Fill degree control for a bulk material gripper of a crane

1. A method for filling a gripper with bulk material, the gripper being suspended on holding cables, raised and lowered by a crane via a tension force controller, and acting on the bulk material with its own weight during a closing and filling procedure, wherein by reducing the effect of the weight of the gripper on the bulk material, a fill degree of the gripper is influenced by adjusting a tensile force acting on the holding cables, the method comprising:

determining in a crane controller a tensile force target value for the holding cables;

supplying the tensile force target value as a first input variable to the tension force controller;

controlling an electric motor via the tensile force controller using the tensile force target value for lifting and lowering the gripper via the holding cables;

ascertaining a tensile force actual value of the holding cables while the gripper is lifted or lowered during said controlling the electric motor via the tensile force controller;

supplying the tensile force actual value as a second input variable to the tensile force controller for controlling the electric motor to adjust the fill degree of the gripper for a subsequent gripping procedure based on differences between the tensile force target value and the tensile force actual value;

determining in the crane controller (i) when a change in the tensile force target value is to be made and (ii) an amount of change of the tensile force target value, based on determining working loads of the crane for a plurality of gripping procedures after the gripper is filled and raised and determining the number of overload cut-offs and/or the number of working loads exceeding a maximum permissible working load for the plurality of gripping procedures to dynamically adjust the tensile force target value, and supplying the amount of change of the tensile force target value to the tension force controller.

2. The method as claimed in claim 1 , wherein a frequency of overload cut-offs and a frequency at which the maximum permissible working load is exceeded are monitored in the crane controller, and wherein the tensile force target value is increased in response to (1) the frequency of overload cut-offs exceeding a preselected value related to the load cycles or (2) the frequency at which the maximum permissible working load is exceeded being greater than a value preselected in relation to the maximum permissible working load for a given working radius.

3. The method as claimed in claim 2 , wherein a frequency of overload cut-offs and a frequency at which the maximum permissible working load is exceeded are monitored in the crane controller, and wherein the tensile force target value is decreased in response to (1) the frequency of overload cut-offs being less than a preselected value related to the load cycles or (2) the frequency at which the maximum permissible working load is exceeded being less than a value preselected in relation to the maximum permissible working load for a given working radius.

4. The method as claimed in claim 3 , further comprising:

adjusting the gripper with the tensile force actual value, which is directed in a direction of lifting, during the closing and filling procedure.

5. The method as claimed in claim 4 , further comprising:

ascertaining a working load after the filled gripper is raised; and

determining the fill degree of the gripper from the determined working load and a known weight of the gripper when empty.

6. The method as claimed in claim 5 , further comprising:

supplying a measurement of length of a freely hanging portion of the holding cable starting from the gripper and in the direction of lifting as an input variable to the crane controller; and

adding a weight of the freely hanging portion of the holding cable to the weight of the gripper during said determining the fill degree of the gripper.

7. The method as claimed in claim 2 , further comprising:

ascertaining a working load after the filled gripper is raised; and

determining the fill degree of the gripper from the determined working load and a known weight of the gripper when empty.

8. The method as claimed in claim 1 , wherein a frequency of overload cut-offs and a frequency at which the maximum permissible working load is exceeded are monitored in the crane controller, and wherein the tensile force target value is decreased in response to (1) the frequency of overload cut-offs being less than a preselected value related to the load cycles or (2) the frequency at which the maximum permissible working load is exceeded being less than a value preselected in relation to the maximum permissible working load for a given working radius.

9. The method as claimed in claim 1 , further comprising:

adjusting the gripper with the tensile force actual value, which is directed in a direction of lifting, during the closing and filling procedure.

10. The method as claimed in claim 1 , further comprising:

determining the fill degree of the gripper from the determined working load and a known weight of the gripper when empty for each of the plurality of gripping procedures in order to determine the amount of change of the tensile force target value for the holding cables, wherein said determining working loads of the crane for the plurality of gripping procedures comprises sensing the weight of the bulk material lifted during the plurality of gripping procedures.

11. The method as claimed in claim 10 , further comprising:

supplying a measurement of length of a freely hanging portion of the holding cable starting from the gripper and in the direction of lifting as an input variable to the crane controller; and

adding a weight of the freely hanging portion of the holding cable to the weight of the gripper during said determining the fill degree of the gripper.

12. The method as claimed in claim 11 , further comprising:

supplying a maximum permissible working load as an input variable to the crane controller, the maximum permissible working load being dependent upon a working radius of the gripper.

13. The method as claimed in claim 12 , further comprising:

iteratively decreasing or increasing the tensile force target value to drive the determined fill degree toward 100 percent.

14. The method as claimed in claim 13 , further comprising receiving a manually input tensile force target value in the crane controller as a start variable for the first input variable prior to said determining in the crane controller the tensile force target value.

15. The method as claimed in claim 10 , further comprising:

iteratively decreasing or increasing the tensile force target value to drive the determined fill degree toward 100 percent.

16. The method as claimed in claim 1 , wherein said crane controller comprises said tensile force controller.

17. The method as claimed in claim 1 , further comprising:

adjusting the gripper with the tensile force actual value, which is directed in a direction of lifting, during the closing and filling procedure.

18. The method as claimed in claim 1 , further comprising:

supplying a maximum permissible working load as an input variable to the crane controller, the maximum permissible working load being dependent upon a working radius of the gripper.

19. The method as claimed in claim 1 , further comprising receiving a manually input tensile force target value in the crane controller as a start variable for the first input variable prior to said determining in the crane controller the tensile force target value.