METHOD FOR PUTTING DOWN A TOOL OF A CONSTRUCTION MACHINE

Abstract

A method is for putting down a tool of a construction machine. A position and an orientation of the tool relative to the construction machine or to a direction of Earth's gravity is determined by one or more of the following sensors including: an inertial measuring unit, an angle sensor, a linear sensor, and/or by an algorithm for determining a kinematic chain of the construction machine. Moreover, an orientation of at least one part of the construction machine, which part touches the ground, and which orientation characterizes an orientation of the construction machine relative to the ground, is determined relative to Earth's gravity. Based on this determination, movement of the tool is controlled, in order to bring a lower face of the tool to the same level and in the same orientation as the at least one part touching the ground, for putting down the tool.

Description

The present invention relates to a method for depositing a tool of a construction machine on the ground with the aid of tool center point estimation. Further, the invention relates to a computer program, which performs each step of the method when executed on a computing device, and to a machine-readable storage medium that stores the computer program. Finally, the invention relates to an electronic control device that is configured to execute the method according to the invention.

PRIOR ART

One of the basic maneuvers of many construction machines such as, for example, excavators, wheel loaders, bulldozers and the like, is to deposit the tool of the construction machine on the ground. The tool in this case must be placed on the ground safely, i.e. without tipping or slipping (off), and with as little impact force as possible. This maneuver is often difficult, especially for inexperienced operators, in particular if the view of the tool and/or of the ground is obstructed.

Algorithms for determining the kinematic chain are known. For this purpose, one or more of the following sensors are arranged on each link of the tool arm, inertial measurement unit (IMU), angle sensors, linear sensors, which send sensor data to a computing device. The sensor data thus ascertained are filtered individually for each sensor and are fused for the purpose of estimating the state of the orientation of the respective sensor relative to a stationary inertial coordinate system. Such an algorithm is used, for example, in tool center point estimation. Tool center point estimation is an algorithm for estimating the state of orientation and position of an end effector. In particular, the end effector is a tool or a part of a tool that has a tool arm having a plurality of links connected by joints.

Typically used methods are described in the paper by Nikolas Trawny and Stergios I. Roumeliotis, “Indirect Kalman filter for 3D attitude estimation”, University of Minnesota, Dept. of Comp. Sei. & Eng, Tech. Rep 2 (2005), in the paper by Robert Mahony, Tarek Hamei, and Jean-Michel Pflimlin, “Nonlinear complementary filters on the special orthogonal group”, IEEE Transactions on automatic control 53.5 (2008): 1203-1218, and in the paper by Sebastian Madgwick, “An efficient Orientation filter for inertial and inertial/magnetic sensor arrays”, Report x-io and University of Bristol (UK) 25 (2010), to which reference is made in this respect.

From the orientation of the sensor estimated in this way, the orientation of the link on which the sensor is located is first determined. This is done for all links of the tool arm. From the relative orientation of two successive links, the joint angle of the joint connecting the two links can be calculated if the kinematics are known (for example, if the Denavit-Hartenberg parameters are known). Finally, if all joint angles and the dimensions of the links are known, the entire configuration of the tool arm follows directly from the forward kinematics, and hence the orientation and position of the end effector.

For a detailed description, reference is made to the paper by Mark W. Spong, Seth Hutchinson and Mathukumalli Vidyasagar, “Robot modeling and control”, Vol. 3. New York: Wiley, 2006.

DISCLOSURE OF THE INVENTION

A method for depositing a tool of a construction machine on the ground is proposed. “Depositing” is understood here as the process of guiding the tool to the ground until the underside of the tool rests securely on the ground.

Throughout the method, the position and orientation of the links of the kinematic chain, including the tool, relative to the construction machine or to the earth's gravity are determined by means of one or more of the following sensors, inertial measurement unit, angle sensor, linear sensor, by use of an algorithm for determining the kinematic chain. The algorithm for determining the kinematic chain is based on sensor signals from the sensors arranged on at least the at least one part of the tool, and preferably arranged on each link of the kinematic chain between the construction machine and the tool. Inertial measurement units can be easily and inexpensively retrofitted and can be used for other methods.

In addition, the orientation of at least one part of the construction machine contacting the ground, that characterizes the orientation of the construction machine relative to the ground, is determined relative to the earth's gravity. The orientation between the at least one part of the construction machine contacting the ground and a part of the construction machine indicating the orientation of the construction machine is known, or can at least be ascertained. Due to the direct contact between the at least one part contacting the ground and the surface of the ground, the two orientations correspond, at least at the point of contact. Since the orientation of the surface typically changes only slightly over a distance corresponding to the distance between the at least one part contacting the ground and the tool—provided the construction machine is not directly on a ledge—the orientation of the surface of the ground at the place where the tool is deposited can be estimated from the orientation of the surface of the ground at the point of contact, and thus substantially corresponds to the orientation of the at least one part of the construction machine contacting the ground.

Preferably, the orientation of the at least one part of the construction machine contacting the ground is determined via the inertial measurement unit, and particularly preferably by the previously mentioned algorithm for determining the kinematic chain. For this purpose, a sensor signal of an inertial sensor of the inertial measurement unit on the construction machine is used. In this case, the inertial sensor is arranged on the construction machine in such a manner that the orientation between this inertial sensor and the at least one part of the construction machine contacting the ground is known from the design of the construction machine, or can at least be ascertained. Optionally, the orientation of the vertical axis of the construction machine relative to the earth's gravity can be determined in order to determine the orientation of the at least one part of the construction machine contacting the ground.

In particular, the at least one part of the construction machine contacting the ground is realized by wheels or a track chain, i.e. elements that contact the ground to move the construction machine. Generally, the construction machine may also stand on the ground with the at least one part contacting the ground; examples of this are a support or a foot.

If the tool is now to be deposited on the basis of a command from an operator or on the basis of automatic control of the construction machine, the movement of the tool is controlled by closed-loop control, taking into account the position and orientation of the tool and the orientation of the at least one part of the construction machine contacting the ground. The closed-loop control of the movement of the tool as the tool is being deposited is executed in such a manner that the underside of the tool, which is to rest on the ground after being deposited, is brought to the same level, hence in particular to the same height, and to the same orientation as the at least one part contacting the ground. As already described, the orientation of the at least one part of the construction machine contacting the ground corresponds substantially to the orientation of the surface of the ground at the place of deposit.

Advantageously, in the determination of the orientation of the tool, the inclination of the tool is determined and, in the determination of the orientation of the at least one part of the construction machine contacting the ground, the inclination of this part is determined. In this case, in the closed-loop control, at least one joint angle of a joint between the tool and the construction machine may be controlled by closed-loop control such that the underside of the tool is deposited horizontally and/or—even if the ground is not horizontal—parallel to the ground. In other words, the joint angle is controlled by closed-loop control such that the inclination of the underside of the tool corresponds to the inclination of the at least one part of the construction machine contacting the ground, which also corresponds substantially to the inclination of the surface of the ground at the place of deposit.

Depositing the tool is a basic maneuver in the case of many construction machines. As a result of the closed-loop control according to the method according to the invention, the depositing of the tool is at least partially automated. For example, depositing of the tool may be triggered by the operator, by the pressing of a button. The automation of this particular maneuver may be performed independently of an autonomous control. However, an autonomous control of the construction machine may make use of this automated depositing of the tool according to the method.

For the operator, the automated depositing of the tool offers, inter alia, the following advantages: if an operator's view of the tool is obstructed, for example by the construction machine itself, manual control for depositing the tool is often difficult and can only be executed by skilled operators. The automated depositing of the tool according to the method therefore facilitates operation, especially for inexperienced operators. If a work sequence in which the tool is deposited is repeated continuously, which is the case, for example, with a so-called Y-cycle for loading and unloading, e.g. in the case of a wheel loader, the automation simplifies the operation. When the operator parks and leaves the vehicle, the tool can be deposited automatically in order to increase safety. In this case, however, it must be ensured that the tool can actually be put down safely at this place and time without causing damage.

An ambient sensor system may be provided on the construction machine to sense the surroundings of the construction machine. This is often able to sense the orientation and level of the ground in the surroundings. Consequently, with the aid of the ambient sensor system, it is possible to detect ledges. The data from the ambient sensor system may be taken into account in the closed-loop control of the movement of the tool. In general, however, this method also makes it possible to dispense with the ambient sensor system.

A further advantage is that the depositing of the tool can be controlled, by closed-loop control, more precisely by this method than by a method based only on the ambient sensor system or by a method in which a change in the hydraulic pressure is evaluated.

The computer program is configured to perform each step of the method, in particular when executed on a computing device or control device. It enables the method to be implemented in a conventional electronic control device without the necessity of making structural changes to it. For this purpose, it is stored on the machine-readable storage medium.

As a result of the computer program being uploaded to a conventional electronic control device, the electronic control device obtained is a device configured to control the depositing of the tool by closed-loop control.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention are represented in the drawings and explained in more detail in the description that follows.

FIG. 1 shows a schematic representation of a construction machine in which, by means of the method according to the invention, a tool, from an initial state (a), is deposited on the ground (b).

FIG. 2 shows a flow diagram of the method according to the invention.

EXEMPLARY EMBODIMENTS OF THE INVENTION

FIG. 1 shows a schematic representation of a construction machine 1 in the form of a wheel loader, having a tool 2 realized as a shovel. The tool 2 is connected to the construction machine 1 via a working arm 3, there being a respective joint 4 arranged between the construction machine 1 and the working arm 3, and between the tool 2 and the working arm 3, which movably connects the respective components. In further exemplary embodiments that are not shown, the working arm may also be of a multi-link design, in which case there is also a joint arranged between each of the individual links. The construction machine 1, the working arm 3 and the tool 2 form a kinematic chain. There is a respective inertial sensor 5, 5′ of an inertial measurement unit arranged on each link of the kinematic chain, i.e. on the construction machine 1, the working arm 3 and the tool 2. The inertial sensor 5′ arranged on the construction machine 1 has a special significance in this case (see below) and is therefore denoted by a dash (′). The inertial sensors 5, 5′ are connected to an electronic control device 6 of the construction machine 1. The construction machine 1 in the form of the wheel loader has wheels 7 that are connected to the construction machine 1 via axles (not shown) and contact the ground 8.

In further embodiments, not shown here, the construction machine 1 is realized, for example, in the form of a bulldozer, in which, instead of the wheels, a track chain contacts the ground. In still further embodiments, the construction machine 1 may contact the ground with a support or a foot, for example when the construction machine 1 is a stationary construction machine 1 or is supported in a working mode.

Represented in FIG. 1 are two states a) and b), which were recorded at different times. In the initial state a), the tool 2 is still raised. In the final state b), the tool 2 is at the same level as the underside of the wheels 7, and the orientation of the tool 2 corresponds to the orientation of the ground 8, such that the tool 2 is deposited on the ground 8. The joints 4 are oriented differently in the two states.

Represented in FIG. 2 is a flow diagram of an exemplary embodiment of the method according to the invention. At the beginning and throughout the method, the orientation, in particular the inclination, and the position of the tool 2 and of the working arm 3 relative to the construction machine 1 or to the earth's gravity are determined, by means of the inertial sensors 5, 5′ on the construction machine 1, the working arm 3 and the tool 5, by use of an algorithm for determining the kinematic chain 10. For this purpose, the sensor data from the inertial sensors 5, 5′ along the kinematic chain are used. From the orientation, or inclination, and the position of the tool 2 and of the working arm 3, current actual joint angles θ_actual for the joints 4 are then determined 11 by means of so-called Denavit-Hartenberg parameters (see, for example, Spong et al. “Robot modeling and control”, Vol. 3. New York: Wiley, 2006). Also determined 20 at the beginning are the contact points of the wheels 7 relative to the earth's gravity, which substantially represent the orientation of the surface of the ground 8. Preferably, the orientation of the inertial sensor 5′ arranged on the construction machine 1 may be determined by means of a part of the same algorithm for determining the kinematic chain, using only the sensor data of this inertial sensor 5′. In the case of the wheel loader shown here, there is a fixed relationship between the contact points of the wheels 7 and the orientation of this inertial sensor 5′, such that the contact points of the wheels 7, and thus the orientation of the ground 8, can be inferred from the orientation of the inertial sensor 5′.

If the depositing of the tool 2 is activated by an operator 30, for example by pressing a button provided for this purpose, the orientation of the tool 2 in the inertial system, i.e. the inclination with respect to the earth's gravity, is ascertained 40. Then target joint angles θ_target are ascertained 41 from the orientation of the tool 2 in the inertial system and the contact points of the wheels 7.

In a further exemplary embodiment, not shown, when the depositing of the tool 2 is activated by an operator 30, trajectories of movement for the tool 2 are ascertained. In the trajectories of movement, trajectories are described in the coordinates of a solid coordinate system. For this purpose, the position of the tool 2 is specified in the coordinates of the construction machine 1. Target joint angles θ_target are then ascertained from these trajectories of movement.

Finally, a closed-loop control 50 is provided for depositing the tool 2 on the ground 8, in which the actual joint angles θ_actual are controlled to the target joint angles θ_target, such that the underside of the tool 2 is brought to the same level, i.e. the same height, as the plane of the contact points of the wheels 7, parallel to the plane of the contact points of the wheels 7 and thus parallel to the ground 8, therefore horizontal in this exemplary embodiment.

Claims

1. A method for depositing a tool of a construction machine on the ground, comprising:

determining a position and an orientation of the tool relative to the construction machine or to a direction of Earth's gravity using one or more of an inertial measurement unit, an angle sensor, a linear sensor, and/or by use of an algorithm for determining a kinematic chain of the construction machine;

determining, relative to Earth's gravity, an orientation of at least one part of the construction machine contacting the ground that characterizes an orientation of the construction machine relative to the ground; and

controlling a movement of the tool by closed-loop control in order to bring an underside of the tool to a same level and to the same orientation as the at least one part of the construction machine contacting the ground, for depositing the tool on the ground.

2. The method as claimed in claim 1, wherein:

the orientation of the at least one part of the construction machine contacting the ground is determined with the inertial measurement unit, and

a sensor signal of an inertial sensor of the inertial measurement unit located on the construction machine is used to determine the orientation of the at least one part of the construction machine contacting the ground.

3. The method as claimed in claim 1, wherein:

determining the orientation of the tool includes determining an inclination of the tool, and

determining the orientation of the at least one part of the construction machine contacting the ground includes determining an inclination of the at least one part of the construction machine contracting ground.

4. The method as claimed in claim 3, wherein, in controlling the movement of the tool by closed-loop control, at least one joint angle of at least one joint between the tool and the construction machine is controlled by closed loop control, such that the underside of the tool is deposited horizontally and/or parallel to the ground.

5. The method as claimed in claim 1, wherein the at least one part of the construction machine contacting the ground includes one or more wheels and/or a drive chain.

6. The method as claimed in claim 1, wherein a computer program is configured to perform the method.

7. The method as claimed in claim 6, wherein the computer program is stored on a non-transitory machine-readable storage medium.

8. The method as claimed in claim 1, wherein an electronic control device is configured to deposit the tool using the method.