Method and device for measuring path following under load

1. A measuring device to measure deviations under load of a programmed path followed by a first part of a machine tool or a robot that is in motion relative to a second part external to the machine tool or the robot, the measuring device comprising:

a telescopic bar comprising: a scale to measure a length of the telescopic bar; a link, at each end of the telescopic bar, comprising two degrees of rotational freedom; an actuator configured to deliver a force along a longitudinal axis of the telescopic bar; and a force sensor to measure a force applied at each end of the telescopic bar along its longitudinal axis;

connectors to link two ends of the telescopic bar to the first and second parts, respectively; and

a controller configured to determine spatial components of a force applied to the connectors by the actuator of the telescopic bar during a motion of the first part.

2. The measuring device according to claim 1 , wherein links comprise a ball link at least at one end of the telescopic bar.

3. The measuring device according to claim 1 , wherein the links comprise a universal joint link at least at one end of the telescopic bar.

4. A method for determining a vibration response of a part in a defined configuration of direction, utilizing a measuring device according to claim 3 comprising a universal joint link at each end of the telescopic bar, the method comprising steps of applying, by the actuator, periodic stress on the two ends of the telescopic bar; and measuring a response to the periodic stress by a length variation of the telescopic bar.

5. The measuring device according to claim 1 , wherein an intensity of a force applied by the actuator of the telescopic bar is adjustable.

6. The measuring device according to claim 1 , wherein the actuator of the telescopic bar comprises a spring to apply a force proportional to the length of the telescopic bar.

7. The measuring device according to claim 1 , wherein a constant force is applied by the actuator of the telescopic bar regardless of the length of the telescopic bar.

8. A method for measuring deviations under load of a programmed path followed by a first part that is moving relative to a second part, utilizing the measuring device according to claim 1 , comprises steps of:

connecting the two ends of the telescopic bar to the first and second parts, respectively;

programming by a controller a relative path of the first part in relation to the second part comprising a path entry movement and a path exit movement, so that a distance between the two parts along the longitudinal axis of the telescopic bar is constant during the relative path;

applying a force, by the actuator of the telescopic bar, with a defined intensity along the longitudinal axis of the telescopic bar to the connectors;

executing the relative path while measuring length variations of the telescopic bar, variations in the force applied to the longitudinal axis of the telescopic bar, and variations of components of the force applied to one of the links.

9. The method according to claim 8 , wherein the actuator comprises a spring to apply a force proportional to the length of the telescopic bar; and wherein the defined intensity of the force applied is determined by the path entry movement.

10. The method according to claim 9 , further comprising a step of measuring a longitudinal force by measuring the length of the telescopic bar.

11. The method according to claim 8 , wherein the first part is fixed; and wherein the relative path is performed by the second part.

12. The method according to claim 9 , wherein the relative path programmed and executed is an arc of a circle.

13. The method according to claim 12 , wherein the longitudinal axis of the telescopic bar is not parallel to the plane of the arc of the circle.

14. The method according to claim 8 , wherein the links comprise a universal joint link at least at one end of the telescopic bar; and further comprising, during the step of executing the relative path, a step of taking a measurement of an azimuth or an elevation of the telescopic bar.