Method and test assembly for determining machine parameters

1. A method for determining machine parameters of a mechanical device in which a first element and a second element are mutually movable in settable patterns of movement, the method comprising:

placing a measuring arm between the first and second elements,

displacing the first and second elements mutually in a predetermined intended movement path,

applying a predetermined force between the first element and the second element substantially in a longitudinal direction of the measuring arm,

recording, while the predetermined force is applied, a resulting actual movement path by means of the measuring arm,

determining a difference between the intended movement path and the actual movement path, and

deriving, based on the determined difference, machine parameters indicating a condition of the mechanical device,

wherein the predetermined force is generated by a power unit and comprises a dynamically varying portion and a static portion that are generated separately, wherein the dynamically varying portion is generated at least partially by a piezo actuator of the power unit,

wherein:

the predetermined force is applied in various mutual positions between the first and second elements, the dynamically varying portion being position dependent, and

recording the resulting actual movement path comprises dynamically determining a current length or a length difference of the measuring arm while the predetermined force is applied.

2. The method according to claim 1 , wherein the dynamically varying portion is sinusoidal, subject to an analytic function or subject to a step function.

3. The method according to claim 2 , wherein the dynamically varying portion is position dependent and sinusoidal.

4. The method according to claim 1 , comprising:

at least one measurement operation comprising moving the first and second elements mutually in a settable pattern of movement and recording the resulting actual movement path, the predetermined force applied during each measurement operation comprising the dynamically varying portion, so that an applied force varies dynamically during each measurement operation, wherein the applied dynamically varying force is different for each measurement operation.

5. The method according to claim 4 , wherein the at least one measurement operation comprises a plurality of subsequently performed measurement operations.

6. The method according to claim 1 , wherein

the predetermined force is defined as

F=F 0 +F ( t ),

where F is the predetermined force, F 0 is the static portion of the force and F(t) is the dynamically varying portion of the force.

7. The method according to claim 1 , wherein the machine parameters comprise at least one of the following:

stiffness in at least two directions based on an applied force vector and on a deflection vector;

displacement in dependence of a direction of movement;

hysteresis;

recti linearity; and/or

damping.

8. The method according to claim 7 , wherein the stiffness comprises a dynamic stiffness value.

9. The method according to claim 1 , wherein

the mechanical device is a machine tool, wherein the first element is adapted to support a machining tool, and the second element is adapted to support a workpiece,

wherein the second element is adaptive to provide a fixation for holding the workpiece in its place, and

wherein the machine parameters comprise a stiffness of the fixation.

10. The method according to claim 1 , wherein the second element is adapted to provide a fixation for holding a workpiece or an object to be measured, respectively, in its place, by means of clamping.

11. The method according to claim 1 , wherein the mechanical device is a machine tool, and the method comprises a tooling simulation of a specific tooling operation of the machine tool, in the course of which

mutual movements between the first element and the second element are performed that are typical for the tooling operation, and

the dynamically varying portion is applied according to forces typically occurring during the tooling operation.

12. The method according to claim 1 , wherein the first element is a spindle and the second element is a worktable.

13. The method according to claim 1 , wherein the measuring arm is telescopic.

14. The method according to claim 1 , wherein the mechanical device is a coordinate measuring machine, wherein the first element is adapted to support a measuring head, and the second element is adapted to support an object to be measured.

15. An assembly for determining machine parameters of a mechanical device in which a first element and a second element are mutually movable, the assembly comprising:

a measuring arm which has at its ends fastening devices for articulated fixing to articulations of the first element and the second element respectively, the measuring arm comprising a telescopic element that links the articulations and measuring equipment for recording changes in the distance between the articulations to make it possible to measure positional change between the first element and the second element while a predetermined force is being applied, and

a power unit that is arranged to apply the predetermined force substantially parallel with the measuring arm to the first element and the second element, the power unit being arranged to apply the predetermined force that comprises at least a dynamically varying portion and a static portion, wherein the dynamically varying portion and the static portion are generated separately by the power unit, wherein the power unit comprises at least one piezo actuator that is adapted to generate the dynamically varying portion,

wherein:

the power unit is arranged to apply the predetermined force in various mutual positions between the first and second elements, and to apply the dynamically varying portion dependent on the position, and

the assembly is arranged to record a resulting actual movement by dynamically determining a current length or a length difference of the measuring arm while the predetermined force is applied.

16. The assembly according to claim 15 , wherein the dynamically varying portion is sinusoidal, subject to an analytic function or subject to a step function.

17. The assembly according to claim 15 , wherein

the power unit is provided with a first bracket for fixing to the first element and with a second bracket for fixing to the second element, wherein the first and second brackets are each provided with a bearing allowing rotation of the power unit, wherein the second bracket is provided with devices for fixing one end to the measuring arm.

18. The assembly according to claim 15 , wherein the first element is a rotating spindle, wherein the assembly

is adapted to measure a stiffness of the spindle, the stiffness varying with a rotational speed of the spindle.

19. The assembly according to claim 15 , wherein the assembly is adapted to be operated cordless.