Reduced-voltage, linear motor systems and methods thereof

A linear motor system includes an element with a threaded passage, a threaded shaft, and a driving system. The threaded shaft has an axis of rotation which extends through and is at least partially engaged with at least a portion of the threaded passage. The driving system comprises at least two members operatively connected to the element. Each of the two members comprises two or more piezoelectric layers and electrodes which are coupled to opposing surfaces of each of the piezoelectric layers. The members are configured to expand and contract in a direction along the axis of rotation. The driving system is configured to subject the element to vibrations causing the threaded shaft to simultaneously rotate and translate in the direction along the axis of rotation through the element and apply an axial force in the direction along the axis of rotation.

FIELD OF THE INVENTION

The present invention generally relates to motor systems and methods thereof and, more particularly, relates to reduced-voltage, linear motor systems and methods thereof.

BACKGROUND

Transducers using piezoelectric technologies are used for precise positioning at the nanometer scale. Typically, piezoelectric devices include a ceramic that is formed into a capacitor that changes shape when charged and discharged. These piezoelectric devices can be used as position actuators because of their shape changing properties (i.e., vibrations). When such a piezoelectric device is used as a position actuator, the shape change of the ceramic is approximately proportional to an applied voltage differential across the ceramic.

Linear motors use piezoelectric generated vibrations to create continuous movement of a threaded shaft with high speed, high torque, small size, and quiet operation. An exemplary prior art linear motor includes a cylinder that supports a threaded element or nut. The cylinder includes four symmetrically positioned piezoelectric transducers to simultaneous excite the orthogonal bending modes of the cylinder at the first bending mode resonant frequency in the ultrasonic range with a plus or minus ninety-degree phase shift to generate a circular orbit. The threaded element orbits the centerline of the cylinder at the resonant frequency, which generates torque that rotates the threaded shaft that moves the threaded shaft linearly.

This linear motor typically operates at about 40 volts. However, optical systems in cell phones, cameras, or the like typically only include about a 3 volt battery. These devices simply cannot supply enough voltage to cause the motor to operate as intended without using a transformer or a DC-DC boost circuit to increase and/or step-up the voltage. The transformer adds extra circuitry, bulk, weight, and extra cost to, for example, a cell phone camera.

SUMMARY

A linear motor system in accordance with embodiments of the present disclosure includes an element with a threaded passage, a threaded shaft, and a driving system. The threaded shaft has an axis of rotation which extends through and is at least partially engaged with at least a portion of the threaded passage. The driving system comprises at least two members operatively connected to the element. Each of the two members comprises two or more piezoelectric layers and electrodes which are coupled to opposing surfaces of each of the piezoelectric layers. The members are configured to expand and contract in a direction along the axis of rotation. The driving system is configured to subject the element to vibrations causing the threaded shaft to simultaneously rotate and translate in the direction along the axis of rotation through the element and apply an axial force in the direction along the axis of rotation.

An optical lens assembly in accordance with other embodiments of the present disclosure includes a linear motor system and an optical lens. The linear motor system comprises an element with a threaded passage, a threaded shaft, and a driving system. The threaded shaft has an axis of rotation which extends through and is at least partially engaged with at least a portion of the threaded passage. The driving system comprises at least two members that subject the element to vibrations causing the threaded shaft to simultaneously rotate and translate in a direction along the axis of rotation through the element and apply an axial force in the direction along the axis of rotation. Each of the at least two members comprises two or more piezoelectric layers which are configured to expand and contract in the direction along the axis of rotation. The optical lens is coupled to the linear motor system. The linear motor system is configured to move the optical lens in a direction substantially parallel with the direction along the axis of rotation.

A method for driving a load in accordance with other embodiments of the present disclosure includes operatively connecting a load to a threaded shaft which has an axis of rotation and which extends through and is at least partially engaged with at least a portion of a threaded passage in an element. Subjecting at least two members which are configured to expand and contract in the direction along the axis of rotation and which are connected to the element to vibrations causing the threaded shaft to simultaneously rotate and translate in a direction along an axis of rotation through the element which moves the load. Each of the two members comprise two or more piezoelectric layers and electrodes which are coupled to opposing surfaces of each of the piezoelectric layers.

A method for making a linear motor in accordance with other embodiments of the present disclosure includes at least partially engaging a threaded shaft with an axis of rotation in a threaded passage in an element. Connecting at least two members of a driving system to the element. Each of the two members comprises two or more piezoelectric layers and electrodes, which are coupled to opposing surfaces of each of the piezoelectric layers. Each of the piezoelectric layers is configured to expand and contract in a direction along the axis of rotation. The driving system is configured to subject the element to vibrations causing the threaded shaft to simultaneously rotate and translate in the direction along the axis of rotation through the element and apply an axial force in the direction along the axis of rotation.

The present disclosure provides a number of advantages including providing a more efficient and a more compact linear motor system. The linear motor system can directly operate on about 2.8 volts without using a DC-DC booster circuit and/or a transformer. The linear motor system can be used to move a variety of different loads in a variety of different applications, such as in auto-focus systems and auto-zoom systems in cameras by way of example only.

DETAILED DESCRIPTION

A linear motor system100in accordance with embodiments of the present disclosure is illustrated inFIGS. 1A-1Band2. The linear motor system100includes an element110with a threaded passage, a threaded shaft120, and a driving system130. The linear motor system100can include other types and numbers of systems, devices, and components which are connected in other manners. The present disclosure provides a more compact and efficient linear motor system.

Referring toFIG. 1A, the linear motor system100generates a force to move a load (e.g., an optical lens) in a linear direction. It is contemplated that the linear motor system100can move other types of loads in other directions. The inner passage of the element110can be partially threaded or threaded throughout. The threaded shaft120has an axis of rotation125about which the threaded shaft120rotates. The threaded shaft120also translates in a direction along the axis of rotation125. In some embodiments, the threaded shaft120includes at least one rounded end122. The rounded end122reduces frictional forces and aids in applying the force to move the load.

According to some embodiments, the driving system130comprises four members132a-d, a flex circuit140, and a full bridge drive system150. It is contemplated that the driving system130can comprise other numbers and types of structures. Each member132a-dis configured to change length upon being subjected to a voltage differential across its thickness T (shown inFIG. 2). Specifically, the members132a-dcan expand and/or contract in the direction along the axis of rotation125of the threaded shaft120. Each of the members132a-dcomprise two or more piezoelectric layers. In some embodiments, the members132a-dcomprise between about 5 piezoelectric layers and about 25 piezoelectric layers. In some embodiments, the members132a-dcomprise about 13 piezoelectric layers.

Each of the piezoelectric layers have a pair of electrodes coupled to opposing surfaces. Examples of the orientation and arrangement of the piezoelectric layers and the electrodes are best seen inFIGS. 1B and 3, which are both discussed in detail below. Referring back toFIG. 1A, the members132a-dare each made from ceramic material and are co-fired with internal conductive electrodes into a multi-layered piezoelectric transducer in the shape of a plate. In some embodiments, it is contemplated that other types and shapes of piezoelectric materials and other manners for forming the members132a-dare possible.

The flex circuit140can also be referred to as an electrical coupler. The flex circuit140electrically couples the electrodes positioned between each piezoelectric layer with the full bridge drive system150. The flex circuit140is configured to be bent and/or wrapped around the element110such that electrical terminals142align with and electrically couple to “L” shaped electrodes134a-dand136a-d(shown inFIG. 2) on the members132a-d. The flex circuit140comprises at least four electrical traces144a-dthat carry at least four different electrical signals470A-D (shown inFIG. 4) to the various electrical terminals142.

The full bridge drive system150comprises a voltage source461and has four signal outputs154a-d, which provide square-wave voltage signals. It is contemplated that other types and numbers of voltage signals, driving circuits, and systems with more or less outputs can be used. Each of the four signal outputs154a-delectrically connect to a respective electrical trace144a-dto distribute one of the square-wave voltage signals via the flex circuit140. The full bridge drive system150effectively doubles the voltage differential across each piezoelectric layer in each of the members132a-dand doubles the mechanical output as compared with a half bridge circuit. Using such a full bridge drive system can reduce a system's input voltage and power requirements, although other types of systems, such as a half bridge circuit system, can still be used. Because the components and operation of full bridge drive systems are well known to those of ordinary skill in the art they will not be described in detail herein.

Referring toFIG. 1B, a partial zoomed-in view of the driving system130is shown according to some embodiments. More specifically, one example of multi-layered piezoelectric members132a, b, anddis shown. Referring to member132a, a plurality of piezoelectric layers133is shown with first and second sets of interwoven electrodes134,136. The first set of interwoven electrodes134are commonly connected to an “L” shaped electrode134a. Similarly, the second set of interwoven electrodes136are commonly connected to an opposing “L” shaped electrode136a(shown inFIG. 2). The “L” shaped electrode134aelectrically connects the first set of interwoven electrodes134to terminal142, which is electrically coupled to the full bridge drive system150via electrical trace144c. Similarly, the opposing “L” shaped electrode136aelectrically connects the second set of interwoven electrodes136to a terminal (not shown in1B), which is also electrically coupled to the full bridge drive system150via electrical trace144d. The members132b-dsimilarly comprise a plurality of piezoelectric layers, a first and second set of interwoven electrodes134,136, and “L” shaped electrodes134b-d,136b-d, respectively.

According to some embodiments, each of the piezoelectric layers133has a thickness T of about fourteen micrometers, although other thicknesses and/or varying thicknesses can be used for each of the piezoelectric layers133. It is contemplated that the piezoelectric layers133can have a thickness T between about five micrometers and about forty micrometers. Using a plurality of thin piezoelectric layers133(e.g., about five micrometers thick to about forty micrometers thick) to form each of the members132a-dallows for a lower voltage to be used than is possible when using a thick monolithic piezoelectric layer (e.g., about two hundred micrometers thick). Specifically, the relatively thinner piezoelectric layers133expand and/or contract in the direction along the axis of rotation125the same amount when a relatively smaller voltage differential is applied across the thickness T of each piezoelectric layer as compared to a thick monolithic piezoelectric layer. Thus, a multi-layered piezoelectric member (e.g., members132a-d) can expand and/or contract in the direction along the axis of rotation125the same amount as a monolithic piezoelectric member but by applying a smaller voltage differential. For example, a typical prior art monolithic piezoelectric member requires about 40 volts to operate, where multi-layered piezoelectric members (e.g., members132a-d) require only about 2.8 volts to operate. As will be explained in more detail below, the expansion and/or contraction of the members132a-dcauses the element110to bend and/or vibrate. It is these vibrations of the element110that linearly drive the threaded shaft120and cause the threaded shaft120to apply the force to the load.

Referring toFIG. 2, an exploded perspective view of the linear motor system100is shown in accordance with some embodiments. The threaded shaft120can be screwed into position within the threaded passage of the element110. A bottom surface of each of the members132a-dis rigidly attached to a corresponding outer surface of the element110. It is contemplated that the members132a-dcan be attached to the element110using various glues and/or adhesives.

The flex circuit140is shown in a partially folded position. The flex circuit140can be predisposed to bend at certain locations to aid in wrapping the flex circuit140around the members132a-dand the element110. The flex circuit140comprises eight terminals142and the four electrical traces144a-d, which are attached to the four signal outputs154a-dof the full bridge drive system150. Each of the electrical traces144a-dis positioned within various layers of the flex circuit140such that each electrical trace144a-delectrically attaches to two different terminals142. It is contemplated that in some embodiments, the flex circuit140can comprise eight electrical traces, where each of the eight electrical traces electrically attaches to one of the eight terminals142. In some embodiments, the flex circuit140can further include several holes147along the predisposed bending lines to further aid in wrapping the flex circuit140around the members132a-dand the element110. The illustrated paths of the electrical traces144a-dare by way of example only and not intended to limit the actual layout of the paths of the electrical traces144a-d. Reference is made toFIGS. 5 and 6for one example of how to connect the electrical traces144a-dto the members132a-d.

Each member132a-dcomprises two “L” shaped electrodes134a-dand136a-d, respectively. According to some embodiments, each of the “L” shaped electrodes134a-d,136a-dare electrically coupled with a first and second set of interwoven electrodes134,136, respectively. The “L” shaped electrodes can be attached to the outer surface of the members132a-dor can be partially internal. Put another way, the “L” shaped electrodes134a-d,136a-dcan be fully exposed on one or more of the outer surfaces of the members132a-dor only partially exposed. However, at least a portion of each of the “L” shaped electrodes134a-d,136a-dmust be positioned on the members132a-dsuch that the “L” shaped electrode134a-d,136a-dcan be electrically coupled with one of the terminals142on the adjacent flex circuit140. The element110includes at least two nodal planes that are perpendicular to the axis of rotation125where the members'132a-dvibration amplitude is minimum for a first bending resonant mode. According to some embodiments, for each of the members132a-d, one of the terminals142is substantially located at each of the two nodal planes of the element110.

Referring toFIG. 3, a cross-sectional view of member132ahaving multiple piezoelectric layers is shown according to some embodiments. Multi-layer piezoelectric members (e.g., members132a-d) can be fabricated according to any conventional technique, such as described in U.S. Pat. No. 4,523,121 to Takahashi et al. and in Micromechatronics by Kenji Uchino and Jayne R. Giniewicz, chap. 4 (2003) (ISBN: 0-8247-4109-9), or any other suitable technique. The cross-section of members132b-dare the same as the cross-section of member132a. Member132acomprises multiple piezoelectric layers133, a first set of interwoven electrodes134, and a second set of interwoven electrodes136. The first set of interwoven electrodes134are electrically connected to “L” shaped electrode134a. The second set of interwoven electrodes136are electrically connected to “L” shaped electrode136a. The “L” shaped electrodes134a,136aare coupled to opposing ends of the member132a. Other types and numbers of electrodes and/or electrical connections are contemplated.

Each one of the electrodes in the first set of interwoven electrodes134is attached to a first surface of a respective piezoelectric layer and a matching one of the electrodes in the second set of interwoven electrodes136is attached to a second opposing surface of the same respective piezoelectric layer. For example, electrode134′ and electrode136′ comprise a first matching pair of electrodes that are coupled and/or sandwiched to opposing surfaces of piezoelectric layer133′, which has a thickness T. Each of the “L” shaped electrodes134a,136aare coupled to a voltage source353.

The “L” shaped electrodes134a,136aare coupled via flex circuit140to the full bridge drive system150. A voltage differential can be applied across the thickness of the member132ausing the voltage source353. Specifically, a voltage differential can be applied across the thickness T of each of the piezoelectric layers133using the first and second sets of interwoven electrodes134,136. According to some embodiments, depending on the orientation of electric dipoles in each of the piezoelectric layers133, the voltage differential causes each of the piezoelectric layers133of the member132ato expand and/or contract in the direction along the axis of rotation125.

Each of the members132a-d(shown inFIG. 2) has a positive and negative polarity137that can be created during the manufacturing process by poling. For example, if “L” shaped electrode134ais positive and “L” shaped electrode136ais negative, then when a voltage differential is applied between the “L” shaped electrodes134aand136asuch that the voltage difference between two terminals353aand353bof the voltage source353is positive, the member (e.g., member132a-d) will contract and/or shrink. Similarly, when a voltage differential is applied between the “L” shaped electrodes134aand136aso that the voltage difference between the two terminals353aand353bis negative, the member (e.g., member132a-d) will expand and/or increase in length. One example of an increase in length of the member132afrom L to L′ is illustrated by dotted line132a′.

Referring toFIG. 4, a circuit block diagram illustrating a first and second full bridge drive system150A,B is shown according to some embodiments. The first and second full bridge drive systems150A,B each include a voltage source152, which can be a battery in, for example, a cell phone, a camera, or a PDA. According to some embodiments, a controller circuit480includes a microcontroller and/or a microprocessor and a phase shifting circuit to generate a first pulse width modulated (PWM) input signal470(1)′ and a second PWM input signal470(2)′. The controller circuit480is configured to phase shift one of the PWM input signals470(1)′,470(2)′ ninety degrees with respect to the other and to transmit the signals470(1)′,470(2)′ to the first and second full bridge drive systems150A,B. Specifically, the first PWM input signal470(1)′ is transmitted to the first full bridge drive system150A and the second PWM input signal470(2)′ is transmitted to the second full bridge drive system150B. According to some embodiments, the phase shifting circuit can be referred to as a limitation circuit.

The first full bridge drive system150A amplifies and splits the first PWM input signal470(1)′ into a first electrical signal470A and a second electrical signal470B. One of the electrical signals470A,B is phase shifted 180 degrees relative to the other electrical signal to double the effective voltage differential across each of the piezoelectric layers133of the members132a,c. The first and second electrical signals470A,B are transmitted to members132a,cvia flex circuit140to drive the members132a,c. Similarly, the second full bridge drive system150B amplifies and splits the second PWM input signal470(2)′ into a third electrical signal470C and a fourth electrical signal470D. One of the electrical signals470C,D is phase shifted 180 degrees relative to the other electrical signal to double the effective voltage differential across each of the piezoelectric layers133of the members132b,d. The third and fourth electrical signals470C,D are transmitted to members132b,dvia the flex circuit140to drive the members132b,d.

According to some embodiments, using a full bridge drive system150A,B to transmit the first and second or the third and fourth electrical signals470A,B,470C,D to their respective members132a-dallows for the driving system130to be commonly grounded462. The electrodes134a-dand136a-dare floating relative to common ground and are driven independently, which eliminates a need for soldering a common ground wire to the element110, as is typically required in prior art linear motor systems. Eliminating the common ground wire soldered to the element110reduces the time and cost it takes to make a linear motor system, such as the linear motor system100.

Referring toFIG. 5, the electrical signals470A-D are illustrated and shown being transmitted to respective members132a-d. The first electrical signal470A is a square-wave voltage signal that is about 180 degrees out of phase from the second electrical signal470B, which is also a square-wave voltage signal. Similarly, the third electrical signal470C is a square-wave voltage signal that is about 180 degrees out of phase from the fourth electrical signal470D, which is also a square-wave voltage signal. The first and second electrical signals470A,B are transmitted through electrical traces144c,dthat are attached via terminals142to respective “L” shaped electrodes134aand136aon the first member132aand also to respective “L” shaped electrodes134cand136c, on the third member132c. The third and fourth electrical signals470C,D are transmitted through electrical traces144a,bthat are attached via terminals142to respective “L” shaped electrodes134band136bon the second member132band also to respective “L” shaped electrodes134dand136don the fourth member132d. The “L” shaped electrodes134a-dand136a-dshown inFIG. 5and illustrated in FIG.4can be located on longer edges of the members132a-dand are electrically identical to the “L” shaped electrodes134a-dand136a-dshown inFIGS. 1-3.

Referring toFIG. 6, a table detailing one example of electrical connections for members132a-dis shown. As shown in the table, the members132a-deach have a positive and a negative polarity137such that electrodes134a-dare positive and electrodes136a-dare negative.

With reference toFIGS. 5 and 6, according to some embodiments, the first member132aand third member132ccomprise a first pair of opposing members that operate together; and the second member132band fourth member132dcomprise a second pair of opposing members that operate together. The electrical signals470A,B provided to the first pair of opposing members are phase shifted about 90 degrees relative to the electrical signals470C,D provided to the second pair of opposing members to cause the threaded shaft120to rotate and translate in the direction along the axis of rotation125. A positive 90 degree phase shift, as shown inFIG. 5, will produce a positive or forward translation of the threaded shaft120, where a negative 90 degree phase shift will produce a negative or backward translation of the threaded shaft120. According to some embodiments, the electrical signal's470A_D frequency is substantially the same as the first bending mode resonance of the motor system100. While certain electrical signals and phase shifts have been described, it is contemplated that other frequency ranges, shapes, and phase differences of the signals470A-D are contemplated.

Operation of the linear motor system100will now be described with reference to FIGS.1A,B to6. As discussed above, the first member132aand the third member132ccomprise the first pair of opposing members that operate together to bend the element110in one direction, as one of the members increases in length and the other member decreases in length when the electrical signals470A,B are applied. Similarly, the second member132band the fourth member132dare the second pair of opposing members that operate together to bend the element110in an orthogonal direction, as one of the members increases in length and the other member decreases in length when the electrical signals470C,D are applied.

The full bridge drive system150A receives the first PWM input signal470(1)′, as shown inFIG. 4. The first PWM input signal470(1)′ is split into the electrical signals470A,B, one being phase shifted 180 degrees relative to the other. Each of the electrical signals470A,B are amplified using voltage source152and transmitted via flex circuit140(SeeFIG. 1A) to the first pair of opposing members. Each of the electrical signals470A,B are transmitted to two opposing “L” shaped electrodes134a,136aand134c,136cattached to the members132a,c(SeeFIGS. 5-6for connections). Specifically, the first electrical signal470A is transmitted to “L” shaped electrodes134aand136cand the second electrical signal470B is transmitted to “L” shaped electrodes136aand134c(SeeFIG. 2for the orientation of the “L” shaped electrodes).

In relation toFIG. 3, the “L” shaped electrode134ais electrically coupled with a first set of interwoven electrodes134and the “L” shaped electrode136ais electrically coupled with a second set of interwoven electrodes136. Similarly, the “L” shaped electrode134cis electrically coupled with a first set of interwoven electrodes134and the “L” shaped electrode136cis electrically coupled with a second set of interwoven electrodes136. The “L” shaped electrodes136aand134celectrically apply the first electrical signal470A and the “L” shaped electrodes134aand136celectrically apply the second electrical signal470B to their respective sets of interwoven electrodes134,136. Application of the electrical signals470A,B to the opposing sets of interwoven electrodes creates a voltage differential across each piezoelectric layer133in the first and third members132a,c.

Similar to the full bridge drive system150A, the full bridge drive system150B receives the second PWM input signal470(2)′, as shown inFIG. 4. The second PWM input signal470(2)′ is split into the electrical signals470C,D, one being phase shifted 180 degrees relative to the other. Each of the electrical signals470C,D are amplified using voltage source152and transmitted via flex circuit140(SeeFIG. 1A) to the second pair of opposing members. Each of the electrical signals470C,D are transmitted to two opposing “L” shaped electrodes134b,136band134d,136dattached to the members132b,d(SeeFIGS. 5-6for connections). Specifically, the third electrical signal470C is transmitted to “L” shaped electrodes134band136dand the fourth electrical signal470D is transmitted to “L” shaped electrodes136band134d(SeeFIG. 2for the orientation of the “L” shaped electrodes).

In relation toFIG. 3, the “L” shaped electrode134bis electrically coupled with a first set of interwoven electrodes134and the “L” shaped electrode136bis electrically coupled with a second set of interwoven electrodes136. Similarly, the “L” shaped electrode134dis electrically coupled with a first set of interwoven electrodes134and the “L” shaped electrode136dis electrically coupled with a second set of interwoven electrodes136. The “L” shaped electrodes136band134delectrically apply the third electrical signal470C and the “L” shaped electrodes134band136delectrically apply the fourth electrical signal470D to their respective sets of interwoven electrodes134,136. Application of the electrical signals470C,D to the opposing sets of interwoven electrodes creates a voltage differential across each piezoelectric layer133in the second and fourth members132b,d.

According to some embodiments that include the full bridge drive system150, the voltage source152is about an 8 volt battery and the effective voltage differential across the thickness T of each piezoelectric layer133is about 16 volts. According to some embodiments that include the full bridge drive system150, the voltage source152is about a 2.8 volt battery and the effective voltage differential across the thickness T of each piezoelectric layer133is about 5.6 volts. According to some embodiments that include the full bridge drive system150, the voltage source152is about a 2 volt battery and the effective voltage differential across the thickness T of each piezoelectric layer133is about 4 volts. It is contemplated that various types of batteries and voltage sources with various voltage outputs may be used in the driving system130.

As shown inFIG. 5, the electrical signals470A-D are square-waves with equal amplitude and a ninety degree phase shift between the electrical signals470A,B and the electrical signals470C,D to produce a circular orbit. Now referring toFIG. 7, a single orbital cycle of the linear motor system100is shown sequentially in ninety degree increments690,692,694,696, and698for one direction of rotation and for the corresponding electrical signal amplitudes.

Referring to the first 90 degree increment690at zero degrees, applying the first and second electrical signals470A,B to the first pair of opposing members, as discussed above, causes member132cto expand and/or elongate, while member132asimultaneously contracts. This simultaneous expansion on one side of the element110and contraction on an opposite of the element110, in the direction along the axis of rotation125, causes the element110to bend as shown at the first 90 degree increment690. The cylindrical bending and orbital movement is shown in the X direction695a/695band the Y direction696a/696b. The element110contacts the side of the threaded shaft120at one location697awith a clearance697bon the opposite side, whereby the contact imparts tangential force and movement that causes the threaded shaft120to rotate698aand translate698ba small amount for each orbital cycle. The amount of rotation and translation per cycle depends on many factors, including orbit amplitude, the magnitude of force acting on the threaded shaft120, and the coefficient of friction and surface finish of the threads.

As shown inFIG. 7, the clearance697bbetween the element110and the threaded shaft120is exaggerated to more clearly show the orbital motion of the element110. According to some embodiments, the amplitude of the orbital motion of the element110(the diameter of the orbit) is in the range of about 0.5 micrometers to about 10 micrometers, with the vibration frequency in the range of about 20,000 Hz to about 500,000 Hz, which corresponds to the first bending mode resonance of element110. The threads of the element110and the threads of the threaded shaft120mate with a thread clearance being the difference in outside diameter of the threaded shaft120and inside diameter of the element110, which is in the range of about 25 micrometers to about 500 micrometers. According to some embodiments, the force is applied to the round end122(shown inFIG. 1A) of the threaded shaft120to aid in frictionally coupling the thread faces of the threaded shaft120and of the element110. According to some embodiments, the orbital vibration amplitude generates tangential force on the thread faces of the threaded shaft120, causing the threaded shaft to rotate and translate. In these embodiments, the orbital vibration frequency is high enough so that the centerline of the threaded shaft120remains substantially fixed.

According to some embodiments, for a zero-slip condition between the contact697aof the element110and the threaded shaft120, the movement of the threaded shaft120per cycle is nominally proportional to the orbital vibration amplitude. In general, as the amplitudes of the electrical signals470A-D increase, the orbit diameter increases, speed increases, and torque/force increases.

There are several advantages to using a reduced-voltage, linear motor system100. For example, the linear motor system100uses two or more piezoelectric layers to reduce the necessary input voltage requirement. Specifically, the reduced-voltage, linear motor system100does not require a transformer or a DC-DC boost circuit to step-up or increase an input voltage. In most of the space-sensitive motor systems of the prior art linear motor systems, a typical battery voltage source is about 2.8 volts. However, the prior art linear motor systems require about 40 volts to properly operate the motor. Thus, a transformer and/or a DC-DC boost circuit is required for the motor to operate. Because the prior art linear motor systems are typically used in auto-zoom and auto-focus applications in cell phones, cameras, and PDAs, the inclusion of additional transformer circuitry adds expense, bulk, weight, and takes up space in an otherwise small environment. Thus, the reduced-voltage, linear motor system100can operate without additional transformer circuitry and still be used for auto-zoom and auto-focus applications in cell phones, cameras, and PDAs, while taking up a smaller footprint. The above advantages are by way of example only, the reduced-voltage, linear motor system100has other advantages, some of which have been described above.

Referring toFIG. 8, an optical system700is shown in accordance with embodiments of the present disclosure. The optical system700is used to control and drive lenses782and784using linear motor systems701and702respectively. The linear motor systems701,702are the same as, or similar to, the linear motor system100described above and shown inFIGS. 1A,1B, and2. The optical system700includes the linear motor systems701,702, a voltage source752, a controller circuit780, the lenses782,784, an image sensor786, an image signal processor (ISP)788, a transformer790, and position sensors792,794. The optical system700can optionally include a shutter and an iris796.

According to some embodiments, the voltage source752supplies power to the transformer790, the image signal processor788, and the controller circuit780. The transformer790can be used to step-up or increase an input voltage supplied by the voltage source752when, for example, the positions sensors792,794require a higher voltage to operate. The controller circuit780receives power directly from the voltage source752without needing a transformer. The controller circuit780controls the linear motor systems701,702individually. The controller circuit780can send one or more electrical signals (e.g., electrical signals470A-D) to the linear motor systems701,702to cause the linear motor systems701,702to adjust the relative positions of lenses782,784.

In some embodiments, the lens782is an auto-focus lens and the lens784is an optical-zoom lens. Each of the lenses782,784comprises a housing with a cover. The cover has an aperture positioned such that the lenses782,784can selectively allow light to enter the housing. According to some embodiments, the controller circuit780can open the aperture in the cover by moving and/or adjusting the shutter796to thereby allow light to transmit through one or both of the lenses782,784. This light is then received in the image sensor786, which can also be referred to as an optical sensor or a digital image sensor. The image sensor786produces data and/or information associated with the received light and transmits that data and/or information to the image signal processor788to generate and/or store an image.

According to some embodiments, as the lenses782,784are adjusted by the linear motor systems701,702, position sensors792,794monitor and/or track the position of the lenses782,784within the housing and send a position signal to the controller circuit780. The position signal can be used by the controller circuit780to fine-tune positional adjustments to the lenses782,784.

Various other applications exist for linear motor systems, such as linear motor systems100,701, and702. For example, several alternative applications for such linear motor systems can be found in U.S. Pat. No. 6,940,209, titled, “Ultrasonic Lead Screw Motor”; U.S. Pat. No. 7,339,306, titled, “Mechanism Comprised of Ultrasonic Lead Screw Motor”; U.S. Pat. No. 7,170,214, titled, “Mechanism Comprised of Ultrasonic Lead Screw Motor”; and U.S. Pat. No. 7,309,943, titled, “Mechanism Comprised of Ultrasonic Lead Screw Motor,” all of which are commonly assigned to New Scale Technologies, Inc. and are all hereby incorporated by reference in their entireties.