WO2000063660A2

WO2000063660A2 - Apparatus for measurement of particle or droplet velocity

Info

Publication number: WO2000063660A2
Application number: PCT/US2000/010794
Authority: WO
Inventors: Zilan Shen; Hyoun Park; Keith Graydon
Original assignee: Sarnoff Corporation
Priority date: 1999-04-21
Filing date: 2000-04-21
Publication date: 2000-10-26
Also published as: US6624434B1; WO2000063660A3; WO2000063660A9

Abstract

An apparatus (34) for measuring the velocity of a droplet a liquid includes a laser (36) for generating a beam of light into the shape of a thin sheet. A beam divider (40) is along the first path (38) of the light for dividing the beam into two separate beams which extends along second (42) and third (44) paths. The second (42) and third (44) paths lie in a common plane. Along the second (42) and third (44) paths is a device (60) for projecting a droplet of liquid across the second (42) and third paths (44) so that the droplet passes through both of the divided beams. At least one photodetector (52, 54) is along both the second (42) and third paths (44) to receive the divided beams and provide an electrical signal corresponding to the beams. A beam divider (40) which is used to divide the beam into two beams includes a body (62) of an optically transparent material having at least two flat front surfaces (68, 70) which are at an angle with respect to each other to form a V having a sharp corner, and at least two flat back surfaces (74, 76) each of which is spaced from and parallel to a separate front surface.

Description

APPARATUS FOR MEASUREMENT OF PARTICLE OR DROPLET VELOCITY

Field of the Invention

The present invention is directed to an apparatus for the measurement of the shape

profile and velocity of an individual particle or an individual droplet of a liquid, and also to a

beam divider for use in such an apparatus.

Background of the invention

There has been developed an apparatus for measuring various characteristics of a

droplet of a liquid, such as a droplet of ink for an ink printer. This apparatus is described in

detail in the application for U.S. Letters Patent of Tzong-Shyng Leu, Serial No. 09/215,018,

filed December 17, 1998. In general, this apparatus comprises a laser for generating and

projecting a beam of light along a path. Along the path of the beam of light is a lens or a lens

combined with a set of knife edges which forms the beam into the shape of a thin sheet at a

focal point beyond the lens. Also along the path of the beam is a photodetector for receiving

the beam and providing an electrical signal corresponding to the light received. Adjacent the

path of the beam is means for projecting a droplet of a liquid through the sheet of the beam.

The droplet passing through the beam of light varies the amount of light receiving by the

photodetector which generates a corresponding signal. From the signal various characteristics of the droplet, such as size and shape, can be determined. However, for various purposes, it

would be desirable to be able to measure the velocity of the droplet. Summary of the Invention

One aspect of the present invention is an apparatus for measuring the velocity of a

droplet of a liquid. The apparatus includes means for generating and projecting a beam of light

along a first path. Along the first beam path is means for dividing the beam into two separate

beams extending along separate second and third paths. Means is adjacent the two beams for

projecting a droplet of a liquid through both of the beams. Means is also provided to detect the

two beams after the droplet has passed therethrough to provide electrical signals from which the

velocity of the droplet can be determined.

Another aspect of the present invention is a beam divider which can be used in the

apparatus for measuring the velocity of a droplet. The beam divider includes a body of a light

transparent material having two light receiving surfaces. The light receiving surfaces are at an

angle with respect to each other and extend from a common point to form a V. The body also

includes two light emitting surfaces. Each of the light emitting surfaces is spaced from and parallel to a separate light receiving surface.

Brief Description of the Drawings

Fig. 1 is a schematic drawing of a form of the apparatus of the present invention;

Fig. 2 is a schematic drawing of a preferred form of an apparatus of the present invention;

Fig. 3 is an enlarged showing of the circled portion of Fig. 2;

Fig. 4 is a graph showing the electrical signals produced by the apparatus of Fig. 2;

Fig. 5 is a graph showing the electrical signals produced by a variation of the apparatus shown in Fig. 2; Fig. 6 is a perspective view of the beam divider of the apparatus shown in Fig. 2;

Fig. 7 is a top view of the beam divider shown in Fig. 6 showing the manner in which

the beam divider operates;

Fig. 8 is a top view of a modification of the beam divider of Fig. 6; and

Fig 9 is a sectional view along line 9-9 of Fig. 8.

Detailed Description of Invention

Referring initially to Fig. 1, a form of the apparatus of the present invention for

measuring the velocity of a drop of liquid is generally designated as 10. Measuring apparatus

10 comprises a laser 12 which is adapted to generated a beam of light and direct the beam along

a path 14 Along the path 14 and in front of the laser 12 are a series of lenses and knife edges 16

and 18 which shape the beam into the form of a thin sheet. The beam then passes through a

beam splitter 20 which divides the beam into two portions, one which extends along the path 22

and the other which extends along a path 24 which is substantially normal to the path 22 A

mirror 26 is along the path 24 and changes the direction of the portion of the beam extending

along path 24 so that the beam proceeds along a path 28 parallel to the path 22. The paths 22

and 28 lie in the same plane. Separate phtotodetectors 30 and 32 are along the paths 22 and 28

and are adapted to receive the beams extending along the paths 22 and 28 respectively. The

phtotodetectors 30 and 32 are adapted to provide an electrical signal corresponding to the beam

received thereby. Adjacent the path 22 is a device 34 for generating and projecting a droplet of

a liquid, such as the print head of an ink jet printer. The device 34 is positioned so as to project

a droplet of a liquid toward and through the beam extending along the path 22.

In the operation of the apparatus 10, after the droplet of liquid passes through the portion of the beam extending along the path 22, it will pass through the portion of the beam

extending along the path 28 since the portion of the beam extending along the path 28 is

parallel to the portion of the beam extending along the path 22. Since the two paths 22 and 28

are spaced apart, the droplet of liquid will pass through the portion of the beam extending along

the path 28 at a later time then when its passes through the portion of the beam extending along

the path 22. As the droplet of liquid passes through each of the portions of the beam, it disrupts

the beam so as to change the amount of light received by each of the photodetectors 30 and 32.

This results in a change in the electrical signal provided by each of the photodetectors 30 and

32. Referring to Fig. 4, it can be seen that the first photodetector 30 provides a change in its

output signal first at time Tl, whereas the second photodetector 32 provides a change in its

output signal as a later time T2. By determining the difference between times Tl and T2, and

knowing the distance between the two parallel paths 22 and 28, the velocity of the droplet of the

liquid can be determined. Thus, the apparatus 10 can be used to measure the velocity of a

droplet of liquid, as well as the profile of the liquid. The apparatus 10 can also be used to

measure the velocity of any particle which can be projected through the beams of light and will

disrupt the amount of light which is received by the photodetectors 30 and 32.

Referring to Fig. 2, a preferred form of the velocity measurement apparatus of the

present invention is generally designated as 34. Apparatus 34 comprises a laser 36 which is adapted to generate and project a beam of light along a path 38. Although not shown, the laser

34 has in front of it, lenses or lenses combined with knife edges which shape the beam of light

into the form of a thin sheet. Along the beam path 38 is a beam divider 40, the details of which

will be described later. However, the divider 40 divides the beam into two separate beams which are emitted from the divider 40 along two separate, spaced and parallel paths 42 and 44. Along the beam paths 42 and 44 is a focusing lens system 46 which receives the beams and

deflects both of the beams so that the beams then travel along paths 48 and 50 which cross each

other beyond the lens 46. The beam paths 48 and 50 lie in the same plane. Along each of the

beam paths 48 and 50 is a separate photodetector 52 and 54 respectively. The photodetectors

52 and 54 are adapted to receive the beams which extend along the beam paths 46 and 48 and

provide an electrical signal output corresponding to the light received. In front of each of the

photodetectors 50 and 52 and along their respective beam paths 46 and 48 is a collecting lens

56 and a mask 58. The masks 58 and collecting lenses 56 serves to confine the respective

beams and direct them into the photodetectors.

As shown more clearly in Fig. 3, at a point along the beam path 50 beyond the point

where the beam paths 48 and 50 cross each other is a device 60 for generating a droplet of a

liquid and projecting the droplet toward and through the beam extending along the beam path

50. The droplet forming device 60 may be the head of an ink jet printer. In the operation of the

apparatus 34, the droplet of liquid passes first through the beam which extends along the beam

path 50 and then continues to pass through the beam which extends along the beam path 48. As

the droplet passes through each beam, it disrupts part of the beam and thereby changes the

output signal from each of the phtotodetectors 52 and 54. Since the points along the beam

paths 48 and 50 at which the droplet passes through the beams are spaced from each other, the

change in the electrical output signal from the photodetectors 52 and 54 will he at different

times. Referring to Fig. 4, it can be seen that the change in the electrical signal from the photodetector 52 will be at a time Tl and the change in the electrical signal from the phtotodetectors 54 will be at a later time T2. By measuring the distance between the beam

paths 48 and 50 at the points where the droplet of liquid pass through the beams and by

determining the time difference between the change in electrical output signals of the

photodetectors, 52 and 54, the velocity of the droplet can be determined. The spacing between

the beam paths 48 and 50 where the droplet pass thereacross can be varied by moving the

droplet forming device 60 along the beam paths 48 and 50, or by varying the structure of the

focusing lens system 46 or, as will be described, by varying the structure of the beam divider

40.

Referring to Fig. 6, there is shown a perspective view of the beam divider 40. Beam

divider 40 comprises a body 62 of an optically transparent material, such as glass. The body 62

has spaced, opposed, substantially flat top and bottom surfaces 64 and 66. At the front or light

receiving side of the body 62 are two substantially flat surfaces 68 and 70, which extend

between the top and bottom surfaces 64 and 66. The front surfaces 68 and 70 are arranged at an

angle with respect to each other and extend forwardly of the body 62 from a common line 72.

Thus, the front surfaces 68 and 70 form a V. A pair of substantially flat back or light emitting

surfaces 74 and 76 extend between the top and bottom surfaces 64 and 66. The back surface 74

is spaced from and parallel to the front surface 68, and the back surface 76 is spaced from and parallel to the front surface 70. The body 62 also has an end surface 78 extending between the

ends of the front and back surfaces 68 and 74, and an end surface 80 extending between the end

of the front and back surfaces 70 and 76.

Referring to Fig. 7, there is shown the manner that the beam divider 40 operates. A

beam 82 having a width a is directed into the body 62 at the front surfaces 68 and 70. The width of the beam 82 is such that the beam 82 can be directed into the body 62 with a portion

of the beam 82 entering the body 62 along a portion of the front surface 68, and the other

portion of the beam 82 enters the body 62 along a portion of the font surface 70. The beam

portions 84 and 86 which enter the body 62 through the front surfaces 68 and 70 respectively,

are deflected by their respective front surfaces 68 and 70 so that they are directed away from

each other. The beam portions 84 and 86 flow through the body 62 to the back surfaces 74 and

76 respectively. When the beam portions 84 and 86 pass through their respective back surfaces

74 and 76, they are deflected so as to be directed along paths parallel to the path of the original

beam 82. Thus, the beam divider 40 divides the single beam 82 into two separate beams 84 and

86 which are directed along spaced, parallel paths. The thickness of the body 62 between the

front surfaces 68 and 70 and the back surfaces 74 and 76 along with the incident angles of the

front surfaces 68 and 70 determine the spacing between the emitted beams 84 and 86. By

increasing the thickness of the body 62 and increasing the incident angles, the spacing between

the emitted beams 84 and 86 can be increased. Although the beam divider 40 is shown as

having two front and back surfaces so as to divide a beam into two separate beams, by

providing the body 62 with more than two front surfaces and back surfaces, the beam divider 40

can provide more than two sub-beams.

In the beam divider 40, the optical quality of the incident surfaces is very important to

achieve the proper division of the beam. This is especially so at the line 72 where the two front

surfaces 68 and 70 meet and where the incident beam is separated. The surfaces at this line must be flat and clean, and the corner has to be sharp. However, sharp angles are difficult to

produce. Referring to Figs. 8 and 9 there is shown a shown another form of the beam divider of the present invention, generally designated as 88, which can be more easily made with the

desired flatness and sharpness. In the beam divider 88, the body is formed of two separate

pieces 90 and 92, each of which forms one-half of the body. The body piece 90 has flat top and

bottom surfaces 94 and 96, flat front and back surfaces 98 and 100, an outer end surface 102

and an inner end surface 104. The top and bottom surfaces 94 and 96, front and back surfaces

98 and 100 and outer end surface 102 are identical to the corresponding surfaces of one-half of

the body 62 of the beam divider 40. The body piece 92 has flat top and bottom surfaces 106

and 108, flat front and back surfaces 110 and 112, an outer end surface 114 and an inner end

surface 116. The top and bottom surfaces 106 and 108, front and back surfaces 110 and 112

and outer end surface 114, are identical to the corresponding surfaces of the other half of the

body 62 of the beam divider 40. The inner end surfaces 104 and 116 of the body portions 84

and 86 are at an angle with respect to the front and back surfaces such that when the two body portions 84 and 86 are placed together with the inner end surfaces 104 and 116 contacting each

other, the front surfaces 98 and 110 of the body portions 84 and 86 are at the desired angle.

Likewise the back surfaces 100 and 112 are at the desired angle with respect to each other. A

top plate 118 is placed on the aligned top surfaces 94 and 106 of the body pieces 90 and 92, and

a bottom plate 120 is placed on he aligned bottom surfaces 96 and 108 of the body pieces 90

and 92. The top and bottom plates 118 and 120 are secured to the body pieces 90 and 92 with a

suitable cement 122 between the top and bottom plates 118 and 120 and the top surfaces 94 and

106 and the bottom surface 96 and 108 of the body pieces 90 and 92. Thus, the two body

pieces 90 and 92 are firmly secured together with the front surfaces 98 and 110 being at the proper angle with respect to each other. By forming the body of two separate pieces, all of surfaces of the two body pieces can be easily formed flat and at the proper angle by suitable grinding. Thus, when the body pieces

are secured together, the front surfaces will be at the proper angle with respect to each other and

the junction of the front surfaces will form a sharp corner. Since the body pieces are secured

together only by cement between the top and bottom plates and the top and bottom surfaces of

the body pieces, there is no cement between the inner end surfaces of the body pieces which

interferes with the sharpness of the corner between the front surfaces. If desired, a groove may

be formed in the inner surface of one of the top and bottom plates in which the body pieces fit.

This will hold the body pieces in place which the parts are cemented together.

Thus, there is provided by the present invention an apparatus for measuring the velocity

of a droplet of a liquid or a particle. The apparatus includes a laser for generating a beam of

light and projecting the beam along a path. The beam is formed into the shape of a thin sheet.

The beam is then divided into two separate beams which are guided along separate and parallel

paths to a photodetector which generates an electrical signal based on the intensity of the beam

received. The beams may be directed into separate photodetectors or into a single photodetector. Means is provided along the path of one of the beams for generating the droplet

of the liquid and projecting the droplet through the beams in succession. When the droplet

passes through each of the beams it disrupts the beam so as to vary the signal provided by the

photodetector receiving the beam. Thus, the photodetector or photodetectors provide two

separate signals as different times. By measuring the time interval between the two signals and

the distance between the two parallel beams, the velocity of the droplet can be determined. The present invention also provides a beam divider which will divide a beam into two or more portions and eject the beams along separate and parallel paths.

Claims

What is claimed is:

1. An apparatus for measuring the velocity and profile of a droplet of liquid

comprising:

means for generating a beam of light and directing the beam along a first path;

means along said first path for dividing the beam into two separate beams which extend

along second and third paths;

means for projecting a droplet of a liquid across both the second and third paths so that

the droplet passes through the beams at separate times; and

means for detecting the two beams after the droplet passes therethrough and for

providing an electrical signal corresponding to the beams.

2. The apparatus of claim 1 wherein the means for dividing the beam includes means

for projecting the two beams along second and third paths which lie in the same plane so that

the droplet can be projected along a single path through both of the divided beams.

3. The apparatus of claim 2 wherein the means for dividing the beam comprises an

optical beam divider which divides the beam into two separate beams with one beam being

projected along the second path and the other beam being projected along a different path at an

angle with respect to the second path, and an optical reflector is adapted to reflect the other

beam along the third path.

4. The apparatus of claim 3 including at least one phtotdetector along the second and third paths for receiving the beams and providing electrical signals corresponding to the beams.

5. The apparatus of claim 4 including two photodetectors with one of the phtotodetectors being along the second path and the other photodetector being along the third path.

6. The apparatus of claim 5 in which the means for generating the beam is a laser.

7. The apparatus of claim 6 including means along the first path between the laser and

the beam divider for forming the beam into the shape of a thin sheet.

8. The apparatus of claim 2 wherein the means for dividing the beam into two beams is

a beam divider which projects the two beams along second and third paths which are parallel to

each other.

9. The apparatus of claim 8 including a lens along the second and third paths for

diverting the paths so that they cross each other and the means for projecting the droplet of

liquid is along the beam paths at a point after they cross each other.

10. The apparatus of claim 9 including at least one photodetector along the second and

third paths for receiving the beams and providing electrical signals corresponding to the beams.

11. The apparatus of claim 10 including two photodetectors with one of the

photodetectors being along the second path and the other phtotdetector being along the third

path.

12. The apparatus of claim 11 in which the means for generating the beam is a laser.

13. The apparatus of claim 12 including means along the first path between the laser

and the beam divider for forming the beam into the shape of a thin sheet.

14. The apparatus of claim 8 in which the beam divider comprises a body of an

optically transparent material having at least two flat front surfaces which are at an angle with

respect to each other to form a V, and at lest two back surfaces each of which is spaced from and parallel to a separate first surface, the first surfaces are positioned to face the light beam generating means so as to receive the light beam and divide the beam into at least two beams which flow through the body to the back surfaces, and the back surfaces project the separate

beams ftherefrom along parallel paths.

15 An optical divider comprising:

a body of an optically transparent material having at least tow flat front surfaces and at

least two flat back surfaces;

the front surfaces are at an angle with respect to each other to form a V having a sharp

common line.

16. The beam divider of claim 15 in which the body includes spaced to and bottom

surfaces which extend between the front and back surfaces, and outer end surfaces extending

between the outer ends of each pair of front and back surfaces.

17. The beam divider of claim 16 wherein the body is formed of two portions with each

portion including front and back surfaces, an outer end surface, portions of the top and bottom

surfaces and an inner end surface, the inner end surfaces are angles with respect to the front and

back surfaces so that when the body portions are placed together with the inner end surfaces

contacting each other, the front surfaces of the portions form the desired angle with respect to

each other.

18. The beam divider of claim 17 including a top plate extending across and seated

again the top surfaces of the body portions, a bottom plate extending across and seated against the bottom surfaces of the body portions, and bonding means between each of the top and

bottom plates and the top and bottom surfaces of the body portions to secure the body portions together.