DE202021105068U1 - Automated guided vehicle and device for reliably detecting vehicle movement - Google Patents

Abstract

Driverless transport vehicle
- with at least three wheels, which are designed as individual wheels (12, 14, 16, 18) and at least two of the wheels (12, 14) are steered individually and each have a steering device,
- and at least some of the wheels (16, 18) are driven so that their rotational speeds are controlled,
- with a steering angle detection device (28) for detecting the steering angle of the at least two steered wheels (12, 14) and for outputting corresponding steering angle signals,
- with an evaluation unit (32) to which the steering angle signals are fed,
- and the evaluation unit (32) has a plausibility check unit (34) which carries out a plausibility check on the steering angle signals,
- and outputs a safety signal at an output (36) in the event of an unsuccessful plausibility check.

Description

The invention relates to a driverless transport vehicle and a device for reliably detecting a movement of the vehicle.

Driverless transport vehicles (also called AGV, "Automated Guided Vehicle") are used in industrial environments, for example in logistics. They often move on the same level as people move. For this reason, these vehicles have safety devices that consist of on-board sensors for detecting objects and a corresponding evaluation unit. An essential point for these safety devices is to reliably record the direction of movement and speed of the transport vehicle. This is done, for example, by recording the movement of the individual wheels (also called odometry) in order to be able to steer the transport vehicle safely and without collisions depending on the direction and speed of movement. This means that, knowing the direction of movement and the speed of movement, optical protective fields from sensors in the vehicle, for example, are adapted to the movement, for example in terms of their orientation or extent.

This applies in particular to omnidirectional vehicles, which can move in all directions due to their kinematics. The kinematics are characterized by the fact that, at least for some of the drive wheels, both the steering angle and their rotational movement can be controlled.

In order to be able to reliably record the movement of the vehicle, the movement of a minimum number of wheels must also be recorded in a fail-safe manner.

According to the prior art, the movement of the minimum number of (drive) wheels is detected in a fail-safe manner, either with fail-safe encoders or with redundant encoders per wheel. This applies at least to the wheels, which can be controlled independently. Wheels that are mechanically coupled to other wheels (e.g. because they are on a common axle) and therefore move according to fixed ratios do not have to be reliably recorded individually.

From the DE 10 2014 211 168 A1 a vehicle is known in which, in order to verify position data or speed data, the rotational speeds of the wheels are checked in pairs to determine whether they are identical.

The DE 10 2012 023 999 A1 describes a transport vehicle with three wheels, in which errors are detected by means of plausibility checks, for example when a differential drive is driven over a known straight stretch for a long time and it is determined that one drive rotates faster than the other. The same applies to curves if the drives are running at different speeds than would be expected for the curve.

Proceeding from this state of the art, it is the object of the invention to provide a vehicle or a device which, for example with a minimum number of encoders that do not have to be failsafe, still allows a failsafe determination of the movement of the vehicle.

This object is achieved by a driverless transport vehicle with the features of claim 1 or with a device for reliably detecting a vehicle movement with the features of claim 7.

A driverless transport vehicle according to the invention comprises at least three wheels, which are designed as individual wheels. At least two of the wheels are individually steered and each have a steering device. At least part of the wheels are driven so that their rotational speeds are controlled. The vehicle also includes a steering angle detection device for detecting the steering angle of the at least two steered wheels and for outputting corresponding steering angle signals, and an evaluation unit to which the steering angle signals are fed. The evaluation unit has a plausibility check unit that carries out a plausibility check on the steering angle signals and outputs a safety signal if the plausibility check is unsuccessful.

In this context, 'single wheels' does not mean the opposite of twin wheels, but 'single wheel' means that one wheel can move essentially independently of the other.

According to the invention, failsafety is not created by complex, failsafe encoders detecting steering angle signals and rotational speed signals of a wheel or by making these signals failsafe through costly redundancy of encoders and the like. Rather, the fail-safety is created by skilful plausibility checks of signals from the individual wheels to one another, with the signals being able to be recorded in a non-fail-safe manner easily and without great effort. For this it is assumed that the wheels are controlled in this way in error-free operation The fact that there is little or no wear on the wheels, be it due to inconsistent steering angle positions or turning speed. This results in a regularity between the wheels, which can be used to check the detected movement of the individual wheels for plausibility and thus to determine a movement of the vehicle in a fail-safe manner. If the plausibility check is unsuccessful, ie either the steering angles are not plausible in relation to one another or the movement of the wheels in relation to one another is not plausible, a safety signal is output. This can, for example, initiate a stop of the vehicle.

Advantageously, the plausibility check is carried out in such a way that it is checked whether, when cornering, orthogonal axes to the rolling direction meet through the wheel center of the steered wheels in a common instantaneous center and when driving straight, all wheels are parallel. This can be carried out in a simple manner, in particular in the case of four-wheeled, driverless transport systems in which all the individual wheels are often steered.

If you look at every steerable wheel as a solid body moving in one plane, then every wheel moves around an instantaneous center (in the case of exclusively translational movement, this is at infinity). If two kinematic measurement variables are recorded on a line-moving transport vehicle, here the steering angle positions on the wheels, the movement of the vehicle on the level is determined and can be calculated using forward kinematics. If more of these variables are now recorded, the recording is overdetermined and therefore redundant and can be used for a plausibility check of the measured value recording and processing system components.

Furthermore, there are vehicles that do not fully utilize the possible degrees of freedom of the drives for vehicle movement, but rather maintain certain symmetries. Such a vehicle has at least two wheels, both driven and steered, each at the same distance from a line of symmetry running between them. The plausibility check is such that the intersection of the axes of rotation of these two wheels must lie on the line of symmetry when cornering.

In a further development of the invention, a route recording device is provided, with which the routes covered by the respective wheels are recorded. A plausibility check is now carried out by comparing the distances covered by the different wheels. These routes are identical, for example, when driving straight ahead per unit of time. When cornering, the outer wheels cover longer distances. The plausibility check unit checks the conditions of travel routes of different wheels. Such a plausibility check serves to further increase security. In the special case when one considers equidistant units of time, one also speaks of speed and speed detection. For the purposes of this invention, 'speed' and 'route' are to be understood as a kind of synonym.

In a further development of the invention, the plausibility check unit is designed to take into account tolerance values with regard to the steering angle and possibly tolerance values with regard to the routes for the plausibility check. Minor deviations that occur again and again in reality can be compensated for via the tolerances.

In a further development of the invention, the steering angle of a steered wheel is detected via an angle sensor and/or, in an even simpler way, is read directly from a steering angle controller for the steering device.

In a similar way, the travel distance detection device can detect the travel distance covered by a wheel via an encoder and/or, in the case of a driven wheel, via a drive controller.

The subject matter of the invention is not only the vehicle itself, but also the device for reliably detecting vehicle movement, which is part of the vehicle and therefore, as already described, comprises a steering angle detection device for detecting the steering angle of at least two wheels of the vehicle, the Individual wheels are each formed with a separate steering device. Corresponding steering angle signals are fed to an evaluation unit that has a plausibility check unit that carries out a plausibility check of the steering angle signals of the at least two steered wheels and optionally of the routes covered by individual wheels. If the plausibility check is unsuccessful, a safety signal is output.

• 1 schematische Ansicht auf ein fahrerloses Transportfahrzeug;
• 2 eine Ansicht wie 1 auf ein weiteres Ausführungsbeispiel eines fahrerlosen Transportfahrzeugs;
• 3 eine schematische Darstellung eines Rades.

The invention is explained in detail below using exemplary embodiments with reference to the drawing. Show in the drawing:

• 1 schematic view of a driverless transport vehicle;
• 2 a view like 1 to a further exemplary embodiment of a driverless transport vehicle;
• 3 a schematic representation of a wheel.

A driverless transport vehicle 10 according to the invention has at least three wheels, which are designed as individual wheels. In the embodiment after 1 there are four individual wheels 12, 14, 16, 18. At least two of the wheels 12, 14, 16, 18, namely the wheels 12 and 14, are individually steered and each have a steering device. The steering device includes a servo motor, not shown, for setting a steering angle α, β about a longitudinal axis 21 ( 3 ). At least some of the wheels, all wheels 12 to 18 in this exemplary embodiment, are driven by a number of individual drives 20, 22, 24, 26, so that the rotational speeds of the driven wheels are controlled. The vehicle 10 also includes a steering angle detection device 28 for detecting the steering angles α, β, γ, δ of the steered wheels 12, 14, 16, 18. For this purpose, the steering angle detection device 28 has first encoders 30 ( 3 ) on. The detected steering angles α, β, γ, δ are sent to an evaluation unit 32 in the form of corresponding steering angle signals. Evaluation unit 32 has a plausibility check unit 34 that carries out a plausibility check on the steering angle signals and outputs a safety signal at an output 36 if the plausibility check is unsuccessful. The output 36 is connected to a safety device 38 that ensures the overall safety of the transport vehicle 10 and will not be described or explained further here. The safety device 38 can bring about an emergency stop of the transport vehicle 10, for example.

According to the invention, the error security of the detection of movement and direction of movement of the transport vehicle 10 is created by skillful plausibility checks of parameters of the individual wheels 12, 14, 16, 18 to one another, the parameters being detected easily and without great effort in a non-fail-safe manner. For this purpose, it is assumed that, in error-free operation, the wheels 12, 14, 16, 18 are controlled in such a way that there is little or no wear on the wheels. This results in a regularity between the wheels, which can be used to check the detected movement of the individual wheels for plausibility and thus to determine a safe movement of the vehicle.

In a first embodiment ( 1 ) the plausibility check is carried out in such a way that it is checked whether when cornering, as described in 1 is shown, the wheels 12, 14, 16, 18 move about the same instantaneous center 40. This instantaneous center 40 is the common point of rotation with respect to cornering of the vehicle with its four wheels. If there is no such instantaneous pole, then there must be an error, so that a safety signal is output. This safety signal can indicate the error or trigger an emergency stop in an emergency. When driving straight, ie without curves, which represents a special case with regard to this plausibility analysis, all wheels 12, 14, 16, 18 must be aligned in parallel.

In a second embodiment ( 2 ) the plausibility check is basically similar, but it may be easier to evaluate. In this embodiment, the transport vehicle 100 has two drive wheels 112 and 114, both of which are steered. The two drive wheels 112 and 114 are preferably located symmetrically at the same distance from a line of symmetry 142. The other wheels 116 are not powered and can move freely and only serve as support wheels and can therefore follow any movement of the vehicle 100. The vehicle 100 is driven and steered exclusively via the two drive wheels 112 and 114.

In this case, it only has to be ensured that the two drive wheels 112 and 114 are mirror-symmetrical, ie have the same steering angle in terms of absolute value, ie |α| = |β|. The point of intersection 140 of the axes of rotation of these two wheels 112 and 114 must therefore lie on the line of symmetry 142 when cornering. When driving straight, the point of intersection 140 is again at infinity, which means that the wheels 112 and 114 must be aligned parallel.

In addition to these plausibility checks with regard to the steering angles α, β, γ, δ, a further plausibility check can be carried out with regard to the travel distances of the wheels, which further increases safety. At this time, a travel distance detection device 50 detects the travel distances of the wheels. The distances traveled by the wheels are dependent on the movement of the vehicle, and the distances traveled by two wheels have a certain relationship to one another. When driving in a straight line, the distance traveled is the same for all wheels. When cornering, the wheels on the inside of the curve cover a shorter distance than those on the outside of the curve. The ratio depends on the curve radius and the geometry of the vehicle. In the plausibility analysis, these ratios are checked to see whether they are in the right range. Such a plausibility check can be carried out for all wheels among themselves.

The driving distance detection device 50 can include encoders 44 arranged on axles 42 of the wheels ( 3 ). With such an encoder 44, the rotational movement of a wheel can be detected and the distance traveled (via the radius of the respective wheel) can be determined therefrom. It is assumed that no slip occurs.

In reality, slight deviations from measured steering angle values or rotational speeds occur again and again, so that these deviations are detected in plausibility check unit 34 be intercepted via suitable tolerance values with regard to the steering angles α, β, γ, δ and, if necessary, tolerance values with regard to the routes.

• - Lenkwinkel-Erfassungsvorrichtung 28,
• - Fahrstrecken-Erfassungsvorrichtung 50,
• - Auswerteeinheit 32,
• - Plausibilisierungseinheit 34

stellen eine Vorrichtung zur sicheren Erkennung einer Fahrzeugbewegung, die Teil des Fahrzeuges 10 bzw. 100 ist, dar.The described components of the transport vehicle 10, viz

• - Steering angle detection device 28,
• - route detection device 50,
• - evaluation unit 32,
• - Plausibility check unit 34

represent a device for the reliable detection of a vehicle movement, which is part of the vehicle 10 or 100.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 102014211168 A1 [0006]
• DE 102012023999 A1 [0007]

Claims (10)

Driverless transport vehicle - with at least three wheels, which are designed as individual wheels (12, 14, 16, 18) and at least two of the wheels (12, 14) are steered individually and each have a steering device, - and at least some of the wheels (16, 18) are driven so that their rotational speeds are controlled, - with a steering angle detection device (28) for detecting the steering angle of the at least two steered wheels (12, 14) and for outputting corresponding steering angle signals, - with an evaluation unit (32) to which the steering angle signals are fed, - and the evaluation unit (32) has a plausibility check unit (34) which carries out a plausibility check on the steering angle signals, - and outputs a safety signal at an output (36) in the event of an unsuccessful plausibility check. Driverless transport vehicle claim 1 , characterized in that the plausibility check is carried out in such a way that it is checked whether all wheels are moving about the same instantaneous center and when driving straight all wheels have the same steering angle (steering angle). Driverless transport vehicle claim 1 , characterized in that the vehicle has at least two both driven and steered wheels at a distance from a line of symmetry running between them and the plausibility check is carried out in such a way that the intersection of the axes of rotation of these two wheels must lie on the line of symmetry when cornering. Automated guided vehicle according to one of the preceding claims, characterized in that a route detection device is provided which is designed to detect routes covered by respective wheels and the plausibility check unit carries out a plausibility check of the routes covered by the various wheels. Automated guided vehicle according to one of the preceding claims, characterized in that the plausibility check unit is designed to take account of tolerance values with regard to the steering angle and possibly tolerance values with regard to the routes covered for the plausibility check. Automated guided vehicle according to one of the preceding claims, characterized in that the steering angle detection device comprises an angle sensor for detecting the steering angle and/or that the steering angle detection device receives the steering angle from a steering angle controller. Automated guided vehicle according to one of the preceding claims, characterized in that the route detection device determines the route covered by a wheel via an encoder and/or, in the case of a driven wheel, receives it from a drive controller. Device for the reliable detection of a vehicle movement - With a steering angle detection device (28) for detecting the steering angle of at least two wheels (12, 14) of a vehicle (10), which are designed as individual wheels, each with a separate steering device - and the steering angle detection device (28) is designed to output corresponding steering angle signals, - with an evaluation unit (32) to which the steering angle signals are fed, - and the evaluation unit (32) has a plausibility check unit (34) which carries out a plausibility check on the steering angle signals of the at least two steered wheels (12, 14), - and outputs a safety signal in the event of an unsuccessful plausibility check. device after claim 8 , characterized in that the plausibility check is carried out in such a way that it is checked whether all wheels are moving about the same instantaneous center and when driving straight all wheels have the same steering angle (steering angle). device after claim 8 , characterized in that the plausibility check is carried out in such a way that the intersection of the axes of rotation of the two steered wheels when cornering lie on a line of symmetry which runs between the two wheels.

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