CN106094391B - Focus control method applied to star loaded camera - Google Patents

Abstract

The focus control system and focus control method applied to space-borne cameras relate to the field of design of space-borne mechanism control systems, including stepping motors, stepping motor drive circuits and camera focal planes; it is characterized in that it also includes ARM microprocessors And the rebound type magnetic linear displacement sensor; the rebound type magnetic linear displacement sensor is installed vertically behind the focal plane of the camera, obtains the analog voltage when the focal plane of the camera moves linearly, and transmits the analog voltage to the ARM microprocessor; the ARM microprocessor According to the pre-adjustment position of the camera focal plane sent by the central computer, the number of rotation steps and direction information of the stepping motor is calculated, and then the driving signal is sent to the stepping motor drive circuit to make the focal plane of the camera reach the pre-adjusting position; the ARM microprocessor according to the center According to the different commands sent by the aircraft, the closed-loop focusing and open-loop focusing of the spaceborne camera can be realized. The method of the invention has the characteristics of low cost, low circuit complexity, simple data processing and the like.

Description

Focus control method applied to spaceborne camera

technical field

The invention relates to the field of micro-satellite mechanism control system design, in particular to a method for designing and implementing a space-borne camera focusing system based on a micro-miniature ARM microprocessor using a rebound linear displacement sensor.

Background technique

With the rapid development of the aerospace industry, small satellites with camera payloads as the core have been widely used, and the imaging quality, field of view, and resolution of space remote sensing images have gradually become the focus of attention from the outside world. Small satellites can accurately complete the attitude control and adjustment due to the size advantage, so that the camera can save the bias flow adjustment mechanism. However, changes in the carrying and environment of the spaceborne camera, such as shock, vibration, temperature, pressure, distance and other uncontrollable factors, may cause the refractive index, thickness, radius of curvature, internal force of the lens material, and reflective surface of the lens in the space optical system to change. Changes in deformation, metal structure, etc. These small deformations will cause the space camera to defocus and seriously affect the imaging quality. In order to ensure that the space camera obtains the best resolution image, the focus plane must be compensated. The focus system has become an important part of the spaceborne camera. In the traditional mode, 51 single-chip microcomputers, code discs and photoelectric conversion circuits are used to complete the closed-loop adjustment of the system. Focus function, this kind of design has complex peripheral circuits, heavy weight, high cost, and large volume, which is not in line with the future development direction of small satellites. Due to its limited resources, 51 single-chip microcomputers have been replaced by more ARM microprocessors due to the need for more peripherals, large size, high power consumption, and slow running speed. However, due to the requirements of aerospace reliability, they still have a place. With the improvement of the manufacturing process, the ARM chip has greatly improved its stability and reliability, and has been gradually applied to low-cost micro-satellite systems by virtue of its low price, abundant resources, and low power consumption.

In order to realize the precise positioning and measurement of the focal plane position, the focusing system must have a feedback signal to form a closed loop. Today, the devices that can provide this feedback signal mainly include resolvers, potentiometers, magnetic linear displacement sensors, magnetic encoders, photoelectric encoders and other equipment. A potentiometer is a typical contact angle sensor with a sliding contact on a material such as a carbon resistor. This variable resistance is proportional to the moving position of the angular sliding contact. Inherent disadvantages of contact sensors are limited lifetime and reliability; resolvers are feedback encoders with cosine and sine signal outputs. When the shaft rotates, the feedback signal of the resolver can provide absolute position information, but it has the disadvantages of poor low-speed performance, complex decoding circuit, weak anti-electromagnetic interference performance, and high cost; the photoelectric encoder is a typical non-contact, The digital angle sensor calculates the actual position of the focal plane by measuring the rotation angle of the worm gear and the reduction ratio of the mechanism, with high precision, non-contact grinding, and high resolution; the magnetic linear displacement sensor (LDT) is a feedback sensor used to measure linear movement, and is suitable for It moves and measures in a straight line position, and can directly act on the focal plane. It has no contact, no wear, high reliability, small size, strong anti-interference ability, easy maintenance, simple interface, and low price. Although the accuracy is lower than that of photoelectric encoders, it is Enough to meet the accuracy of the focal plane index.

In view of the space camera focusing system based on the blank of the rebound magnetic linear displacement sensor and the limitation of the use of the ARM microprocessor, it is necessary to propose a low-cost micro-satellite with low circuit complexity, low power consumption, low cost, and small mechanism size. The design and implementation method of an easy-to-modular spaceborne camera focusing system.

Contents of the invention

The present invention provides a focus control system and a focus control method applied to space-borne cameras to solve the problems of complex circuit structure, cumbersome data processing, poor reliability and low precision existing in the focus control system of space-borne cameras.

A focusing control system applied to a spaceborne camera, including a stepping motor, a stepping motor drive circuit and a camera focal plane; it is characterized in that it also includes an ARM microprocessor and a rebound type magnetic linear displacement sensor;

The rebound type magnetic linear displacement sensor is installed vertically behind the focal plane of the camera, obtains the analog voltage when the focal plane of the camera moves linearly, and transmits the analog voltage to the ARM microprocessor; the ARM microprocessor according to the center Calculate the number of rotation steps and direction information of the stepping motor based on the pre-adjustment position of the camera focal plane sent by the camera, and then send a driving signal to the stepping motor drive circuit, which drives the stepping motor to make the focal plane of the camera reach the preset position. Focusing position: The ARM microprocessor realizes the closed-loop focusing and the open-loop focusing of the spaceborne camera according to the different commands sent by the central computer.

A focus control method applied to a spaceborne camera, the method is implemented by the following steps:

Step 1. Adjust the focusing transmission mechanism and the linear motion mechanism, and install the stepper motor on the focusing transmission mechanism;

Step 2. Put the measuring probe of the springback magnetic linear displacement sensor on the focal plane of the camera and fix it. The position feedback analog voltage of the probe is received by the ARM microprocessor;

Step 2. Install the measuring probe of the rebound type magnetic linear displacement sensor behind the focal plane of the camera and fix it, and the ARM microprocessor collects the analog voltage fed back by the rebound type magnetic linear displacement sensor when the camera focal plane moves;

Step 3, the ARM microprocessor performs focusing according to the focusing instruction sent by the central computer; if the instruction of open-loop focusing is received, the focusing process of the ARM microprocessor is:

Step 31: Receive the number of open-loop focusing steps sent by the central computer;

Step 32: Send a sequential driving signal to the stepper motor drive circuit, and decrease the number of focusing steps by 1;

Step 33, determine whether the number of focusing steps is 0, if not, return to step 32; if yes, the focusing is completed;

If the closed-loop focusing instruction is received, the focusing process of the ARM microprocessor is:

Step three and four receive the closed-loop focus pre-adjustment position information sent by the central computer;

Step three and five, the ARM microprocessor reads the value of the rebound type magnetic linear displacement sensor;

Step 36: Calculate the number of focusing steps according to the difference between the preset position and the read sensor;

Step 37: Send a sequential driving signal to the motor drive circuit, and decrease the number of focusing steps by 1 at the same time;

Step 38, determine whether the number of focusing steps is 0, if yes, execute step 39; if not, execute step 37;

Step 39, the ARM microprocessor reads the value of the rebound type magnetic linear displacement sensor;

Step 30: Determine whether the difference between the read sensor value and the preset position is less than the closed-loop threshold, if not, go back to step 36; if yes, focus adjustment is completed.

Beneficial effects of the present invention: According to the requirements of the micro-satellite focusing system, the present invention adopts the rebound type magnetic linear displacement sensor and carries out the design and realization of the on-board camera focusing system based on the tiny ARM microprocessor, so that the on-board focusing The system has the characteristics of low cost, low circuit complexity, simple data processing, high reliability and high precision, and is very suitable for micro-satellite focusing systems. Specifically reflect the following points:

1. The present invention adopts a rebound type magnetic linear displacement sensor as a focal plane measuring device, and the output is a three-wire system. The output voltage of the displacement sensor can be directly collected by the ARM without the need for RS422S data communication lines. The connection is simple, the control is convenient, the power supply voltage is optional, and the AD acquisition accuracy is high.

2. In the present invention, the displacement sensor probe directly acts on the focal plane, which is different from the traditional method of using an encoder to measure the worm gear and the focal plane to measure the position fitting. The method has higher precision and reliability, and is easy to design and install.

3. In the present invention, the focusing system is not powered on all the time in orbit, which can reduce its single event flipping and latching problems. It is completely possible to use an industrial-grade tiny ARM chip as the processor of the focusing system, which has abundant resources and fast processing speed. , low cost, low power consumption, and can still operate normally under vacuum high and low temperature conditions.

4. The drive circuit of the stepper motor in the present invention is connected in series with multiple MOS tubes to ensure that the drive circuit still works normally after a MOS tube breaks down. The front end of the drive adopts triode primary isolation to isolate digital signals from analog signals. The driving circuit can improve the working reliability of the motor under the condition of no backup in space.

5. In the present invention, the ARM microprocessor is used as a separate system, and the entire focusing system only has a power supply and a central computer communication interface, which is more convenient and easy to modularize during focusing tests and focusing environment tests.

Description of drawings

Fig. 1 is the functional block diagram of the focusing control system applied to space-borne cameras according to the present invention;

FIG. 2 is a flow chart of the focusing control method applied to a spaceborne camera according to the present invention.

Detailed ways

Specific Embodiments 1. This embodiment is described in conjunction with FIG. 1. A novel focusing control system applied to space-borne cameras includes an ARM microprocessor, a stepping motor, a stepping motor drive circuit, a central machine, a focusing transmission mechanism, a linear Motion mechanism and rebound magnetic linear displacement sensor;

The rebound type magnetic linear displacement sensor described in this embodiment replaces the traditional encoder to complete the measurement of the focal plane position. The sensor measurement probe is installed behind the focal plane, and the 12-bit AD that comes with the industrial-grade tiny ARM microprocessor is used to complete the alignment. The analog voltage output by the displacement sensor is collected, quantified and coded to obtain the focal plane position at this time, and the ARM microprocessor calculates the number of rotation steps and direction of the stepping motor according to the pre-focus position given by the central computer, and then outputs the corresponding number The motor drives the electric signal. Drive the motor to make the focal plane reach the preset position. The ARM microprocessor can realize closed-loop and open-loop control of the focal plane of the camera according to different instructions received from the central computer. Finally, the focal plane reaches the desired position.

The stepper motor drive circuit described in this embodiment converts the output level of the ARM microprocessor into a drive signal that can control the rotation of the motor; the focusing transmission mechanism and the linear motion mechanism complete the connection between the rotation of the motor and the linear movement of the focal plane ; The rebound type magnetic linear displacement sensor feeds back the analog voltage fed back by the rebound type magnetic linear displacement sensor to the ARM microprocessor when the focal plane moves in a straight line.

The output of the resilient magnetic linear displacement sensor described in this embodiment is a three-wire system, that is, one power line, one analog voltage line, and one ground line. The analog output of the displacement sensor can be directly collected and utilized by the ARM without additional RS422S data communication lines. The connection is simple, the control is convenient, the power supply voltage is optional, and the AD acquisition accuracy is high. The measuring probe of the rebound type magnetic linear displacement sensor is directly applied to the focal plane of the camera, and the depth of the focal plane of the camera is directly measured to output the corresponding analog voltage, which is different from the traditional method of using the encoder to measure the worm gear and the position fitting of the focal plane of the camera. method. The method has higher precision and reliability, and is easy to design and install.

The stepper motor drive circuit described in this embodiment adopts the form of series connection of field effect tubes to ensure that the drive circuit still works normally after a MOS tube breaks down. The drive front end adopts triode primary isolation to isolate digital signals from analog signals. The driving circuit can improve the working reliability of the motor under the condition of no backup in space.

The ARM microprocessor described in this embodiment forms a separate system, and the entire focusing system only has a power supply and a central computer communication interface externally, which is more convenient and easy to modularize during focusing tests and focusing environment tests.

The focus control system applied to the spaceborne camera described in this embodiment is not powered on all the time in orbit, which can reduce its single event flipping and latching problems, and it is completely possible to use an industrial-grade tiny ARM chip as the processor of the focus system. It has rich resources, fast processing speed, low cost, and low power consumption. Experiments have proved that it can still operate normally under vacuum high and low temperature conditions.

Specific embodiment 2. This embodiment is described in conjunction with FIG. 2. This embodiment is the focusing control method of the novel focusing control system applied to the spaceborne camera described in the specific embodiment 1. The method is implemented by the following steps:

1. Design the focusing transmission mechanism and linear motion mechanism according to the focusing requirements, install the stepper motor on the transmission mechanism, and confirm the motor reduction ratio;

2. Use the rebound type magnetic linear displacement sensor as the device for measuring the feedback signal. The probe is firmly placed on the focal plane of the camera and fixed. The feedback analog voltage at the position of the probe is near the middle of the range to ensure that the front and back of the focal plane are stretched within the sensor. within the measurement range.

3. The ARM microprocessor performs focusing according to the focusing instruction sent by the central computer; if the instruction of open-loop focusing is received, the focusing process of the ARM microprocessor is:

Step 31: Receive the number of open-loop focusing steps sent by the central computer;

Step 32: Send a sequential driving signal to the stepper motor drive circuit, and decrease the number of focusing steps by 1;

Step 33, determine whether the number of focusing steps is 0, if not, return to step 32; if yes, the focusing is completed;

If the closed-loop focusing instruction is received, the focusing process of the ARM microprocessor is:

Step three and four receive the closed-loop focus pre-adjustment position information sent by the central computer;

Step three and five, the ARM microprocessor reads the value of the rebound type magnetic linear displacement sensor;

Step 36: Calculate the number of focusing steps according to the difference between the preset position and the read sensor;

Step 37: Send a sequential driving signal to the motor drive circuit, and decrease the number of focusing steps by 1 at the same time;

Step 38, determine whether the number of focusing steps is 0, if yes, execute step 39; if not, execute step 37;

Step 39, the ARM microprocessor reads the value of the rebound type magnetic linear displacement sensor;

Step 30: Determine whether the difference between the read sensor value and the preset position is less than the closed-loop threshold, if not, go back to step 36; if yes, focus adjustment is completed.

In this embodiment, the minimum system with the ARM microprocessor as the center is designed, which is an independent box, and is mainly composed of an ARM microprocessor module, a motor drive module, a power supply module, and a signal acquisition module. Among them, the motor drive adopts the design of series field effect tube, and the front end of the drive adopts triode first-level isolation to improve the working reliability of the space motor.

In this embodiment, the rebound type magnetic linear displacement sensor and the stepping motor are connected to the above-mentioned minimum system electric box. Download the software through the download port. The software part mainly includes: interrupt service subroutine: mainly used to control the rotation frequency of the motor and respond to the instructions issued by the central computer; displacement sensor acquisition subroutine: mainly for AD acquisition and quantification of the analog voltage of the displacement sensor , coding and processing for closed-loop focusing; RS422 communication subroutine: RS422 communication subroutine receives instructions from the central computer and feeds back focal plane position information at the same time; watchdog reset subroutine: processor feeds the built-in watchdog regularly to ensure Reset and restart when the program runs away; open-loop focusing subroutine: send four corresponding motor drive level signals; closed-loop focusing subroutine: continuously collect the actual focal plane position and send drive level signals to make the camera focal plane reach the preset adjust the position.

The focusing method described in this embodiment replaces the traditional encoder method of collecting the position of the worm gear and linearly fitting the position of the focal plane. Instead, the displacement sensor measuring probe is directly placed on the focal plane, and the depth of the focal plane is directly measured through the voltage analog feedback when the focal plane moves in a straight line. At the same time, it is the first time to use an industrial-grade micro-miniature ARM microprocessor for analog acquisition, central computer communication and focusing motor drive signal generation, making the focusing system independently controllable and realizing two functions of closed-loop focusing and open-loop focusing. The ARM microprocessor and linear displacement sensor in the whole design are applied in the aerospace focusing system for the first time. This method has the characteristics of low cost, low circuit complexity, simple data processing, high reliability and high precision. In practical applications, the focus control accuracy can reach 6um, which is suitable for low-cost micro-satellites.

Claims (3)

1. The focusing control method applied to space-borne cameras, including a focusing control system, the focusing control system includes a stepping motor, a stepping motor drive circuit, a camera focal plane ARM microprocessor and a rebound type magnetic linear displacement sensor; The rebound type magnetic linear displacement sensor is installed vertically behind the focal plane of the camera, obtains the analog voltage when the focal plane of the camera moves linearly, and transmits the analog voltage to the ARM microprocessor; the ARM microprocessor according to the center The pre-focus position of the camera focal plane sent by the machine calculates the number of rotation steps and direction information of the stepping motor, and then sends a driving signal to the stepping motor drive circuit, and the stepping motor driving circuit drives the stepping motor to make the focal plane of the camera Reach the pre-focusing position; the ARM microprocessor realizes the closed-loop focusing and the open-loop focusing of the spaceborne camera according to the commands sent by the central computer; it also includes a focusing transmission mechanism and a linear motion mechanism, so The stepper motor is fixed on the focusing transmission mechanism, and the focal plane of the camera is fixed on the linear motion mechanism; it is characterized in that the focusing control method is realized by the following steps: Step 1. Adjust the focusing transmission mechanism and the linear motion mechanism, and install the stepper motor on the focusing transmission mechanism; Step 2. Put the measuring probe of the springback magnetic linear displacement sensor on the focal plane of the camera and fix it. The position feedback analog voltage of the probe is received by the ARM microprocessor; Step 3, the ARM microprocessor performs focusing according to the focusing instruction sent by the central computer; if the instruction of open-loop focusing is received, the focusing process of the ARM microprocessor is: Step 31: Receive the number of open-loop focusing steps sent by the central computer; Step 32: Send a sequential driving signal to the stepper motor drive circuit, and decrease the number of focusing steps by 1; Step 33, determine whether the number of focusing steps is 0, if not, return to step 32; if yes, the focusing is completed; If the closed-loop focusing instruction is received, the focusing process of the ARM microprocessor is: Step three and four, receiving the closed-loop pre-focus position information sent by the central computer; Step three and five, the ARM microprocessor reads the value of the rebound type magnetic linear displacement sensor; Step 36: Calculate the number of focusing steps according to the difference between the pre-focus position and the read sensor; Step 37: Send a sequential driving signal to the motor drive circuit, and decrease the number of focusing steps by 1 at the same time; Step 38, determine whether the number of focusing steps is 0, if yes, execute step 39; if not, execute step 37; Step 39, the ARM microprocessor reads the value of the rebound type magnetic linear displacement sensor; Step 30: Determine whether the difference between the read value of the rebound type magnetic linear displacement sensor and the pre-focusing position is less than the closed-loop threshold, if not, return to step 36; if yes, the focusing is completed. 2 . The focusing control method applied to a spaceborne camera according to claim 1 , wherein the stepping motor driving circuit adopts a plurality of MOS transistors connected in series, and a triode is connected to the front end of the driving circuit. 3 . 3 . The focusing control method applied to spaceborne cameras according to claim 1 , wherein the output of the resilient magnetic linear displacement sensor adopts a three-wire system. 4 .