Search

CN-121995742-A - Control loop parameterization for CMM

CN121995742ACN 121995742 ACN121995742 ACN 121995742ACN-121995742-A

Abstract

The present invention relates to control loop parameterization for a CMM, and in particular to a computer implemented method of setting control parameters for a CMM, the CMM comprising a stylus having a sensor for determining at least one coordinate of one or more measurement points on a surface of an object, one or more actuators, and a control unit configured to control the actuators according to predefined control parameters to move the stylus to a target position, the method comprising controlling the actuators by the control unit to excite one or more parts of the CMM, receiving sensor feedback signals comprising sensor values captured by the sensor when said parts of the CMM are excited, the sensor values being indicative of acceleration of the stylus, determining a behaviour of the CMM based on the received sensor feedback signals, and calculating an adapted control parameter for the control unit based on the determined behaviour.

Inventors

  • K. Imhoter
  • R.Sun
  • C. Ashley

Assignees

  • 海克斯康创新中心有限公司

Dates

Publication Date
20260508
Application Date
20251106
Priority Date
20241108

Claims (15)

  1. 1. A computer-implemented method (100) of setting control parameters for a coordinate measuring machine (1), the coordinate measuring machine comprising: A stylus having a sensor for determining at least one coordinate of one or more measurement points on a surface of an object, -One or more actuators, and A control unit configured to control the actuator to move the gauge head to a target position according to predefined control parameters, The method (100) comprises: -controlling the actuator by the control unit to excite (120) one or more parts of the coordinate measuring machine (1), wherein exciting a part of the coordinate measuring machine (1) comprises oscillating or vibrating the part at one or more known frequencies; -receiving (130) a sensor feedback signal comprising sensor values captured by the sensor when the one or more parts of the coordinate measuring machine (1) are excited, the sensor values being indicative of acceleration of the gauge head when the one or more parts of the coordinate measuring machine (1) are excited; -determining (140) the behaviour of the coordinate measuring machine (1) based on the received sensor feedback signal, and -Calculating (150) an adapted control parameter for the control unit based on the determined behavior.
  2. 2. The method (100) of claim 1, comprising controlling the actuator -To move (110) the probe to a first target position, wherein the actuator is controlled to energize (120) the one or more parts of the coordinate measuring machine (1) when the probe is in the first target position, in particular wherein the first target position is a scanning position enabling the probe to determine at least one coordinate of the at least one measuring point, and/or -To subsequently move (110) the gauge head to a plurality of target positions, wherein the step of controlling the actuator to excite (120) the one or more parts of the coordinate measuring machine (1) and the step of receiving (130) the sensor feedback signal are repeated at each of the plurality of target positions, in particular wherein the plurality of target positions or a subset of the plurality of target positions are scanning positions, each scanning position enabling the gauge head to determine at least one coordinate of the at least one measurement point.
  3. 3. The method (100) according to claim 1 or claim 2, comprising controlling the actuator to move (110) the gauge head along a path, wherein, -Controlling the actuator to continuously energize (120) the one or more parts of the coordinate measuring machine (1) as the stylus moves along the path, and/or -The step of controlling the actuator to excite (120) the one or more parts of the coordinate measuring machine (1) and the step of receiving (130) the sensor feedback signal are repeated at each of a plurality of positions along the path, In particular, the path is a scanning path which enables the stylus to determine at least one coordinate of a plurality of measurement points on the object.
  4. 4. The method (100) according to any one of the preceding claims, wherein, -The step of controlling the actuator to excite (120) the one or more parts of the coordinate measuring machine (1) and the step of receiving (130) the feedback sensor values are repeated with a plurality of settings of the coordinate measuring machine (1), in particular wherein each setting differs at least in terms of the configuration of the probe, in particular in terms of the length of the probe, and/or -The step of controlling the actuator to energize (120) the one or more parts of the coordinate measuring machine (1) and the step of receiving (130) the feedback sensor values are repeated with a plurality of settings of the object, in particular wherein each setting differs at least in terms of the pose or shape of the object.
  5. 5. The method (100) of claim 3 or claim 4, further comprising generating a set of response models based on a number of sensor feedback signals, wherein at least one of determining (140) the behavior of the coordinate measuring machine (1) and calculating (150) the adapted control parameters is also based on the set of response models, in particular wherein the response models are frequency response models or time response models.
  6. 6. The method (100) according to any one of the preceding claims, wherein the coordinate measuring machine (1) is one of a plurality of identical coordinate measuring machines, wherein adjusting the control parameter comprises adjusting the control parameter for each of the plurality of identical coordinate measuring machines.
  7. 7. The method (100) according to any one of the preceding claims, wherein, The sensor is a force sensor configured to determine a force applied to the gauge head when the gauge head contacts the object, and The sensor feedback signal comprises a sensor value captured by the force sensor when at least a part of the coordinate measuring machine (1) is excited, In particular, wherein the method comprises controlling the actuator to move (110) the stylus to a scanning position in which the stylus contacts a measurement point on a surface of the object, wherein, -Controlling the actuator to excite (120) the one or more parts of the coordinate measuring machine (1) when the stylus contacts the measuring point, and -The sensor feedback signal comprises a sensor value captured by the force sensor when the at least a portion of the coordinate measuring machine (1) is excited.
  8. 8. The method (100) according to claim 7, wherein the probe does not contact an object when the at least a portion of the coordinate measuring machine (1) is excited.
  9. 9. The method (100) according to any one of claims 1 to 6, wherein, -The sensor is a distance sensor configured to determine a distance between a scanning stylus and a surface of the object; -the method comprises controlling the actuator to move (110) the gauge head to a scanning position enabling the distance sensor to determine a distance between the scanning gauge head and one or more measurement points on the surface of the object; -controlling the actuator to energize (120) the one or more parts of the coordinate measuring machine (1) when the distance sensor continuously determines the distance between the scanning gauge head and the one or more measurement points, and -The sensor feedback signal comprises a sensor value captured by the distance sensor when at least a part of the coordinate measuring machine (1) is excited.
  10. 10. The method (100) according to any one of the preceding claims, wherein the coordinate measuring machine comprises one or more encoders configured to provide encoder signals indicative of a nominal position of the gauge head, wherein, -The method further comprises receiving encoder signals from the one or more encoders when at least a part of the coordinate measuring machine (1) is excited, and -Determining (140) the behaviour of the coordinate measuring machine (1) is also based on the received encoder signal.
  11. 11. The method (100) according to any one of the preceding claims, wherein the control parameters comprise feedback and feedforward control loop parameters, and calculating (150) the adapted control parameters comprises generating optimized feedback and feedforward control loop parameters.
  12. 12. The method (100) according to any one of the preceding claims, wherein, -The step of determining (140) the behaviour and the step of calculating (150) the adapted control parameters are performed by the control unit, in particular in real time, or -The sensor values are acquired by the control unit and provided to an external computing unit, in particular together with information about constraints and/or settings of the coordinate measuring machine, and the steps of determining (140) the behaviour and calculating (150) the adapted control parameters are performed by the external computing unit.
  13. 13. The method (100) according to any one of the preceding claims, wherein the coordinate measuring machine (1) -Having a closed loop scanning mode for measuring an unknown object, wherein calculating (150) the adaptation control parameters comprises calculating (150) adaptation control parameters for the closed loop scanning mode, and/or -Having an observer-based open-loop scanning mode for measuring a known object, wherein calculating (150) the adaptation control parameters comprises calculating (150) adaptation control parameters for the open-loop scanning mode.
  14. 14. A coordinate measuring machine (1), the coordinate measuring machine (1) comprising: A stylus having a sensor for determining at least one coordinate of one or more measurement points on a surface of an object, -One or more actuators, and A control unit configured to control the actuator to move the gauge head to a target position according to predefined control parameters, It is characterized in that the method comprises the steps of, The coordinate measuring machine (1), in particular the control unit, is configured to perform the method (100) according to any one of the preceding claims.
  15. 15. Computer program product comprising a program code with computer executable instructions for performing the method (100) according to any one of claims 1 to 13, in particular when executed on a control unit of a coordinate measuring machine (1) according to claim 14.

Description

Control loop parameterization for CMM Technical Field The present invention relates to a computer-implemented method of setting control parameters for a Coordinate Measuring Machine (CMM) based on feedback signals from stylus sensors while exciting components of the CMM by oscillating or vibrating them at one or more known frequencies. In particular, the method includes feedback and feedforward control loop parameterization of an outer control loop using end effector sensor data as feedback. Background CMMs are important in various industries, such as in production measurement, quality control or reverse engineering. They can be used, for example, to determine deviations of the geometry of the manufactured product from the design model, and in particular to determine whether these deviations are within manufacturing tolerances. Such measurements are typically performed automatically or semi-automatically based on a computer generated or operator selected measurement path provided relative to the design model. Another increasingly important application for CMMs is reverse engineering of objects. In this case, no design model exists, but the operator directs the three-dimensional movement of the gauge head through manual steering commands (e.g., using a joystick/joystick). Or the operator may direct the hand-held sensor. In general, a CMM includes a body structure, a detection system, and a data acquisition and data processing system. The body structure typically includes a set of actuators responsible for positioning the detection system. One widely used example is a triaxial system, as disclosed for example in DE 43 25 347. For example, the body structure may include a base with a movable frame of the measuring station. The workpiece may be placed or mounted on a measurement table. The frame is mounted on the base such that it can move along a first axis. The frame includes an arm mounted thereon, the arm being movable along a second axis perpendicular to the first axis. The detection system comprises a probe and is mounted on the arm so that it can move along a third axis, perpendicular to the first and second axes. This configuration enables three-dimensional guidance of the stylus so that the relevant 3D coordinates of the object can be measured. Contemporary triaxial systems also typically include components, such as stacked turrets, to provide five degrees of freedom (5 DoF) with respect to the pose of the stylus relative to the workpiece. Another exemplary embodiment of a CMM is the so-called Articulated Arm Coordinate Measuring Machine (AACMM). AACMM includes a fixed base and an arm made up of a plurality of articulated arm segments. These joints provide mobility to the movable end of the arm (the end opposite the base) to which the gauge head can be attached. Because of its design principle, this system is not as accurate as the 3-axis or 5-axis system described above, but on the other hand it provides more flexibility. For example, EP 2 916 099 B1 discloses such an AACMM instrument. The detection system of the CMM may be based on contact or non-contact technology. In the first case, the mechanical stylus (typically implemented as a probe) is brought into direct mechanical contact with the workpiece and the stylus is guided along a given measurement path, with the endpoint coordinates of the stylus being derived from the sensor readings for the CMM state. The non-contact technique is based on projecting a primary measuring beam onto the workpiece and recording a secondary beam emanating from an object surface area. One advantage of non-contact technology is that there is less likelihood of damage to the work object due to the lack of mechanical contact. Furthermore, the non-contact method allows for parallel acquisition of the extended region, unlike the probe-based method (which only records the coordinates of a single point). In order to obtain high quality data, the CMM measurements should be performed under steady state measurement conditions. For a contact probe, this may be provided by, for example, maintaining the contact force and/or friction force between the probe and the work object within a particular range. This simple feedback method is not suitable for automatically guiding non-contact probes. This problem is particularly acute in the case of manual measurement of unknown work objects, since in this case it is not even possible to provide a sufficiently good approximation path based on a digital model or previous measurement data. EP 4 386 A1 discloses a method for controlling the distance between a non-contact measurement probe of a CMM and a workpiece during measurement. EP 3 781,901 B1 discloses dynamically adapting the operation of a CMM. For effective automatic control of the CMM, it should be appreciated that the behaviour of the system so that the control parameters can be adapted to that behaviour. The known method for adapting control loop parameters is mainly based on trial