US20160208460A1

US20160208460A1 - System and method for calibrating blade of motor grader

Info

Publication number: US20160208460A1
Application number: US15/080,233
Authority: US
Inventors: Karl A. Kirsch
Original assignee: Caterpillar Inc
Current assignee: Caterpillar Inc
Priority date: 2016-03-24
Filing date: 2016-03-24
Publication date: 2016-07-21

Abstract

A method for calibrating a blade of a motor grader is disclosed. The method comprises resting the blade on a ground plane in a first configuration and then a second configuration, calculating coordinates of a left blade tip and a right blade tip of the blade with reference to coordinates of a frame, while the blade being rested on the ground plane in each of the first configuration and the second configuration, determining a pitch offset, a roll offset and a height offset from the coordinates of the left blade tip and the right blade tip of the blade, and transforming the coordinates of the frame to coordinates of the ground plane using the pitch offset, the roll offset, and the height offset. The transforming equalizes height for the left blade tip with respect to the right blade tip as a constant in each of the first and second configurations and the constant determines a cut depth of the blade in the ground.

Description

TECHNICAL FIELD

The present disclosure relates to motor graders, and more specifically, to a system and method for calibrating a blade of a motor grader.

BACKGROUND

Motor graders are utilized for displacement and leveling of materials, such as sand, gravel, dirt across a variety of applications. A motor grader has a blade assembly suspended on a frame of a chassis. The blade assembly includes a blade that is maneuvered by an operator. The motor grader includes hydraulic actuator system that exerts force for maneuvering the blade. The blade is set for pitch, roll and height positioning for carrying out operations as per an operator's input.
Currently, conventional systems utilize various sensors, such as a GPS (global positioning system), IMU (Inertial Measurement Unit) sensors for detecting the pitch, the roll and a cutting depth of the blade assembly during operational procedures. Further, the conventional systems suffer from operational complexity and also involve additional costs due to sophisticated GPS based systems. There is a need for a GPS independent system and method for calibrating the blade of the motor grader.
Russian Patent Publication Number 2469151, discloses a method of determining a blade height with the help of rigidly mounted GPS satellite navigation. The piston displacement sensors are used to continuously determine the extension stroke of traction frame suspension hydraulic cylinder rods and the input is given to a controller. Data of said piston displacement sensor is fed to controller to compute coordinates of blade cutting edge points in the motor grader coordinate system. Simultaneously, a satellite navigation system and antennas rigidly attached to motor grader main frame are used to define the motor grader blade position and coordinates of origin for the system of global coordinates. After detection of all three coordinates, the computation is done for accurate determination of the blade height relative to the global coordinates, Therefore, there is a need for a GPS independent system and method for calibrating the blade of the motor grader.

SUMMARY OF THE DISCLOSURE

In one aspect of the present disclosure, a method for calibrating a blade of a motor grader is disclosed. The method comprises resting the blade on a ground plane in a first configuration and then a second configuration, calculating coordinates of a left blade tip and a right blade tip of the blade with reference to coordinates of a frame, while the blade being rested on the ground plane in each of the first configuration and the second configuration, determining a pitch offset, a roll offset and a height offset from the coordinates of the left blade tip and the right blade tip of the blade, and transforming the coordinates of the frame to coordinates of the ground plane using the pitch offset, the roll offset, and the height offset. The transforming equalizes height for the left blade tip with respect to the right blade tip as a constant in each of the first and second configurations and the constant determines a cut depth of the blade in the ground.
Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a motor grader, in accordance with the concepts of the present disclosure;

FIG. 2 is a perspective view of a blade assembly of the motor grader, in accordance with the concepts of the present disclosure;

FIG. 3 is a perspective view of the blade assembly showing the blade in a first configuration, in accordance with the concepts of the present disclosure;

FIG. 4 is a perspective view of the blade assembly showing the blade in a second configuration, in accordance with the concepts of the present disclosure; and

FIG. 5 is a flowchart of a method for calibrating the blade of the motor grader, in accordance with the concepts of the present disclosure.

DETAILED DESCRIPTION

Referring to FIG. 1, a motor grader 10 includes a blade assembly 12, a frame 14, a number of hydraulic cylinders 16, a number of wheels 18, and an operator's cabin 20. The blade assembly 12 includes a blade 22, a drawbar 24 and various other components as described later. The drawbar 24 is mounted with the frame 14 of the motor grader 10. The number of hydraulic cylinders 16 provide an extend force and/or retract force using a hydraulic pressure applied to the actuator piston which alters the orientation of the blade 22. The motor grader 10 includes various other components that are not shown in the FIG. 1 without departing from the meaning and scope of the disclosure.
Referring to FIGS. 2 and 3, the blade assembly 12 having a left lift arm 26 (FIG. 3), a right lift arm 28, a left yoke 30 (as shown in FIG. 3), a right yoke 32, a left lift cylinder 34, a right lift cylinder 36, a drawbar ball joint 38, a circle assembly 40, a retainer 42, a pitch cylinder 44, a pitch cylinder circle joint 46, a left blade tip 48, and a right blade tip 50. Further, a number of sensors are disposed within the motor grader 10. For example, a left link arm sensor 52, a right link arm sensor 54, a left yoke sensor 56, a right yoke sensor 58, a left lift cylinder position sensor 60, a right lift cylinder position sensor 62, a circle rotation angle sensor 64, a retainer pitch sensor 66, a pitch cylinder angle sensor 68, among others. The motor grader 10 having a number of inertial measuring units (IMUs) (not shown) to provide information about an orientation and acceleration of various components. The readings from the IMUS and the sensors are provided to a control unit (not shown) for performing calibration procedures (as described in FIG. 5). It will be apparent to the one skilled in the art that other kind of sensors may be used within the motor grader 10 not described herein without departing the scope of the disclosure.
Referring to FIGS. 2 and 3, the blade assembly 12 performs various functions, such as pitch positioning, height positioning and roll positioning of the blade 22. The blade 22 changes its orientation for carrying out various operations. The blade 22 having coordinates (also called coordinates system) X_B, Y_B, Z_B. The frame 14 having coordinates (also called coordinates system) X_F, Y_F, Z_F. A ground (also called a ground plane or a ground surface) having coordinates (also called coordinates system) X_G, Y_G, Z_G(not shown).
Referring to FIG. 3, the blade 22 is positioned in a first configuration. In the first configuration, the blade 22 is rotated in a clockwise direction (rotation about Y_Baxis) till an acute angle, for example, 30-45 Deg. and is rested on the ground. Under this configuration, coordinates of the left blade tip 48, and the right blade tip 50 are calculated. The coordinates of the left blade tip 48 are X_L, Y_L, Z_Land the right blade tip 50 are X_R, Y_R, Z_R. The coordinates of the left blade tip 48 and the right blade tip 50 in the first configuration are calculated by the sensors within the motor grader 10 as described below.
Referring to FIG, 3, the left link arm sensor 52, the left lift cylinder position sensor 60, the left yoke sensor 56, the retainer pitch sensor 66 and the pitch cylinder angle sensor 68 provide coordinates of the left blade tip 48, i.e. X_L, Y_L, Z_L. The right link arm sensor 54, the right lift cylinder position sensor 62, the right yoke sensor 58, the retainer pitch sensor 66 and the pitch cylinder angle sensor 68 provide coordinates of the right blade tip 50, i.e. X_R, Y_R, Z_R.
Referring to FIG. 4, the blade 22 is positioned in a second configuration. In the second configuration, the blade 22 is rotated in an anti-clockwise direction (rotation about Y_Baxis) till an acute angle, for example, 30-45 deg. and is rested on the ground plane. It will be apparent to the one skilled in the art that the blade 22 may be rotated in the clockwise and anti-clockwise direction (rotation about Y_Baxis) at any other acute angle different from 30-45 Deg. for capturing the coordinates of the left blade tip 48 and the right blade tip 50 without departing from the meaning and scope of the disclosure. Under this configuration, coordinates of the left blade tip 48, and the right blade tip 50 are recorded. The coordinates of the left blade tip 48 are X′_L, Y′_L, Z′_Land the right blade tip 50 are X′_R, Y′_R, Z′_R. The coordinates of the left blade tip 48 and the right blade tip 50 in the second configuration are calculated by the sensors within the motor grader 10 as described below.
Referring to FIG. 4, the left link arm sensor 52, the left lift cylinder position sensor 60, the left yoke sensor 56, the retainer pitch sensor 66 and the pitch cylinder angle sensor 68 provide coordinates of the left blade tip 48, i.e. X′_L, Y′_L, Z′_L. The right link arm sensor 54, the right lift cylinder position sensor 62, the right yoke sensor 58, the retainer pitch sensor 66 and the pitch cylinder angle sensor 68 provide coordinates of the right blade tip 50, i.e. X′_R, Y′_R, Z′_R.
Referring to FIGS. 3 and 4, the coordinates of the left blade tip 48 in the first configuration and the second configuration, i.e. (X_L, Y_L, Z_L), (X′_L, Y′_L, Z′_L) respectively are grouped with the coordinates of the right blade tip 50 in the first configuration and the second configuration, i.e. (X_R, Y_R, Z_R), (X′_R, Y′_R, Z′_R) respectively. (X_L, Y_L) and (X′_L, Y′_L) are used to calculate the left pitch. (X_R, Y_R) and (X′_R, Y′_R) are used to calculate the right pitch. The average of left pitch and right pitch gives the final desired pitch offset. All points are then transformed using the pitch offset to obtain pitched left coordinates and pitched right coordinates: (X_PL, Y_PL, Z_PL), (X′_PL, Y′_PL, Z′_PL), (X_PR, Y_PR, Z_PR), (X′_PR, Y′_PR, Z′_PR), pitched left points are paired with the pitched right points to calculate the roll offset. (Y_PL, Z_L) and (Y_PR, Z_R) are used to calculate roll. (Y′_PL, Z′_L) and (Y′_PR, Z′_R) are used to calculate roll. The desired final roll offset is the average of all roll calculations Obtained from the different configurations.
The coordinates of the left blade tip 48 in the first configuration and the second configuration, i.e. (X_L, Y_L, Z_L), (X′_L, Y′_L, Z′_L) and the coordinates of the right blade tip 50 in the first configuration and the second configuration, i.e. (X_R, Y_R, Z_R), (X′_R, Z′_R) are used for calculating the pitch offset, the roll offset and the height offset as described in subsequent description (in FIG. 5 below). it will be apparent to the one skilled in the art that the blade 22 may be rotated in other multiple configurations not limited to the first configuration and the second configuration for capturing the coordinates of the left blade tip 48 and the right blade tip 50 without departing from the meaning and scope of the disclosure.

INDUSTRIAL APPLICABILITY

Referring to FIG. 5, a method 70 for calibrating the blade 22 of the motor grader 10 is disclosed, in conjunction with FIGS. 1-4.
At step 72, the blade 22 is rested on the ground plane in the first configuration and then the second configuration. In an embodiment, the blade 22 is rested on the ground in the first configuration and the second configuration (as described in FIGS. 3 and 4).
At step 74, coordinates of the left blade tip 48 and the right blade tip 50 of the blade 22 are calculated, while the blade 22 being rested on the ground plane in each of the first and the second configurations. In an embodiment, the coordinates of the left blade tip 48 and the right blade tip 50 are calculated in the first configuration and the second configuration, i.e. (X_L, Y_L, Z_L), (X′_L, Y′_L, Z′_L), (X_R, Y_R, Z_R), (X′_R, Y′_R, Z′_R) respectively.
At step 76, the pitch offset, the roll offset and the height offset are determined. The pitch offset is calculated by measuring a slope of a best fit line through coordinates of the left blade tip 48 and the right blade tip 50 projected on a side view plane (XY). The roll offset is calculated using the average of each blade line segment slope in the YZ plane. The height offset is calculated by averaging new Y coordinates for both the left blade tip 48 and the right blade tip 50.
The pitch offset set is calculated by first subtracting each left Y coordinate from the mean of all left Y coordinates. Mean Y coordinate=mean Y_L. The pitch slope is the slope of a best fit line through points (X_L, mean Y_L−Y_L) and (X′_L, mean Y_L−Y′_L). The pitch offset is atan (pitch slope). This is repeated for the right points, and the final desired pitch offset is the average of the left and right pitch offsets. All points are then transformed using the pitch offset to obtain pitched left coordinates and pitched right coordinates: (X_PL, Y_PL, Z_PL), (X′_PR, Y′_PL, Z′_PL), (X_PR, Y_PR, Z_PR), (X′_PR, Y′_PR, Z′_PR), pitched left points are paired with the pitched right points to calculate the roll offset, (Y_PL, Z_L) and (Y_PR, Z_R) are used to calculate roll. Delta Y=Y_PR−Y_PL. Delta Z=Z_R−Z_L. The roll angle is atan (delta Y/delta Z). (Y′_PL, Z′_L) and (Y′_PR, Z′_R) are used to calculate roll' in the same way. The desired final roll offset is the average of all roll calculations obtained from the different configurations.
At step 78, the coordinates of the frame 14, i.e. X_F, Y_F, Z_Fare transformed to the coordinates of the ground plane, i.e. X_G, Y_G, Z_G(not shown) using the pitch offset, the roll offset and the height offset (also vertical offset) as described below:
$Rotz = [\begin{matrix} cuzP & - \sin P & 0 \\ \sin P & \cos P & 0 \\ 0 & 0 & 1 \end{matrix}]$ $Rotz = [\begin{matrix} 1 & 0 & 0 \\ 0 & \cos R & - \sin R \\ 0 & \sin R & \cos R \end{matrix}]$
Apply est_pitch and est_roll of the frame 14 with respect to ground plane to get coordinates of the blade 22 in the ground coordinate system.
The average of the transformed Y coordinates provides the estimated ground plane Y position in this coordinate system. The vertical offset is the negative value of the average transformed Y coordinates.
Transformed_left_vec=Rotx*Rotz*Left_vec;
Transformed_right_vec=Rotx*Rotz*Right_vec; and
Ground coordinates=Rotx*Rotz*frame_height_coordinate+vertical offset.
After applying the transformation, the left blade tip 48 and the right blade tip 50 of the blade 22 having a constant height that determines a desired cut depth of the blade 22 with respect to the ground.
The method 70 disclosed herein offers an effective way of calibration of the blade 22 without requiring costly setups, such as laser mast, high accuracy GPS systems, among others. Further, the method 70 offers advancements in calibration of the blade 22 using the sensors disposed in the motor grader 10. The method 70 enables efficient calibration of the blade 22 that reduces equipment runtime costs and better operator assistance. Due to non use of GPS systems in the proposed disclosure, the blade calibration is easily completed regardless of the weather conditions where the GPS systems might have connectivity issues.
While aspects of the present disclosure have been particularly shown and described with reference to the embodiments above, it will be understood by those skilled in the art that various additional embodiments may be contemplated by the modification of the disclosed machines, systems and methods without departing from the spirit and scope of what is disclosed. Such embodiments should be understood to fall within the scope of the present disclosure as determined based upon the claims and any equivalents thereof.

Claims

What is claimed is:

1. A method for calibrating a blade of a motor grader, the method comprising:

resting the blade on a ground plane in a first configuration and then a second configuration;

calculating coordinates of a left blade tip and a right blade tip of the blade with reference to coordinates of a frame, while the blade being rested on the ground plane in each of the first and second configurations;

determining a pitch offset, a roll offset and a height offset from the coordinates of the left blade tip and the right blade tip of the blade; and

transforming the coordinates of the frame to coordinates of the ground. plane using the pitch offset, the roll offset, and the height offset;

wherein transforming equalizes height for the left blade tip with respect to the right blade tip as a constant in each of the first and second configurations, the constant determines a cut depth of the blade in the ground.