Method for determining the mass and the centre of mass of a demountable platform

Abstract

The present invention relates to a method for determining the mass and the centre of mass of a demountable platform by using a mathematical model, the parameters of which are estimated using an iterative procedure.

Claims

1. A method for determining the mass and the centre of mass of a demountable platform, comprising: using a hooklift to lift the demountable platform from the ground onto a vehicle, measuring, during the lifting of the demountable platform, a physical quantity that varies as a function of the movement of the hooklift, determining, at predetermined values of the physical quantity, values of the load force of a main cylinder of the hooklift, providing a mathematical model of the load force of the main cylinder as a function of the physical quantity, the mathematical model comprising a set of constants related to the physical dimensions of the hooklift, a first parameter for the mass of the demountable platform, a second parameter for the longitudinal position of the centre of mass of the demountable platform and a third parameter for the vertical position of the centre of mass of the demountable platform, setting initial values for the parameters, calculating with the mathematical model the values of the load force at the prede-termined values of the physical quantity, calculating a difference between the determined and calculated values of the load force, if the difference is larger than a predetermined threshold, repeating the following steps until the difference becomes smaller than the predetermined threshold: changing at least one of the values of the first parameter for the mass of the demountable platform, the second parameter for the longitudinal position of the centre of mass of the demountable platform, and the third parameter for the vertical position of the centre of mass of the demountable platform, recalculating with the mathematical model the values of the load force at the predetermined values of the physical quantity based on the at least one changed value, and recalculating the difference between the determined and recalculated values of the load force; selecting the value of the first parameter as the mass of the demountable platform, the value of the second parameter as the longitudinal position of the centre of mass of the demountable platform, and the value of the third parameter as the vertical position of the centre of mass of the demountable platform.

2. The method according to claim 1, wherein the mathematical model is represented by an equation:
F.sub.cylinder=R(p,X.sub.cm,Y.sub.cm,k.sub.1, . . . ,k.sub.n)mg, where R is a set of values of the transmission ratio parameter, p is a set of values of the physical quantity, X.sub.cm is the longitudinal position of the centre of mass of the demountable platform, Y.sub.cm is the vertical position of the centre of mass of the demountable platform, k.sub.1 to k.sub.n are the constants related to the physical dimensions of the hooklift, m is the mass of the demountable platform and g is the acceleration of gravity.

3. The method according to claim 1, wherein the method comprises, before the step of calculating a difference between the determined and calculated values of the load force, modifying the determined values of the load force by subtracting from them the values of the load force determined for the hooklift without the demountable platform.

4. The method according to claim 1, wherein the mathematical model comprises, for a first phase of the lifting of the demountable platform, the friction force represented by an
F.sub.fric_ground=F.sub.a_ground+mk.sub.ground(X.sub.cm/l), where F.sub.a_ground is the constant friction force, m is the mass of the demountable platform, k.sub.ground is the friction parameter, X.sub.cm is the longitudinal position of the centre of mass of the demountable platform and l is the length of the demountable platform.

5. The method according to claim 1, wherein the mathematical model comprises, for a second phase of the lifting of the demountable platform, the friction force represented by an equation:
F.sub.fric_roll=mk.sub.roll, where m is the mass of the demountable platform and k.sub.roll is the friction parameter.

6. The method according to claim 1, wherein the changing of the at least one of the values of the parameters is based on iterating the parameters in two nested loops, wherein in the inner loop the first parameter and the second parameter are varied to find the local minimum, and in the outer loop the third parameter is varied to find the global minimum.

7. The method according to claim 1, wherein the difference between the determined and calculated values of the load force is calculated as a sum of absolute differences.

8. The method according to claim 1, wherein the physical quantity is the rotation angle of a part of the hooklift.

9. The method according to claim 8, wherein the part of the hooklift is one of the following: a middle frame, a sliding frame or a hook.

10. The method according to claim 1, wherein the physical quantity is the position of a piston rod of the main cylinder.

11. The method according to claim 1, wherein the values of the load force are determined based on pressures in a bottom chamber and a piston rod chamber of the main cylinder.

12. The method according to claim 1, wherein the values of the load force are determined based on the strain in the main cylinder.

13. The method according to claim 1, wherein the set of constants related to the physical dimensions of the hooklift comprises one or more of the following: horizontal or vertical component of the distance between a main joint and a joint of a piston of the main cylinder, the main joint and a joint of the main cylinder, the main joint and the hook, the main joint and a rear roller, a bottom rear corner of the demountable platform and a gripping arch, the height of the main joint from the ground.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates an example of a hooklift assembled on a truck;

(2) FIGS. 2A-2C illustrate a method according to an embodiment of the invention for determin-ing the mass and the centre of mass of a demountable platform; and

(3) FIG. 3 is a flowchart illustrating a method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(4) Now, referring to the drawings the invention is described in more details.

(5) FIG. 1 illustrates an example of a hooklift 100 that is assembled on a truck 200. The hooklift 100 comprises a tipping frame 101, which is connected through a tipping joint 102 to a subframe 103 of the hooklift 100. The tipping frame 101 is arranged to be moved relative to the subframe 103 by two parallel main cylinders 104, which are controlled with a hydraulic system 105. The bottom sides 106 of the main cylinders 104 are attached to the subframe 103 and the piston rods 107 of the main cylinders 104 are attached to the tipping frame 101. The subframe 103 is attached to a chassis 201 of the truck 200.

(6) The tipping frame 101 comprises a sliding frame 108, a middle frame 109 and a rear frame 110. The sliding frame 108 comprises a hook 111 with which the hooklift 100 is releasably attached to a demountable platform 300. The sliding frame 108 is connected to the middle frame 109 in such a manner that part of the sliding frame 108 is arranged inside the middle frame 109, and that the sliding frame 108 can be moved relative to the middle frame 109. The middle frame 109 is connected to the rear frame 110 through a middle frame joint 112, and the rear frame 110 is connected to the subframe 103 through the tipping joint 102. The hooklift 100 comprises locks (not shown in FIG. 1) with which the relative movement of parts of the hooklift 100 can be prevented. The hooklift 100 also comprises locks (not shown in FIG. 1) for locking the demountable platform 300 to the hooklift 100 when the demountable platform 300 is transported by the truck 200.

(7) During loading of the demountable platform 300 onto the truck 200 and unloading of the demountable platform 300 from the truck 200, the rear frame 110 is locked to the subframe 103, and the middle frame 109 is rotated around the middle frame joint 112 by using the main cylinders 104. Rear rollers 113 that are mounted close to the tipping joint 102 enable the demountable platform 300 to be easily moved with the hooklift 100 during the loading and unloading work tasks. During tipping and lowering of the demountable platform 300, the middle frame 109 is locked in parallel direction with the rear frame 110 (as shown in FIG. 1), and the rear frame 110 is rotated around the tipping joint 102 by using the main cylinders 104. The position of the demountable platform 300 on the tipping frame 101 can be changed by moving the sliding frame 108 relative to the middle frame 109.

(8) The hooklift 100 comprises pressure sensors 114 and 115 for measuring a pressure in a bottom chamber and a piston rod chamber of the main cylinder 104, respectively. The load force of the main cylinder 104 can be determined based on the pressures in the bottom and piston rod chambers.

(9) The hooklift 100 comprises inclinometers 116 and 117, which are attached to the middle frame 109 and the subframe 103, respectively. By using the inclinometers 116 and 117, an angle between the middle frame 109 and the subframe 103 can be determined, which angle varies as a function of the movement of the main cylinder 104.

(10) The hooklift 100 comprises a data processing unit 118 for processing and storing the data received from the pressure sensors 114 and 115, and from the inclinometers 116 and 117. The data processing unit 118 is configured to determine the angle between the middle frame 109 and the subframe 103 based on the signals received from the inclinometers 116 and 117, and to determine, at predetermined values of the angle, values of the load force of the main cylinder 104 of the hooklift 100 based on the signals received from the pressure sensors 114 and 115. The data processing unit 118 is also configured to determine the mass and the centre of mass of the demountable platform 300 by using a mathematical model of the load force of the main cylinder 104, the model having parameters for the mass and the centre of mass of the demountable platform 300, which are estimated using an iterative procedure.

(11) FIGS. 2A-2C illustrate a method according to an embodiment of the invention for determining the mass and the centre of mass of the demountable platform 300. In FIG. 2A, there is shown a situation where the truck 200 has been reversed to the demountable platform 300. The middle frame 109 is at an angle that enabled the attachment of the hook 111 to the demountable platform 300.

(12) The lifting of the demountable platform 300 is done by driving the main cylinders 104 inwards. As a result, the middle frame 109 rotates relative to the subframe 103, and the front end of the demountable platform 300 rises off the ground. The rear frame 110 is held locked to the subframe 103 during the lifting of the demountable platform 300.

(13) After a certain time as the lifting of the demountable platform 300 is continued, the demountable platform 300 comes into contact with the rear rollers 113, as shown in FIG. 2B. When the main cylinders 104 are driven further inwards, also the back end of the demountable platform 300 rises off the ground, and the demountable platform 300 becomes supported by the hook 111 and the rear rollers 113. The middle frame 109 is rotated until it becomes essentially parallel with the rear frame 110. The demountable platform 300 rests now on the truck 200, as shown in FIG. 2C.

(14) During the lifting of the demountable platform 300 from the ground onto the truck 200, an angle between the middle frame 109 and the subframe 103 is measured by using the inclinometers 116 and 117. The values of the load force of the main cylinder 104 are determined, at predetermined values of the angle, by measuring with the pressure sensors 114 and 115 pressures in the bottom and piston rod chambers of the main cylinder 104 and then multiplying the pressures with the piston areas in either chamber. The mass and the centre of mass of the demountable platform 300 is then calculated by using the mathematical model of the load force of the main cylinder 104 and the iteration procedure.

(15) Only advantageous exemplary embodiments of the invention are described in the figures. It is clear to a person skilled in the art that the invention is not restricted only to the examples presented above, but the invention may vary within the limits of the claims presented hereafter. Some possible embodiments of the invention are described in the dependent claims, and they are not to be considered to restrict the scope of protection of the invention as such.