. Level 4 is a high level of automation.

[0032] At level 5, the vehicle controls all driving operations. During operation, the vehicle monitors road traffic, moving objects on the road (humans, animals), stationary obstacles, and the road surface. At level 5, no interaction with a human driver is required. Level 5 represents complete automation. It should be noted that at levels 3 through 5, the vehicle is equipped to monitor both driving operations and its external environment.

[0033] To perform the various driving operations at these different levels of autonomy, the vehicle 10 includes a number of sensors such as: a front radar 11A, 11B; a rear radar 12A, 12B; an ultrasonic sensor 13; a video camera 14; a LIDAR 15; a GPS antenna 16.

[0034] The front radar comprises two front radar elements 11A and 11B arranged on the front of the vehicle on either side of an axis of symmetry of said vehicle 10. The front radar has a detection zone 111 at the front of the vehicle. It is thus adapted to detect the positions of surrounding objects. It allows the speed of the vehicle to be measured. The information gathered by the front radar 11A and 11B is particularly useful for implementing certain driving operations such as emergency braking or lane departure warning.

[0035] The rear radar comprises two rear radar elements 12A and 12B positioned on the rear of the vehicle, on either side of the vehicle's axis of symmetry 10. The rear radar has a detection zone 112 at the rear of the vehicle. It is thus adapted to detect the positions of surrounding objects. It allows the speed of other vehicles following the vehicle 10 to be measured. The information gathered by the rear radar 12A and 12B is particularly useful for implementing certain driving operations such as emergency braking or lane departure warning.

[0036] The ultrasonic sensor 13 is located on the front of the vehicle between the two front radar elements 11A and 11B. The ultrasonic sensor 13 has a detection zone 113 that is significantly smaller than the detection zone 111 of the front radar 11A and 11B. This ultrasonic sensor 13 is therefore suitable for detecting very close obstacles. The information gathered is particularly useful for implementing driving maneuvers such as maintaining a safe following distance from another vehicle directly in front of the vehicle 10.

[0037] Video camera 14 is located here behind the rearview mirror. The information gathered by this video camera 14 is particularly useful for carrying out certain driving operations such as deciphering road signs, identifying curbs and center lines, and detecting moving objects on the road (humans, animals).

[0038] The LIDAR 15 (for "Light Detection and Ranging") is a sensor located here on the roof of the vehicle 10. It enables laser remote sensing measurements. Laser remote sensing is a remote measurement technique based on analyzing the properties of a light beam reflected back to its emitter. The LIDAR has a fairly large detection area 115, for example, on the order of 50 meters in diameter. It allows for continuous 360° scanning of the environment to create a 3D map. The information gathered by the LIDAR 15 is useful for implementing certain driving operations such as obstacle detection, including at night.

[0039] The GPS antenna 16 is located on the rear of the vehicle 10. It receives GPS (Global Positioning System) signals. Navigation data can then be updated in the vehicle 10 based on these GPS signals.

[0040] The motor vehicle also includes a central computer 17 adapted to process the various data from sensors 11A, 11B, 12A, 12B, 13, 14, 15. The central computer 17 and the sensors 11A, 11B, 12A, 12B, 13, 14, 15 are connected in the motor vehicle by one or more networks (not shown) of the CAN bus type (for "Controller Area Network" in English) for the transport of said sensor data.

[0041] There figure 2 illustrates the autonomous vehicle 10 of the figure 1 on a road 20. This autonomous vehicle 10 has a center of gravity 23. To simplify Figure 22, sensors 11A, 11B, 12A, 12B, 13, 14, 15, 16 have not been shown on the figure 2 Route 24 is bordered by two curbs 21. It is further divided into two lanes separated by a plurality of median strips 22. On the figure 2 The vehicle is traveling in the right lane, following an actual trajectory. This actual trajectory is offset by a lateral offset D between a center of gravity and the reference trajectory T. This reference trajectory was previously calculated by the vehicle's navigation system 10, notably from GPS signal data received by the GPS antenna 16. This reference trajectory T extends here to the midpoint between the edge 21 and the central bands 22. It is formed by a plurality of points A0,..., Ai,...An.

[0042] The invention aims to minimize the lateral offset D. To this end, the motor vehicle 10 includes a control device 20 that selects an ideal point Ai from among all the points forming the reference trajectory T. This ideal point Ai constitutes an anticipation point. A reference distance L is then determined between the center of gravity 23 and the anticipation point Ai. Depending on the external constraints around the autonomous vehicle, for example, environmental or traffic constraints, the control device 20 selects an anticipation point Ai that is closer to or further from the center of gravity 23. Thus, if the external environment is simple and traffic is light, the control device will select an anticipation point far from the center of gravity 23. The reference distance L will therefore be significant.This will correct the lateral deviation to smoothly bring the autonomous vehicle back onto the reference trajectory T, limiting jolts. Conversely, if the external environment is complex (rainy weather, etc.) and / or traffic is congested, the control system will select a close anticipation point relative to the center of gravity 23 to force a rapid return of the autonomous vehicle to the reference trajectory T. This control system 20 is, in a preferred embodiment, integrated directly into the central computer 17 of the vehicle. figure 1 Thus, the control device 20, in a preferred embodiment, allows the lateral movement of the autonomous motor vehicle 10 to be controlled.

[0043] There figure 3 illustrates a control device 20 to control the movement of the autonomous motor vehicle 10.

[0044] The control device 20 includes: a speed block 201; a reference trajectory block 202; a vehicle position block 203; a yaw rate block 204; an intelligent reference optimizer module 205; a lateral control module 206; a steering acceleration block 207.

[0045] The speed block 201 is suitable for measuring the speed vx of the motor vehicle 10.

[0046] The reference trajectory block 202 is suitable for storing the reference trajectory T data of the motor vehicle 10.

[0047] The vehicle position block 203 is adapted to determine the position of vehicle P at any time t.

[0048] The yaw rate block 204 is suitable for determining an actual yaw rate W of the motor vehicle.

[0049] The intelligent reference optimizer module 205 is suitable for determining a desired yaw rate W from the speed vx, reference trajectory data T, vehicle position P and a steering acceleration δ°°.

[0050] The lateral control module 206 is adapted to provide a lateral control K lat command from the desired yaw rate W des and the actual yaw rate W.

[0051] The steering acceleration block 207 is adapted to provide the steering acceleration δ°° from the lateral control K lat command.

[0052] There figure 4 details the contents of the intelligent reference optimizer module 205. This module 205 includes: a lateral error block 2051; a control function block 2052; a reference distance block 2053; a desired yaw rate block 2054.

[0053] The lateral error block 2051 is adapted to receive the reference trajectory T, the position P of the vehicle and a reference distance L' determined at a time t-1. This lateral error block 2051 delivers a lateral error y L.

[0054] The control function block 2052 is adapted to receive the vehicle speed vx 10, the lateral error y L, the reference distance L' and the steering acceleration δ°°. This block 2052 includes a lateral function K LAS adapted to deliver a reference distance L determined at time t.

[0055] The reference distance block 2053 is designed to receive the reference distance L determined at time t. This block 2053 delivers this reference distance L to the desired yaw rate block 2054. Block 2053 also delivers the reference distance L' determined at time t-1 to the lateral error block 2051 and to the control function block 2052.

[0056] The desired yaw rate block 2054 receives the reference distance L determined at time t. It outputs the desired yaw rate W.

[0057] There figure 5 details the lateral control module 206. This module 206 includes: a yaw error block 2061; a lateral control block 2062; a steering speed block 2063; a diverter block 2064.

[0058] The yaw error block 2061 is adapted to compare the desired yaw rate Wdes to the actual yaw rate Wdes. This yaw error block 2061 provides a yaw error ErrLace. In the invention, this yaw error ErrLace is less than or equal to a predetermined yaw error threshold S1. Preferably, this yaw error threshold S1 corresponds to 10% of the desired yaw rate Wdes.

[0059] The lateral control block 2062 is adapted to receive the yaw error Err Yaw and to determine a steering speed δ°.

[0060] The steering speed block 2063 is adapted to receive the steering speed δ° and to supply this steering speed to the diverter block 2064.

[0061] The control method for controlling the movement of the autonomous motor vehicle 10 is described below in support of the figures 1 à 5 and of the figure 6 .

[0062] On the figure 6 , in a determination step E1, input data concerning the speed vx of the vehicle 10, the reference trajectory T, as well as the position P of the vehicle are determined.

[0063] In a step E2, block 2051 of module 205 determines a lateral error y L from the reference trajectory T, the position P of the vehicle and the reference distance L' determined at time t-1.

[0064] In step E3, block 2052 of module 205 determines a reference distance L at time t from the vehicle's speed vx 10, the lateral error yL, the reference distance L' determined at time t-1, and the steering acceleration δ°°. In a preferred embodiment, we have the equation: L = K LAS ( ρ ) × δ̈ , with, as a reminder, K LAS the control function, with ρ a parameter dependent on the speed vx of the vehicle, the lateral error y L and the reference distance L' determined at time t-1, and with δ°° the steering acceleration.

[0065] In step E4, block 2053 of module 205 transmits the reference distance L' to blocks 2051 and 2052. In this step E4, block 2053 also transmits the reference distance L determined at time t.

[0066] In step E5, block 2054 determines the desired yaw rate Wdes. This desired yaw rate Wdes is a function of the reference distance L between the vehicle and the reference trajectory at time t. In a particular embodiment, the desired yaw rate Wdes is determined according to the equation: w des = 2 × y L L 2 × v x , with, as a reminder, y L the lateral error at the reference distance L and vx the speed of the autonomous motor vehicle.

[0067] In step E6, block 2061 of module 206 determines a yaw error Err_yaw. This yaw error Err_yaw corresponds to the comparison of the desired yaw rate W_des with the actual yaw rate W_of the motor vehicle.

[0068] In a step E7, block 2062 of module 206 determines a steering speed δ° from the yaw error Err yapt.

[0069] In step E8, block 2064 of module 206 determines and transmits a steering acceleration δ°° to a suitable actuator to control the autonomous vehicle. This steering acceleration is therefore determined from the yaw error Err Yaw via steps E7 and E8. The actuator is, for example, a steering column of the autonomous vehicle.

[0070] It should be noted that the yaw error is kept less than or equal to the yaw error threshold S1 when the lateral error is greater than a certain lateral error threshold S2.

[0071] Dans un mode In an alternative implementation, the yaw error is kept less than or equal to the yaw error threshold S1 when the speed vx of the autonomous vehicle is greater than a certain speed, for example a speed of 80 km / h.

[0072] The control method and the associated control device 20 were validated on the Satory test track in a mixed section including straight lines and curves. figure 7 This allows for a comparison between a first trajectory 31 and a second trajectory 32 during a sudden change of reference trajectory T. The first trajectory 31 represents the response of an autonomous vehicle according to the prior art. This response oscillates around the reference trajectory. The second trajectory 32 represents the response of the autonomous vehicle 10 according to the invention. This response exhibits a much smaller oscillation. The actual trajectory of the autonomous vehicle thus "sticks" much more quickly to the reference trajectory T.

[0073] The control method for controlling the movement of an autonomous motor vehicle and the associated control device 20 thus allow: to find the optimal anticipation point in the reference trajectory to feed the lateral controller; to have a control device that can be applied to any autonomous lateral maneuver (lane change, dynamic change, parking maneuver, ...); to have a control device compatible with any trajectory navigation system and capable of being connected to any ADAS / AD lateral controller; to have human-like driving of an autonomous vehicle in critical situations where the desired trajectories may be either inconsistent or impossible to achieve given the vehicle's capabilities; to have smooth driving of the vehicle in the event of significant noise or errors caused by sensors or road conditions; to have a control device that can also be used to start an autonomous mode in the event of significant initial lateral errors; to have a control device that allows verification of the desired steering acceleration based on the condition and capabilities of the actuator.

[0074] The invention also relates to a computer program product comprising program instructions usable by the control device 20, which, when executed or interpreted by said control device 20, trigger the implementation of the control method as described in the figure 5 .

[0075] The invention also relates to an autonomous motor vehicle 10 comprising the control device 20. This autonomous motor vehicle is a passenger vehicle, as shown in the figure 1 and on the figure 2 Alternatively, a motor vehicle is a completely different type of vehicle such as a bus or a truck.

[0076] The invention is not limited to the embodiments and variants shown, and other embodiments and variants will be obvious to a person skilled in the art.

Claims

1. Control method for controlling the movement of an autonomous motor vehicle (10) along a reference trajectory (T), said method being characterized in that it comprises: - a step of determining a reference distance L between the vehicle and a point (Ai) situated on the reference trajectory (T) at an instant t, said reference distance L being selected such that the yaw error is less than or equal to a predetermined yaw error threshold (S1) and determined according to the equation L = KLAS(ρ) × δ̈, where • KLAS is a control function, • ρ is a parameter dependent on the speed vx of the vehicle, on a reference distance L' determined at an instant t-1 and on the lateral error yL between the vehicle and the reference trajectory (T) at the distance L', and • δ°° is a steering wheel angular acceleration - a step (E5) of determining a desired yaw rate (Wdes) of the autonomous motor vehicle, said desired yaw rate (Wdes) being a function of the reference distance (L); - a step (E6) of determining a yaw error (Erryaw) corresponding to a comparison of the desired yaw rate (Wdes) with an actual yaw rate (W) of the autonomous motor vehicle; - a step (E7) of transmitting a steering wheel angular acceleration (δ°°) to an actuator suitable for controlling the autonomous motor vehicle, said steering wheel angular acceleration being determined from the yaw error (Erryaw).

2. Control method according to Claim 1, wherein the yaw error (Erryaw) is maintained less than or equal to said yaw error threshold (S1) when a lateral error (yL) is above a certain lateral error threshold (S2), said lateral error (yL) being determined at the reference distance (L) from the reference trajectory (T) and from a position (P) of the vehicle (10).

3. Control method according to any one of Claims 1 or 2, wherein the yaw error (Erryaw) is maintained less than or equal to said yaw error threshold (S1) when the speed (vx) of the autonomous vehicle is greater than a certain speed.

4. Control method according to any one of Claims 1 to 3, wherein the desired yaw rate (Wdes) is determined according to the equation: w des = 2 × y L L 2 × v x , where yL is the lateral error at the reference distance L and vx is the speed of the autonomous motor vehicle.

5. Control method according to any one of Claims 1 to 5, wherein said control method is adapted to control the lateral movement of the autonomous motor vehicle.

6. Control device for controlling, via an actuator, the movement of an autonomous motor vehicle along a reference trajectory, said control device comprising: - a lateral controller (206) suitable for providing a steering wheel angular acceleration (δ°°) to said actuator, said steering wheel angular acceleration (δ°°) being determined from a yaw error (Erryaw) corresponding to a comparison between a desired yaw rate (Wdes) and an actual yaw rate (W) of said autonomous motor vehicle (10); - a smart reference optimizer (205) suitable for supplying the desired yaw rate (Wdes) to the controller, said desired yaw rate (Wdes) being a function of a reference distance (L) between said autonomous motor vehicle and a point (Ai) situated on said reference trajectory at a time t, said reference distance L being determined according to the equation L = KLAS(ρ) × δ̈, where • KLAS is a control function, • ρ is a parameter dependent on the speed vx of the vehicle, on a reference distance L' determined at an instant t-1 and on the lateral error yL between the vehicle and the reference trajectory (T) at the distance L' , said reference distance (L) being selected such that the yaw error (Erryaw) is less than or equal to a predetermined yaw error threshold (S1).

7. Computer program product comprising program instructions which may be implemented by a control device (20) of Claim 6 and which, when they are executed or interpreted by said control device (20), trigger the implementation of the control method according to any one of Claims 1 to 5 in an autonomous motor vehicle (10).

8. Autonomous motor vehicle comprising a control device (20) according to Claim 6.