CN105911557B - FM-CW laser ranging light beam autofocus based on liquid lens - Google Patents

Abstract

The invention discloses a kind of FM-CW laser ranging system beam autofocus based on liquid lens, including tunable laser, red laser, liquid lens unit, camera, computer hot spot judgement unit, lens drive circuit；Tunable laser provides the measurement that linear frequency modulation laser is used for target point distance to be measured, red laser produces the guiding positioning that red visible laser is used for target point to be measured, computer hot spot judgement unit forms reponse system with lens drive circuit, computer hot spot judgement unit by cameras capture to the light spot image on object under test surface be identified and compare the spot size under different liquids lens driving current to search out the liquid lens driving current value corresponding to minimum light spot, realize the fast automatic focusing of light beam.Simple in construction, small volume of the invention, fast response time, FM-CW laser ranging systematic survey light beam can be realized with positioning the full-automatic focusing of light beam based on spot size index.

Description

Automatic focusing device of frequency modulated continuous wave laser ranging beam based on liquid lens

technical field

The invention relates to the field of frequency-modulated continuous wave laser ranging, in particular to a liquid-lens-based automatic focusing device for frequency-modulated continuous wave beams.

Background technique

Frequency modulated continuous wave laser ranging technology has been widely used in more and more fields due to its advantages of non-contact and high precision. This technology solves the problem that distance measurement requires the assistance of cooperative targets such as reflective prisms, cat's eyes, and target balls, which cannot be realized on site. The frequency-modulated continuous wave laser ranging system uses a beam of high-frequency laser with continuous frequency modulation for ranging, and at the same time requires a beam of visible light to guide and locate the target point to be measured. The two laser beams are coupled into the same optical fiber by a coupler and then exit, and the outgoing laser beams will have a certain divergence angle. As the distance increases, the beam spread will become more and more serious, and it will be impossible to accurately locate and measure the target point. Zoom technology is the key to achieve beam focusing requirements.

A traditional mechanical zoom system is usually composed of multiple lenses, and the focal length is changed by moving one or more lenses in the lens group back and forth. The mechanical focusing method and its structure have obvious deficiencies. First of all, mechanical focusing requires precise control of the position of the optical element, precise calculation of the movement trajectory of the element or component, and the movement of the original or component needs to be synchronized. These stringent requirements make the structure of the traditional zoom system complex. , the processing is difficult and the cost is high; secondly, the mechanical focusing needs to repeatedly move the position of the components to achieve the change of the focal length, which has the disadvantages of easy wear and low life; here, the traditional mechanical focusing system needs to adjust the mechanical length to meet the focal length. needs, and cannot adapt to the development trend of instrument miniaturization.

Contents of the invention

Aiming at the deficiencies of the existing focusing technology, the utility model provides a liquid lens-based frequency-modulated continuous wave laser ranging system beam automatic focusing device with simple structure, small volume, and full-automatic fast focusing. The focusing device replaces the traditional mechanical focusing lens group with an electric liquid lens, and adds a compensating plano-convex lens on this basis, so that the overall size of the device is further reduced. Aiming at the problem of chromatic aberration between the red guiding positioning laser and the frequency-modulated continuous wave laser wavelength, a time-sharing focusing scheme is adopted to focus the red guiding laser in the positioning stage, and correct the lens drive current according to the wavelength values of the two laser beams in the measuring stage, so that the frequency modulation The continuous wave laser achieves the best focus state. The device can quickly and fully automatically focus the measuring beam and the positioning beam within the range of 1m-30m, realize the precise positioning of the target point to be measured, and improve the distance measurement accuracy.

In order to solve the above problems, the present invention proposes a liquid lens-based frequency-modulated continuous wave laser ranging system beam automatic focusing device, including a tunable laser, a red laser, a fiber coupler, a liquid lens unit, a half-transparent mirror, camera and computer spot discrimination unit; the tunable laser is used to generate narrow-linewidth frequency-modulated continuous wave laser; the red laser is used to generate red guide laser; the fiber coupler is used to combine the laser generated by the tunable laser The laser light generated by the red laser is coupled into the same optical fiber, and the laser light exits from the optical fiber and enters the liquid lens unit; the liquid lens unit includes a housing and a lens driving circuit, and the housing is sequentially provided with aperture light along the laser direction diaphragm, compensating plano-convex lens and liquid lens; the half-mirror is arranged on the outgoing light side of the liquid lens unit, the camera is arranged on the transmitted light side of the half-mirror, and the target point to be measured It is arranged on the reflected light side of the half-mirror; the half-mirror reflects a part of the laser light back to the ranging system and forms a beat frequency with the emission signal of the tunable laser for the calculation of the distance of the target point to be measured, Another part of the laser light is transmitted into the camera; the camera is used to capture the focused spot image of the red guiding laser, and transmit the focused spot image to the computer spot discrimination unit; the computer spot discrimination unit is connected to the camera through a data interface , the computer spot discrimination unit is connected to the lens driving circuit through the USB interface; the computer spot discrimination unit finds the drive current value of the liquid lens when the focus spot is the smallest in all the focus spot images received by comparison; the lens drive The circuit keeps outputting the driving current value, so that the liquid lens maintains a constant focal length.

Compared with prior art, the beneficial effect of the present invention is:

The focusing device of the invention has the advantages of simple structure, small size, fast focusing speed and can realize automatic focusing according to the discrimination of the spot size. The time-sharing focusing of the red guiding and positioning laser and the frequency-modulated continuous wave laser ensures that the red guiding and positioning laser and the frequency-modulated continuous wave laser reach the best focusing state respectively in the positioning stage and the measuring stage, so that the target point to be measured can be accurately positioned, and Ensure that the echo power of frequency modulated continuous wave laser is strong.

Description of drawings

Fig. 1 is a schematic diagram of the structure and optical path of the beam focusing device of the present invention;

Fig. 2 is a diagram of spot changes during the focusing process of the red guiding laser according to the embodiment of the present invention;

Fig. 3 is a front sectional view of the connection structure between the liquid lens unit and the optical fiber in the present invention;

Fig. 4 is a top view of the connection structure between the liquid lens unit and the optical fiber shown in Fig. 3;

Fig. 5 is a focus spot diagram when the FM continuous wave measurement laser of the example of the present invention reaches the best focus state.

In the picture:

1-Tunable laser 2-Red laser 3-Fiber coupler

4-liquid lens unit 5-half mirror 6-camera

7-computer spot discrimination unit 8-lens drive circuit 9-target point to be measured

10-aperture diaphragm 11-compensated plano-convex lens 12-liquid lens

13-FC/PC fiber optic adapter plate 14-threaded adapter 15, 17-gasket

16-C Thread Extension Tube 18-Housing

Detailed ways

The technical solution of the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments, and the described specific embodiments are only for explaining the present invention, and are not intended to limit the present invention.

As shown in Figure 1, the present invention is a liquid lens-based frequency-modulated continuous wave laser ranging system beam automatic focusing device, including a tunable laser 1, a red laser 2, a fiber coupler 3, a liquid lens unit 4, a semi-transparent A mirror 5, a camera 6 and a computer spot discrimination unit 7.

The tunable laser 1 is used to generate narrow-linewidth frequency-modulated continuous wave laser; the red laser 2 is used to generate red guide laser; the fiber coupler 3 is used to combine the laser generated by the tunable laser 1 with the The laser light generated by the red laser 2 is coupled into the same optical fiber all the way, and the laser light exits from the optical fiber and enters the liquid lens unit 4 .

The liquid lens unit 4 includes a housing 18 and a lens driving circuit 8. An aperture stop 10, a compensating plano-convex lens 11 and a liquid lens 12 are sequentially arranged in the housing 18 along the laser direction, and the lens driving circuit 8 can drive The liquid lens 12 moves in the axial direction.

The half mirror 5 is arranged on the outgoing light side of the liquid lens unit 4, the camera 6 is arranged on the transmitted light side of the half mirror 5, and the target point 9 to be measured is arranged on the The reflected light side of the half-mirror 5; the half-mirror 5 reflects a part of the laser light back to the ranging system and forms a beat frequency with the emission signal of the tunable laser 1 for the calculation of the distance of the target point 9 to be measured, Another part of the laser light is transmitted into the camera 6;

The camera 6 is used to capture the focused spot image of the red guiding laser, and transmit the focused spot image to the computer spot discrimination unit 7;

The computer facula discrimination unit 7 is connected with the camera 6 through a data interface, and the computer facula discrimination unit 7 is connected to the lens drive circuit 8 through a USB interface; The drive current value of the liquid lens 12 when the focus spot in the spot image is the smallest; the lens drive circuit 8 keeps outputting the drive current value, so that the liquid lens 12 maintains a constant focal length.

Fig. 3 and Fig. 4 have shown the connection structure embodiment between the optical fiber of liquid lens unit and fiber optic coupler 3 in the present invention, from the end of optical fiber to housing 18, be provided with FC/PC fiber adapter plate 13 in sequence , thread adapter 14, washer 15, C-thread extension pipe 16, washer 17, the external thread of the C-thread extension pipe 16 is connected with the internal thread of the housing 18. In the present invention, the optical fiber liquid lens unit is connected with the liquid lens unit through FC/PC optical fiber adapter plate 13, threaded adapter 14, C threaded extension tube 16, gasket, as shown in Figure 4, FC/PC optical fiber The adapter plate 13 is connected to the thread adapter 14, the thread adapter 14 is connected to the C thread extension tube 16, the C thread extension tube is connected to the liquid lens 18, and the gasket 15 and the gasket 17 are respectively located on the thread adapter 14 and the C thread extension tube 16 , between the C-thread extension tube 16 and the liquid lens 18, for fine-tuning the length of the connection structure. The connection structure connects the optical fiber connector and the liquid lens together, which saves the complicated process of alignment adjustment between the optical fiber connector and the liquid lens, increases the stability of the device, and improves the shock resistance of the device. A plano-convex compensation lens 11 and an aperture stop 10 are added to the liquid lens unit, wherein the plano-convex compensation lens 11 reduces the overall focusing range of the liquid lens 12, and the aperture stop 10 limits the incident laser light to the paraxial area, reducing the impact of spherical aberration.

Using the liquid lens-based frequency-modulated continuous-wave laser ranging system beam automatic focusing device to realize fast automatic focusing of the red guiding laser and frequency-modulated continuous-wave measuring laser dual-beam fast automatic focusing is to couple the red guiding laser and frequency-modulated continuous wave measuring laser into the same optical fiber to synthesize one The light beam enters a liquid lens, and the aperture diaphragm is used in the liquid lens to limit the beam to the paraxial region of the optical system. The red guiding laser and the frequency-modulated continuous wave are used to measure the time-sharing focusing of the laser, and finally automatic focusing is realized. It mainly includes the automatic focusing of the red guide laser to realize the positioning of the target point to be measured, and the correction of the corresponding drive current value when the red guide laser reaches the best focus state to obtain the drive current of the liquid lens when the frequency modulation continuous wave measures the best focus of the laser, and the use of the liquid lens The driving current drives the liquid lens to realize the automatic focusing of the frequency modulated continuous wave measurement laser.

Specific steps are as follows:

Step 1, the automatic focusing of the red guiding laser realizes the positioning of the target point to be measured: the narrow-linewidth frequency-modulated continuous wave measurement laser and the red guiding laser are generated by the tunable laser 1 and the red laser 2; the fiber coupler 3 is used to The frequency-modulated continuous wave laser and the red guided positioning laser are coupled into the same optical fiber, and the coupled beam enters the liquid lens unit 4 after exiting the optical fiber, and converges after passing through the aperture stop 10, the compensation plano-convex lens 11, and the liquid lens 12 respectively; the lens The drive circuit 8 outputs an initial drive current to drive the liquid lens 12, the light beam is converged by the liquid lens 12 and then reflected by the half-mirror 5 to the surface of the target to be measured to form a red spot; Capture and transmit the spot image on the surface of the object to be measured to the computer spot discrimination unit 7; the computer spot discrimination unit 7 recognizes the spot on the captured image and quantifies and stores the spot size; the lens drive circuit 8 Gradually reduce the drive current value of the liquid lens 12, the computer spot discrimination unit 7 compares the spot sizes under different drive current values until the minimum value of the spot is found, and the lens drive circuit 8 stops driving after finding the minimum value of the spot. The value of the current and stabilize the driving current value at this value and output; including the following steps:

1-1. Coarse adjustment of liquid lens driving current:

After the lens driving circuit 8 is started, the initial driving current is output to the liquid lens unit 4. The initial driving current is the allowable maximum current value of the liquid lens, and the liquid lens driving current decreases with a step size I _coarse , and the nth driving current value is

I _n ＝I _U-1 -I _coarse (1)

In the formula (1), _In is the nth liquid lens driving current value in the liquid lens driving current adjustment process, and I _n-1 is the n-1 liquid lens driving current value in the liquid lens driving current adjustment process, I _coarse is the adjustment step size of the liquid lens drive current;

Comparing the size S _n of the focused spot of the red-guided laser in the images captured by the camera under different driving currents of the liquid lens, the size of the focused spot of the red-guided laser will first decrease and then increase with the decrease of the driving current of the liquid lens The trend of , when S _n1-1 >S _n1 , S _n1+1 >S _n1 appears from a certain point n1, the liquid lens drive current stops decreasing, at this time, the lens drive current is I _n1 , where S _n1-1 , S _n1 , S _n1+1 are respectively the size of the focus spot of the red guiding laser when the liquid lens driving current value is adjusted for the n1-1th, n1th, n1+1th time;

1-2. Medium adjustment of liquid lens driving current:

The driving current of the liquid lens starts from I _n1 -I _coarse and decreases with the step size I _mid . I _mid <I _coarse . When S _n2-1 >S _n2 and S _n2+1 >S _n2 appear from a certain point n2, The driving current of the liquid lens stops decreasing, and at this moment, the driving current of the lens is _In2 ;

1-3. Liquid lens drive current fine-tuning:

_The driving current of _the liquid lens _starts from I _{n2 -I mid and} decreases with the step size _{I fine} . The driving current of the liquid lens stops decreasing. At this time, the driving current of the lens is I _n3 ; the driving current I _n3 of the liquid lens is output to the liquid lens, and the red-guided laser auto-focusing process ends.

Step 2. According to the relationship between the frequency-modulated continuous wave measurement laser and the wavelength of the red guiding laser, the parameters of the driving current value finally output to the liquid lens in the above step 1 are corrected to ensure that the frequency-modulated continuous wave laser reaches the best focusing state:

I'=I _n3 +A (2)

In formula (2), A is a constant value, is 658nm at red guide laser wavelength, and when frequency modulation continuous wave measures laser wavelength is 1550nm, A=32.4nm;

Step 3, outputting the liquid lens drive current I determined in step 2 to the liquid lens, so as to realize the automatic focusing of the frequency-modulated continuous wave measurement laser.

Applications:

The wavelength of the red guiding laser is 658nm, and the central wavelength of the FM continuous wave measurement laser is 1550nm. Connect the structure of each part according to the structure shown in Figure 1, and connect the optical fiber and the liquid lens unit according to the structure shown in Figure 3 and Figure 4. The device of the present invention turns to the direction of the object to be measured, and the object to be measured is about 7m away from the beam automatic focusing device of the FM continuous wave laser ranging system. Start the device of the present invention and perform automatic focusing according to the above steps 1, 2, and 3. It can be observed The light spot that the red guiding laser irradiates on the surface of the object quickly changes from large to small and finally stabilizes at the smallest spot. The changing process of the light spot is shown in Figure 2. The diameter of the light spot after stabilization is only 0.917mm. After completing step 2 and performing step 3, Use an infrared beam analyzer to observe the focusing of the frequency-modulated continuous wave measurement laser. It is observed that the frequency-modulated continuous wave measurement laser is rapidly focused to a point. The focused spot is shown in Figure 5, and the diameter of the focused spot is 1.344mm. It is verified by the above examples that the present invention can realize fast and fully automatic focusing of the light beam of the frequency-modulated continuous wave laser ranging system.

Although the present invention has been described above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific embodiments, and the above-mentioned specific embodiments are only illustrative, rather than restrictive. Under the enlightenment of the present invention, many modifications can be made without departing from the gist of the present invention, and these all belong to the protection of the present invention.

Claims (1)

1. A kind of 1. FM-CW laser ranging system beam autofocus based on liquid lens, it is characterised in that bag Include tunable laser (1), red laser (2), fiber coupler (3), liquid lens unit (4), semi-transparent semi-reflecting lens (5), Camera (6) and computer hot spot judgement unit (7)；

   The tunable laser (1) is used to produce narrow linewidth CW with frequency modulation laser；

   The red laser (2) is used to produce red guiding laser；

   The fiber coupler (3) is used to produce laser caused by the tunable laser (1) and the red laser (2) Raw laser coupled enters same optical fiber, and laser enters the liquid lens unit (4) from fiber exit；

   The liquid lens unit (4) includes housing and lens drive circuit (8), and the housing interior edge laser direction is set gradually There are aperture diaphragm (10), compensation planoconvex spotlight (11) and liquid lens (12)；

   The semi-transparent semi-reflecting lens (5) are arranged on the emergent light side of the liquid lens unit (4), and the camera (6) is arranged in The transmitted light side of the semi-transparent semi-reflecting lens (5), target point (9) to be measured are arranged on the reflected light one of the semi-transparent semi-reflecting lens (5) Side；The semi-transparent semi-reflecting lens (5) make a part of laser reflection return range-measurement system and with the transmission signal shape of tunable laser (1) It is used for the calculating of target point to be measured (9) distance into beat frequency, another part laser is transmitted into the camera (6)；

   The camera (6) is used for the focal beam spot image for catching red guiding laser, and the focal beam spot image is passed to and calculated Machine hot spot judgement unit (7)；

   The computer hot spot judgement unit (7) is connected by data-interface with the camera (6), and the computer hot spot differentiates Unit (7) is connected to lens drive circuit (8) by USB interface；The computer hot spot judgement unit (7) is found out by comparing The driving current value of liquid lens (12) in all focal beam spot images received during focal beam spot minimum；The lens drive Dynamic circuit (8) keeps exporting the driving current value, liquid lens (12) is kept constant focal length.