Method for determining the mass and the position of the centre of gravity of an additional load of a movement system, in particular in the case of a machine tool

Abstract

The invention relates to a method for determining the mass and the center of gravity location of a load (10) of a moving system (12), particularly of a machine tool (14), which comprises a support (20) that is for accommodating the load (10) and is able to rotate around a first axis (16) and a second axis (18) as well as electronically controlled drive units (22, 24) for rotating the support (20) around the first axis (16) and around the second axis (18), wherein a total moment of inertia and a holding torque with regard to the first axis (16) are determined in a loaded state; a total moment of inertia and a holding torque with regard to the second axis (18) are determined in the loaded state; and the mass and the center of gravity location of the load (10) relative to the support (20) are determined based on the total moments of inertia and the holding torques with regard to the first axis (16) and second axis (18). The invention also relates to a moving system (12), which is equipped to determine the mass and the center of gravity location of a load (10) according to such a method.

Claims

1. A method for determining the mass and the center of gravity location of a load of a moving system so that resulting load-dependent forces and holding torques can be compensated for to allow precision movement control of the load, the method comprising: providing a machine tool having a moving system comprising a support for accommodating the load, wherein the support is structured to rotate around a first axis and a second axis, wherein the machine tool comprises electronically controlled drive units for rotating the support around the first axis and around the second axis, the moving system further comprising a control unit in operable communication with the electronically controlled drive units; determining using the control unit a total moment of inertia and a holding torque for the first axis in a loaded state; determining using the control unit a total moment of inertia and a holding torque for the second axis in the loaded state; determining using the control unit the mass and the center of gravity location of the load relative to the support based on the total moments of inertia and the holding torques for the first axis and second axis; and moving the load using the electronically controlled drive units, wherein movement of the load is based, at least in part, on the determined mass and the center of gravity location of the load relative to the support.

2. The method according to claim 1, wherein determining the total moments of inertia and the holding torques of at least one of the first axis or the second axis are determined based on at least one parameter that is available in control loops of the electronically controlled drive units without a use of additional sensors.

3. The method according to claim 2, wherein the at least one parameter comprises at least one selected from the group consisting of an operating current, a rotation position, a rotation speed, and an acceleration time.

4. The method according to claim 1, wherein the holding torque of the first axis is determined in a position of the first axis in which the holding torque of the first axis is at its maximum.

5. The method according to claim 4, wherein the holding torque of the first axis is determined when the first axis is positioned perpendicular to a direction of gravity.

6. The method according to claim 1, wherein determining the total moment of inertia for the first axis in the loaded state comprises determining, an acceleration torque around the first axis by rotating the load around the first axis.

7. The method according to claim 1, wherein at least one of the mass or the center of gravity location of the load is determined based on a stored value of at least one selected from the group consisting of (i) a moment of inertia of the unloaded support for the first axis, (ii) a moment of inertia of the unloaded support for the second axis, (iii) a mass of the unloaded support, and (iv) at least one geometric dimension of the support.

8. The method according to claim 1, further comprising performing at least one calibration step in an unloaded state of the support in which reference values are determined that are taken into consideration when determining the mass and the center of gravity location in the loaded state.

9. The method according to claim 1, further comprising: for at least one of the first axis or second axis, approaching at least three different angular positions; determining a respective holding torque for the at least one of the first axis or second axis for each of the at least three different angular positions; and determining an eccentricity of the load based on the respective holding torques for each of the at least three different angular positions.

10. The method according to claim 1, further comprising determining at least one of the mass or the center of gravity location of the load between machining steps of a machining of the load without changing a loading state of the load.

11. The method according to claim 1, wherein the first axis comprises a rotation axis for the support and wherein the second axis comprises a pivot axis for the support.

12. The method according to claim 1, wherein the first axis and the second axis are positioned perpendicular to each other.

13. The method according to claim 1, wherein the first axis at least approximately intersects the second axis.

14. The method according to claim 1, wherein the holding torque of the second axis is determined in a position of the second axis in which the holding torque of the second axis is at its maximum.

15. The method according to claim 14, wherein the holding torque of the second axis is determined when the first axis is positioned perpendicular to a direction of gravity.

16. The method according to claim 1, wherein determining the total moment of inertia for the second axis in the loaded state comprises determining an acceleration torque around the second axis by rotating the load around the second axis.

17. A moving system of a machine tool for determining the mass and the center of gravity location of a load so that resulting load-dependent forces and holding torques can be compensated for to allow precision movement control of the load, comprising: a support structured to accommodate a load and to rotate around at least a first axis and a second axis; electronically controlled drive units for rotating the support around the first axis and around the second axis; and a control unit in operable communication with the electronically controlled drive units, the control unit determining a mass and center of gravity location of the load, the control unit determining a total moment of inertia and a holding torque for the first axis in a loaded state; the control unit determining a total moment of inertia and a holding torque for the second axis in the loaded state; and the control unit determining the mass and the center of gravity location of the load relative to the support based on the total moments of inertia and the holding torques for the first axis and second axis; and wherein the electronically controlled drive units move the load based, at least in part, on the determined mass and the center of gravity location of the load relative to the support.

18. The moving system according to the claim 17, wherein after the mass and the center of gravity location of the load are determined, the control unit takes the mass and the center of gravity location of the load into consideration when the load is at least one of moved or positioned.

19. The moving system according to claim 17, comprising a swivel/rotation table, wherein the support is a workpiece table of the swivel/rotation table.

20. A machine tool having at least one moving system according to claim 17.

Description

(1) In the following, the present invention will be described by way of example based on the attached figures. The drawings, the description, and the claims contain numerous features in combination. The person skilled in the art will also suitably consider the features individually and unite them into other meaningful combinations. In the drawings:

(2) FIG. 1 shows a schematic side view of a moving system;

(3) FIG. 2 shows a schematic side view of a support of the moving system with a load in a rotated position;

(4) FIG. 3 shows a schematic top view of the support with the load; and

(5) FIG. 4 shows a schematic flowchart of a method for determining the mass and the center of gravity location of a load of a moving system.

(6) FIG. 1 shows a moving system 12 in a schematic side view. The moving system 12 comprises a support 20 for accommodating a load 10. The support 20 is able to rotate around a first axis 16 and a second axis 18. In addition, the moving system 12 has a first electronically controlled drive unit 22 for rotating the support 20 around the first axis 16. The moving system 12 also has a second electronically controlled drive unit 24 for rotating the support 20 around the second axis 18.

(7) The moving system 12 also comprises a control unit 28, which is equipped to determine a mass and a center of gravity location of the load 10. This determination is made using a method that will be described in greater detail below.

(8) In the case shown, the moving system 12 is part of a machine tool 14. The moving system 12 in this case is positioned in a machining chamber, not shown, of the machine tool 14. The load 10 is also a workpiece, which can be machined in the machining chamber by means of the machine tool 14.

(9) The moving system 12 comprises a swivel/rotation table 30, which can also be referred to as a swivel bridge. The support 20 in this case is a workpiece table of the swivel/rotation table 30. By means of the swivel/rotation table 30, it is possible to change a position of the load 10 relative to a machining tool, not shown, of the machine tool 14, for example a milling tool, a drill bit, a laser head, a grinding tool, or the like. In the case shown, the control unit 28 is equipped to correspondingly trigger the electronically controlled drive units 22, 24. The control unit 28 can be connected to another control unit of the machine tool 14, which controls the machining tool. According to the invention, however, it is also possible for a shared control unit to be provided.

(10) The first axis 16 is a rotation axis for the support 20. It is thus possible to adapt a rotation position of the load 10 by rotating the support 20 around the first axis 16. In the case shown, the first axis 16 extends through a center of gravity 32 of the support 20 (see FIG. 2). In this case, the support 20 is rotationally symmetrical.

(11) The second axis 18 is a pivoting axis for the support 20. The second axis 18 in this case is positioned perpendicular to the first axis 16. A pivot position of the load 10 can be adjusted by rotating the support 20 around the second axis 18. The first axis 16 and the second axis 18 intersect. The second axis 18 in this case extends above the support and does not intersect it.

(12) In combination with a movable machining tool, which is also able to rotate and/or pivot around at least one axis, it is possible to achieve a machinability of the load 10 in various ways.

(13) The support 20 is positioned in rotary fashion on a bridge unit 36 of the moving system 30. The bridge unit 36 can be pivoted around the second axis 18, with the support 20 and first axis 16 being pivoted along with it. The support 20 in turn can be rotated around the first axis 16 relative to the bridge unit 36. The first electronically controlled drive unit 22 is positioned in the bridge unit 36. The second electronic drive unit 24 is positioned outside the bridge unit 36 and is stationary relative to the machine tool 14.

(14) In general, however, other positions of the support 20, the axes 16, 18, and the electronically controlled drive units 22, 24 are possible according to the invention. The support 20 can, for example, be positioned eccentrically relative to the first axis 16. Alternatively or in addition, the second axis 18 can extend through the support 20 and particularly through its center of gravity 32. In addition, the second electronically controlled drive unit 24 can also be positioned under the support 20. The embodiment of the moving system 12 in such a way that it comprises a swivel/rotation table 30 is thus only an example.

(15) In FIG. 2, the support 20 with the load 10 is schematically depicted in a position that is pivoted by 90° relative to the home position shown in FIG. 1. In the home position, the first axis 16 is positioned parallel to a direction of gravity 26. In the position shown in FIG. 2, however, the first axis 16 is positioned perpendicular to the direction of gravity 26. The position shown in FIG. 2 is reached by pivoting the support 20 and the bridge unit 36 around the second axis 18. As is apparent in FIG. 2, the second axis 18 does not extend through the center of gravity 32 of the support 20. In the case shown, the second axis 18 also does not extend through a center of gravity 34 of the load; this depends on the type and geometry of the load. In most cases, the second axis 18 will also not extend through a shared center of gravity of the support 20 and the load 10. With a pivoting of the support 20 and the bridge unit 36, torques therefore occur that are dependent on a pivot angle.

(16) In FIG. 3, the support 20 with the load 10 is schematically depicted in a top view, seen parallel to the first axis 16. In the case shown, the load 10, which is depicted as cylindrical by way of example, but can have any desired geometry, is positioned on the support 20 eccentrically relative to the axis 16. Such a positioning can occur due to imprecise positioning, due to intentional positioning, and/or due to the asymmetrical geometry of the load 10, which is the most frequent case in actual use. In particular, the load 10, as in the case shown, can be positioned on the support 20 in such a way that the first axis 16 does not extend through the center of gravity 34 of the load. An eccentricity of this kind causes corresponding torques to occur during a rotation of the support 20 around the first axis 16.

(17) A mass and a center of gravity location of the load 10 can then be determined as follows. The method described below, in the case shown, is performed by the control unit 28 by means of suitable control and processing of the determined values.

(18) According to the invention, a total moment of inertia and a holding torque with regard to the first axis 16 are determined in a state of the support 20 in which it is loaded with the load 10. A total moment of inertia and a holding torque with regard to the second axis 18 are also determined in the loaded state. The mass and the center of gravity location of the load 10 are then determined based on the total moments of inertia and the holding torques with regard to the first axis 16 and the second axis 18.

(19) The control unit 28 is equipped to take the thus-determined mass and center of gravity location of the load 10 into consideration when moving and/or positioning the load 10. In this case, corresponding operating currents of the electronically controlled drive units 22, 24 are chosen in such a way that resulting load-dependent forces and holding torques can be compensated for so that a high precision movement control can be achieved.

(20) According to the method, the total moments of inertia and the holding torques are determined from variables that are available in control loops of the electronically controlled drive units 22, 24 without a use of additional sensors. In the case shown, this variable includes an operating current, a rotation position, a rotation speed, and/or an acceleration time.

(21) The holding torque of the first axis 16 is determined in a position of the first axis 16 in which the holding torque of the first axis 16 is at its maximum. This occurs in a position of the first axis 16 in which it is positioned perpendicular to the direction of gravity 26. As is apparent in FIG. 3, in this position, the holding torque depends on an angular position of the load 10. When the support 20 is rotated around the first axis 16, the holding torque is at its maximum when the distance between the center of gravity 34 of the load 10 and the first axis 16 perpendicular to the direction of gravity 26 is at its maximum, and is at its minimum when the center of gravity 34 of the load 10 and the first axis 16 are aligned relative to the direction of gravity 26.

(22) The holding torque of the second axis 18 is determined in a position of the second axis 18 in which the holding torque of the second axis 18 is at its maximum. This position is also dependent on the position of the center of gravity 34 of the load 10 and on the position of the center of gravity 32 of the support 20 or bridge unit 26 with regard to the second axis 18. Typically, the holding torque of the second axis 18 is at its maximum when the first axis 16 is positioned perpendicular to the direction of gravity 26.

(23) In order to determine the respective total moment of inertia, an acceleration torque around the respective axis 16, 18 is determined in the loaded state of the support 20 by rotating the load 10 around the respective axis 16, 18. The acceleration torque in this case is determined at a constant operating current.

(24) For the first axis 16, this can be carried out in a position in which the first axis 16 is positioned parallel to the direction of gravity 26. But according to the invention, a determination is also possible in the perpendicular position.

(25) For the determination of the mass and the center of gravity location, at least one stored value is used, which characterizes the unloaded support 20. Possibilities for this include moments of inertia of the support 20 relative to the axes 16, 18 as well as its mass, its geometry, its density distribution, and the like.

(26) In addition, in a calibration step, which is performed in an unloaded state of the support 20, at least one reference value is determined, which is taken into consideration when determining the mass and the center of gravity location in the loaded state. In this case, a reference value is determined for friction losses that occur with a rotation of the support 20. The values that result from this can be derived from values that are determined in the loaded state in order to correspondingly take friction losses into account. The calibration step can take place when putting the moving system 12 into operation for the first time. In addition, other calibration steps can be carried out between uses of the moving system 12, for example in order to take into account a chronological change in the at least one reference value.

(27) An eccentricity of the load 10 is determined by approaching at least three different angular positions for at least one of the axes 16, 18 and determining a respective holding torque for each. These holding torques are then used to determine the eccentricity. In the case shown, it is possible to select a number of different angular positions that make it possible to adjust a precision of the determination of the eccentricity.

(28) With a use of the moving system 12 for the positioning of the load 10, the mass of the load 10 and/or its center of gravity location can be determined between machining steps and without a change of the loading state of the load 10, depending on the desired extent of machining. If, for example, a rough machining is performed in a first machining step during which a larger quantity of material is removed, the mass and the center of gravity location of the roughly machined load 10 can then be determined again. A subsequent fine machining can then be performed with a high precision since a positioning is carried out based on a precise determination of the mass and the center of gravity location of the roughly machined load 10.

(29) In this case, the mass and the center of gravity location are determined based on the following four fundamental equations:
M.sub.2,Halte=F.sub.T×a.sub.T−F.sub.Z×a.sub.Z  (1)
where M.sub.2,Halte is the holding torque of the second axis 18, F.sub.T is the weight of the unloaded support 20, a.sub.T is the distance between the center of gravity 32 of the support 20 and the second axis 18, F.sub.Z is the weight of the load 10, and a.sub.Z is the distance between the center of gravity 34 of the load 10 and the second axis 18 (see FIG. 2).
J.sub.1=J.sub.1,T+J.sub.1,Z  (2)
where J.sub.1 is the total moment of inertia with regard to the first axis 16, J.sub.1,T is the moment of inertia of the unloaded support 20 with regard to the first axis 16, and J.sub.1,Z is the moment of inertia of the load 10 with regard to the first axis 16.
J.sub.2=J.sub.2,T+J.sub.2,Z  (3)
where J.sub.2 is the total moment of inertia with regard to the second axis 18, J.sub.2,T is the moment of inertia of the unloaded support 20 with regard to the second axis 18, and J.sub.2,Z is the moment of inertia of the load 10 with regard to the second axis 18.
M.sub.1,Halte=F.sub.Z×x  (4)
where M.sub.1,Halte is the holding torque of the first axis 16 and x is the distance between the center of gravity 34 of the load 10 and the first axis 16 (see FIG. 3).

(30) In the present case, a mass and a moment of inertia of the bridge unit 26 are already taken into account in the control of the electronically controlled drive units 22, 24 by the control unit 28.

(31) The sequence of a method according to the invention for determining the mass and the center of gravity location of the load 10 is schematically depicted in FIG. 4.

(32) In a first method step 38, a calibration step is performed with an unloaded support 20. In this connection, frictional torques of the first axis 16 and second axis 18 are determined.

(33) The first method step 38 can be performed independently of the other method steps, for example upon initial placement into service or after a change of the support 20. The remaining method steps are performed in a loaded state of the support 20.

(34) In a second method step 40, a position of the maximum holding torque of the first axis 16 is determined by determining a power consumption of the electronically controlled drive unit 22 while the support 20 and the load 10 mounted thereon are being rotated around the first axis 16. This can take place in a position in which the first axis 16 is positioned perpendicular to the direction of gravity 26. Alternatively, the position of the maximum holding torque of the first axis 16 can be determined through rotation around both axes 16, 18. The holding torque of the first axis 16 is then determined in the position of the maximum holding torque of the first axis 16.

(35) In a third method step 42, a position of the maximum holding torque of the second axis 18 is determined by determining a power consumption of the second electronically controlled drive unit 24 while the support 20 and the load 10 mounted thereon are being rotated around the second axis 18. This can take place in any position with regard to the first axis 16. Alternatively, the position of the maximum holding torque of the second axis 18 can be determined through rotation around both axes 16, 18. Then the holding torque of the second axis 18 is determined in the position of the maximum holding torque of the second axis 18.

(36) In a fourth method step 44, the total moment of inertia with regard to the first axis 16 is determined through rotation around the first axis 16 with a predetermined operating current of the electronically controlled drive unit 22.

(37) In a fifth method step 46, the total moment of inertia with regard to the second axis 18 is determined through rotation around the second axis 18 with a predetermined operating current of the second electronically controlled drive unit 24.

(38) In a sixth method step 48, the eccentricity of the load 10 is determined, as described above, by approaching at least three different angular positions relative to the corresponding axes 16, 18.

(39) In a seventh method step 50, the mass and the center of gravity location of the load 10 are calculated based on the above equations and through the use of reference values determined during the calibration step as well as the at least one stored value that characterizes the unloaded support 20.

(40) The above-described sequence in which the method steps 38-50 are performed should be understood here as only an example. If need be, individual steps can be skipped/omitted or the steps can be performed in another sequence.

(41) The determined mass and the determined center of gravity location are taken into consideration in a subsequent position control by the control unit 28 so that a high degree of precision can be achieved. At least some of the method steps, as mentioned above, can also be performed as needed between machining steps in order, in the case of changes in the load 10, to be able to correspondingly compensate for these.