Transverse piezoelectric deformable mirror control method and adaptive optical system

Abstract

The invention relates to the technical field of adaptive optics, and particularly provides a transverse piezoelectric deformable mirror control method and an adaptive optical system.The method includes the steps that a piezoelectric self-sensing circuit is constructed, and induced charges generated on a piezoelectric ceramic piece after strain is generated by applying voltage to a transverse piezoelectric deformable mirror are collected; on the basis of the piezoelectric self-sensing principle, the stress charges are converted into the current strain of the piezoelectric ceramic piece, and then mirror surface shape information of the piezoelectric deformable mirror is obtained through calculation. According to the method, elements are not additionally arranged on the structure of the transverse piezoelectric deformable mirror, the structural complexity of the transverse piezoelectric deformable mirror is not increased, only expansion is carried out on an existing driving circuit, a piezoelectric self-sensing circuit is constructed, and the advantage that the structure of the transverse piezoelectric deformable mirror is simple is kept. By using the method to control the transverse piezoelectric deformable mirror in the adaptive optical system, the correction precision of the distorted wavefront of the adaptive optical system can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of adaptive optics, and specifically provides a lateral piezoelectric deformable mirror control method and an adaptive optical system. Background Art

[0002] Adaptive optics technology is a key technology that has developed rapidly in recent decades and has been widely used in many fields such as astronomical observation, laser shaping, ophthalmic imaging, and space optical communications.

[0003] The wavefront corrector is a core device in adaptive optical systems and is usually implemented by a deformable mirror. Among various types of deformable mirrors, the transverse piezoelectric deformable mirror driven by the transverse inverse piezoelectric effect has the significant advantages of simple structure, small size and low cost, and has broad application prospects in miniaturized adaptive optical systems. However, due to the nonlinear factors such as creep and hysteresis of piezoelectric ceramics themselves, high-precision control of the transverse piezoelectric deformable mirror is a difficult point. Although wavefront sensors are used in conjunction with deformable mirrors in adaptive optical systems, the wavefront sensors detect the wavefront aberration in the optical system rather than the surface shape of the deformable mirror; therefore, some researchers have proposed adding sensors inside the deformable mirror to detect the surface shape in real time, forming a local closed loop of the deformable mirror, so as to improve the control accuracy of the deformable mirror. The above scheme has been successfully applied to the control of a deformable mirror driven by stacked piezoelectric ceramics, that is, by pasting strain gauges on the side of the stacked piezoelectric actuator to obtain displacement information to correct the control error.

[0004] For the transverse piezoelectric deformable mirror, due to its very simple structure and the driving element being only one or more piezoelectric ceramic sheets, it is difficult to design a sensor to realize a local closed loop and feedback displacement information. Fan Zhanbin et al. tried to prepare a single-electrode transverse piezoelectric deformable mirror with an integrated strain layer, and experimentally confirmed the role of displacement feedback in compensating for hysteresis nonlinearity. However, this scheme has not yet been reported to be applied to a transverse piezoelectric deformable mirror with multiple driving units. Alcock et al. arranged an interferometric distance sensor array behind the transverse piezoelectric deformable mirror lens to detect the surface shape. Although this scheme can obtain local displacement information with high accuracy, it also has many disadvantages. It not only requires additional costs, but also adds a complex structure to the deformable mirror, which seriously weakens the inherent advantages of the transverse piezoelectric deformable mirror. Xu et al. proposed to set a sensing electrode outside the driving electrode of the transverse piezoelectric deformable mirror and obtain local strain by using the piezoelectric effect generated by the deformation of the piezoelectric ceramic sheet. This scheme seriously sacrifices the spatial frequency of the deformable mirror, has an adverse effect on its wavefront correction capability, and also adds an additional burden to the electronic connection of the deformable mirror.

[0005] Therefore, it is urgent to design a method that can detect the surface shape changes of the lateral piezoelectric deformable mirror without the need for additional wavefront sensors or displacement sensors, thereby achieving high-precision control. Summary of the invention

[0006] In order to solve the above problems, the present invention provides a high-precision control method for a lateral piezoelectric deformable mirror based on the piezoelectric self-sensing principle. The method does not require an additional wavefront sensor or displacement sensor to detect the surface shape change of the lateral piezoelectric deformable mirror. Based on the piezoelectric self-sensing principle, a local structural loop control loop of the lateral piezoelectric deformable mirror is established, and a control algorithm is used to improve the control accuracy of the lateral piezoelectric deformable mirror. The method is simple, reliable and easy to implement. Without increasing the structural complexity of the deformable mirror, the control accuracy of the deformable mirror is significantly improved.

[0007] To achieve the above object, the technical solution created by the present invention is implemented as follows: On the one hand, the present invention provides a method for controlling a transverse piezoelectric deformable mirror, comprising: Calculating a first difference between an initial strain and a desired strain of the transverse piezoelectric deformable mirror, and applying a strain instruction to the transverse piezoelectric deformable mirror according to the first difference; Collecting the induced charge generated by the piezoelectric ceramic piece in the transverse piezoelectric deformable mirror after the transverse piezoelectric deformable mirror executes the strain instruction; Based on the piezoelectric self-sensing principle, the induced charge is converted into the current strain of the lateral piezoelectric deformable mirror, the second difference between the current strain and the expected strain is calculated, and the strain instruction is corrected according to the second difference.

[0008] Preferably, the process of obtaining the expected strain is: The distorted wavefront of the adaptive optical system is obtained through a wavefront sensor, and the distorted wavefront is resolved into the expected strain of the lateral piezoelectric deformable mirror.

[0009] Preferably, the adaptive optical system is an open-loop control system or a closed-loop control system.

[0010] Preferably, the strain command is calculated by adopting a PI control algorithm.

[0011] Preferably, the strain instruction is a control variable in the form of voltage.

[0012] Preferably, the strain instruction is: ; in, is the proportional gain, is the integral gain, is the first difference.

[0013] Preferably, the induced charges generated on the piezoelectric ceramic sheet in the transverse piezoelectric deformable mirror are collected.

[0014] Preferably, a piezoelectric self-sensing circuit is constructed by connecting a reference capacitor in series at the rear end of the piezoelectric ceramic plate for obtaining the induced charge.

[0015] Preferably, the induced charge can be calculated by measuring the piezoelectricity across the reference capacitor.

[0016] On the other hand, the present invention provides an adaptive optical system, comprising: A wavefront sensor for acquiring a distorted wavefront; A wavefront controller for solving for a desired strain based on a distorted wavefront; And, a wavefront corrector, the wavefront corrector includes: a lateral piezoelectric deformable mirror controlled by using a lateral piezoelectric deformable mirror control method.

[0017] Compared with the prior art, the invention can achieve the following beneficial effects: The present invention is based on the piezoelectric self-sensing principle, expands the driving circuit of the lateral piezoelectric deformable mirror, and constructs a piezoelectric self-sensing loop. Without introducing additional sensors such as strain gauges, distance sensors, and wavefront sensors to detect the surface shape of the lateral piezoelectric deformable mirror, the self-sensing principle can be directly used to obtain the strain feedback information of the deformable mirror, thereby constructing a local structural loop control loop, thereby improving the control accuracy of the lateral piezoelectric deformable mirror.

[0018] The hardware of the piezoelectric self-sensing circuit of the present invention is completely independent of the hardware structure of the lateral piezoelectric deformable mirror. During the design process, there is no need to expand the structure of the lateral piezoelectric deformable mirror, thereby maintaining the advantages of the lateral piezoelectric deformable mirror such as simple structure, small size and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The drawings constituting part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments and descriptions of the present invention are used to explain the present invention and do not constitute an improper limitation on the present invention. In the drawings: Figure 1 is a schematic diagram of an open-loop adaptive optical system provided according to an embodiment of the present invention; Figure 2 is a schematic diagram of a closed-loop adaptive optical system provided according to an embodiment of the present invention; Figure 3 is a block diagram of a local closed-loop control of a lateral piezoelectric deformable mirror provided according to an embodiment of the present invention; Figure 4 is a schematic diagram of an electromechanical model of an actuator of a piezoelectric ceramic sheet provided according to an embodiment of the present invention; Figure 5 is a schematic diagram of a piezoelectric self-sensing circuit provided according to an embodiment of the present invention. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical scheme and advantages of the invention clearer, the invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the invention and do not constitute a limitation to the invention. Similar components in different embodiments use associated similar component numbers. In the following embodiments, many detailed descriptions are to enable the invention to be better understood. However, those skilled in the art can easily recognize that some of the features can be omitted in different situations, or can be replaced by other components, materials, and methods. In some cases, some operations related to the invention are not shown or described in the specification, in order to avoid the core part of the invention being overwhelmed by too much description, and for those skilled in the art, it is not necessary to describe these related operations in detail, and they can fully understand the related operations according to the description in the specification and the general technical knowledge in the art.

[0021] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other to form various implementation methods. At the same time, the steps or actions in the method description can also be interchanged or adjusted in a manner that is obvious to those skilled in the art. Therefore, the various sequences in the specification and the drawings are only for the purpose of clearly describing a certain embodiment and are not meant to be a necessary sequence, unless otherwise specified that a certain sequence must be followed.

[0022] In the description of the invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the invention, unless otherwise specified, the meaning of "multiple" is two or more.

[0023] In the description of the invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the invention can be understood according to specific circumstances.

[0024] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0025] In one embodiment of the present invention, a control method for a transverse piezoelectric deformable mirror is provided. Without introducing additional sensors such as strain gauges, distance sensors, and wavefront sensors to detect the shape of the transverse piezoelectric deformable mirror, the strain feedback information of the deformable mirror is obtained through the piezoelectric self-sensing principle, and a local structure loop control loop is constructed to achieve high-precision control of the transverse piezoelectric deformable mirror. The control method provided by the embodiment of the present invention is applicable to both Figure 1 The open-loop controlled adaptive optical system shown is also applicable to Figure 2 The closed-loop controlled adaptive optics system is shown.

[0026] See also Figure 1 and Figure 2 The adaptive optical system mainly includes: a wavefront sensor 1, a wavefront controller 2 and a wavefront corrector 3, wherein the wavefront sensor 1 is mainly used to detect the distorted wavefront to be corrected in the adaptive optical system, and transmit the distorted wavefront to the wavefront controller 2, and the wavefront controller 2 calculates the strain required by the wavefront corrector 3 to correct the distorted wavefront. The strain is the expected strain, which is recorded as The main functional device of the wavefront corrector 3 in the adaptive optical system is Figure 3 The lateral piezoelectric deformable mirror 6 shown in the figure, so the wavefront controller 2 actually solves the distorted wavefront to be corrected into the expected strain of each channel of the lateral piezoelectric deformable mirror 6.

[0027] The wavefront controller 2 will expect the strain After being transmitted to the wavefront corrector 3, the initial strain of the current lateral piezoelectric deformable mirror 6 is calculated by the piezoelectric self-sensing circuit 7 inside the wavefront corrector 3. Since the lateral piezoelectric deformable mirror 6 is not driven to generate corresponding strain, the piezoelectric self-sensing circuit 7 collects the initial strain feedback. At this time, the controller 4 inside the wavefront corrector 3 performs a differential calculation on the initial strain and the desired strain to obtain the initial strain of the lateral piezoelectric deformable mirror 6. Expected Change The difference between , which is the first difference. And the difference As the input of the controller 4, the control quantity, namely the strain instruction, is output through the control algorithm. The strain instruction is the control quantity in the form of voltage.

[0028] In the embodiment of the present invention, the controller 4 adopts PI (proportional-integral) control algorithm to obtain the strain instruction. for: ; in, is the proportional gain, is the integral gain.

[0029] PI control is a commonly used feedback control algorithm, which combines proportional control and integral control, and can reduce the steady-state error of the system and improve the stability of the system. It should be noted that in the embodiment of the present invention, only the PI control algorithm is used as an example, and the algorithm that the controller 4 can adopt is not limited to the PI control algorithm given in the embodiment of the present invention.

[0030] The controller 4 sends the strain instruction Output to high voltage amplifier 5, after amplification by high voltage amplifier 5, obtain amplified signal , which will amplify the signal The driving unit of the transverse piezoelectric deformable mirror 6 is applied to the transverse piezoelectric deformable mirror 6. It can be understood that the driving unit of the transverse piezoelectric deformable mirror 6 actually refers to the driving electrode on the piezoelectric ceramic sheet in the transverse piezoelectric deformable mirror 6, which can also be broadly understood as the amplified signal. That is, it is applied to the transverse piezoelectric deformable mirror 6.

[0031] Amplifying the signal After being applied to the lateral piezoelectric deformable mirror 6, the lateral piezoelectric deformable mirror 6 will produce a corresponding strain response, see Figure 4 According to the principle of transverse inverse piezoelectric effect, the driving electrode on the piezoelectric ceramic sheet will drive the piezoelectric ceramic sheet of the transverse piezoelectric deformable mirror 6 to generate strain. , record this strain as the current strain , which in turn drives the lateral piezoelectric deformable mirror 6 to change its surface shape and generates induced charges on the piezoelectric ceramic sheet. Specifically, in the frequency range far below the fundamental resonance of the piezoelectric ceramic, its electromechanical behavior can be described by a second-order model. This model involves parameters such as equivalent mass, equivalent spring constant, equivalent damping coefficient and capacitance value. The electromechanical behavior is specifically described by the second-order model as follows: ; ; in, , , , They correspond to the equivalent mass, equivalent spring constant, equivalent damping coefficient and equivalent capacitance of the piezoelectric ceramic piece, respectively. is the electro-mechanical conversion coefficient, is the electromechanical conversion coefficient, is the first-order derivative of the strain produced by the piezoelectric ceramic. is the second-order derivative of the strain generated by the piezoelectric ceramic. is the voltage applied across the piezoelectric ceramic. The driving force generated by the piezoelectric ceramic. is the total charge flowing through the piezoelectric ceramic.

[0032] When a voltage is applied to the piezoelectric ceramic The driving charge is stored in the piezoelectric ceramic , according to the inverse piezoelectric effect, the actuator will generate a driving force: , which is related to the external mechanical force applied to the piezoelectric ceramic The combined effect causes the piezoelectric ceramic to produce strain According to the piezoelectric effect, the strain of the piezoelectric material will cause the piezoelectric ceramic to generate induced charges: The induced charge and the driving charge stored in the piezoelectric ceramic Together they make up the total charge flowing into the piezoelectric ceramic Therefore, by measuring the induced charge Or measure the total charge directly , which can be related to the strain generated by the piezoelectric ceramic A connection is established to obtain the strain information of the piezoelectric ceramic sheet (i.e., the mirror surface of the lateral piezoelectric deformable mirror 6), and then a structural ring control loop is constructed in the lateral piezoelectric deformable mirror 6 itself to improve the surface shape control accuracy.

[0033] Due to the hysteresis nonlinearity of the piezoelectric ceramic, there will be an error between the current strain generated by the lateral piezoelectric deformable mirror and the expected strain. The characterization does not affect the realization of the piezoelectric self-sensing principle. Therefore, in order not to add a sensing device to the main structure of the lateral piezoelectric deformable mirror 6, the embodiment of the present invention measures the current strain of the lateral piezoelectric deformable mirror 6 after applying the amplified signal based on the piezoelectric self-sensing principle. For details, please refer to Figure 5 Based on the piezoelectric self-sensing principle, the induced charge generated on the piezoelectric ceramic piece is collected by the piezoelectric self-sensing circuit 7 In the embodiment of the present invention, the piezoelectric self-sensing circuit 7 is an extension of the driving circuit of the lateral piezoelectric deformable mirror 6, and the main structure of the lateral piezoelectric deformable mirror 6 is not complicated. The hardware structure of the piezoelectric self-sensing circuit 7 is completely independent of the hardware structure of the lateral piezoelectric deformable mirror 6. The piezoelectric self-sensing circuit 7 is constructed by connecting capacitors in series and detecting the total charge. Specifically, due to the current strain generated by the piezoelectric ceramic sheet, The voltage across the piezoelectric ceramic There is a linear relationship between them, so it can be considered that The induced charge generated on the piezoelectric ceramic There is also a linear relationship between them and the equivalent capacitance flowing through the piezoelectric ceramic The driving charge Therefore, the total charge flowing through the piezoelectric ceramic can be expressed as To measure the current strain .

[0034] In order to measure the total charge of the piezoelectric self-sensing circuit 7 In the embodiment of the present invention, a reference capacitor is connected in series in the back-end circuit of the piezoelectric ceramic plate. This design makes the amplified signal output by the high-voltage amplifier 5 Will be loaded into the load and On, among them, There is also an equivalent resistor in parallel , the equivalent resistance Characterizes the charge leakage of piezoelectric ceramics under low frequency operation. In an ideal situation, the reference capacitor The charge is equal to the total charge flowing through the piezoelectric ceramic , due to the reference capacitor The voltage across It is proportional to the charge flowing through it, so it can be measured by the reference capacitor Both ends Obtain the total charge flowing through the piezoelectric ceramic , and then calculate the current strain generated by the piezoelectric ceramic .

[0035] Due to the hysteresis nonlinearity of the piezoelectric ceramic, there will be an error between the strain generated by the lateral piezoelectric deformable mirror and the expected strain. Therefore, the electric self-sensing circuit 7 obtains the current strain After that, the current strain Feedback to controller 4, through which controller 4 and The difference between the current strain and the expected strain is calculated, i.e., the second difference. After the controller 4 obtains the second difference, the control amount of the strain instruction is corrected through the control algorithm to form a closed-loop feedback control of the local structure, thereby realizing high-precision control of the 6-surface shape of the lateral piezoelectric deformable mirror.

[0036] In short, the above description is only a preferred embodiment of this specification and is not intended to limit the protection scope of this specification. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this specification shall be included in the protection scope of this specification.

[0037] The systems, devices, modules or units described in one or more of the above embodiments may be implemented by a computer chip or entity, or by a product having a certain function. A typical implementation device is a computer. Specifically, the computer may be, for example, a personal computer, a laptop computer, a cellular phone, a camera phone, a smart phone, a personal digital assistant, a media player, a navigation device, an email device, a game console, a tablet computer, a wearable device, or a combination of any of these devices.

[0038] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.

[0039] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

[0040] The above is a description of a specific embodiment of the specification. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recorded in the claims can be performed in an order different from that in the embodiments and still achieve the desired results. In addition, the processes depicted in the drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

Claims

1. A method for controlling a transverse piezoelectric deformable mirror, characterized in that: include: Calculating a first difference between an initial strain and a desired strain of the transverse piezoelectric deformable mirror, and applying a strain instruction to the transverse piezoelectric deformable mirror according to the first difference; collecting induced charges generated in the transverse piezoelectric deformable mirror after the transverse piezoelectric deformable mirror executes a strain instruction; The induced charge is converted into the current strain of the lateral piezoelectric deformable mirror based on the piezoelectric self-sensing principle, a second difference between the current strain and the expected strain is calculated, and the strain instruction is corrected according to the second difference.

2. The method for controlling a transverse piezoelectric deformable mirror according to claim 1, wherein: The process of obtaining the expected strain is as follows: The distorted wavefront of the adaptive optical system is acquired through a wavefront sensor, and the distorted wavefront is resolved into the desired strain of the lateral piezoelectric deformable mirror.

3. The method for controlling a transverse piezoelectric deformable mirror according to claim 2, wherein: The adaptive optical system is an open-loop control system or a closed-loop control system.

4. The method for controlling a transverse piezoelectric deformable mirror according to claim 2, wherein: The strain command is calculated by adopting a PI control algorithm.

5. The method for controlling a transverse piezoelectric deformable mirror according to claim 4, wherein: The strain instruction is a control variable in the form of voltage.

6. The method for controlling a transverse piezoelectric deformable mirror according to claim 5, characterized in that: The strain instructions are: ； in, is the proportional gain, is the integral gain, is the first difference.

7. The method for controlling a transverse piezoelectric deformable mirror according to claim 1, wherein: The induced charge generated on the piezoelectric ceramic sheet in the transverse piezoelectric deformable mirror is collected.

8. The method for controlling a transverse piezoelectric deformable mirror according to claim 7, wherein: A piezoelectric self-sensing circuit is constructed by connecting a reference capacitor for obtaining the induced charge in series at the rear end of the piezoelectric ceramic sheet.

9. The method for controlling a transverse piezoelectric deformable mirror according to claim 7, wherein: The induced charge can be calculated by measuring the piezoelectricity across the reference capacitor.

10. An adaptive optical system, characterized in that: include: A wavefront sensor for acquiring a distorted wavefront; A wavefront controller for solving for a desired strain based on a distorted wavefront; And, a wavefront corrector, the wavefront corrector comprising: a lateral piezoelectric deformable mirror controlled by the lateral piezoelectric deformable mirror control method as described in any one of claims 1 to 9.

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