Operating an at least two-axle machine tool

Abstract

In a method for operating an at least two-axle machine tool, a geometric description of a path is specified, and according to the path, an advancing movement is carried out by simultaneously moving at least in one section a first axle and a second axle. A first maximum value for a first kinematic parameter relating to the advancing movement along the section of the path is defined by a control unit based on the geometric description. The advancing movement along the section is planned by the control unit by taking the first maximum value into consideration, and the axles are actuated so as to carry out the advancing movement according to the planned movement.

Claims

1. A method for operating of a machine tool having at least two axes, comprising: predetermining a geometric description of a path and performing an advancing movement in accordance with the path by simultaneously moving at least sectionally a first axis and a second axis of the machine tool; with a control unit of the machine tool setting a first maximum value for a first kinematic parameter relating to the advancing movement along a section of the path dependent on the geometric description; planning the advancing movement along the section with the control unit by taking into account the first maximum value; activating the first axis and the second axis for executing the advancing movement in accordance with the planned movement along the section; setting a second maximum value for a second kinematic parameter relating to the advancing movement along the section of the path dependent on the geometric description; planning of the advancing movement along the section by taking account of the second maximum value; determining a range of values for the first maximum value depending on a predetermined first kinematic limit value for the first axis; determining a first range of values for the second maximum value depending on the first kinematic limit value for the first axis; and for setting the first maximum value and the second maximum value, determiningdependent on the geometric descriptiona division parameter, which is used to uniquely define both the first maximum value and the second maximum value within the first range of values.

2. The method of claim 1, further comprising defining the first maximum value by a maximum path velocity of the advancing movement.

3. The method of claim 1, further comprising: determining the division parameter with an optimization method executed by the control unit, and using the division parameter as an optimization parameter.

4. The method of claim 3, further comprising using as a target function for the optimization method a throughput time for processing or measuring a workpiece in accordance with the path.

5. The method of claim 3, further comprising using as a target function for the optimization method a characteristic variable for an accuracy for processing or measuring a workpiece in accordance with the path.

6. The method of claim 5, further comprising using as a target function for the optimization method a characteristic variable for a surface quality for processing the workpiece in accordance with the path.

7. The method of claim 1, wherein the second maximum value is defined by a maximum path acceleration of the advancing movement.

8. The method of claim 1, further comprising: setting a third maximum value for a third kinematic parameter relating to the advancing movement along the section depending on the geometric description; and planning the advancing movement along the section by taking into account the third maximum value.

9. The method of claim 8, wherein the third maximum value is defined by a maximum path jerk of the advancing movement.

10. A non-transitory computer-readable storage medium storing a computer program comprising commands, which when loaded into a memory of a control system controlling a machine tool having at least two axes and executed by a processor of the control system, causes the control system to carry out a method as set forth in claim 5.

11. A control system for a machine tool having at least two axes, said control system comprising: a control unit configured to control the machine tool for executing an advancing movement by simultaneously moving at least sectionally a first axis and a second axis of the machine tool in accordance with a path defined by a predetermined geometric description, wherein the control unit is further configured to set a first maximum value for a first kinematic parameter relating to the advancing movement along a section of the path dependent on the geometric description; plan the advancing movement along the section by taking into account the first maximum value; activate the first axis and the second axis for executing the advancing movement in accordance with the planned movement along the section; set a second maximum value for a second kinematic parameter relating to the advancing movement along the section of the path dependent on the geometric description; plan of the advancing movement along the section by taking account of the second maximum value; determine a range of values for the first maximum value depending on a predetermined first kinematic limit value for the first axis; determine a first range of values for the second maximum value depending on the first kinematic limit value for the first axis; and for setting the first maximum value and the second maximum value, determinedependent on the geometric descriptiona division parameter, which is used to uniquely define both the first maximum value and the second maximum value within the first range of values.

12. A machine tool having at least two axes and comprising a control system as set forth in claim 11.

Description

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(1) Shown schematically in the FIGURE is an example of a form of embodiment of a machine tool 1 according to the improved concept, which is configured to be able to move a tool 3 relative to a workpiece 4 along at least two linear axes, in the present example three linear axes X1, X2, X3 are shown. The advancing movement can be undertaken in this case by movement of the tool 3 with a fixed-location workplace 4 or vice versa. The diagram of the machine tool 1 in the FIGURE is to be understood as purely schematic and by way of example and in particular does not restrict the improved concept with regard to the type of the machine tool or the type of the advancing movements.

(2) The machine tool 1 moreover has a control unit 2, which represents a control system according to the improved concept.

(3) The maximum realizable path velocity v.sub.B at the machine tool 1 is restricted by the axial dynamic restrictions. Dynamic restrictions of an axis i can for example be maximum axis velocity v.sub.i,max, maximum axis acceleration a.sub.i,max and maximum axis jerk j.sub.i,max. The axis velocity is given by v.sub.i=dx.sub.i/dt, the acceleration by a.sub.i=d.sup.2x.sub.i/dt.sup.2 and the axis jerk by j.sub.i=d.sup.3x.sub.i/dt.sup.3 wherein x.sub.i designates the coordinate corresponding to axis i or the degree of freedom corresponding to the axis i. With .sub.i=dx.sub.i/ds, k.sub.i=d.sup.2x.sub.i/ds.sup.2 and m.sub.i=d.sup.3x.sub.i/ds.sup.3 the following then applies
v.sub.i=.sub.i*v.sub.B(1)
a.sub.i=k.sub.i*v.sub.B.sup.2+.sub.i*a.sub.B and(2)
j.sub.i=m.sub.i*v.sub.B.sup.3+3*k.sub.i*v.sub.B*a.sub.B,.sub.i*j.sub.B.(3)

(4) The axis velocities v.sub.i have a direct influence on the path velocity v.sub.B. Equation (1) represents a linear relationship between the axis velocity v.sub.i and path velocity v.sub.B. With knowledge of the maximum allowed axis velocities v.sub.i,max, this first maximum realizable path velocity v.sub.B can be determined from equation (1).

(5) By contrast with this the relationship from equation (2) is not linear and cannot be easily resolved. The maximum axis acceleration a.sub.i must optimally be distributed between the two terms on the right-hand side of equation (2), which can be referred to a centripetal term and path acceleration term. This division can be realized with the aid of division parameters CEOPA.sub.i with 0CEOPA.sub.i1, which to certain extent reserves a part of the maximum axis acceleration a.sub.i,max for the centripetal term:
CEOPA.sub.i*a.sub.i,max:=k.sub.i*v.sub.B,max.sup.2(4)
so that the maximum path velocity v.sub.B,max is given by:
v.sub.B,max=(CEOPA.sub.i*a.sub.i,max/k.sub.i).sup.1/2.(5)

(6) Thus the following is produced for the path acceleration term
(1CEOPA.sub.i)*a.sub.i,max=.sub.i*a.sub.B,max(6)
or
a.sub.B,max=(1CEOPA.sub.i)*a.sub.i,max/.sub.i(7)

(7) With knowledge of the maximum axis acceleration a.sub.i,max and the factor CEOPA.sub.i, with the aid of the equations (5) and (7), a further maximum realizable path velocity v.sub.B,max and a maximum realizable path acceleration a.sub.B,max can be determined, wherein the restriction by equation (1) is to be taken in account where necessary.

(8) Stored on a memory unit of the control unit 2 is a parts program, which contains a geometric description of a path along which the advancing movement is to be carried out. The control unit 2 can plan the advancing movement for the individual sections or for all sections of the path based on the predetermined geometric description.

(9) To this end the control unit 2 can for example determine the maximum path velocity v.sub.B,max and plan the advancing movement along the section, taking into account the maximum path velocity v.sub.B,max, i.e. plan it in such a way that the amount of the actual path velocity v.sub.B along the section does not fall below the maximum or programmed path velocity v.sub.B,max.

(10) In order to ascertain the maximum path velocity v.sub.B,max, the control unit 2 in particular ascertains the values for CEOPA.sub.i. In this case it is to be noted that the relationship (5) applies for all axes of the machine tool 1. The ascertaining of the maximum path velocity v.sub.B,max is therefore undertaken in particular while taking account of all corresponding relationships, for example as minimum value of the corresponding possible values for the maximum path velocity v.sub.B,max.

(11) Through the ascertaining of CEOPA.sub.i via the equation (7) the maximum path acceleration a.sub.B,max can also be ascertained, wherein here too the corresponding relationships for all axes are taken into account.

(12) The choice of CEOPA.sub.i can be made differently in this case for different classes of workpiece or for each actual workpiece 4 and where necessary also be changed dynamically for different sections of a path during the processing or measurement of a single workpiece 4.

(13) The larger the values ascertained for CEOPA are in this case, the more the focus lies on the achievement of as high a path velocity or centripetal acceleration as possible at the expense of the available maximum path acceleration and vice versa. For example with small path curves rather large CEOPA.sub.i i.e. in particular larger than 0.5, can be chosen. With greater curves within the same workpiece 4 or with other components or classes of component, a smaller value for CEOPA.sub.i can be chosen for example, in particular a value of approximately 0.5, in order in this way to achieve a symmetrical division between centripetal acceleration and path acceleration.

(14) A similar division of the maximum axis jerk j.sub.i,max can be undertaken starting from equation (3). Two further division parameters CEOPJ.sub.i and CEOPJ.sub.i are required for this:
CEOPAJ.sub.i*j.sub.i,max:=m.sub.i*v.sub.B,max.sup.3,(8)
CEOPJ.sub.i*(1CEOPAJ.sub.i)*j.sub.i,max:=3*k.sub.i*v.sub.B,max*a.sub.B,max,(9)
so that it follows that
[1CEOPJ.sub.i*(1CEOPAJ.sub.i)]*j.sub.i,max=.sub.i*j.sub.B,max,(10)
or
j.sub.B,max=[1CEOPJ.sub.i*(1CEOPAJ.sub.i)]*j.sub.i,max/.sub.i,(11)

(15) As stated above for CEOPA.sub.i the division parameters CEOPAJ.sub.i and CEOPJ.sub.i can also be adapted and optimized according to actual requirements.

(16) In different forms of embodiment, when the processing or measurement of workpieces 4 is being carried out by the machine tool 1 corresponding real time parameters are also stored for each pass. The real time parameters or real time data can be taken into account during later passes. For the processing of identical workpieces 4, in this way the computing steps necessary for optimization or ascertaining of the division parameters can be saved where necessary in this case. As an alternative or in addition there can also be an iterative adaptation of the division parameters, in order in this way to obtain an optimum result step-by-step.

(17) As described, the improved concept makes it possible to control a machine tool with at least two axes in particular individually and to parameterize it optimally, so that compromises, as are to be made with universally parameterizable controllers, can be avoided and in this way overall, depending on the actual requirement, a reduced throughput time and/or an increased production or measurement quality can be achieved.

(18) In corresponding developments the improved concept can also be used accordingly for the combination of other relevant parameters for pan-axis precision or for regulation of drives.