EP0116786B1

EP0116786B1 - Fluid jet print head and stimulator therefor

Info

Publication number: EP0116786B1
Application number: EP19830307925
Authority: EP
Inventors: Hilarion Braun
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1982-12-27
Filing date: 1983-12-22
Publication date: 1989-04-05
Also published as: CA1215577A; DE3379536D1; JPS59150754A; EP0116786A2; EP0116786A3

Description

This invention relates generally to fluid jet printing and, more particularly, to a fluid jet print head and stimulator which are simple in construction and which provide reliable drop breakup.
Jet drop printers are known in which a plurality of streams of drops are produced by a single fluid jet print head. The print head includes a manifold, defining a fluid receiving reservoir, and an orifice plate, defining a plurality of orifices which communicate with said reservoir. As ink is applied under pressure to the fluid receiving reservoir, it flows through the orifices in the orifice plate and emerges from the orifices as continuously flowing fluid filaments. The filaments tens to break up into drops of irregular and unpredictable size and spacing. Such jet drop streams are generally unacceptable for purposes of printing. It is known that to enhance drop formation, mechanical disturbances may be produced in the fluid or the print head structure and coupled to the fluid filaments.
One prior art technique for producing uniform drop breakup is shown in US―A―3,701,476. In this printer, a probe, coupled to an electromechanical transducer, extending into the fluid receiving cavity of the print head,, contacts the interior surface of the orifice plate at one end of the plate. The electromechanical transducer vibrates the probe and the orifice plate is caused to vibrate at the point of probe contact. This, in turn produces bending waves which travel along the length of the orifice plate. The bending waves produce surface vibrations on the fluid filaments which result in drop breakup in the desired manner.
JP-A-56 101869 describes a jet drop printing head having stimulating means comprising a vibrating plate positioned along the back of the head and provided on its back with an electrostriction vibrator. The thickness t of the vibrating plate is determined by t=n λ/2 where n=1, 2 ... etc. and λ is the vibration wavelength of the electrostriction vibrator.
The prior art printers which operate on the basis of travelling wave stimulation of the above type have included relatively complicated piezoelectric, electromechanical transducers in the stimulator structures. Not only are such transducer devices expensive, but they are also somewhat unreliable. Furthermore, the amplitude of the mechanical vibration produced may vary. Accordingly, it is seen that there is a need for a fluid jet print head, and a stimulator therefor, which are simple in construction and reliable in operation and which may provide for vibrational amplitude monitoring.
From one aspect, the present invention consists in a fluid jet print head for producing a plurality of jet drop streams, including manifold means defining a fluid receiving reservoir to which fluid may be applied under pressure, an orifice plate mounted on said manifold means, said orifice plate defining a plurality of orifices which communicate with the fluid receiving reservoir such that fluid from the reservoir flows through the orifices and emerges therefrom as fluid filaments, stimulator means mounted in contact with the orifice plate for vibrating the orifice plate to produce a series of bending waves which travel along the orifice plate and break up the fluid filaments into drops of substantially uniform size and spacing, and driver means for applying an electrical drive signal to stimulator means, characterized in that the stimulator means comprises a stimulator member of a length L which is substantially equal to n A/2, where n is a positive integer and \ is the wavelength of an acoustic wave travelling along the stimulator member, A being equal to (Y/pP^/2/f, where Y is Young's modulus, p is the density of the stimulator member, and f is the frequency of acoustic waves generated in the stimulator member, a pair of piezoelectric crystals mounted on opposite sides of the stimulator member, said piezoelectric crystals being of a length which is less than or equal to 1/2 X for alternately compressing and extending in a direction parallel to the axis of elongation of the stimulator member when driven by the electrical drive signal supplied by the driver means so as to produce acoustic waves in the stimulator member, and mounting means for supporting the stimulator member at a nodel plane therealong.
From another aspect, the invention consists in a stimulator for mechanically vibrating a structure, including transducer means for producing acoustic waves in response to an A.C. drive signal, and driver means for applying an A.C. drive signal at a frequency f to the transducer means, whereby acoustic waves travel along the stimulator and are transmitted to the structure for producing mechanical vibration thereof, characterized in that the stimulator comprises an elongated stimulator member having a length substantially equal to an integer half wavelength of acoustic waves of said frequency in the stimulator member, the transducer means comprises a pair of piezoelectric transducers bonded to opposite sides of the stimulator member for alternately compressing and extending a portion of the stimulator in response to the A.C. drive signal, thereby producing acoustic waves in the stimulator member which travel parallel to the axis of elongation thereof, each transducer extending substantially an equal distance parallel to the axis of elongation of the stimulator member in opposite directions from a nodal plane and being configured for compression and extension along said direction of extent, and mounting means for supporting the stimulator member at a nodal plane.
The length of the stimulator member may be such that n is greater than or equal to 2. The stimulator means or stimulator may contact the orifice plate inside the manifold means, entering the manifold means through an opening including a seal. This seal may contact the stimulator member at a nodal plane therealong.
The stimulator member may be of a length equal to 1/2 X. The stimulator may further include a pin, mounted on the end of the stimulator member, in direct contact with the orifice plate. The pin has a cross-sectional area, taken in a plane perpendicular to the axis of elongation of the member, which is substantially less than the cross-sectional area of the member taken in a parallel plane.
The stimulator may further comprise a feedback transducer means which is mounted at the end of the stimulator member opposite the end which contacts the orifice plate, and which provides an electrical signal proportional in frequency and amplitude to the frequency and amplitude of the acoustic waves passing through the stimulator member.
The stimulator member may be tapered towards the end thereof which contacts the orifice plate such that the member contacts the orifice plate substantially at a point.
In order that the invention may be more readily understood, reference will now be made to the accompanying drawings in which:

Fig. 1 is a perspective view of a first embodiment of the print head and stimulator of the present invention, with portions broken away to reveal interior structure;
Fig. 2 is a sectional view of the stimulator of Fig. 1, taken through the center of the stimulator in a plane parallel to the axis of elongation thereof;
Fig. 3 is a sectional view taken generally along line 3-3 in Fig. 2; and
Fig. 4-is an enlarged perspective view of a second embodiment of the present invention, -with portions broken away and in section.

Figs. 1, 2 and 3 illustrate a fluid jet print head and stimulator therefor constructed according to a first embodiment of the present invention. The print head includes a manifold means consisting of an upper manifold element 10, a lower manifold element 12, and a gasket 14 therebetween. the manifold means defines a fluid receiving reservoir 16 to which fluid may be applied under pressure via fluid inlet tube 18. Fluid may be removed from reservoir 16 through oulet tube 20 during cleaning operations or prior to extended periods of print head shutdown.
An orifice plate 22 is mounted on the manifold means. The plate is formed of a metal material and is relatively thin so as to be somewhat flexible. Orifice plate 22 is bonded to the manifold element 12, as for example by solder or by an adhesive, such that it closes and defines one wall of the reservoir 16. Orifice plate 22 defines a plurality of orifices 24 which are arranged in at least one row and which communicate with the reservoir 16 such that fluid in the reservoir 16 flows through the orifices 24 and emerges therefrom as fluid filaments.
As is known, the fluid filaments, left to naturally occurring random stimulating disturbances, will tend to break up into drops of non-uniform size and spacing. In order to improve the uniformity of breakup, a stimulator means 26 mounted in contact with the orifice plate 22 vibrates the orifice plate to produce a series of bending waves which travel along the orifice plate 22 in a direction generally parallel to the row of orifices.
The stimulator means 26 includes a stimulator member 28, configured as a thin metal rod. The type of metal for the stimulator member 28 is selected to be compatible with the fluid supplied to reservoir 16. The stimulator member 28 is of a length L which is substantially equal to nN2, where n is a positive integer and λ is the wavelength of an acoustic wave travelling along the stimulator member 28. As is known, the wavelength of such a wave, travelling along a thin rod, is substantially equal to (Y/p)"2/f, where Y is Young's modulus, p is the density of the stimulator member material, and f is the frequency of acoustic waves generated in the member.
The end 30 of member 28 is tapered so that the member 28 contacts the orifice plate 22 substantially at a point. As is known, such point contact on the center line of the orifice plate 22 insures that bending waves of a first order are generated in the orifice plate 22, and that satisfactory stimulation is obtained.
The stimulator means 26 further includes piezoelectric crystal means, comprising piezoelectric crystals 32 and 34, which are mounted on the stimulator member 28. The crystals 32 and 34 each include a thin, electrically conductive layer on their outer surfaces to which conductors 36 and 38 are electrically connected. The inner surfaces of the crystals are in contact with and are grounded by the member 28. Member 28, in turn, may be grounded through orifice plate 22 or through ground conductor 42. The crystals 32 and 34 are configured such that they tend to compress or extend in a direction parallel to the axis of elongation of the member 28 when a fluctuating electrical potential is placed across the crystals. As a consequence, when an A.C. electrical drive signal is applied to lines 36 and 38 by driver circuit means 40, the crystals 32 and 34 produce acoustic waves in the stimulator member 28. The circuit 40 supplies an electrical drive signal at a frequency f, as specified above in relation to the length of the member 28.
In the embodiment illustrated in Figs. 1-3, the stimulator member is substantially equal in length to one wavelength, that is, n is equal to 2. The member 28 extends into the manifold means through an opening 44 defined by element 10. The member 28 contacts the orifice plate 22 inside the reservoir 16. A seal, such as 0-ring 46 surrounds the member 28, contacting the member 28 and element 10.
The stimulator means is mounted by tapered pins 48 which engage generally conical detents 50 in the sides of member 28. The pins and detents 50 provide a pivotal mounting which restricts movement of member 28 vertical. As may be noted, the detents 50 are positioned 1/4λ from the upper end of the member 28, as seen in Fig. 2, while the O-ring 46 contacts the member 28 substantially 1/4 λ from the lower end of member 28. It will be appreciated that since crystals 32 and 34 extend above and below the detents 50 by substantially equal distances, pins 48 support the stimulator means in a nodal plane. Since the ring 46 contacts the member 28 1/2 λ below the pins 48, O-ring 46 also contacts the member 28 at a nodal plane. Thus substantial damping between the member 28 and the ring 46 does not occur. Additionally, the end of 30 of the member 28 is 1/4 A below a nodal plane and therefor at an anti-node, producing maximum amplitude mechanical stimulation for generation of the bending waves in the orifice plate 22. It will be understood that it is desirable to limit the length L_a of the crystals 32 and 34 to 1/2λ or less. If the length of the crystals is greater than this, their vibratory motion will tend to counteract formation of standing waves in the member 28 and the production of nodal planes.
It will be appreciated that member 28 could be substantially longer than illustrated. The length of the member can be increased in multiples of 1/2 wavelength with predictable harmonic progressions. In any event, however, it is desirable that the mounting for the member 28 be at a nodal plane and that sealing also occur at a nodal plane so that vibrational energy is not lost through the sealing or the mounting structures and that the member 28 contacts the orifice plate 22 at an anti-node.
An additional pair of piezoelectric crystals 52 may also be mounted on the member 28. Crystals 52 acts as sensors and provide an electrical feedback signal on line 54 which is proportional in frequency and amplitude to the frequency and amplitude of the acoustic waves travelling through the member 28. The feedback signal on line 54 may be used by the driver circuit 40 to control the frequency and amplitude of the drive signal applied on lines 36 and 38.
Fig. 4 illustrates a second embodiment of the present invention in which the elements corresponding to those in the first embodiment have been designated by the same numerals as those used in Figs. 1-3. The stimulator member 28 of Fig. 4, rectangular in cross-section, is substantially 1/2 wavelength long, that is, L equals 1/2 X. Piezoelectric crystals 32 and 34 (not shown) are mounted on-opposing faces of the member 28.
A vibration transmission pin 56 is mounted on one end of the member and is preferably pressed into a hole in the end of the member or is machined on the end of the member. The pin 56 directly transmits the movement of the lower end of the member 28 to the orifice plate 22. The pin 56 has a cross-sectional area, taken in a plane substantially perpendicular to the direction of the elongation of member 28, which is substantially less than the cross-sectional area of the member. Thus, the acoustic waves in the member 28 do not pass through pin 56, but rather are reflected back toward the nodal plane which passes through pins -48. The length of pin 56 is not related to the frequency of operation of the stimulator means, since the pin acts merely as a means of transmitting the vibrations from the anti-node at the end of member 28 to the plate 22. The pin 56 passes through opening 44 and is engaged by a small diameter 0-ring 58 which prevents leakage of fluid from reservoir 16. Preferably, an automatic gain control in the driver circuit allows the stimulation amplitude to be held constant, regardless of the degree of damping provided by 0-ring 58.
A single piezoelectric transducer 60 is mounted on a side of the member 28 other than the sides upon which the piezoelectric transducers 32 and 34 are mounted. Transducer 60 provides a feedback signal on line 54 which may be used by a driver circuit to control operation of the stimulator.

Claims

1. A fluid jet print head for producing a plurality of jet drop streams, including manifold means (10, 12) defining a fluid receiving reservoir (16) to which fluid may be applied under pressure, an orifice plate (22) mounted on said manifold means, said orifice plate defining a plurality of orifices (24) which communicate with the fluid receiving reservoir such that fluid from the reservoir flows through the orifices and emerges therefrom as fluid filaments, stimulator means (26) mounted in contact with the orifice plate for vibrating the orifice plate to produce a series of bending waves which travel along the orifice plate and break up the fluid filaments into drops of substantially uniform size and spacing, and driver means (40) for applying an electrical drive signal to the stimulator means, characterized in that the stimulator means comprises:

a stimulator member (28) of a length L which is substantially equal to nλ/2, where n is a positive integer and is the wavelength of an acoustic wave travelling along the stimulator member, A being equal to (Y/p)^1/2/f, where Y is Young's molulus, p is the density of the stimulator member, and f is the frequency of acoustic waves generated in the stimulator member,

a pair of piezoelectric crystals (32, 34) mounted on opposite sides of the stimulator member, said piezoelectric crystals being of a length which is less than or equal to 1/2 \ for alternately compressing and extending in a direction parallel to the axis of elongation of the stimulator member when driven by the electrical drive signal supplied by the driver means (40) so as to produce acoustic waves in the stimulator member, and

mounting means (48) for supporting the stimulator member at a nodal plane therealong.

2. A fluid jet print head as claimed in claim 1, characterized in that n is greater than or equal to 2, and in that the stimulator means (26) contacts the orifice plate (22) inside the manifold means, said stimulator means entering the manifold means through an opening (44) including a seal (46, 58) which contacts the stimulator means substantially at a nodal plane therealong.

3. A fluid jet print head as claimed in claim 1, characterized in that n equals 1, and in that the stimulator means (26) includes a pin (56) mounted on the end of the stimulator member (28) in direct contact with the orifice plate (22).

4. A print head as claimed in claim 3, characterized in that the pin (56) has a cross-sectional area, taken in a plane perpendicular to the axis of elongation of the stimulator member (28), which is substantially less than the cross-sectional area of said member taken in a parallel plane.

5. A fluid jet print head as claimed in any one of the preceding claims, characterized in that the stimulator means (26) includes feedback transducer means (52, 60) mounted at the end of the stimulator member (28) opposite the end adjacent the orifice plate (22), said feedback sensor means providing an electrical signal proportional in frequency and amplitude to the frequency and amplitude of the acoustic waves passing through the stimulator member.

6. A fluid jet print head as claimed in claim 1 or 2, characterized in that the stimulator member (28) is tapered towards an end (30) thereof which contacts the orifice plate (22) such that the stimulator member contacts the orifice plate substantially at a point.

7. A stimulator for mechanically vibrating a structure (22), including transducer means (32, 34) for producing acoustic waves in response to an A.C. drive signal, and driver means (40) for applying an A.C. drive signal at a frequency f to the transducer means, whereby acoustic waves travel along the stimulator and are transmitted to the structure for producing mechanical vibration thereof, characterised in that the stimulator comprises:

an elongated stimulator member (28) having a length substantially equal to an integer half wavelength of acoustic waves of said frequency in the stimulator member,

said transducer means comprises a pair of piezoelectric transducers (32, 34) bonded to opposite sides of the stimulator member (28) for alternately compressing and extending a portion of the stimulator member in response to the A.C. drive signal, thereby producing acoustic waves in the stimulator member which travel parallel to the axis of elongation thereof, each transducer extending substantially an equal distance parallel to the axis of elongation of the stimulator member in opposite directions from a nodal plane and being configured for compression and extension along said direction of extent, and

mounting means (48) for supporting the stimulator member at a nodal plane.

8. A stimulator as claimed in claim 7, characterized in that the nodal plane from which the pair of piezoelectric transducers (32, 34) extend in opposite directions is the same nodal plane at which the mounting means (48) supports the stimulator member (28).

9. A stimulator as claimed in claim 7 or 8, characterized in that the transducers (32, 34) extend a distance less than A/4 in opposite directions from the nodal plane.

10. A stimulator as claimed in claim 7, 8 or 9, characterized in that the stimulator member (28) is one wavelength in length.

11. A stimulator as claimed in claim 7, 8, 9 or 10, characterized in that the end (30) of the stimulator member (28) opposite the transducers (32, 34) is tapered to provide for contacting the structure (22) substantially at a point.

12. A stimulator as claimed in claim 7, 8 or 9, characterized in that the stimulator member (28) is one-half wavelength in length.

13. A stimulator as claimed in claim 7, 8, 9 or 12, characterized in that the stimulator member (28) is of a generally rectangular shape in section, taken in a plane perpendicular to the axis of elongation of said member.

14. A stimulator as claimed in claim 13, characterized by a vibration transmission pin (56) mounted on one end of the stimulator member (28) for directly transmitting the movement of said one end of the stimulator member to the structure (22) to be vibrated.

15. A stimulator as claimed in claim 14, characterized in that the pin (50) has a cross-sectional area, taken in a plane substantially perpendicular to the direction of elongation of the stimulator member (28), which is substantially less than the cross-sectional area of said member taken in a parallel plane.

16. A stimulator as claimed in claim 13,14 or 15, characterized by sensor means (60) mounted on a side of the stimulator member (28) other than the sides upon which the piezoelectric transducers (32, 34) are mounted, for providing an electrical feedback signal in response to vibration of the stimulator member.

17. A stimulator as claimed in any one of claims 7 to 15, characterized by sensor means (52, 60) mounted on a side of the stimulator member (28) for providing a feedback signal in response to acoustic waves travelling through said member.

18. A stimulator as claimed in any one of claims 7 to 17, characterized in that the mounting means comprises pivot means (48) engaging opposite sides of the stimulator member (28) in the nodal plane for supporting said member without affecting the transmission of acoustic waves therethrough.