Piezoelectric actuator and optomechanical system comprising such actuator

Abstract

A piezoelectric actuator, comprising a voltage source, a first cantilever (4a) and a second cantilever (4b), said first and second cantilever being arranged along an actuating axis (A1) of said actuator. Each of the first and second cantilever have a fixed end (5a, 5b) and a free end (6a, 6b). A rigid spacer (7) interconnects said first and second cantilever such that the fixed end (5b) of said second cantilever is connected to the free end (6a) of said first cantilever, and such that a voltage generated by said voltage source generates movement of the free end of at least one of said first and second cantilever. An optomechanical system comprises an optical unit and at least one of said piezoelectric actuator.

Description

[0001] PIEZOELECTRIC ACTUATOR AND OPTOMECHANICAL SYSTEM COMPRISING SUCH ACTUATOR

[0002] TECHNICAL FIELD

[0003] The disclosure relates to a piezoelectric actuator comprising a voltage source and a plurality of cantilevers, as well as an optomechanical system comprising said piezoelectric actuator and an optical unit.

[0004] BACKGROUND

[0005] Small optical devices such as smartphone cameras are commonly equipped with autofocus (AF), optical image stabilization systems (OIS), and mechanisms to operate the optical unit of the device in vertical (Z), horizontal (XY) and tilt (XYZ-axis) directions. Some of the essential parameters that need optimizing in such a system are overall size and compactness, power consumption, speed, sensitivity, dynamic tilt, resolution / accuracy, control / driving methods, reliability, ease of manufacturability, and price.

[0006] There have been attempts at using volumetrically shape-changing capacitive solutions, such as piezoelectric actuators, to generate movement of the optical unit. Disadvantages with existing solutions include low mechanical quality, which prevents high-speed application, and the need for external amplification mechanisms, such as lever-based compound mechanisms to increase the actuation range from nano-micrometer level to millimeter level.

[0007] Hence, there is a need for an improved actuator for optomechanical systems, in particular those used in small devices, wherein the improved actuator has a larger actuation range and reduced complexity.

[0008] SUMMARY

[0009] It is an object to provide an improved piezoelectric actuator for electronic apparatuses such as smartphones. The foregoing and other objects are achieved by the features of the independent claims. Further implementation forms are apparent from the dependent claims, the description, and the figures.

[0010] According to a first aspect, there is provided a piezoelectric actuator comprising a voltage source, a first cantilever and a second cantilever, each of the first cantilever and the second cantilever having a fixed end and a free end, the first cantilever and the second cantilever being arranged along an actuating axis of the actuator, and a rigid spacer, the spacer interconnecting the first cantilever and the second cantilever such that the fixed end of the second cantilever is connected to the free end of the first cantilever, and such that a voltage generated by the voltage source generates movement of the free end of at least one of the first cantilever and the second cantilever.

[0011] This solution allows an increased actuation range, compared to existing solutions, without use of separate amplification mechanisms while maintaining a small actuator form factor since the length of the actuator can be reduced up to 40-50 %.

[0012] In a possible implementation form of the first aspect, the free end of the first cantilever and the second cantilever is movable, along the actuating axis, relative to the fixed end of the first cantilever and the second cantilever. This allows individual movement of one cantilever to be amplified by the additional cantilever(s). In a further possible implementation form of the first aspect, the fixed end of the first cantilever is connected to the voltage source, the free end of the first cantilever is electromechanically connected to the fixed end of the second cantilever, facilitating reliable voltage supply that can be transmitted throughout the entire actuator.

[0013] In a further possible implementation form of the first aspect, the piezoelectric actuator comprises at least one further cantilever, a fixed end of the further cantilever being electromechanically connected to the free end of the second cantilever by means of a further spacer, further increasing the actuation range of the actuator.

[0014] In a further possible implementation form of the first aspect, either the free end of the second cantilever or a free end of the further cantilever is configured to be operably connected to a component of the optomechanical system, facilitating reliable operation using the least amount of components.

[0015] In a further possible implementation form of the first aspect, the fixed end of the first cantilever is configured to be rigidly connected to a substrate comprising the voltage source, facilitating a reliable voltage supply unaffected by cantilever movement.

[0016] In a further possible implementation form of the first aspect, the first cantilever, the second cantilever, and the further cantilever extend in parallel when no voltage is generated by the voltage source, and voltage from the voltage source generates bending of the free end of at least one of the first cantilever, the second cantilever, and the further cantilever around a cantilever bending axis extending through the fixed end of the first cantilever, the second cantilever, and the further cantilever and perpendicular to the actuating axis. This solution facilitates a small form factor in combination with a large actuating range.

[0017] In a further possible implementation form of the first aspect, the voltage generates bending movement of at least one of the first cantilever, the second cantilever, and the further cantilever in a first direction such that a stroke of the piezoelectric actuator, along the actuating axis, is reduced, and the voltage generates bending movement of at least one of the first cantilever, the second cantilever, and the further cantilever in a second direction such that the stroke of the piezoelectric actuator is increased. This allows the movement of one cantilever to be amplified by additional cantilevers.

[0018] In a further possible implementation form of the first aspect, the piezoelectric actuator further comprises a flexible printed circuit attached to at least one of the first cantilever, the second cantilever, and the further cantilever, simplifying assembly of the actuator.

[0019] According to a second aspect, there is provided an optomechanical system comprising an optical unit defining an optical axis, the optical unit comprising a lens assembly and a housing accommodating the lens assembly, a substrate comprising an image sensor, at least one piezoelectric actuator according to the above, the piezoelectric actuator being configured to generate movement of the optical unit relative to the substrate.

[0020] The actuation of such an optomechanical system has ultra-fast operation, high force, ultra-low power consumption, and is silent, which facilitates use for key applications such as lens autofocus, module tilt OIS, lens shift OIS, and lens pop-out.

[0021] In a possible implementation form of the second aspect, the optomechanical system comprises a plurality of piezoelectric actuators arranged equidistantly along a periphery of the optical unit, the actuating axis of each piezoelectric actuator extending parallel with the optical axis, each individual piezoelectric actuator being configured to individually engage the optical unit and pivot the optical unit around a pivot axis associated with the individual actuator assembly, each pivot axis extending perpendicular to the optical axis. This allows tilting of the optical unit, in particular of large and heavy units, since each piezoelectric actuator generates vertical movement and, hence, the unit can be tilted from several different coupling points. In a further possible implementation form of the second aspect, the optomechanical system comprises two piezoelectric actuators arranged adjacent a periphery of the optical unit, the actuating axis of one actuator extending perpendicular to the actuating axis of the other actuator and perpendicular to the optical axis. This allows each piezoelectric actuator to generate horizontal movement and shifts the, possibly large and heavy unit, in two directions.

[0022] In a further possible implementation form of the second aspect, the actuating axis of the piezoelectric actuator extends parallel with the optical axis, the piezoelectric actuator being configured to engage the optical unit and generate movement of the optical unit linearly along the optical axis. This solution allows linear movement of, in particular, large and heavy optical units, since the piezoelectric actuator engages the optical unit in a way that limits the movement to one axis.

[0023] According to a third aspect, there is provided an electronic apparatus comprising the optomechanical system according to the above.

[0024] Such a solution allows protruding zoom optics to be used in small electronic apparatuses, ensuring in particular the thickness of the apparatus is kept small.

[0025] These and other aspects will be apparent from the embodiments described below.

[0026] BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In the following detailed portion of the present disclosure, the aspects, embodiments, and implementations will be explained in more detail with reference to the example embodiments shown in the drawings, in which:

[0028] Fig. 1 shows a schematic side view of a part of a piezoelectric actuator in accordance with an example of the embodiments of the disclosure;

[0029] Fig. 2 shows schematic side views of a part of a piezoelectric actuator in accordance with an example of the embodiments of the disclosure;

[0030] Fig. 3 shows perspective views of a part of a piezoelectric actuator in accordance with an example of the embodiments of the disclosure;

[0031] Fig. 4 shows perspective views of an optomechanical system in accordance with an example of the embodiments of the disclosure;

[0032] Fig. 5 shows an exploded view of an optomechanical system in accordance with an example of the embodiments of the disclosure;

[0033] Fig. 6 shows a perspective view of an optomechanical system in accordance with an example of the embodiments of the disclosure;

[0034] Fig. 7 shows an exploded view of an optomechanical system in accordance with an example of the embodiments of the disclosure;

[0035] Fig. 8 shows a top view of an optomechanical system in accordance with an example of the embodiments of the disclosure; Fig. 9 shows a perspective view of an optomechanical system in accordance with an example of the embodiments of the disclosure;

[0036] Fig. 10 shows an exploded view of an optomechanical system in accordance with an example of the embodiments of the disclosure;

[0037] Fig. 11 shows a perspective view of an optomechanical system in accordance with an example of the embodiments of the disclosure;

[0038] Fig. 12 shows a top view of a part of an optomechanical system in accordance with an example of the embodiments of the disclosure;

[0039] Fig. 13 shows a perspective view of an optomechanical system in accordance with an example of the embodiments of the disclosure; and

[0040] Fig. 14 shows an illustration of an electronic apparatus in accordance with an example of the embodiments of the disclosure.

[0041] DETAILED DESCRIPTION

[0042] The present invention relates to a piezoelectric actuator 1 comprising a voltage source 3, a first cantilever 4a and a second cantilever 4b, each of the first cantilever 4a and the second cantilever 4b having a fixed end 5a, 5b and a free end 6a, 6b, the first cantilever 4a and the second cantilever 4b being arranged along an actuating axis Al of the actuator 1 , and a rigid spacer 7, the spacer 7 interconnecting the first cantilever 4a and the second cantilever 4b such that the fixed end 5b of the second cantilever 4b is connected to the free end 6a of the first cantilever 4a, and such that a voltage generated by the voltage source 3 generates movement of the free end 6a, 6b of at least one of the first cantilever 4a and the second cantilever 4b.

[0043] The piezoelectric actuator 1 comprises a voltage source 3, or signal source / voltage source control system, as illustrated in Fig. 3.

[0044] The piezoelectric actuator 1 furthermore comprises a first cantilever 4a and a second cantilever 4b, each of the first cantilever 4a and the second cantilever 4b having a fixed end 5a, 5b and a free end 6a, 6b, as illustrated in Fig. 1. The first cantilever 4a and the second cantilever 4b are arranged along an actuating axis Al of the actuator 1.

[0045] A rigid spacer 7 interconnects the first cantilever 4a and the second cantilever 4b such that the fixed end 5b of the second cantilever 4b is connected to the free end 6a of the first cantilever 4a, and such that a voltage generated by the voltage source 3 generates movement of the free end 6a, 6b of at least one of the first cantilever 4a and the second cantilever 4b. The spacer 7 provides an electrical as well as mechanical connection, i.e. spacer 7 functions as an electrical signal conductor.

[0046] The fixed end 5a of the first cantilever 4a may be configured to be rigidly connected to a substrate 9 comprising the voltage source 3.

[0047] The fixed end 5a of the first cantilever 4a may be connected to the voltage source 3, and the free end 6a of the first cantilever 4a may be electromechanically connected to the fixed end 5b of the second cantilever 4b. As shown in Figs. 2 and 13, the piezoelectric actuator 1 may comprise at least one further cantilever 4c. A fixed end 5c of one further cantilever 4c is electromechanically connected to the free end 6b of the second cantilever 4b by means of a further spacer 7. In embodiments composing more than one further cantilever 4c, the fixed end 5c of each further cantilever 4c is connected to a free end of a further cantilever 4c.

[0048] The free end 6b of the second cantilever 4b may be operably connected to a component of the optomechanical system 2, such as an optical unit 8, as illustrated in Figs. 5, 7, 8, or 10. Optionally, the free end 6c of a further cantilever 6c may be operably connected to a component of the optomechanical system 2 as illustrated in Fig. 13.

[0049] As illustrated in Fig. 1, the free end 6a, 6b of the first cantilever 4a and the second cantilever 4b may be movable, along the actuating axis Al , relative to the fixed end 5a, 5b, of the first cantilever 4a and the second cantilever 4b.

[0050] As illustrated in the middle example of Fig 1 and in Fig. 2b, the first cantilever 4a, the second cantilever 4b, and the further cantilever 4c may extend in parallel, along actuating axis Al, when no voltage is generated by the voltage source 3. In other words, the cantilevers may be stacked or superposed over each other, along actuating axis Al, and arranged such that they extend in parallel when there is no actuation. The first cantilever 4a, the second cantilever 4b, and the further cantilever 4c may also be arranged at angles to each other, or to the actuating axis Al, when no voltage is generated by the voltage source 3 (not shown).

[0051] The voltage from the voltage source 3 may generate bending of the free end 6a, 6b, 6c of at least one of the first cantilever 4a, the second cantilever 4b, and the further cantilever 4c around a cantilever bending axis A2 extending through the fixed end 5a, 5b, 5c of the first cantilever 4a, the second cantilever 4b, and the further cantilever 4c and perpendicular to the actuating axis Al . The free end 6a, 6b, 6c being moveable means the first cantilever 4a, the second cantilever 4b and the further cantilever 4c can bend. The fixed end 5a, 5b, 5c is held in place and does not bend or move relative the spacer 7 which it abuts, however, as the remainder of the first cantilever 4a, the second cantilever 4b and the further cantilever 4c bends, the free end 6a, 6b, 6c moves.

[0052] In other words, the free end 6a of the first cantilever 4a may move, or be bent, around cantilever bending axis A2 of the first cantilever 4a, as illustrated in Figs. 2a and 2c. Correspondingly, the free end 6b of the second cantilever 4b may move, or be bent, around cantilever bending axis A2 of the second cantilever 4b, and the free end 6c of the further cantilevers) 4c may move, or be bent, around cantilever bending axis A2 of the further cantilever 4c, as also illustrated in Figs. 2a and 2c

[0053] The voltage from the voltage source 3 may generate bending movement of the first cantilever 4a, the second cantilever 4b, and / or the further cantilever 4c in a first direction D 1 , such that a stroke of the piezoelectric actuator 1 , along the actuating axis Al, is reduced. This is illustrated in the bottom illustration of Fig. 1 and in Fig. 2c. By bending the first cantilever 4a such that the free end 6a of the first cantilever 4a moves in a first direction D3 along actuating axis Al, the fixed end 5b of the second cantilever 4b is moved in a corresponding manner. This movement of the fixed end 5b of the second cantilever 4b generates corresponding movement of the free end 6b of the second cantilever 4b in a second direction D4 along actuating axis Al . In other words, the angular change between the first cantilever 4a and the second cantilever 4b (or any other adjacent cantilevers) results in amplification of the stroke that the first cantilever 4a and the second cantilever 4b achieve.

[0054] Correspondingly, the voltage from the voltage source 3 may generate bending movement of at least one of the first cantilever 4a, the second cantilever 4b, and the further cantilever 4c in a second direction D2 such that the stroke of the piezoelectric actuator 1 is increased. This is illustrated in the top illustration of Fig. 1 and in Fig. 2c. By bending the first cantilever 4a such that the free end 6a of the first cantilever 4a moves in the second direction D4 along actuating axis Al , the fixed end 5b of the second cantilever 4b is moved in a corresponding manner. This movement of the fixed end 5b of the second cantilever 4b generates corresponding movement of the free end 6b of the second cantilever 4b in the first direction D3 along actuating axis Al.

[0055] The piezoelectric actuator 1 may further comprise a flexible printed circuit 12 attached to at least one of the first cantilever 4a, the second cantilever 4b, and the further cantilever 4c, as illustrated in Fig. 3. The flexible printed circuit 12 may follow the dynamic movement of the cantilever during operation.

[0056] As previously mentioned, the free end 6b of the second cantilever 4b or the free end 6c of a further cantilever may be operably connected to a component of the optomechanical system 2, such as optical unit 8. A flexible spring adapter 15 may be arranged between the coupling point of the cantilever arranged, i.e. the free end 6b, 6c, and optical unit 8. The flexible spring adapter 15 may comprise a flexible metal spring flexure 14. The flexible spring adapter 15 facilitates additional, small displacement that might be required by the activation action, enabling smoother movement and filtering out of the slightly curved movement of the free end.

[0057] The present invention also relates to an optomechanical system 2 comprising at least one of the above-described piezoelectric actuator 1 , an optical unit 8, and a substrate 9, the piezoelectric actuator 1 being configured to generate movement of the optical unit 8 relative to the substrate 9, as illustrated in Figs. 5, 7, 8, 10, and 13. Substrate 9 comprises an image sensor 10.

[0058] The optical unit 8 defines an optical axis A3, and comprises a lens assembly 8a and a housing 8b accommodating the lens assembly 8a.

[0059] The optomechanical system 2 may comprise a plurality of piezoelectric actuators 1 arranged equidistantly along a periphery of the optical unit 8, the actuating axis Al of each piezoelectric actuator 1 extending parallel with the optical axis A3, as illustrated in Fig. 5. Each individual piezoelectric actuator 1 is configured to individually engage the optical unit 8 and pivot the optical unit 8 around a pivot axis A4 associated with the individual actuator assembly, each pivot axis A4 extending perpendicular to the optical axis A3. This allows tilting of the optical unit 8 as illustrated in Fig. 4. For example, module tilt OIS of 3-4° may be achieved.

[0060] The optomechanical system 2 may instead comprise two piezoelectric actuators 1 arranged adjacent a periphery of the optical unit 8, the actuating axis Al of one actuator 1 extending perpendicular to the actuating axis Al of the other actuator 1 and perpendicular to the optical axis A3 as illustrated in Figs. 7 and 8. Each piezoelectric actuator 1 generates horizontal movement and shifts the unit in two directions, as illustrated in Fig. 6. For example, lens shift OIS of ± 300 pm may be achieved. The curved movement paths illustrated in Fig. 8 by dashed circles cover normal XY-lens OIS offset.

[0061] Furthermore, the optomechanical system 2 may be configured such that the actuating axis Al of the piezoelectric actuator 1 extends parallel with the optical axis A3, the piezoelectric actuator 1 being configured to engage the optical unit 8 and generate only linear movement of the optical unit 8 along the optical axis A3 as illustrated in Fig. 9. The piezoelectric actuator 1 may engage the optical unit 8 by means of guiding elements 11, as illustrated in Fig. 10. The flexible spring adapter 15 may enable the transition from cantilever bending, i.e. circular movement of fixed end 5b, 5c, to linear movement of the optical unit 8.

[0062] The present invention furthermore relates to an electronic apparatus 13 comprising the optomechanical system 2 as described above, see Fig. 14. The electronic apparatus may be any type of apparatus, in particular a smartphone, tablet, or laptop. The various aspects and implementations have been described in conjunction with various embodiments herein. However, other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed subject-matter, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0063] The reference signs used in the claims shall not be construed as limiting the scope. Unless otherwise indicated, the drawings are intended to be read (e.g., cross-hatching, arrangement of parts, proportion, degree, etc.) together with the specification, and are to be considered a portion of the entire written description of this disclosure. As used in the description, the terms “horizontal”, “vertical”, “left”, “right”, “up” and “down”, as well as adjectival and adverbial derivatives thereof (e.g., “horizontally”, “rightwardly”, “upwardly”, etc.), simply refer to the orientation of the illustrated structure as the particular drawing figure faces the reader. Similarly, the terms “inwardly” and “outwardly” generally refer to the orientation of a surface relative to its axis of elongation, or axis of rotation, as appropriate.

Claims

CLAIMS1. A piezoelectric actuator ( 1 ) comprising : a voltage source (3); a first cantilever (4a) and a second cantilever (4b), each of the first cantilever (4a) and the second cantilever (4b) having a fixed end (5a, 5b) and a free end (6a, 6b), the first cantilever (4a) and the second cantilever (4b) being arranged along an actuating axis (Al) of the actuator (1); and a rigid spacer (7), the spacer (7) interconnecting the first cantilever (4a) and the second cantilever (4b) such that the fixed end (5b) of the second cantilever (4b) is connected to the free end (6a) of the first cantilever (4a), and such that a voltage generated by the voltage source (3) generates movement of the free end (6a, 6b) of at least one of the first cantilever (4a) and the second cantilever (4b).

2. The piezoelectric actuator (1) according to claim 1, wherein the free end (6a, 6b) of the first cantilever (4a) and the second cantilever (4b) is movable, along the actuating axis (Al), relative to the fixed end (5a, 5b) of the first cantilever (4a) and the second cantilever (4b).

3. The piezoelectric actuator (1) according to claim 1 or 2, wherein the fixed end (5a) of the first cantilever (4a) is connected to the voltage source (3), and the free end (6a) of the first cantilever (4a) is electromechanically connected to the fixed end (5b) of the second cantilever (4b)4. The piezoelectric actuator (1) according to any one of the previous claims, comprising at least one further cantilever (4c), a fixed end (5c) of the further cantilever (4c) being electromechanically connected to the free end (6b) of the second cantilever (4b) by means of a further spacer (7).

5. The piezoelectric actuator ( 1 ) according to any one of the previous claims, wherein either the free end (6b) of the second cantilever (4b) or a free end (6c) of the further cantilever (6c) is configured to be operably connected to a component of the optomechanical system (2).

6. The piezoelectric actuator (1) according to any one of the previous claims, wherein the fixed end (5a) of the first cantilever (4a) is configured to be rigidly connected to a substrate (9) comprising the voltage source (3).

7. The piezoelectric actuator (1) according to any one of the previous claims, wherein the first cantilever (4a), the second cantilever (4b), and the further cantilever (4c) extend in parallel when no voltage is generated by the voltage source (3), and wherein voltage from the voltage source (3) generates bending of the free end (6a, 6b, 6c) of at least one of the first cantilever (4a), the second cantilever (4b), and the further cantilever (4c) around a cantilever bending axis (A2) extending through the fixed end (5a, 5b, 5c) of the first cantilever (4a), the second cantilever (4b), and the further cantilever (4c) and perpendicular to the actuating axis (Al).

8. The piezoelectric actuator (1) according to any one of the previous claims, wherein the voltage generates bending movement of at least one of the first cantilever (4a), the second cantilever (4b), and the further cantilever (4c) in a first direction (DI) such that a stroke of the piezoelectric actuator (1), along the actuating axis (Al), is reduced, andwherein the voltage generates bending movement of at least one of the first cantilever (4a), the second cantilever (4b), and the further cantilever (4c) in a second direction (D2) such that the stroke of the piezoelectric actuator (1) is increased.

9. The piezoelectric actuator (1 ) according to any one of the previous claims, further comprising a flexible printed circuit (12) attached to at least one of the first cantilever (4a), the second cantilever (4b), and the further cantilever (4c).

10. An optomechanical system (2) comprising: an optical unit (8) defining an optical axis (A3), the optical unit (8) comprising a lens assembly (8a) and a housing (8b) accommodating the lens assembly (8a); a substrate (9) comprising an image sensor (10); at least one piezoelectric actuator (1) according to any one of claims 1 to 10, the piezoelectric actuator (1) being configured to generate movement of the optical unit (8) relative to the substrate (9).

11. The optomechanical system (2) according to claim 10, comprising a plurality of piezoelectric actuators (1) arranged equidistantly along a periphery of the optical unit (8), the actuating axis (Al) of each piezoelectric actuator (1) extending parallel with the optical axis (A3), each individual piezoelectric actuator (1) being configured to individually engage the optical unit (8) and pivot the optical unit (8) around a pivot axis (A4) associated with the individual actuator assembly, each pivot axis (A4) extending perpendicular to the optical axis (A3).

12. The optomechanical system (2) according to claim 10, comprising two piezoelectric actuators (1) arranged adjacent a periphery of the optical unit (8), the actuating axis (Al) of one actuator (1) extending perpendicular to the actuating axis (Al) of the other actuator (1) and perpendicular to the optical axis (A3).

13. The optomechanical system (2) according to claim 10, wherein the actuating axis (Al) of the piezoelectric actuator (1) extends parallel with the optical axis (A3), the piezoelectric actuator (1) being configured to engage the optical unit (8) and generate movement of the optical unit (8) linearly along the optical axis (A3).

14. An electronic apparatus (13) comprising the optomechanical system (2) according to any one of claims 10 to 13.

Images