EP0976566A1 - Driving arrangement for printhead - Google Patents

Abstract

A piezoelectric actuator (4), separate from the lever assembly (1d) is used. The lever assembly exerts compressive force on the piezoelectric actuator, which is supported on a rigid abutment. An Independent claim is included for use as a transducer, producing a signal from deflection.

Description

This invention relates to a drive arrangement, for example for a Write head comprising a piezoelectrically actuated lever arrangement, to move a writing tip in the direction of a record carrier, when writing on the record carrier. This drive arrangement can also be used in accordance with the invention for a number of others Applications can be used as an actuator and can also be according to the invention can be used as a signal generator.

The printhead, which has at least one nib for printing on one Recording medium includes, can be used for example to apply ink to a recording medium such as paper, wherein the records of alphanumeric text and / or measured values represent. Multiple writing tips can be used to Print inks of different colors. However, it is not essential Use ink because records are also thermal or by Printed on a suitably sensitive record carrier can be. The recordings on the record carrier can either discontinuously, e.g. B. points, or continuously, e.g. B. be a line. The records can also be traces of that too Protocol or measurement purposes should be included.

A write head of the type mentioned is, for example, from the DE-OS-38 32 564 known. This movement of the nibs against you There, recording media is carried out via a lever arm that prevents movement a piezooelectric actuator follows. This actuator includes one Arm, this in the form of a bending piezoelectric Vibration element (in the manner of a flexible tongue) is realized that is made of a sintered ceramic material. The vibration element has a longitudinal dimension that is much larger than its cross section is so that it is elastically deformable. One end of the tongue is on attached to the body of the printhead so that when the piezoelectric Vibrating element is excited by a suitable control signal that free end of the tongue extending in a direction perpendicular to its longitudinal axis emotional. The free end of the tongue is connected to the lever arm that can rotate around an axis to a certain extent. At the Applying the control signal to the vibration element moves it end engaging on the lever arm, the lever arm swings around its end Pivot point and drives the writing tip with its forked free end on. This becomes the one with reference to the record carrier leading roller raised and lowered, causing periodic ink which fed from a reservoir via a feed tube to the writing tip is brought from this onto the record carrier.

The structure according to DE-OS-38 32 564 only achieves a small translation over the lever arm. The expansion of the piezoelectric vibrating elements is essentially for the amplitude of the movement of the Responsible for writing tip, i.e. this amplitude depends on the Movement of the piezoelectric arm itself.

It is a problem with this known arrangement that a frequent and rapid reciprocation of the piezoelectric vibrating elements, which itself form part of the lever arrangement, fatigue which is exacerbated by the fact that their cross-section is very small compared to its longitudinal dimension. Therefore break the piezoelectric vibrating elements easily and frequently.

This leads to complete or partial destruction of the print head, and the printer cannot be used until the damage is repaired is. In addition, these are tongue-like piezoelectric vibrating elements relatively expensive because they are made in relatively small numbers and this makes the print head more expensive.

The reset of the piezoelectric tongue is also problematic is accomplished by an applied voltage. Will the power supply switched off or if a fault occurs, the flexible tongue moves a position closer to the record carrier, which will happen can that the writing tip contacts the record carrier and Ink runs up, which leads to contamination.

The object of the present invention is a drive arrangement of the to implement inexpensive and reliable type mentioned above while ensuring a long service life, preferably the drive arrangement is automatically mechanically reset should. The drive arrangement should also be generally suitable as an actuator be and can serve in reverse as a signal generator.

According to the invention, one of the lever arrangement is used to achieve this object separate piezoelectric actuator used, the Lever arrangement a compressive force on the piezoelectric Actuator exercises.

In other words, a drive arrangement according to the invention provided type, which is characterized in that the piezoelectric actuator is arranged in a yoke that the yoke a compressive force on the piezoelectric by spring action Actuator exercises and as a gearbox or as part of a gearbox is designed, the input side with electrical control of the piezoelectric actuator whose change in length occurs follows as an input movement and a multiple on the output side has greater movement amplitude.

The invention enables the use of conventional piezoelectric Elements for the actuator, making the fragile and expensive, tongue-like Piezoelectric ceramic actuator according to the prior art can be avoided. It is intended that the expression "Piezoelectric Actuator (or PZ Actuator)" the application of one piezoelectric element or of several piezoelectric elements covers.

In the present invention, the PZ actuator preferably comprises one Pieces of piezoelectric elements, for example in the form of disks or plates, stacked side by side along an axis are perpendicular to the aligned parallel sides of the elements runs. Because each piezoelectric element expands slightly, when a drive voltage is applied, the individual add up Extents of each PZ element along the axis, causing resulting in a larger amplitude movement. This movement, which can be 5µ, for example, is then via the transmission gear further enlarged, for example about 400 times, which makes taking into account any deformations that occur, an amplitude of movement and tolerances of about 1.5 mm can be achieved, which leads to Actuation of the writing tip is sufficient. Because the lever arrangement advantageously a compressive force on the PZ actuator, e.g. B. exercises on the stack of PZ elements, this results in a more robust and more stable arrangement for the same amount of movement as the arrangement known from DE-OS-38 32 564, while conventional (e.g. commercially available) PZ elements can be used. It is therefore the same effective but less expensive and more durable than the arrangement according to the state of the art.

It is particularly favorable that the forces caused by the expansion of the piezoelectric Elements arise, do not have an external effect, i.e. so to speak internally received in the yoke or frame, if necessary, by the transmission gear and therefore not on the housing of the print head or the swivel axes and guides contained therein act. Both compact dimensions of the write head according to the invention provides this Compared to the prior art is a significant advantage because also relatively small unbalanced forces for deformation and misconduct of the print head.

In addition, the application leads to the piezoelectric elements compressive force favorably to a mechanically defined one Reset position of the actuator and therefore the writing tip.

The PZ actuator (e.g. a stack of PZ elements) is preferably between a movable part of the lever arm and a fixed part of the Arrangement compressed. For example, it can be between a section a lever arm and a carrier attached to the write head to be appropriate. It is preferably in a U-shaped yoke or closed Compressed frame that expands when the PZ actuator is excited. In one embodiment of the invention a U- or C-shaped yoke that has an integral flexible section has (which acts like a hinge or joint), the PZ actuator is elastic, so that the yoke expands slightly when the PZ element or the PZ elements are excited. The yoke returns to its starting position back when the excitement stops. The PZ actuator can by a releasable means of adjusting the compressive force, for example a wedge in which the yoke is attached.

To increase the movement of the PZ actuator, the yoke can be one Have leg that over the flexible portion on the rigid rest of the Yokes is articulated and works as a lever arrangement.

This lever arrangement is designed to itself a mechanical gear ratio to generate, so that the of the PZ actuator (e.g. on an input section of a lever arm) generates significantly larger movement at its exit section. This can easily and advantageously be achieved in embodiments of the invention become.

As stated above, the leg is over the flexible section hinged to the rest of the yoke, so that the flexible section a Forms pivot axis. If the distance between the point of attack of the piezoelectric actuator on the mentioned leg and the pivot axis is smaller than the distance between the free end of the leg and the swivel axis, there is a mechanical enlargement of the movement of the piezoelectric actuator at the free end of the leg. In other words, in a first preferred embodiment the invention, a U- or C-shaped frame, the PZ actuator, and a movable leg of the yoke swivels with respect to the Rest of the yoke. The leverage is preferably such that the Movement of the PZ actuator or the PZ elements from the movable one Leg of the frame is enlarged. This lever arrangement thus forms a first stage of a multi-stage transmission gear.

However, other translation levels can be used in addition or instead used to control the movement of the PZ actuator or the PZ elements to enlarge and thus the required amplitude of movement to provide the writing tip.

A drive arrangement according to claim 6, according to which is particularly preferred the transmission gear or the second gear stage of the transmission gear is realized as a sliding gear. This arrangement draws is particularly characterized in that the sliding gear from two elongated Limbs, with the first limb at one end of the called leg of the yoke is operated, the second link on his one end is held by another part of the yoke and the two Links are attached together at their other ends. With one Sliding gear can even, depending on the aspect ratio of the both preferably designed as a leaf spring, very large Translations are realized, but with limited overall amplitudes, but for a print head of the type mentioned Kind enough.

This variant will be the first embodiment of the invention thus elastic components or strips, i.e. the trained as leaf springs Limbs used to move the movable leg transfer to a distant point where the transferred motion is used either directly or indirectly. The free ends of the elastic Components or strips are together at the distant point attached. By attaching the other ends of the strips to the yoke, i.e. on the movable leg or on a rigid part of the yoke, a differential movement occurs when the movable legs move of the strip and is translated into a movement of the far ends, whose amplitude is a multiple of that of the free end of the movable Thighs.

In general, it should be noted that when using a stack of PZ elements is, these can be kept suitable by a carrier. It an adjustment means can be provided on the carrier to adjust the adjust the PZ elements applied compression forces. It can for example a wedge between the PZ elements and one side of the Carrier can be used to attach them and / or a preload to provide. Alternatively, one engaged in the carrier Screw to secure a stack of PZ elements and / or preload.

Fig. 1

eine Perspektivansicht einer Antriebsanordnug, die bei einer bevorzugten Ausführungsform der Erfindung verwendet wird,

Fig. 2

eine Perspektivansicht der Antriebsanordnung von Fig. 1, die in einer Schreibkopfunterbaugruppe eingebaut ist,

Fig. 3

eine schematische perspektivische Darstellung des Schreibkopfs der Figur 2 zu einem größeren Maßstab, und

Fig. 4

eine Seitenansicht des Schreibkopfs der Figur 3 mit Schreibspitze und Führungswalze für den Aufzeichnungsträger.

The invention is described in more detail below by way of example with reference to the drawing, in which:

Fig. 1

2 shows a perspective view of a drive arrangement used in a preferred embodiment of the invention,

Fig. 2

1 is a perspective view of the drive assembly of FIG. 1 installed in a printhead subassembly;

Fig. 3

a schematic perspective view of the write head of Figure 2 to a larger scale, and

Fig. 4

a side view of the write head of Figure 3 with writing tip and guide roller for the record carrier.

Fig. 1 shows a drive arrangement for a write head according to one preferred embodiment of the invention. A generally C-shaped Yoke 1 has rigid sections 1a, 1b and 1c (which normally are stationary) and a movable leg ld on the lower stationary section lc through a flexible section le with thinner Cross section is connected. The flexible section le acts as one - piece joint, whereby the leg ld swivels (around the Joint le) can move with respect to the fixed lower section 1c. The movable leg 1d has a projection or cam 2 which is shown in contact with a wedge 3. A stack of PZ elements 4 is held in the frame and by the between one side of the PZ stack 4 and the protrusion or cam 2 constrained wedge 3 attached and preloaded. The inner tension of the pre-stressed yoke exerts a compressive force on the stack of piezoelectric elements 4 out. When the stack of PZ elements 4 is excited, they expand each one and exert a compound force between the fixed Side portion 1b of the frame and the wedge 3. This practices one Force on the cam 2, which causes the movable leg ld pivots around the joint, i.e. while increasing the spring tension of the Yokes. If the excitation of the PZ elements is reduced or stops, they contract and the movable leg 1d returns due to the elasticity of the flexible portion le in a starting position back. When a pulsating signal is used to the PZ stack 4, the movable leg 1d of the yoke 1 becomes the joint will oscillate or swing. This oscillating or vibrating Movement is increased by the leverage of the leg ld and translated to the nib as translated below is explained. The leg 1d forms a first step of translation here three-stage transmission gear.

The yoke 1 carries two flexible strips or leaf springs 5, 6, for example can be made of spring steel and form a sliding gear. The upper strip 5 is at one end 5a on the upper part of the movable Arms 1d attached. It is at the other end 5b at the free End 6b of the lower strip 6 attached. (The attached ends 5b, 6b swing in a vertical direction as described below). The other end 6a of the strip 6 is on a shoulder section 7 the upper part of the fixed frame portion la and can to be attached to section la des yokes. This shoulder 7 acts as one Stop to prevent the end 6a of the strip from moving of the leg 1d is moved.

When a pulsating signal is applied to the PZ elements 4, the movable leg 1d oscillates or oscillates, causing the upper strip 5 extends in the horizontal direction (i.e. parallel to it Longitudinal axis) back and then moved forward. The distal end 5b of the Strip 5 is connected to the distal end 6b of the lower strip 6, however, the near end 6a of the strip 6 is firmly on the shoulder 7 or at section la, and the result is a pulling, pushing and bending action of strips 5 and 6, which causes the connected ends 5b and 6b in the vertical direction first move up and then down. When interpreting with approximately Ratios shown in Figs. 1 and 2 can translate from about 20: 1 can be easily achieved by the sliding gear and can easily be enlarged by extending the leaf springs 5 and 6 become. This means that a pivoting movement of the leg 1d around the hinge le to a horizontal movement in FIG. 1 of the free end of the leg 1d with an amplitude A, via the sliding gear vertical movement of the fastened ends 5b and 6b the sliding gear with an amplitude of 20 A leads the sliding gear thus forms a second translation stage, the input (the end 5a of the leaf spring 5) with the output (the free end of the leg 1d) the first translation stage is coupled.

The vertical movement or vibration of the fastened ends 5b, 6b, i.e. the output of those formed by the sliding gear second gear ratio, is by a clutch 8 (the one forked Section 8a and an eye section 8b) to another Transfer lever assembly 11 as shown in Fig. 2.

2 shows a subassembly 10 of a write head (which is not is shown in all details), which comprises a support portion 9 in which several yokes 1 can be accommodated, of which only one in Fig. 2 is shown. The lever assembly 11 includes a short arm 11a and a long arm 11b on respective sides of a pivot (or an axis of rotation) 12. This increases the oscillating movement of the ends 5b, 6b of strips 5, 6, causing the distal end 14 of the longer arm section 11b over a greater distance in the vertical direction swings.

This further lever arrangement 11 forms a third gear ratio, here with a ratio of 8: 1. The exit end of the sliding gear, i.e. the mutually attached ends 5b, 6b of the leaf spring 5 and 6 are thus in with the input end of the third translation stage Form of the lever 11 connected. The forked end 14 of the lever 11 drives a writing tip 16 directly, for example in the same way as described in the document DE OS 38 32 564 mentioned at the outset.

In a practical example of the arrangement shown in FIGS. 1 and 2 was the stack of PZ elements with about 10-50% of it Preloaded.

If you go for the first translation stage in the form of leg 1d Gear ratio of 2.5: 1, for the second gear ratio in Form of the sliding gear 5, 6 a gear ratio of 20: 1 and a gear ratio of 8: 1 is used for the third gear ratio, this results in an overall translation of the three-stage transmission gear of 2.5 x 20 x 8: 1 = 400: 1, resulting in one stack of five piezo elements with a total expansion of 5 µ Movement at the exit end of the third translation stage, i.e. at the Writing tip of 400 x 5 µ = 2 mm, can be expected.

The drive arrangement shown in Fig. 1 has various advantages the arrangement disclosed in DE-OS-38 32 564. For example the yoke 1 holds the stack of PZ elements 4 securely. The PZ elements 4 can consist of a conventionally readily available variety, which is far less fragile and expensive than the ceramic type PZ actuator, which is used in DE-OS-38 32 564. The Yoke 1 has a simple but firm structure, and the PZ elements 4 can be easily attached or removed in the frame by simply remove the wedge 3 and reset it. This makes it easier maintenance apart from being more robust. The frame 1 points its own, one-piece, flexible hinge le on that the need for separate springs. The movable leg 1d of the frame 1 has a simple shape (with the projection or cam 2), however it creates a first degree of enlargement of the movement of the PZ elements 4. A second stage of enlargement is through the elastic strips 5, 6 created. These can simply be made from spring steel and are therefore solid, reliable and less expensive (than the ceramic PZ actuator DE-OS-38 32 564). 1 can can also be easily accommodated in a carrier 9 with a simple structure, which makes maintenance easier.

There are no significant forces acting within the yoke, outward. Only the forces needed to make the writing tip must be operated from the housing or from parts outside the actuator be included.

As shown in FIG. 3, the carrier 9 can, for example, five more Drive assemblies l carry side by side around a nib assembly to drive in the write head 15. The write head 15 is attached its left end in Fig. 3, a circuit board 17, which the drive voltages available for the piezoelectric elements 4 poses. The write head is along the guide shaft 18 in the direction the double arrows P are movable. The angular orientation of the print head 15 is ensured by a further guide shaft 19 by a part 20 is partially encompassed, as shown in Fig. 4.

Figure 4 also shows how the forked end 14 of the lever 11 Writing tip 21 moved in the direction of the double arrow D, the Pen tip is guided in the vertical direction in the head 21a and with a Ink cartridge communicates, which is not shown, but in the shot 21b can be inserted (one cartridge per writing tip 21). The roller 21c, which guides the record carrier, can also be seen in FIG. 4.

The writing tip 21 is closed toward the roller 21c by the operation of the piezoelectric actuator moves and by the spring tension of the leg 1d reset.

The above description deals with the application of the invention Drive arrangement for a write head. This arrangement can also be used as a general actuator for a wide variety of applications Tasks are used. For example, it can be used as a switch to switch optical fibers for news channels. In a such application, one end of an optical fiber, which is attached to the output end of the sliding gear, either depending after switch position in alignment with two further optical fiber ends be brought to realize a switch function.

The drive arrangement could also act as an actuator for the deflection a mirror can be used, for example in an optical instrument. It would also be quite conceivable to have an optical element like for example a laser diode on the transmission gear on the output side attached and by the corresponding movement of the transmission gear to realize an optical scanning function.

Finally, the drive arrangement in reverse form as a signal generator be used. In such an arrangement, which in the Claims 23 to 27 is described, the previous output page of the transmission gear as the input side of a reduction gear used and the piezoelectric part previously used as an actuator then the signal generation. For example, the end of the sliding gear, where the two elongated links are attached to each other, used to detect movement - think for example the movement of a tool at the end of its journey to work - the electrical output signal of the piezoelectric part being proportional to move up.

Claims (27)

A drive arrangement, for example for a write head, which comprises a piezoelectrically actuated lever arrangement (1d) in order to move a writing tip (21) in the direction of a record carrier when writing on the record carrier,
characterized by
that a piezoelectric actuator (4) separate from the lever arrangement (1d) is used, and that the lever arrangement (1d) exerts a compressive force on the piezoelectric actuator (4) which is supported on a rigid abutment (section 1b). A drive arrangement, for example for a write head, which comprises a piezoelectrically actuated lever arrangement (1d) in order to move a writing tip (21) in the direction of a record carrier when writing on the record carrier,
characterized by
that the piezoelectric actuator (4) is arranged in a yoke (1a, 1b, 1c, 1d), that the yoke exerts a compressive force on the piezoelectric actuator (4) by spring action and as a transmission gear (1d, 5, 6) or. is designed as part of a step-up gear (5, 6) which on the input side, when the piezoelectric actuator (4) is electrically actuated, follows its change in length as an input movement and on the output side has a movement amplitude which is several times greater. Drive arrangement according to claim 2,
characterized by
that the yoke (1a, 1b, 1c, 1d) is at least substantially U-shaped. Drive arrangement according to claim 2 or 3,
characterized by
that the transmission gear (1d, 5, 6) is at least two stages. Drive arrangement according to one of the preceding claims,
characterized by
that the first transmission stage is realized by one leg (1d) of the yoke (1a, 1b, 1c, 1d) which is resiliently attached or articulated at a first end (1e) to the rest of the yoke to generate the compressive force, and acts at its second end at the input (5a) of the second transmission stage (5, 6), the piezoelectric actuator (4) acting on the said leg (1d) at a point whose distance from the first end (le) to achieve the desired transmission of the leg (1d) is smaller than its distance from the second end of the leg (1d). Drive arrangement according to one of the preceding claims,
characterized by
that the transmission gear or the second gear stage of the transmission gear (5, 6) is realized as a sliding gear. Drive arrangement according to claim 6,
characterized by
that the sliding gear (5, 6) consists of two elongated links, the first link (5) being actuated at one end (5a) by said leg (1d) of the yoke (1a, 1b, 1c, 1d), the second Link (6) is held at one end (6a) by a further part (1a, 7) of the yoke (1a, 1b, 1c, 1d) and the two links (5,6) at their other ends (5a, 6a ) are attached to each other. Drive arrangement according to claim 7,
characterized by
that at least the second link (6) and preferably also the first link (5) is designed as a leaf spring. Drive arrangement according to one of the preceding claims,
characterized by
that the sliding gear (5, 6) is coupled at its output end (5b, 6b) to the input end (11a) of a third gear ratio (11). Drive arrangement according to one of the preceding claims,
characterized by
that the translation of the transmission gear (1d, 5, 6) is greater than five and preferably in the range between ten and one thousand. Drive arrangement according to one of the preceding claims, with a two-stage transmission gear, the first stage (1d) a ratio of about 2.5: 1 and the second stage (5, 6) one Ratio of about 20: 1 generated and at a three-stage Transmission gear the third stage (11) a translation of about 8: 1 generated. Drive arrangement according to one of the preceding claims,
characterized by
that the piezoelectric actuator (4) comprises a plurality of piezoelectric elements, preferably in the form of disks or plates, stacked side by side along an axis perpendicular to each of these parallel sides of the elements. Drive arrangement according to one of the preceding claims,
characterized by
that the piezoelectric actuator (4) is compressed between a movable part (1d) and a fixed part (1b) of the lever arrangement. Drive arrangement according to one of the preceding claims,
characterized by
that the lever arrangement for increasing the movement of the piezoelectric actuator (4) has a movable arm section (1d) which rotates about an axis (le), and that the piezoelectric actuator (4) has an input section (2) of the movable arm section (1d) gives a movement so that a larger movement is generated at an output section (5a) of the movable arm section (1d). Drive arrangement according to claim 14,
characterized by
that the distance between the input section (2) and the axis (1e) is shorter than the distance between the output section (5a) and the axis (1e). Drive arrangement according to one of claims 14 or 15,
characterized by
that the lever arm section (1d) is part of a frame (1) for holding the piezoelectric actuator (4). The drive assembly of claim 16, wherein the movable Arm section (1d) pivotable on the frame (1) by an elastic Section (le) is attached, which provides a preload, around the movable arm section (1d) in a starting position attributed. Drive arrangement according to one of the preceding claims,
characterized by
that the lever arrangement comprises a generally U-shaped or C-shaped frame which is set up in such a way that it grips the PZ actuator (4) elastically so that the frame (1) expands when the PZ actuator (4) is excited, causing the movable arm portion (1d) to move. Drive arrangement according to claim 18,
characterized by
that the first and second elongate elastic members (5, 6) are mechanically connected to a movable arm portion (1d) so as to cause them to move differentially, thereby connecting the interconnected end portions (5b, 6b) of the elongate members ( 5, 6) are caused to move. Drive arrangement according to one of the preceding claims,
characterized by
that an adjusting means (3) is provided to adjust the compression forces exerted on the piezo actuator (4). Drive arrangement according to one of the preceding claims in a reverse version, in which the previous output side of the transmission gear now represents the input side and the Piezoelectric part previously referred to as an actuator as a signal generator works and generates a signal, for example Amplitude proportional to the amplitude of the movement at the current one Input side of the transmission gear is or a signal only then releases when the amplitude of the movement at the current input side exceeds a threshold. Print head with at least one writing tip for printing on a record carrier, a carrier for holding the record carrier and one or more drive arrangements any of the preceding claims. Signal generator consisting of a piezoelectric, signal-giving Part that is arranged in a yoke, the yoke a compressive force on the piezoelectric by spring action Exercises part and as a reduction gear, for example is designed as part of a reduction gear, the reduction gear follows a movement on the input side or detects and on the output side the compressive force on the piezoelectric Part changes and thereby generates an electrical signal. A signal generator according to claim 23, wherein the reduction gear is formed at least in two stages. A signal generator according to claim 23 or 24, wherein the or one Reduction step through one leg (1d) of the yoke (1a, 1b, 1c, 1d) is realized, which at a first end (le) with the rest of the yoke to generate the compressive force resiliently attached is articulated and at its second end an input movement follows, achieving the desired reduction said leg (1d) on the piezoelectric part (4) a point whose distance from the first end (1e) of the Leg (1d) is smaller than its distance from the second end of the Thigh (1d). Signal generator according to one of claims 23 to 25, wherein the Reduction gear or a reduction stage of the reduction gear is realized as a sliding gear. Signal generator according to claim 26, wherein the sliding gear (5, 6) consists of two elongated links, the first link (5) one end (5a) of said leg (1d) of the yoke (1a, 1b, 1c, 1d) is attached, the second link (6) at one end (6a) attached to a further part (1a, 7) of the yoke (1a, 1b, 1c, 1d) and the two links (5,6) at their other ends (5a, 6a) are attached to each other and here the input side of the corresponding Form reduction gear.

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