Patent Description:
A motion carrier of a conventional magnetorheological polishing device is generally a multi-axis linkage-based computerised numerical control (CNC) machining center. With development of technology, a magnetorheological polishing module can be integrated on a mechanical arm, i.e., the mechanical arm is acted as the motion carrier of the magnetorheological polishing device. The mechanical arm has advantages of high motion speed and acceleration, flexible motion, and high processing efficiency. In addition, the mechanical arm costs much less than a multi-axis linkage-based CNC machining center for the same range of machining and has a smaller footprint.

However, compared with a multi-axis linkage-based CNC machine tool, the mechanical arm has disadvantage of low precision of a trajectory, i.e., a tail end of the mechanical arm is unable to accurately move along a predetermined trajectory in an optical processing process. An error of the precision of the trajectory reaches sub-millimeter level. A precision of a trajectory of the multi-axis linkage-based CNC machine tool with high precision is generally an order of magnitude higher than the mechanical arm. The reason for the low precision of the trajectory of the mechanical arm is closely related to a multi-joint tandem structure of the mechanical arm, making a polishing gap between a magnetorheological polishing wheel and a surface of a workpiece unstable or uncontrollably changing, which in turn leads to unstable or unpredictable changes in a removal function, and finally shows up as limitations on a processing precision of the magnetorheological polishing device based on the mechanical arm. Therefore, surface residual errors after processing contain typical low and medium frequency errors introduced by the mechanical arm.

Therefore, when processing various optical elements by the magnetorheological polishing device, how to make the polishing gap between the polishing wheel and a surface of an optical element to be processed to maintain within an allowable error range is an urgent technical problem for those skilled in the art.

<CIT> disclosed a calibration method and a calibration device of magnetorheological finishing clearance.

<CIT> discloses a workpiece polishing detection method.

A purpose of the present disclosure is to provide a precision calibrating device for a magnetorheological polishing device, which effectively improves a processing precision of the magnetorheological polishing device. Another purpose of the present disclosure is to provide a precision calibrating method for the magnetorheological polishing device.

To realize above purposes, the present disclosure provides the precision calibrating device for the magnetorheological polishing device.

The magnetorheological polishing device comprises a polishing wheel and a support base configured to mount the polishing wheel. The precision calibrating device comprises an arc-shaped support bracket, a sensor, a signal acquisition module, an industrial personal computer (IPC), and a motion control module.

The arc-shaped support bracket is detachably connected with the support base. The arc-shaped support bracket defines an arc-shaped surface attached to the polishing wheel. The sensor is fixed on the arc-shaped support bracket. The sensor is configured to detect a polishing gap between the polishing wheel and a surface of an optical element to be processed.

The signal acquisition module is connected with the sensor. The IPC is connected with the signal acquisition module and the motion control module. The motion control module is connected with a control system of the magnetorheological polishing device. The IPC is configured to send an instruction to the signal acquisition module and the motion control module. The signal acquisition module is configured to control the sensor to acquire data. The motion control module is configured to send the instruction to the control system, so that the polishing wheel moves along a predetermined processing trajectory to process on the surface of the optical element to be processed.

Optionally, the sensor is a displacement sensor or a pressure sensor.

Optionally, the arc-shaped support bracket defines a through hole. An effective working hole of the sensor coincides with the through hole. A center of the effective working hole of the sensor coincides with a vertex of a spherical crown of the polishing wheel.

Optionally, an adjusting bracket is arranged on the arc-shaped support bracket. Strip-shaped holes configured to adjust a height of the adjusting bracket are defined on the adjusting bracket. Fasteners pass through the strip-shaped holes to fix the adjusting bracket to the support base.

Optionally, the adjusting bracket defines two strip-shaped holes parallel to each other.

The precision calibrating method for the magnetorheological polishing device comprises:.

Optionally, a step of controlling the sensor to collect the displacement values between the sensor and the optical element to be processed and controlling the polishing wheel to move along the predetermined processing trajectory comprises:
sending an instruction to a signal acquisition circuit and a motion control circuit through an IPC; controlling the sensor to collect data through the signal acquisition circuit; sending the instruction to a control system of the magnetorheological polishing device and the motion control circuit, so that the polishing wheel moves along the predetermined processing trajectory.

Optionally, a step of obtaining the error values between the displacement values and the predetermined values comprises:
processing the data collected by the sensor by the IPC; comparing collected displacement values with the predetermined values to obtain the error values.

Optionally, the error values comprise low frequency errors, medium frequency errors, and high frequency errors.

In the precision calibrating device for the magnetorheological polishing device of the present disclosure, when precision calibration is required, the arc-shaped support bracket with the sensor is mounted on the support base. The sensor of the present disclosure is mounted in such a way that a distance between the polishing wheel and the optical element to be processed is very short when the precision is calibrated. The distance between the polishing wheel and the optical element corresponds to the polishing gap in millimeter scale during actual processing, which effectively ensures a calibration precision and a precision during actual use. After the calibration is completed, the arc-shaped support bracket with the sensor is detached from the support base. Then the optical element to be processed is processed by the magnetorheological polishing device.

In the precision calibrating method for the magnetorheological polishing device of the present disclosure, a data collection process of the precision calibrating device and a motion of the mechanical arm are synchronized, which effectively ensures that the data measured is corresponding to a motion position of the mechanical arm and ensures validity of the data. By executing the precision calibrating method, errors in all frequency bands that affect the polishing gap are measured, and the low frequency errors, the medium frequency errors, and the high frequency errors in a system are effectively compensated, thereby improving the precision of the magnetorheological polishing device. Further, the errors directly measured are converted into polishing gap errors in an actual processing process. Therefore, it is easy to obtain an actual processing code with significantly improved precision of the trajectory of the magnetorheological polishing device after the errors are compensated.

In order to clearly describe technical solutions in the embodiments of the present disclosure, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Apparently, the drawings in the following description are merely some of the embodiments of the present disclosure, and those skilled in the art are able to obtain other drawings according to the drawings without contributing any inventive labor. In the drawing:.

In the drawings:
<NUM>-mechanical arm, <NUM> - optical element, <NUM> - polishing wheel, <NUM> - sensor, <NUM> - arc-shaped support bracket, <NUM> - adjusting bracket, <NUM> -support base, <NUM> - signal acquisition circuit, <NUM> -IPC, <NUM> - motion control circuit, <NUM> - power cable, <NUM> - through hole.

In order to make purposes, features, and advantages of the present disclosure obvious and understandable, a detailed description of specific embodiments of the present disclosure is given below in connection with accompanying drawings.

Specific details are set forth in the following description to facilitate a full understanding of the present disclosure. However, the present disclosure can be implemented in a variety of ways than those described herein, and those skilled in the art may make similar extensions without contradicting the context of the present disclosure. The present disclosure is therefore not limited by the specific embodiments disclosed below.

As shown in <FIG>, <FIG> is a schematic diagram of a precision calibrating device and a magnetorheological polishing device according to one embodiment of the present disclosure, <FIG> is an enlarged schematic diagram of area A shown in <FIG>, <FIG> is a schematic diagram of the area A shown in <FIG> where the precision calibrating device is removed, <FIG> is a schematic diagram of the area A shown in <FIG> that views from a Y direction, and <FIG> is a schematic diagram of the area A shown in <FIG> that views from a Z direction.

In one specific embodiment, the present disclosure provides the precision calibrating device for the magnetorheological polishing device. The magnetorheological polishing device comprises a polishing wheel <NUM> and a support base <NUM> configured to mount the polishing wheel <NUM>. The precision calibrating device comprises an arc-shaped support bracket <NUM>, a sensor <NUM>, a signal acquisition module, an industrial personal computer (IPC), and a motion control module. The arc-shaped support bracket <NUM> defines an arc-shaped surface. The sensor <NUM> is fixed on the arc-shaped support bracket <NUM>. Optionally, the sensor <NUM> is a displacement sensor <NUM> or a pressure sensor <NUM>. The pressure sensor determines a size of a polishing gap by measuring a contact force.

The signal acquisition module is connected with the sensor <NUM> through signals and a power cable <NUM>. The IPC <NUM> is connected with the signal acquisition module and the motion control module through the signals and the power cable <NUM>. The motion control module is connected with a control system of the magnetorheological polishing device through the signals and the power cable <NUM>. When it is necessary to calibrate a precision, the arc-shaped support bracket <NUM> with the sensor <NUM> is mounted on the support base <NUM>, and a surface of the arc-shaped support bracket <NUM> contacting the polishing wheel <NUM> is defined as the arc-shaped surface. A curvature radius of the arc-shaped surface of the arc-shaped support bracket <NUM> is same as a curvature radius of the polishing wheel <NUM>. The arc-shaped support bracket <NUM> defines a through hole <NUM>. An effective working hole of the sensor <NUM> coincides with the through hole <NUM>. A center of the effective working hole of the sensor <NUM> coincides with a vertex of a spherical crown of the polishing wheel <NUM>. The effective working hole of the sensor <NUM> is ensured to coincide with the through hole <NUM> by following implements:.

The sensor <NUM> of the present disclosure is mounted in such a way that a distance between the polishing wheel <NUM> and the optical element <NUM> to be processed is very short when the precision is calibrated. The distance between the polishing wheel <NUM> and the optical element <NUM> to be processed corresponds to the polishing gap in millimeter scale during actual processing, which effectively ensures a calibration precision and a precision during actual use. It is understood that a position posture of each joint of the mechanical arm <NUM> in a precision calibration state and the position posture of each joint of the mechanical arm <NUM> in an actual processing state are consistent, which effectively improves a precision of the polishing gap during the actual processing. After the calibration is completed, the arc-shaped support bracket <NUM> with the sensor <NUM> is detached from the support base <NUM>. That is, once the precision is calibrated for a first time, a position of each sub-component does not need to be re-calibrated when used again. When in precision calibration, the IPC <NUM> sends an instruction to the signal acquisition module and the motion control module. The signal acquisition module controls the sensor to collect data. At the same time, the motion control module sends the instruction to the control system, so that the polishing wheel <NUM> is controlled to move along a predetermined processing trajectory. Data collected by the sensor <NUM> is processed in the IPC <NUM>, and displacement values collected by the sensor4 are compared with predetermined values to obtain error values. Then it is determined whether the error values meet a precision requirement. If not, the predetermined processing trajectory is compensated according to the error values, and the error values are continuously obtained until the pre0cision requirement is met and when current error values meets the precision requirement, the current error values are compensated into the predetermined processing trajectory of the magnetorheological polishing device to complete the precision calibration. After the precision calibrating device is removed, the magnetorheological polishing device is applied to process the optical element <NUM>.

Furthermore, an adjusting bracket is arranged on the arc-shaped support bracket <NUM>. Strip-shaped holes are defined on the adjusting bracket. Optionally, two strip-shaped holes parallel to each other are provided. Fasteners pass through the strip-shaped holes to fix the adjusting bracket to the support base <NUM>. A height of the adjusting bracket is adjusted by the strip-shaped holes, so a height of the sensor <NUM> is adjusted accordingly.

One specific embodiment of the present disclosure further provides a precision calibrating method for the magnetorheological polishing device. The precision calibrating method comprises:.

If the error values do not satisfy the precision requirement;, the predetermined processing trajectory is corrected according to the error values. Then the error values between the displacement values and the predetermined values are obtained again according to a corrected predetermined processing trajectory, i.e., the steps <NUM>-<NUM> are repeated. The precision calibrating device and the mechanical arm <NUM> are automatically and synchronously controlled by the IPC <NUM>. After presetting of the parameters is completed, the key steps <NUM>-<NUM> of the error calibration are automated, which do not require manual participation.

If the error values satisfy the precision requirement, a next step is performed.

Step <NUM>: compensating the error values into a processing code;
If the error values satisfy the precision requirement in the step <NUM>, the step <NUM> is performed. The error values are compensated into the predetermined processing trajectory of the magnetorheological polishing device. In the step, the low frequency errors, the medium frequency errors, and the part of the high frequency errors in step <NUM> are accumulated and compensated into the processing code which is obtained by combining the processing trajectory and the actual residual time calculated according to the actual surface error of the optical element to be processed. It should be noted that the displacement values measured in steps <NUM> and <NUM> does not represent the real polishing gap, but the distance between the sensor <NUM> mounted on the polishing wheel <NUM> and the surface of the optical element <NUM> to be processed as mentioned in step <NUM>. However, the displacement values are corresponding to the polishing gap. Therefore, when converting the executing code after the error compensation in the step, the difference between calibrated displacement values and the polishing gap should be considered, and a linear difference between the displacement values and the polishing gap is eliminated to obtain the actual processing code after compensation that ensures constant of the polishing gap.

Step <NUM>: removing the precision calibrating device; and
In the step, after the step <NUM> is completed, the precision calibrating device is completely removed before an actual processing of the optical element <NUM> to be processed.

Step <NUM>: processing the optical element <NUM> to be processed.

After completing all of above steps, the optical element <NUM> to be processed is processed by the magnetorheological polishing device.

In summary, the present disclosure provides the precision calibrating device and the precision calibrating method for the magnetorheological polishing device, which realize automatic and quick calibration process and ensure that the polishing gap is kept within an allowable error range when the magnetorheological polishing device processes surfaces of different optical elements, thereby effectively controlling the removal function, reducing or eliminating the surface residual errors after processing and the low frequency errors and the medium frequency errors introduced by insufficient trajectory precision of the mechanical arm <NUM>, and improving a processing precision of the magnetorheological polishing device based on the mechanical arm <NUM>. The present disclosure has at least followed advantages.

The present disclosure is able to calibrate a wide range of error frequency bands, so all of the frequency errors affecting the polishing gap are measured, of which the low frequency errors, the medium frequency errors, and the part of the high frequency errors (systematic errors) are effectively compensated, thereby improving the processing precision of the magnetorheological polishing device.

The present disclosure is highly applicable. The optical element <NUM> to be processed may be flat, spherical, aspherical, free-form, convex, concave, etc. The optical element <NUM> to be processed may be made of various materials such as the optical glass, the SiC ceramics, the alloys, etc. The precision calibrating device is not limited to be mounted on the magnetorheological polishing device, and other devices based on the mechanical arm or devices based on a multi-axis linkage-based CNC machine tool can directly adopt schemes of the preset disclosure or use the schemes of the preset disclosure as references for calibrating or improving the precision.

The calibration precision of the present disclosure is high. The precision of an existing displacement sensor <NUM> generally reaches the micron level. Based on the sensor <NUM>, the present disclosure performs the error compensation through repeated iterations, which effectively improves the precision. The errors measured by the present disclosure are the displacement values corresponding to the required polishing gap, and there is a linear relationship between the displacement values and the polishing gap, which further ensures the calibration precision of the present disclosure. The trajectory of the mechanical arm <NUM> during the calibration process coincides with the trajectory during the actual processing, which ensures the consistency of calibration precision and the precision during actual use.

On a main aspect of improving the processing precision, the present disclosure improves an actual processing precision of the optical element <NUM> to be processed and improves the precision of the trajectory of the mechanical arm <NUM>, so the polishing gap is constant. Thus, the stability of the removal function is ensured. On the other hand, the calibration steps of the present disclosure further compensate errors generated by misalignment of the optical element to be processed, which further improves the actual processing precision.

The present disclosure has a high calibration efficiency. Calibration hardware is quickly assembled and disassembled. A running speed of the mechanical arm <NUM> during executing the executing code is adjustable. Further, error measurement and iterative compensation process are relatively automatic.

The present disclosure applies to a wide range of structures. The present disclosure is not only applied to the structure where the optical element (a reflector <NUM>) is arranged on a bottom position thereof and tools (a magnetorheological polishing module and the mechanical arm <NUM>) are arranged at a top position thereof. The present disclosure can also be applied to other structures, such as a structure where a position of the reflector <NUM> is interchanged with a position of the magnetorheological polishing module (including the polishing wheel <NUM>) in <FIG>. That is, the reflector is grasped by the mechanical arm <NUM> and is arranged above the mechanical arm and the magnetorheological polishing module is arranged below the reflector, i.e., the optical element is arranged on the top position thereof and the tools are arranged on the bottom position thereof. Except for the structure where the optical element is arranged on the bottom position and the tools are arranged at the top position or the structure where the optical element is arranged on the top position and the tools are arranged on the bottom position, a structure where the optical element and the tools are placed horizontally is also applied. All structures that conform to the principle of relationship between relative positions of the optical element and the tools in the present disclosure are applicable, which is not limited thereto.

In addition, the present disclosure ensures the stability of the removal function by ensuring that the polishing gap is constant. That is, a controllable change in the polishing gap is guaranteed to ensure a controllable change in the removal function. Based on the controllable change, the high precision processing of the optical element <NUM> is realized.

It should be noted that, in the present disclosure, relational terms, such as "first" and "second", are only used to distinguish one feature or operation from another feature or operation, and do not necessarily require or imply any actual relationship or sequence exists between these features or operations. Moreover, terms "comprise", "include" or any other variation thereof are intended to encompass non-exclusive inclusion, such that a process, method, article or device not only comprises elements explicitly listed, but also comprises elements not explicitly listed or other elements inherent to such a process, method, article, or device. Without further limitation, elements defined by the statement "including a. " do not preclude the existence of additional identical elements in the process, method, article, or device including the elements.

Embodiments in the specification are described in a progressive manner, with each embodiment focusing on what is different from other embodiments, and same and similar parts between each embodiment can be cross-referenced.

Claim 1:
A precision calibrating device for a magnetorheological polishing device including a polishing wheel (<NUM>) and a support base (<NUM>) configured to mount the polishing wheel (<NUM>), comprising:
an arc-shaped support bracket (<NUM>),
a sensor (<NUM>),
a signal acquisition module (<NUM>),
an industrial personal computer (IPC) (<NUM>), and
a motion control module (<NUM>);
wherein the arc-shaped support bracket (<NUM>) is detachably connected with the support base (<NUM>); the arc-shaped support bracket (<NUM>) defines an arc-shaped surface attached to the polishing wheel (<NUM>); the sensor (<NUM>) is fixed on the arc-shaped support bracket (<NUM>); the sensor (<NUM>) is configured to detect a polishing gap between the polishing wheel (<NUM>) and a surface of an optical element (<NUM>) to be processed;
wherein the signal acquisition module (<NUM>) is connected with the sensor (<NUM>); the IPC (<NUM>) is connected with the signal acquisition module (<NUM>) and the motion control module (<NUM>); the motion control module (<NUM>) is connected with a control system of the magnetorheological polishing device; the IPC (<NUM>) is configured to send an instruction to the signal acquisition module (<NUM>) and the motion control module (<NUM>); the signal acquisition module (<NUM>) is configured to control the sensor (<NUM>) to collect data; the motion control module (<NUM>) is configured to send the instruction to the control system, so that the polishing wheel (<NUM>) moves along a predetermined processing trajectory.