A laser tracker target ball automatic fixing device for measuring inner and outer diameters of shaft parts

Abstract

The application discloses a kind of laser tracker target ball automatic fixing device for measuring inner and outer diameter of shaft parts, belong to the cross technical field of precision measurement and automation control. Including visual host computer, target ball fixing device unit and controller driving unit, communication control is realized by RS-485 bus. Target ball fixing unit adopts two-phase hybrid closed-loop stepper motor to drive left and right rotation precision ball screw, and synchronous opening and closing movement is realized by driving measuring claw;Controller driving unit adopts STM32 single-chip microcomputer as core, adopts "position-velocity-current" three closed-loop cascade control strategy, combined with fuzzy PID algorithm and S-shaped acceleration and deceleration algorithm, the clamping force control of ±5N precision is realized.The application has the characteristics of full automation operation, stroke self-calibration and wide adaptability, solves the problems of large manual operation error, poor force / position control coordination, etc., improves the precision and efficiency of large shaft parts measurement, especially suitable for precision detection of large shaft parts.

Description

Technical Field

[0001] This invention relates to the field of precision measurement and automated control technology, and in particular to an automatic target ball fixing device for a laser tracker used to measure the inner and outer diameters of shaft-type parts. Background Technology

[0002] As an industrial-grade high-precision, large-size measuring device, the laser tracker integrates core technologies such as laser interferometric ranging, photoelectric detection, precision mechanical transmission, and computer control. It boasts advantages such as high measurement accuracy, fast response speed, and convenient operation, and has become a key device for detecting the inner and outer diameters of large shaft parts. During the measurement process, the target sphere, acting as the receiver and reflector of the laser signal, directly determines the accuracy of the measurement data due to its stability, making it a core component of the laser tracking measurement system.

[0003] However, existing laser trackers still have the following technical shortcomings in the target ball fixing and workpiece clamping methods when measuring large shaft parts:

[0004] (1) High dependence on manual operation and large measurement error: The existing target ball fixing methods mostly rely on manual hand-holding or magnetic chuck fixing. When manually holding the target ball, the smooth surface of the target ball is easy to fall off and be damaged, and the operator's hand shaking will cause the target ball to shift in spatial position, introducing millimeter-level measurement error; although the magnetic chuck does not require hand-holding, the surface of large shaft parts often has oil stains or oxide layers, which can easily cause the magnetic chuck to loosen, further amplifying the measurement deviation. Moreover, large shaft parts are large in size and heavy in weight, and clamping often requires the cooperation of multiple people, resulting in low operating efficiency.

[0005] (2) Poor force / position control coordination, easily damaging the workpiece: Traditional clamping devices only have a single position control function, or rely on manual adjustment of the clamping force. When the device switches from the "non-contact workpiece" position control mode to the "contact workpiece" force control mode, due to the lack of a smooth transition mechanism, system oscillation is prone to occur, which not only affects the measurement stability, but may also cause surface scratches on shaft parts due to overload of clamping force, failing to meet the measurement protection requirements of precision parts.

[0006] (3) Low adaptability and high cost of use: The clamping structure of the existing target ball fixing device is mostly customized and can only be adapted to shaft parts of a single specification. When measuring parts of different sizes and shapes, the entire fixing device needs to be replaced, which increases the equipment procurement cost. At the same time, frequent device replacement will also prolong the measurement preparation time and further reduce the measurement efficiency.

[0007] In summary, there is an urgent need for a target ball fixing device that combines automated clamping, precise force control, wide adaptability, and low cost to address the technical requirements of laser tracking measurement systems in the inspection of large shaft parts and improve measurement accuracy and efficiency. Summary of the Invention

[0008] The purpose of this invention is to provide an automatic target ball fixing device for laser trackers used to measure the inner and outer diameters of shaft-type parts. This device solves the problems of cumbersome manual operation, force / position control conflicts, poor adaptability, and high cost of existing target ball fixing devices. It achieves automated clamping, precise force control, and stable operation, reduces measurement errors, eliminates the need for manual operation, and improves operational efficiency.

[0009] To achieve the above objectives, this invention provides an automatic target ball fixing device for laser trackers used to measure the inner and outer diameters of shaft-type parts. The device comprises three parts: a visualization host computer, a target ball fixing device unit, and a controller drive unit. These three components work collaboratively with a control algorithm via a communication link. The specific structure is as follows:

[0010] The visualization host computer establishes a communication connection with the controller drive unit via RS-485 bus and uses the Modbus RTU protocol to achieve bidirectional data interaction; it sends control commands such as target position, running speed and clamping force parameters to the controller drive unit; and it receives real-time feedback from the controller drive unit on the device operating status (idle / clamping / running), motor operating parameters (position, speed, current) and measurement auxiliary data, which facilitates debugging and optimization.

[0011] The target ball fixing device unit is a mechanical actuator, including a two-phase hybrid closed-loop stepper motor, coupling, left and right turn precision ball screws, retaining ring, radial bearing, nut, measuring claw, magnetic target ball seat, target ball, guide shaft, target ball fixing device housing, left and right turn precision ball screw support side support, left and right turn precision ball screw fixing side support, handle and handle bracket.

[0012] Preferably, the power transmission assembly consists of: the output shaft of a two-phase hybrid closed-loop stepper motor being coaxially fixed to the right end of a left- or right-hand precision ball screw via a coupling; each of the left-hand and right-hand sections of the left- or right-hand precision ball screw is fitted with a nut, and the two nuts are rigidly connected to two measuring jaws via bolts; one end of each left- or right-hand precision ball screw is rotatably connected to a support bracket for the left- or right-hand precision ball screw via a radial bearing, and a retaining ring is fitted at the protruding end of the left- or right-hand precision ball screw passing through the radial bearing to restrict the axial displacement of the radial bearing;

[0013] Preferably, the target ball fixing assembly consists of: a magnetic target ball holder fixed to the front end of the measuring claw via screws; the magnetic surface of the magnetic target ball holder is an arc-shaped structure adapted to the target ball (e.g., a radius of curvature of 12.7±0.01mm when adapting to a 25.4mm target ball), and contains a built-in strong magnet (e.g., N52 neodymium iron boron) to ensure coaxiality between the target ball and the magnetic target ball holder; the target ball contains a corner cube prism, the reflection center of which coincides with the geometric center of the target ball, for accurately receiving and reflecting the laser signal emitted by the laser tracker; the inner surface of the measuring claw is designed as a planar structure, which is aligned with the geometric center of the target ball. The centers of the measuring jaws are located in the same vertical plane (i.e., the plane normal coincides with the central axis of the target ball). The inner surface is used to directly clamp the outer cylindrical surface of the workpiece being measured. By coordinating the distance between the inner surfaces of the measuring jaws on both sides with the target ball coordinates of the laser tracker, the outer diameter of the workpiece can be accurately measured. The outer surface of the measuring jaws adopts an arc surface structure that is compatible with the inner hole of common shaft parts. The vertical distance from the generatrix of the arc surface that contacts the inner diameter of the workpiece to the inner surface of the measuring jaws is a preset fixed value. During measurement, the target ball coordinates are collected by the laser tracker, and the inner diameter of the workpiece can be calculated by combining this fixed distance without the need for additional adjustment of the measurement reference.

[0014] Preferably, the guiding and protective components are as follows: four guide shafts are set parallel to the left and right precision ball screws and are evenly distributed at the four corners of the measuring claw. The two ends of the guide shafts are respectively interference-fitted with the left and right precision ball screw support side brackets and the left and right precision ball screw fixing side brackets. The measuring claw and the guide shafts are slidably connected by linear bearings to ensure the linearity of the measuring claw movement. The front cover, rear cover, upper cover and lower cover of the target ball fixing device are spliced ​​with screws to form a closed shell. The shell material is aluminum alloy with a thickness of 3-5mm, which combines lightweight and protective performance. The top of the target ball fixing device upper cover is fixed with a handle bracket by screws. The handle bracket and the handle are connected by screws. The outer surface of the handle is covered with an anti-slip sleeve to facilitate manual or robotic arm handling.

[0015] Preferably, the controller drive unit uses an STM32F407IGT6 microcontroller as the main control core and integrates a power supply module, a power drive module, a current detection module, a position detection module, and a communication module.

[0016] Preferably, the power supply module adopts a wide voltage input (12-24V DC) design, and outputs 5V DC (to power the encoder and driver chip) and 3.3V DC (to power the main control chip and communication module) through a DC-DC converter, and has built-in overvoltage and overcurrent protection circuits.

[0017] Preferably, the power drive module adopts a dual H-bridge topology, with the core drive chip being the DRV8825. It supports PWM signal isolation amplification and can output a maximum current of 3.5A (continuous) and 5A (peak), meeting the drive requirements of a two-phase hybrid closed-loop stepper motor. The module has built-in freewheeling diodes and overheat protection circuits to prevent damage to components when the motor stalls.

[0018] Preferably, the current detection module uses a high-precision sampling resistor connected in series in the motor winding circuit, and acquires the two-phase current of the motor through a differential amplifier chip. , The collected data is transmitted to the main control chip via the SPI interface.

[0019] Preferably, the position detection module uses the encoder built into the two-phase hybrid closed-loop stepper motor to obtain the real-time position of the motor rotor through the AB phase quadrature decoding circuit.

[0020] Preferably, the communication module integrates an RS-485 communication interface and a TTL level debugging interface. The RS-485 interface is used to communicate with the host computer, and the TTL interface is used to output motor position, speed, and current data in real time, which is convenient for parameter debugging.

[0021] Preferably, the control algorithm design adopts a three-closed-loop cascade control strategy of "position-velocity-current", combined with fuzzy PID algorithm and S-curve acceleration / deceleration algorithm to achieve precise force / position coordinated control, as follows:

[0022] Current loop control: Employs a fuzzy PID control algorithm, using the quadrature-axis current in a rotating coordinate system. For control quantities. The two-phase currents in the stationary coordinate system are transformed using the Park transformation. , ) converted to The coordinate system current is then transformed into a direct-axis current in a rotating coordinate system via the Park transformation. With cross-axis current ,set up To maximize motor torque; the fuzzy PID controller is based on The deviation and rate of change of deviation are determined, and the PID parameters are adaptively adjusted using a fuzzy rule base. The output voltage signal, after inverse Park transform and SVPWM modulation, drives the dual H-bridge circuit to generate the target current, thereby achieving precise control of the clamping force. and (Satiates on a linear relationship).

[0023] Speed ​​loop control: Employs a PI control algorithm, using the deviation between the target speed output from the position loop and the real-time motor speed as input, and the output as the target speed for the current loop. The output is limited to restrict the maximum speed of the motor and avoid system oscillation caused by inertial impact.

[0024] Position loop control: The PID control algorithm is adopted, which takes the deviation between the target position set by the host computer and the real-time position fed back by the encoder as the input and the output as the target speed of the speed loop; combined with the S-shaped acceleration and deceleration algorithm, the soft start, constant speed operation and soft stop of the measuring claw are realized.

[0025] The performance comparison between the present invention and the prior art is as follows:

[0026] (1) Measurement error: The error of the existing manual handheld method is >0.1mm, while the error of the present invention is ≤0.01mm (tested with a standard shaft with a diameter of 1000mm and a laser tracker accuracy of ±0.005mm).

[0027] (2) Clamping force accuracy: The existing manual clamping force adjustment error is ±20N, while that of this invention is ±5N (measured by a tension sensor, clamping force range 5-50N).

[0028] (3) Measurement efficiency: The existing multi-person collaborative operation for measuring a single workpiece requires 15 minutes, while the automatic operation of this invention requires only 3 minutes, improving efficiency by 80%.

[0029] Therefore, the automatic target ball fixing device for laser tracker used in measuring the inner and outer diameters of shaft-type parts, which adopts the above-described structure, has the following beneficial effects:

[0030] This invention achieves fully automated measurement of shaft parts through a sensorless force control design, seamless force / position switching mechanism, and stroke self-calibration function, eliminating the need for manual intervention and effectively removing human error. Utilizing a three-loop cascade control and fuzzy PID algorithm, force / position switching is oscillating-free, and clamping force control accuracy reaches ±5N, adapting to workpieces of different materials and avoiding surface damage. Stroke self-calibration enables universal measurement of the inner and outer diameters of large shaft parts without requiring device replacement, significantly reducing operating costs and improving efficiency. The combination structure of a double-ended support screw and guide shaft, along with a full-module protection circuit, ensures the straightness of the measuring jaw movement and long-term stable operation of the device, comprehensively meeting the industrial measurement requirements of high precision, high efficiency, and high reliability.

[0031] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0032] Figure 1 This is a front view of the target ball fixing device in an embodiment of the present invention.

[0033] Figure 2 This is a schematic diagram of the left side of the target ball fixing device in an embodiment of the present invention;

[0034] Figure 3This is a schematic diagram of the left front view isometric structure of the target ball fixing device in an embodiment of the present invention;

[0035] Figure 4 This is a schematic diagram of the right front view isometric structure of the target ball fixing device in an embodiment of the present invention;

[0036] Figure 5 This is a hardware structure block diagram of the controller driver unit in an embodiment of the present invention;

[0037] Figure 6 This is a flowchart illustrating the three-closed-loop control algorithm in an embodiment of the present invention;

[0038] Figure 7 This is a schematic diagram of the automatic workpiece clamping and outer diameter measurement process of the target ball fixing device in an embodiment of the present invention;

[0039] Figure Labels

[0040] 1-Two-phase hybrid closed-loop stepper motor; 2-Coupling; 3-Left and right turn precision ball screw; 4-Snap ring; 5-Radial bearing; 6-Nut; 7-Measuring claw; 8-Magnetic target ball holder; 9-Target ball; 10-Guide shaft; 11-Front cover of target ball fixing device; 12-Rear cover of target ball fixing device; 13-Side support of left and right turn precision ball screw; 14-Side fixing support of left and right turn precision ball screw; 15-Upper cover of target ball fixing device; 16-Lower cover of target ball fixing device; 17-Handle; 18-Handle bracket. Detailed Implementation

[0041] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0042] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0043] Example

[0044] like Figure 1As shown, the present invention provides an automatic target ball fixing device for a laser tracker for measuring the inner and outer diameters of shaft-type parts, as detailed below:

[0045] A two-phase hybrid closed-loop stepper motor 1 is bolted to a fixed side support 14 of a left- or right-hand precision ball screw, and its output shaft is coaxially connected to the left- or right-hand precision ball screw 3 via a coupling 2; Figure 2 As shown, the radial bearing 5 is press-fitted into the bearing hole of the left-hand and right-hand precision ball screw support 13. After one end of the left-hand and right-hand precision ball screw 3 passes through the radial bearing 5, a retaining ring 4 is assembled to restrict axial displacement. Figure 3 As shown, nuts 6 are respectively installed on the left-hand and right-hand sections of the left-hand and right-hand precision ball screws 3. Nuts 6 are rigidly connected to measuring claws 7 by screws. Mounting holes are machined at the front end of the measuring claws 7, and magnetic target ball seats 8 are fixed in the mounting holes, ensuring that the axis of the magnetic target ball seats 8 is perpendicular to the moving direction of the measuring claws 7. Target balls 9 are attracted to the magnetic target ball seats 8. The two ends of the four guide shafts 10 are respectively pressed into the guide holes of the left-hand and right-hand precision ball screw support side supports 13 and the left-hand and right-hand precision ball screw fixing side supports 14. The measuring claws 7 and guide shafts 10 are slidably connected by linear bearings to ensure smooth and unobstructed movement of the measuring claws 7. Figure 4 As shown, the front cover 11, rear cover 12, upper cover 15 and lower cover 16 of the target ball fixing device are spliced ​​together with screws to form a closed shell; two threaded holes are machined on the top of the upper cover 15 of the target ball fixing device, the handle bracket 18 is fixed with screws, and the handle 17 is connected to the handle bracket 18 with screws.

[0046] like Figure 5 As shown, the controller driver unit uses the STM32F407IGT6 microcontroller as the main control core and integrates a power supply module, a power drive module, a current detection module, a position detection module, and a communication module. The specific implementation methods of each module are as follows:

[0047] The power module adopts a wide voltage input design, supporting external DC power input of 12-24VDC. Voltage conversion is performed via a DC-DC converter, outputting both 5VDC and 3.3VDC. The 5VDC powers the encoder and the driver chip module in the dual H-bridge drive circuit. The 3.3VDC powers the main control chip and communication module. Simultaneously, the power module incorporates overvoltage and overcurrent protection circuits. When the input voltage exceeds the set overvoltage threshold or the output current exceeds the overcurrent threshold, it can promptly cut off or limit the power output, ensuring the electrical safety of the entire controller drive unit.

[0048] The power drive module adopts a dual H-bridge topology. This module supports isolated amplification of the PWM control signal output from the main control chip, enabling it to output drive current to a two-phase hybrid closed-loop stepper motor, meeting the motor's drive requirements. Furthermore, the module incorporates a freewheeling diode to provide a freewheeling path when the motor windings are de-energized, preventing excessive back electromotive force. It also features an overheat protection circuit; when the module temperature exceeds the overheat threshold, it automatically limits or stops the output, preventing damage to components due to abnormal conditions such as motor stall.

[0049] The current detection module connects a high-precision sampling resistor in series in the motor winding circuit and acquires the two-phase current of the motor through a differential amplifier chip. The acquired analog current signal is processed and transmitted to the main control chip via the SPI interface for the main control chip to perform current loop control and other related calculations and processing.

[0050] The position detection module utilizes the encoder built into the two-phase hybrid closed-loop stepper motor. It decodes the AB-phase quadrature pulse signal output by the encoder through the AB-phase quadrature decoding circuit, thereby obtaining the real-time position information of the motor rotor and providing feedback for position loop control.

[0051] The communication module integrates an RS-485 communication interface and a TTL level debugging interface. The RS-485 communication interface is used to communicate with a PC host computer to issue control commands and upload data such as motor operating status. The TTL level debugging interface is used to output real-time data such as motor position, speed, and current during the debugging phase, facilitating the adjustment and optimization of various parameters.

[0052] like Figure 6 As shown, this invention employs a three-loop cascade control strategy of "position-velocity-current," combined with fuzzy PID algorithm and S-curve acceleration / deceleration algorithm, to achieve precise force / position coordinated control. The specific implementation methods of each loop are as follows:

[0053] The current loop control employs a fuzzy PID control algorithm, using the quadrature-axis current reference value in a rotating coordinate system. As a control variable, firstly, the two-phase current detected in the stationary coordinate system is transformed using the Park transformation. , Converted to direct-axis current in rotating coordinate system With cross-axis current To maximize motor torque, set a reference value for the direct-axis current. Then, the fuzzy PID controller takes the deviation of the quadrature-axis current and its rate of change as input, and adaptively adjusts the proportional, integral, and derivative coefficients of the PID controller through a pre-established fuzzy rule base. Finally, the voltage signal output by the fuzzy PID controller is converted into a voltage signal in a stationary coordinate system through inverse Park transform, and then a drive signal is generated by two-phase SVPWM (space vector pulse width modulation) control to drive the dual H-bridge inverter circuit to output the target current, thereby achieving precise control of the clamping force (the clamping force and the quadrature-axis current satisfy a linear relationship).

[0054] The speed loop control employs a PI control algorithm, with its input being the deviation between the target speed output from the position loop and the real-time motor speed fed back by the encoder. The output of the PI controller serves as the quadrature-axis current reference value for the current loop. Simultaneously, the output of the PI controller is limited to restrict the maximum motor speed, preventing system oscillations caused by inertial shocks and ensuring stable system operation.

[0055] The position loop control employs a PID control algorithm, with the input being the deviation between the target position set by the host computer and the real-time motor position fed back by the encoder. The output of the PID controller serves as the target speed reference value for the speed loop. Furthermore, combined with an S-shaped acceleration / deceleration algorithm, the measuring jaw achieves soft start, constant speed operation, and soft stop during movement, avoiding adverse effects of rigid impacts on the measuring jaw and the workpiece being measured, while simultaneously improving measurement accuracy.

[0056] like Figure 7 As shown, after the device is powered on, the controller drive unit automatically performs current zero-point calibration and stroke self-calibration; the drive motor drives the measuring claw 7 to first fully close inward (stops when the stall current threshold is triggered, and the coordinates of the closed position are recorded), and then runs in reverse to fully open outward (stops when the stall current threshold at the other end is triggered, and the coordinates of the open position are recorded), and defines the fully open position as the mechanical zero point, and automatically establishes the absolute position coordinate system; the visualization host computer polls the status of the controller drive unit in real time through the RS-485 bus, and displays the "idle" status after initialization is completed.

[0057] Workpiece clamping and outer diameter measurement process:

[0058] Clamping Operation: The large shaft-like part to be measured is placed in the central area between the two measuring jaws 7, ensuring that the axis of the part is perpendicular to the moving direction of the measuring jaws; the host computer issues an "outer diameter clamping command", configuring parameters including: clamping force, moving speed, and S-shaped acceleration and deceleration time; the controller drive unit drives the motor to move the measuring jaws 7 to synchronously retract along the guide axis center, achieving a smooth speed transition under the action of the S-shaped acceleration and deceleration algorithm; when the inner side of the measuring jaw contacts the outer cylindrical surface of the workpiece, the motor enters a stall state, and the current detection module collects the cross-axis current i qGradually increase the current to the set value (linearly corresponding to the target clamping force), then the current loop fuzzy PID control is activated, maintaining the current by dynamically adjusting the PWM duty cycle. Stable; the host computer receives the clamping position signal from the controller drive unit, and the status display switches to "outer diameter clamping".

[0059] Laser tracking measurement: The laser tracker is activated and aligned with the target sphere 9 on the measuring claw 7. The target sphere 9 contains a built-in corner cube prism, which reflects the laser signal. The laser tracker acquires the coordinates, and the device automatically tracks the three-dimensional spatial coordinates of the two target spheres; according to the formula for the distance between two points in space:

[0060] ;

[0061] The straight-line distance between the centers of the two target balls is calculated, and this distance is consistent with the actual outer diameter of the workpiece (because the inner surface of the measuring jaw and the center of the target ball are on the same plane).

[0062] Workpiece clamping and inner diameter measurement process:

[0063] Clamping Operation: First, fully close the two measuring jaws 7 inwards, inserting them into the inner hole of the large shaft-like part being measured, with the arc generatrix parallel to the inner hole axis; issue an "inner diameter clamping command" via the host computer, configuring parameters including: clamping force, moving speed, and S-shaped acceleration / deceleration time; the controller drive unit drives the motor to synchronously expand the measuring jaws 7 outwards along the guide shaft, achieving a smooth start under the action of the S-shaped acceleration / deceleration algorithm; when the arc surface of the outer side of the measuring jaws contacts the inner hole wall, the motor enters a stall state, and the current detection module collects the i q Gradually increase to the set value, the current loop fuzzy PID control starts and maintains i q Stable, ensuring a tight fit between the arc surface and the hole wall without overpressure deformation; the host computer receives the clamping position signal from the controller drive unit, and the status display switches to "inner diameter clamping" status.

[0064] Laser tracking measurement: Start the laser tracker and align it with the target ball 9 on the measuring claw 7. The target ball 9 has a built-in corner cube prism that reflects the laser signal. The laser tracker collects the coordinates, and the equipment automatically tracks the three-dimensional spatial coordinates of the two target balls. First, calculate the straight-line distance between the centers of the two target balls. Then, combined with the preset parameters, "the fixed distance from the outer arc surface of the measuring claw to the inner surface of the contact line", ", through formula The actual inner diameter of the workpiece can be calculated. This is the measured inner diameter value. (This is the sum of the fixed distances on both sides).

[0065] Workpiece release and system shutdown:

[0066] After the measurement is completed, the host computer issues a "release command" and sets the moving speed; the controller drive unit drives the motor to move the measuring claw 7 in the opposite direction (expanding outward when measuring the outer diameter and contracting inward when measuring the inner diameter) until it returns to the fully opened mechanical zero position, and the host computer status display switches to "idle"; disconnect the device power supply, remove the target ball fixing device, and complete a single measurement.

[0067] In summary, the laser tracker target ball fixing device for automatically measuring the inner and outer diameters of shaft parts of the present invention can be used in conjunction with a laser tracker to form an automated measurement system. With the help of sensorless force control, seamless force / position switching and stroke self-calibration technologies, it can realize the integrated operation of "automatic clamping-automatic measurement-automatic release" of shaft parts without manual intervention. It can accurately adapt to shaft parts of different sizes and shapes for measuring inner and outer diameters, thus improving measurement efficiency and accuracy.

[0068] This invention is adaptable to shaft parts made of different materials: for aluminum alloys (clamping force tolerance ≤30N), the clamping force can be set to 10-20N via a host computer; for stainless steel (tolerance ≤50N), the clamping force can be set to 20-40N; for hollow shaft parts (thin inner wall, easily deformable), the response speed is reduced through a current loop fuzzy PID (adjusting the fuzzy rule library ΔKi to 0.1-0.3) to avoid overpressure deformation. Furthermore, by replacing the measuring jaws with different arc radii (e.g., arc radii of 50mm and 100mm), it can adapt to shaft parts with inner diameters of 50-2000mm without replacing the entire device.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. An automatic target ball fixing device for a laser tracker used to measure the inner and outer diameters of shaft-type parts, characterized in that, include: Visualization host computer, target ball fixing device unit, and controller drive unit; The visualization host computer communicates with the controller drive unit via an RS-485 bus to send clamping force and movement speed parameters and receive operating status. The target ball fixing device unit includes a measuring claw, a magnetic target ball holder, and a left-right rotating ball screw driven by a stepper motor. The measuring claw can open and close synchronously and is adaptable to workpieces of different sizes. The controller drive unit uses an STM32 microcontroller as its core and integrates a 'position-speed-current' three-closed-loop cascade control module and a stroke self-calibration module to achieve ±5N accuracy control of clamping force and automatic coordinate system establishment. The target ball fixing device unit works in conjunction with the controller drive unit to complete the automatic clamping and laser tracking measurement adaptation of shaft parts. The target ball fixing device unit also includes a two-phase hybrid closed-loop stepper motor, a coupling, left-hand and right-hand precision ball screws, nuts, and a guide shaft; the output shaft of the two-phase hybrid closed-loop stepper motor is coaxially fixed to the left-hand and right-hand precision ball screws through the coupling; each of the left-hand and right-hand sections of the left-hand and right-hand precision ball screws is equipped with a nut, and each nut is rigidly connected to a measuring claw; the guide shaft is arranged parallel to the left-hand and right-hand precision ball screws, and the measuring claw is slidably connected to the guide shaft through a linear bearing; The inner surface of the measuring jaw is designed as a planar structure, which is in the same vertical plane as the geometric center of the target ball. The inner surface is used to directly clamp the outer cylindrical surface of the workpiece being measured. By coordinating the distance between the inner surfaces of the measuring jaws on both sides with the coordinates of the target ball of the laser tracker, the outer diameter of the workpiece can be accurately measured. The outer surface of the measuring jaw adopts an arc surface structure that is compatible with the inner hole of common shaft parts, and the vertical distance from the generatrix of the arc surface that contacts the inner diameter of the workpiece to the inner surface of the measuring jaw is a preset fixed value. During measurement, the coordinates of the target ball are collected by a laser tracker, and the inner diameter of the workpiece can be calculated by combining this fixed distance, without the need for additional adjustment of the measurement reference.

2. The automatic target ball fixture for a laser tracker according to claim 1, wherein, The target ball fixing device unit also includes a magnetic target ball holder; the magnetic target ball holder is fixed to the front end of the measuring claw and is used to attract the target ball; the magnetic surface of the magnetic target ball holder has an arc-shaped structure and a built-in strong magnet to ensure that the target ball and the magnetic target ball holder are coaxial.

3. The automatic target ball fixture for a laser tracker according to claim 1, wherein, The controller drive unit uses an STM32F407IGT6 microcontroller as its main control core and integrates a power supply module, a power drive module, a current detection module, a position detection module, and a communication module. The power supply module is configured to provide multiple voltage outputs. The power drive module adopts a dual H-bridge topology. The current detection module acquires the motor current through a sampling resistor. The position detection module uses an encoder to obtain the motor rotor position. The communication module includes an RS-485 interface and a TTL debugging interface.

4. The automatic target ball fixture for a laser tracker according to claim 1, wherein, The controller drive unit is also equipped with a control algorithm, which adopts a three-closed-loop cascade control strategy of position loop, speed loop and current loop; the position loop adopts a PID control algorithm combined with an S-shaped acceleration and deceleration algorithm to control the movement of the measuring claw; the speed loop adopts a PI control algorithm to limit the motor speed; and the current loop adopts a fuzzy PID control algorithm to accurately control the clamping force.

5. The automatic target ball fixing device for laser tracker according to claim 4, characterized in that, The control process of the current loop includes: converting the two-phase current of the motor into direct-axis current and quadrature-axis current in a rotating coordinate system through Park transformation, setting the direct-axis current to zero, and adaptively adjusting the PID parameters of the quadrature-axis current through a fuzzy PID controller to achieve linear control of the clamping force and the quadrature-axis current.

6. The automatic target ball fixture for a laser tracker according to claim 1, wherein, The visualization host computer communicates with the controller drive unit via an RS-485 bus and uses the Modbus RTU protocol for data interaction; the visualization host computer is configured to display the device's operating status, motor parameters, and measurement data in real time.

7. The automatic target ball fixture for a laser tracker according to claim 1, wherein, The target ball fixing device unit also includes a housing and a handle; the housing is formed by splicing a front cover, a rear cover, an upper cover and a lower cover, and is made of aluminum alloy; the handle is fixed to the top of the upper cover by a handle bracket for easy handling.

8. The automatic target ball fixture for a laser tracker according to claim 1, wherein, The device is also equipped with a stroke self-calibration function; the controller drive unit drives the measuring jaw to move from a fully closed position to a fully open position, automatically establishing an absolute position coordinate system to adapt to workpieces of different sizes.

9. A method of measuring using the automatic fixture of the target ball of the laser tracker according to any one of claims 1 to 8, characterized in that, Includes the following steps: The clamping command is issued through the visual host computer, and the clamping force, moving speed and acceleration / deceleration parameters are set. The controller drive unit drives the measuring claw to move, and after contacting the workpiece, it enters the force control mode to maintain the set clamping force. The laser tracker measures the coordinates of the target ball and calculates the outer or inner diameter of the workpiece. After the measurement is completed, the measuring claw returns to the mechanical zero point.

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