CN-117754399-B - Control method for forming constant grinding force of ultra-light aspheric mirror

Abstract

The invention relates to a control method for forming and processing constant grinding force of an ultra-lightweight aspheric mirror, which adopts piezoelectric ceramics to convert force signals acting on a three-dimensional force measuring table into electric signals, and the electric signals are amplified and conditioned to become analog voltage signals and transmitted to a grinding force acquisition and processing module; the grinding force acquisition processing module acquires three-dimensional force in real time according to the linear relation between the force and the voltage signal, and finally obtains the resultant force of the diamond abrasive wheel acting on the surface of the aspherical mirror at any moment, and on the basis, the maximum grinding force threshold value of the diamond abrasive wheel acting on the surface of the aspherical mirror is set on the grinding force acquisition processing module. The grinding force constant force in the whole processing process is not more than the threshold value of mirror surface breaking by means of dynamic regulation and control of processing technological parameters and the sharpness of the surface of the grinding wheel, and the ultra-precise forming processing of the large-caliber aspheric element is realized on the premise of ensuring the mirror surface to be perfect.

Inventors

• ZHOU LIAN
• ZHANG QINGHUA
• Ma Houcai
• LIU YAN
• JI BAOJIAN
• ZHANG LIPING
• LIU ANG
• ZHONG BO
• WEI QIANCAI
• FAN FEI

Assignees

• 中国工程物理研究院激光聚变研究中心

Dates

Publication Date

20260508

Application Date

20240118

Claims (4)

1. 1. The control method for the forming processing constant grinding force of the ultra-lightweight aspheric mirror is characterized by comprising the following steps of: S1, installing a three-dimensional force measuring table on a workbench of an ultra-precise grinding machine, converting force signals acting on the three-dimensional force measuring table into electric signals by adopting piezoelectric ceramics, amplifying and conditioning the electric signals to become analog voltage signals, and transmitting the analog voltage signals to a grinding force acquisition processing module, wherein the grinding force acquisition processing module acquires three-dimensional forces F x 、F y and F z in real time according to the linear relation between the force signals and the voltage signals; S2, when the three-dimensional force measuring table is reversed, certain inertia force F i is generated in the acceleration and deceleration process, and the acquired relationship among the force F x , the inertia force F i and the grinding force G x of the grinding wheel on the surface of the aspheric mirror along the X direction is G x =F x -F i ; Therefore, in the grinding process, the grinding force acquisition processing module acquires the speed v x of the left and right feeding movement of the three-dimensional force measuring table from the numerical control system in real time, and the grinding force of the final diamond grinding wheel acting on the surface of the aspheric mirror along the X direction is calculated by the formula (1): (1); Wherein m t is the static mass of the three-dimensional force measuring table, and m o is the mass of the aspherical mirror and the clamp; S3, respectively collecting Z-direction force F z0 measured when the three-dimensional force measuring table is not provided with the aspherical mirror and the clamp in a static state and Z-direction force F z1 when the aspherical mirror and the clamp are provided with the aspherical mirror and the clamp, and calculating by a formula (2), wherein g is gravity acceleration; (2); s4, calculating and obtaining resultant force of the diamond grinding wheel acting on the surface of the aspheric mirror at any moment according to the formula (3): (3); S5, setting a maximum grinding force threshold G T of the diamond grinding wheel acting on the surface of the aspherical mirror on the grinding force acquisition processing module; because the aspheric mirror only performs left and right feeding movement along with the three-dimensional force measuring table in the grinding process, namely G y =F y ,G z =F z ; s5, the maximum grinding force threshold G T is related to the lightweight hole structure, the mirror surface thickness, the mechanical parameters of the reflector material and the size factors of the diamond grinding wheel of the aspherical reflector; when G is less than or equal to eta G T , mirror surface breakage does not occur in the processing process, wherein the safety coefficient is eta, eta is less than 1; When G > eta G T , the grinding force acquisition processing module calculates a feed speed attenuation coefficient zeta according to the following formula (4), and reduces the actual feed speed of the reflector moving leftwards and rightwards along the X axis so as to reduce the actual grinding force G and ensure that G is less than or equal to eta GT; (4); After the feed speed attenuation coefficient zeta is calculated, the feed speed attenuation coefficient zeta is sent to a feed multiplying power module of a numerical control system, and the feed speed in the grinding process is reduced by reducing the feed multiplying power, so that the aim of reducing the grinding force is fulfilled; Carrying out online electrolytic machining on the diamond grinding wheel by adopting an electrolytic electrode, uniformly removing a thin layer bonding agent on the surface of the grinding wheel, protruding and exposing diamond abrasive particles, and recovering the grinding performance of the grinding wheel; According to the grinding force G of the diamond grinding wheel on the aspheric mirror, which is detected in real time, a grinding force acquisition processing module calculates to obtain the increase rate of the grinding force, calculates to obtain the online electrolysis current value of the grinding wheel according to a formula (6), and sends a control signal to an electrolysis power supply to enable the electrolysis power supply to output the corresponding current value to an electrolysis electrode, so that the online electrolysis of the diamond grinding wheel is realized, the diamond grinding particles are exposed, the grinding performance of the grinding wheel is recovered, the increase of the grinding force is restrained, and finally the purpose of stabilizing the grinding force is achieved; (6); Wherein K is a linear coefficient and is related to factors of the conductivity of the grinding fluid, the electrolytic electrode and the rotating speed of the grinding wheel.
2. 2. The method for controlling constant grinding force for forming and processing an ultra-lightweight aspheric mirror according to claim 1, wherein the diamond grinding wheel is a bronze bonding agent with conductivity, an anode of an electrolysis power supply is connected with a cathode of the electrolysis power supply through an electric brush, an electrolysis electrode is arranged on a grinding wheel housing in an insulating manner, a working face of the electrolysis electrode is a toroidal face, and the relation between radial curvature radius R m and sagittal curvature radius R s of the electrolysis electrode and total radius R w and arc radius R a of the diamond grinding wheel is shown as formula (5), wherein d is a gap between the working face of the electrolysis electrode and the surface of the diamond grinding wheel; (5)。
3. 3. the method for controlling the constant grinding force for forming and processing the ultra-lightweight aspheric mirror according to claim 2, wherein the relative axial position and the relative radial position of the electrolytic electrode and the diamond grinding wheel can be adjusted.
4. 4. The method for controlling the constant grinding force for forming and processing the ultra-lightweight aspheric mirror according to claim 2, wherein holes are formed in the working surface of the adopted electrolytic electrode for flowing out grinding fluid, and a grinding fluid cavity is formed between the electrolytic electrode and the connecting base.

Description

Control method for forming constant grinding force of ultra-light aspheric mirror Technical Field The invention relates to the technical field of ultra-precise manufacturing of large-caliber optical elements, in particular to a control method for forming and processing constant grinding force of an ultra-light aspheric mirror. Background Compared with the traditional spherical optical element, the aspherical optical element can avoid adverse effects such as spherical aberration, coma aberration and aberration, can reduce light energy loss during light beam focusing, improves focusing and calibration precision, and is widely applied to modern large-scale optical systems. In order to reduce the emission cost, the space detection optical system has extremely high light-weight requirements on the optical aspheric mirror, and the mirror surface thickness reaches the millimeter level. In the ultra-precise forming and manufacturing process of the large caliber (caliber is hundreds of millimeters to thousands of millimeters) and the hard and brittle material and the ultra-thin ultra-lightweight aspheric mirror of the space detection system, the influence of factors such as the performance degradation of a processing tool, the inconsistent gradient of the aspheric surface points and the like causes the fluctuation growth of the processing force, so that the element is extremely easy to crack and break the mirror surface under the action of the processing force, and finally the element is scrapped. On the premise of ensuring the processing efficiency and the accuracy, how to stabilize the grinding force in the forming processing process is the key for ensuring the perfect mirror surface. Patent document CN211193241U discloses an electric constant force grinding device, which measures grinding force in real time through a force transducer and feeds back to a control system, and adjusts the direct distance between a grinding head and a workpiece through a motor to control the grinding force, so as to keep the grinding head in constant force contact with the surface of the workpiece. Patent document CN107962480a discloses a blade robot abrasive belt grinding processing force control method, after voltage signals of six channels of a sensor are obtained, the voltage signals are subjected to software filtering and converted into force signals, then zero drift compensation and gravity compensation of the end load of the robot are performed on the force, and finally constant force control is realized through force position mixed control and PI/PD control. Patent document CN106078515A discloses a constant force grinding system integrating detection and grinding functions, comprising a workbench, an on-line detection system arranged on the workbench, a constant force grinding system and a controller, wherein the grinding force is detected on line and fed back to the controller, and when the grinding force exceeds a set value, the horizontal work of the workbench is controlled to retract, so that the purpose of constant force grinding is achieved. Patent document CN102059649a discloses a method for monitoring the magnitude of grinding radial force of a grinding machine and a method for realizing constant force feeding, which detects the feeding force of a workpiece or a grinding wheel in the feeding process of the grinding machine, and controls a driving mechanism for driving the workpiece or the grinding wheel according to the detected feeding force value so as to apply a constant feeding force to the workpiece or the grinding wheel. The disclosed patent technology realizes constant force control by monitoring the grinding force in real time and then changing the direct cutting depth of the grinding wheel and the workpiece. However, in the ultra-precise forming process of the aspheric element, after the grinding force is fluctuated due to inconsistent gradient of the aspheric surface, the actual motion track of the grinding wheel is different from the ideal aspheric surface appearance by changing the direct cutting depth of the grinding wheel and the workpiece, and the forming and processing precision of the element is finally affected. In the ultra-precise forming manufacturing process of the ultra-thin ultra-light aspheric reflecting mirror with large caliber and hard and brittle materials, how to solve the problem of fluctuation type increase of the processing force caused by factors such as degradation of the processing performance of the grinding wheel, inconsistent gradient of the aspheric surface point and the like is a problem which needs to be solved by the person skilled in the art. Disclosure of Invention Therefore, the invention aims to provide a control method for forming and processing constant grinding force of an ultra-light aspheric mirror, and solves the technical problem of fluctuation type increase of the processing force caused by factors such as degradation of grinding wheel processing performance, incon