WO2004020870A1

WO2004020870A1 - Linear actuator and method of minimizing axial movement of the spindle

Info

Publication number: WO2004020870A1
Application number: PCT/CA2003/001309
Authority: WO
Inventors: Steve Bartlett; Uzo Okeke; Eugen-Florin Craciun
Original assignee: Ats Automation Tooling Systems Inc.; Johnson Controls Technology Company
Priority date: 2002-08-27
Filing date: 2003-08-27
Publication date: 2004-03-11
Also published as: AU2003264199A8; AU2003264199A1

Abstract

An actuator includes a motor (15) having a transmission worm (20) thereon. A transmission housing (22) surrounds the transmission worm (20). The transmission worm (20) engages a helical gear (24) to produce rotation of a leadscrew (26). A drive nut bracket (15) engages the leadscrew (14), whereby rotation of the leadscrew (14) produces linear movement of the drive nut bracket (15). The housing (22) has a bearing surface against which the leadscrew (26) locates, an opening through which the leadscrew (26) extends, and a housing end cap (42) installed across the opening. The housing end cap (42) urges the leadscrew (26) toward the bearing surface, such that axial play of the leadscrew (26) may be minimized by screwing the housing end cap (26) to a position where the leadscrew (26) optimally contacts the bearing surface.

Description

LINEAR ACTUATOR AND METHOD OF MINIMIZING AXIAL MOVEMENT OF THE SPINDLE

TECHNICAL FIELD

The present invention relates to a transmission system. More particularly, the present invention relates to an integrated motor-transmission linear actuator and seat adjustment mechanism.

This application claims priority from United States Patent Application No. 60/406,054 titled "Integrated Motor-Transmission Linear Actuator" filed August 27, 2002, which is hereby incorporated by reference.

BACKGROUND ART

The demand for reliable power seat adjustment mechanisms in the automotive industry has driven a need for highly customer-focused and cost-effective actuators for power seat adjustment systems. There has been an increase in demand for high- quality actuating mechanisms, especially for high-end vehicles equipped with high comfort level seating. This has driven the automotive industry to more stringent engineering specifications on all components and assemblies of such mechanisms.

Actuating mechanisms for power seat adjustment for a vehicle seat are known. Such known actuating mechanisms typically reconfigure the vertical height of a cushion of the seat relative to a floor of the vehicle. Such known actuating mechanisms are typically electrically powered by an electric DC motor coupled to a gear reducer. The gear reducer uses a gear to transform rotary motion of the motor to linear motion of a moveable seat attachment point. However, such known actuating mechanisms have several disadvantages including looseness of a leadscrew and nut assembly which provide axial movement - which may cause a high level of "chuck" or sound/noise and vibration/impact, and excessive tightness in the leadscrew and nut assembly, which may result in increased friction and therefore reduced efficiency of the mechanical system.

Accordingly, there remains a need for a seat actuation mechanism which is relatively quiet, relatively tight and relatively vibration-free, and yet also reasonably efficient. There is also a need for a transmission system and actuators having one or more of these or other advantageous features.

DISCLOSURE OF INVENTION

The present invention relates to an actuator having an electric motor producing rotation of a motor output shaft extending therefrom, the motor output shaft having a transmission worm thereon. A transmission housing is secured to the electric motor, surrounding the motor output shaft and transmission worm. The housing carries a helical gear on a leadscrew at ninety degrees to the motor output shaft, and the transmission worm engages the helical gear to produce rotation of the leadscrew. The leadscrew has a threaded distal portion. A drive nut bracket has a nut engaged by the threads of the threaded distal portion of the leadscrew, whereby rotation of the leadscrew via the transmission worm and helical gear, by operation of the motor, produces linear movement of the drive nut bracket. The housing has a bearing surface against which a proximal end of the leadscrew locates, an opening through which the leadscrew extends distally, and a housing end cap installed across the opening. The transmission housing and the housing end cap have complementary threads accordingly, and the housing end cap has a central aperture through which the leadscrew extends distally to expose the threaded distal portion of the leadscrew. The housing end cap urges the leadscrew towards the bearing surface, such that axial play of the leadscrew may be minimized by screwing the housing end cap to a position where the proximal end of the leadscrew optimally contacts the bearing surface.

A particular use for the actuator is in seat adjustment mechanisms as described herein, but a wide variety of potential applications exists, in automotive seating, other automotive applications, and potentially many non-automotive applications.

BRIEF DESCRIPTION OF DRAWINGS

The invention will become more fully understood from the following detailed description, taken in conjunction with the accompanying drawings, wherein like reference numerals refer to like parts, and in which: FIGURE 1 is a side elevation view of a transmission system having one actuator for adjusting the height of the front of a seat and another actuator for adjusting the height of the rear of the seat and showing the seat in a retracted position according to a preferred embodiment;

FIGURE 2 is a side elevation view of the transmission system of FIGURE 1 showing the seat in an extended position according to an exemplary embodiment;

FIGURE 3 is a plan view of the transmission system of FIGURE 1 showing the actuators coupled to a mounting bracket according to an exemplary embodiment;

FIGURE 4 is a perspective view of the actuator of FIGURE 1 for adjusting the height of the front of a seat according to an exemplary embodiment;

FIGURE 5 is an exploded perspective view of the actuator of FIGURE 4 according to an exemplary embodiment;

FIGURE 6 is an exploded perspective view of the actuator of FIGURE 4 according to an exemplary embodiment;

FIGURE 7 is a perspective view of a motor and transmission housing portion of the actuator of FIGURE 4 according to an exemplary embodiment;

FIGURE 8 is a plan view of the actuator of FIGURE 4 according to an exemplary embodiment;

FIGURE 9 is a side elevation view of the actuator of FIGURE 4 according to an exemplary embodiment;

FIGURE 10 is a sectional view of a leadscrew, drive nut and transmission housing assembly of the actuator of FIGURE 4 in an extended position according to an exemplary embodiment;

FIGURE 11 is a sectional view of the leadscrew, drive nut and transmission housing assembly of the of actuator of FIGURE 4 in a retracted position and showing a drive nut fully retracted against a washer stop according to an exemplary embodiment; FIGURE 12 is a perspective view of a housing end cap of the actuator of FIGURE 4 from an outer side according to an exemplary embodiment;

FIGURE 13 is a perspective view of the housing end cap of FIGURE 12 from an inner side according to an exemplary embodiment;

FIGURE 14 is a side elevation view of the housing end cap of FIGURE 12 according to an exemplary embodiment;

FIGURE 15 is a fragmentary side elevation view of the housing end cap of FIGURE 12 showing a buttress thread according to an exemplary embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

A rotary to linear motion actuator and seat adjustment mechanism is shown as a transmission system in FIGURE 1 according to a preferred embodiment. The transmission system includes an electro-mechanical actuator 1 for converting rotation of an electric motor 15 into linear movement of a nut 14 (i.e. via a gear arrangement) with minimal axial play in the direction of linear motion. In an automotive seating application, the linear movement results in desired powered seat motion through a linkage arrangement for an automotive seat, (see FIGURE 1). Minimizing axial play reduces looseness in a leadscrew 26, which may cause a high level of "chuck" or sound/noise and vibration/impact in the transmission system.

As can be seen particularly from FIGURES 5 and 6, rotational motion from an output shank or shaft 16 of a motor 15 is converted to linear motion through leadscrew 26 and a drive nut bracket 14. Specifically, motor 15 and a worm gear arrangement (shown as a transmission gear 24 driven by a worm 20) produce rotation of leadscrew 26. Leadscrew 26 produces axial movement of drive nut bracket 14 along the leadscrew 26 as can be seen by comparing FIGURES 10 and 11.

A housing end cap 42 (see FIGURES 12 through 15) facilitates adjustment of the transmission system during the assembly process to limit axial play of leadscrew 26 hence of drive nut bracket 14. This is intended to reduce the need for secondary operations to adjust the axial play, and therefore enhances the overall stability of the transmission system according to a preferred embodiment. Referring to FIGURES 1 and 2, the transmission system is shown having a front actuator 1 and a rear actuator 1 for adjusting the height of a seat cushion support 2 relative to a seat upper track 3. FIGURE 1 shows front actuator 1 and rear actuator 1 each in a retracted configuration (resulting in the seat being in a lowered position). FIGURE 2 shows front actuator 1 and rear actuator 1 each in an extended configuration (resulting in the seat being in a raised position). The seat upper track is moveable along a seat rail (not shown) for forward and backward adjustment of the seat position relative to a floor of the vehicle according to an exemplary embodiment.

One of the actuators (shown in FIGURE 1 as front actuator 1) adjusts the height of the front of the seat. The other of the actuators (shown in FIGURE 1 as rear actuator 1 ) adjusts the height of the rear of the seat. The simultaneous extension or retraction of both front actuator 1 and rear actuator 1 produce raising or lowering of the position of seat support 2 relative to track 3. The independent (or opposite direction) extension and retraction of front actuator 1 and rear actuator 1 produces tilting of seat support 2 relative to track 3.

Referring to FIGURES 1 through 3, front actuator 1 and rear actuator 1 are each shown mounted between a fixed mounting interface shown as a mounting bracket 4 (see FIGURE 3) and a rotatable link shown as a linkage 5 (see FIGURES 1 and 2). Each linkage 5 is mounted to pivot about a fixed pivot pin 6 (see FIGURES 1 and 2), to convert generally horizontal movement of front actuator 1 and rear actuator 1 to generally vertical movement of the seat cushion support 2 through movable pivot pins 7.

One of moveable pivot pins 7 is mounted directly to seat cushion support 2 as shown in FIGURES 1 and 2. The other of moveable pivot pins 7 is connected via a "lost motion" link 8 to avoid binding, as shown in FIGURES 1 and 2. Front actuator 1 and rear actuator 1 are mounted by means of spiral roll pins 9 or are otherwise affixed through mounting holes 10 in a transmission housing 22 and the fixed mounting bracket 4 according to a preferred embodiment as shown in FIGURES 1 and 2. Front actuator 1 and rear actuator 1 are also mounted via pivot pins through holes (not shown) in drive nut brackets 14 and corresponding holes in the linkages 5 (not shown) according to a preferred embodiment as shown in FIGURE 3. Front actuator 1 and rear actuator 1 transform rotary motion from an electric motor 15 to linear motion of drive nut bracket 14 according to a preferred embodiment as shown in FIGURES 5 and 6. As can be seen from FIGURES 5 and 6, each of front actuator 1 and rear actuator 1 include an electric motor 15. The electric motor is a permanent magnet brush type DC electric motor according to a preferred embodiment.

Shaft 16 of motor 15 has a worm 20 for engaging and driving transmission gear 24. The worm is roll-formed onto the shaft of the motor according to a preferred embodiment. The worm is otherwise assembled onto on the shaft of the motor according to other alternative embodiments.

The motor is supplied as a sub-assembly, as shown in FIGURE 7 according to a preferred embodiment, complete with a transmission housing 22, into which worm 20 extends. See also FIGURES 8 and 9.

Mounted in transmission housing 22 is helical transmission gear 24 molded onto leadscrew 26. The helical transmission gear has teeth cut on an angle to be driven by the worm of the output shaft of the motor according to a preferred embodiment. The leadscrew is a threaded shaft used to convert rotational to longitudinal motion according to a preferred embodiment. Gear 24 meshes with worm 20 as shown in FIGURES 10 and 11 according to a preferred embodiment.

The thread profile of the leadscrew is preferably but not necessarily roll-formed on a mild steel bar material, previously cut and turned, to produce a smooth surface finish as desired according to a particularly preferred embodiment, but could be manufactured otherwise. The leadscrew in the area of the transmission gear over- mold preferably is knurled to prevent torsional slippage of the transmission gear under load according to a particularly preferred embodiment. The thread inhibits axial slippage of the gear on the leadscrew. According to a preferred embodiment, the helical transmission gear is a plastic material injection over-molded or otherwise assembled onto the leadscrew. According to an alternative embodiment, the helical transmission gear may be press fit onto the leadscrew.

Worm gearing is preferred in the gear reducer due to the high gear ratios which can be achieved, thereby providing high torque in a compact space. For any given design, the transmission ratio is chosen according to a preferred embodiment to realize an optimal combination of lifting capacity at a reasonable speed of operation, to cover a broad range of specifications across the automotive seating industry. The gear and thread meshes are also optimized to obtain the highest possible power transmission efficiencies within the given packaging constraint according to a preferred embodiment. The worm gear arrangement is a two-start worm gear, meshing with a 32-tooth transmission gear at a gear ratio of 16:1 , with a 73.2 percent efficiency at 0.1 coefficient of friction, according to a particularly preferred embodiment.

The leadscrew and nut assembly is a one-start 3.18 lead Stub-Acme thread or screw, according to a particularly preferred embodiment. The Stub-Acme screw may be made of cold-rolled steel or stainless steel according to any preferred or alternative embodiments. Efficiency of the Stub-Acme screw may range from at least about 30% to about 65% according to any preferred or other alternative embodiments. The Stub-Acme screw is self-locking according to a preferred embodiment. The leadscrew and nut assembly may include a ball-screw assembly according to an alternative embodiment.

As seen in FIGURES 10 and 11 , transmission housing 22 has a recess 28 aligned axially with leadscrew 26. A steel thrust plate 30 is press-fitted into recess 28 according to a preferred embodiment. A ball bearing 32 is inserted in a cavity 34 at the rear tip of leadscrew 26. The tip of the leadscrew is crimped to secure the ball bearing in place according to a particularly preferred embodiment. This provides a point contact of the leadscrew via the ball bearing and the thrust plate, and reduces friction according to a preferred embodiment. The thrust plate serves as the load- bearing surface and evenly disperses the load from the ball bearing contact to the plastic housing according to a preferred embodiment.

Upon assembly, which may be achieved by automation or manually according to any preferred or alternative embodiments, leadscrew 26 is loaded into transmission housing 22 so that transmission gear 24 meshes with the worm 20 on the armature (motor output) shaft, with the ball bearing 32 contacting the thrust plate 30. A ring washer 36 is slipped over the threaded end of the leadscrew and nested on a shoulder 38 of the transmission gear journal, as best seen in FIGURES 5, 10 and 11. The washer reduces the surface area contact between the housing end cap and the shoulder of the transmission gear journal, and reduces friction. The ring washer is coated or lubricated with DUPONT TEFLON (trademark) resin commercially available from E.I. du Pont de Nemours Company of Wilmington, Delaware according to a particularly preferred embodiment. The ring washer is coated with another material providing a low coefficient of friction according to another alternative embodiment.

After an application of grease according to a preferred embodiment, a housing end cap 42, produced by injection-molding for example, is then installed, to position and retain the leadscrew 26 by capturing transmission gear 24. Housing end cap 42 in a preferred embodiment as shown in FIGURES 12 through 14 has male threads 44, which engage female threads in the transmission housing. Preferably, these are buttress threads, as seen in FIGURES 14 and 15, for enhanced axial thrust-bearing capacity. The threads inhibit "back driving" or axial translation of the end cap relative to the housing according to a preferred embodiment. The leadscrew 26 extends out through an axial hole in housing end cap 42 as shown according to a preferred embodiment in FIGURES 10 and 11.

The housing end cap performs at least three functions. Firstly, it acts as a cover for the transmission housing (as described above), the housing have only the one open face. Secondly, it acts as a second bearing journal for the transmission gear. Thirdly, it provides a means of regulating and adjusting the axial play of the leadscrew in the housing. This third function permits axial play of the leadscrew to be minimized (reduced to near zero for all practical purposes), as a final step in the assembly process.

Axial play (e.g. movement or free operation within a bounded space of the housing of the transmission system) is minimized by rotating the end cap sufficiently to obtain essentially zero axial play without excessive friction. That is, it is desirable to stop rotating the housing end cap into the housing just at the point where zero play is reached and before there is a large spike in friction. Determining when the housing end cap has been rotated in to the optimum position may be accomplished by measuring current draw, torque applied to the cap, or actual amount of play according to any preferred or alternative embodiment. When the end cap is set to the desired position for minimized axial play, the plastic cap is then fastened to the housing by ultrasonic welding intended to inhibit subsequent movement or removal according to a preferred embodiment. The plastic cap may be otherwise secured to the housing (e.g. by any number of suitable means including for example a screw, wedge, adhesive or heat staking) according to any alternative embodiment. The housing end cap facilitates adjustment and limitation of axial play during the assembly process. This reduces the need for secondary operations to adjust the axial play, and therefore enhances the overall stability of the system according to a preferred embodiment.

The preferred manner by which this optimum positioning of the housing end cap is achieved is by monitoring the current draw of the motor while rotating the housing end cap into position. When the shoulder of the housing end cap pushes against the shoulder of the transmission gear (through the coated ring washer), the current draw will increase, indicating that clearance has been reduced to zero and that friction is increasing.

Alternatively, instead of monitoring current draw, the amount of play may be regulated by measuring the torque applied to the housing end cap during its installation, and stopping rotation of the housing end cap when a predetermined optimum torque is reached. The torque will increase generally linearly at a modest rate due to increasing frictional resistance from the threads as more threads are engaged, but will ramp up as zero axial play is reached, indicating the optimum position of the housing end cap. The predetermined torque should be set at or just below the torque at which that ramp-up occurs, as determined by experiment.

As yet another alternative, the amount of play could be regulated by actual measurement of the amount of play.

Drive nut bracket 14 is then threaded onto leadscrew 26 until the tip of leadscrew 26 protrudes in inner cavity 34 of drive nut bracket 14 (see FIGURES 10 and 11). To prevent disengagement of drive nut bracket 14 and leadscrew 26, and to set a specific length of travel of the drive nut bracket 14, a stop washer 46 is mounted on the distal end of leadscrew 26 and secured by means of a threaded fastener 48 as shown in FIGURES 10 and 11 according to a preferred embodiment. Stop washer 46 contacts full-retraction stop surfaces 49 at full retraction, and full-extension stop surface 50 at full extension, on the drive nut bracket 14, as best seen in FIGURES 4, 8, 10 and 11.

The length of travel of the drive nut bracket is defined by its inside profile and in a preferred embodiment is stopped by a washer bolted to the end of the leadscrew. As explained in more detail below, the attachment provides the washer with float, thereby inhibiting seizure of the nut on the leadscrew, which inhibits motor failure and enhances durability over the life cycle of the actuator according to a preferred embodiment.

The stop washer is intended to avoid seizure resulting from the stall torque of the electric motor according to a preferred embodiment. The stop washer nests on a turned neck at the tip of the leadscrew, with the neck outside diameter turned to be always smaller than the washer inside diameter according to a preferred embodiment. Furthermore, the thickness of the stop washer is always less than the width of the neck, allowing the threaded fastener (e.g. shown as fastener 48 in FIGURES 10 and 11) to seat on the neck front face with clearance to the washer according to a preferred embodiment. This configuration tends to ensure that the stop washer is free to rotate on the leadscrew neck, by providing it with "float", and in this manner enhances breakaway from the stops after stall.

It is important to note that the construction and arrangement of the elements of the transmission system as shown in the preferred and other exemplary embodiments is illustrative only. Although only a few embodiments of the present invention have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g. variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited in the claims. For example, seat cushions may be mounted above the seat cushion support according to an alternative embodiment. The specific details of gearing and threads may be varied according to alternative embodiments. The actuators are shown for use in an automotive seat, but may be used in other applications including: vehicle market applications, such as seat and interior systems including tracks, recliners, lumbar, head restraints, doors actuators, window regulators, internal and external mirrors, overheads, cockpits, pedals, steering column, etc. according to alternative embodiments, and in a wide variety of application in non-automotive areas as well. Accordingly, all such modifications are intended to be included within the scope of the present invention as defined in the appended claims. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. Other substitutions, modifications, changes and omissions may be made in the design, operating conditions and arrangement of the preferred and other exemplary embodiments without departing from the spirit of the present invention as expressed in the appended claims.

INDUSTRIAL APPLICABILITY

The invention provides an actuator and transmission system useful in automotive seating and potentially useful in a variety of other automotive and non-automotive applications.

Claims

CLAIMS:

1. An actuator for converting rotary motion into linear motion, comprising: an electric motor (15), producing rotation of a motor output shaft (16) extending therefrom, the motor output shaft (16) having a transmission worm (20) thereon; a transmission housing (22) secured to the electric motor (15) , surrounding the motor output shaft (16) and transmission worm (20), the housing (22) carrying a helical gear (24) engaging a leadscrew (26) at an angle to the motor output shaft

(16), the transmission worm (20) engaging the helical gear (24) to produce rotation of the leadscrew (26), the leadscrew (26) having a threaded distal portion; and a drive bracket (14) engaged by the threads of the threaded distal portion of the leadscrew (26), whereby rotation of the leadscrew (26) via the transmission worm (20) and helical gear (24) produces linear movement of the drive bracket (14); wherein the housing (22) comprises: a bearing surface against which a proximal end of the leadscrew (26) locates; an opening through which the leadscrew extends; and a housing end cap (42) installed across the opening, the transmission housing (22) and the housing end cap (42) having complementary threads, the housing end cap (42) having a central aperture through which the leadscrew (26) extends to expose the threaded distal portion of the leadscrew (26), the housing end cap (42) urging the leadscrew (26) towards the bearing surface; whereby axial play of the leadscrew (26) may be minimized by positioning the housing end cap (42) to a position where the proximal end of the leadscrew (26) optimally contacts the bearing surface.

2. The actuator according to claim 1 , wherein the housing end cap (42) urges the leadscrew (26) via a shoulder (38) of the gear (24).

3. The actuator according to claim 2, wherein a lubricated washer (36) is positioned between the housing end cap (42) and the shoulder (38).

4. The actuator according to claim 1 , wherein the bearing surface is a thrust plate (30) mounted perpendicularly to the leadscrew (26) in a recess in the housing.

5. The actuator according to claim 4, wherein the proximal end of the leadscrew (26) has an axial cavity having a ball bearing (32) positioned therein, the ball bearing (32) contacting the thrust plate (30).

6. The actuator according to claim 2, wherein the shoulder (38) urges the distal end of the leadscrew (26) toward the bearing surface.

7. The actuator according to claim 6, wherein the proximal end of the leadscrew (26) has an axial cavity having a ball bearing (32) positioned therein, the ball bearing

(32) contacting the thrust plate (30).

8. The actuator according to claim 3, wherein the housing end cap (42) is configured to urge the gear (24) which is configured to urge the leadscrew (26) against the bearing surface (30).

9. The actuator according to claim 8, wherein the proximal end of the leadscrew (26) has an axial cavity having a ball bearing (32) positioned therein, the ball bearing (32) contacting the thrust plate (30).

10. The actuator according to claim 1 , wherein the length of travel of the drive bracket (14) is determined by a the distal end of the leadscrew (26) having stop means thereon, the drive bracket (14) having surfaces arranged to contact the stop means at opposite ends of the length of travel.

11. The actuator according to claim 10, wherein the stop means comprises a stop washer (46) positioned at the distal end of the leadscrew (26) in a neck sized to ensure float of the washer (26).

12. The actuator according to claim 11 , wherein the neck is defined by a shoulder on the distal end of the leadscrew (26), and a proximal surface of a head of a threaded fastener secured into the distal end of the leadscrew (26).

13. A transmission system configured for coupling to an output shaft (16) of an electric motor (15) and for converting rotary motion of the electric motor (15) into linear motion, comprising: a leadscrew (26) having a first end and a second end; a gear(24) carried by the leadscrew (26) configured to engage the output shaft (16) at an angle to produce rotation of the leadscrew (26); a drive bracket (14) configured to engage the first end of the leadscrew (26), whereby rotation of the leadscrew (26) produces linear movement of the drive bracket (14) relative to the leadscrew (26); a housing (22) comprising: a thrust plate (30) having a bearing surface against which the proximal end of the leadscrew (26) is configured to engage; and an end cap (42) configured to urge the leadscrew (26) toward the bearing surface; wherein axial play of the leadscrew (26) relative to the housing (22) is minimized by positioning the end cap (42) to a location where the second end of the leadscrew (26) engages the bearing surface of the thrust plate (30).

14. The transmission system of Claim 13 wherein the leadscrew (26) passes through the gear (24).

15. The transmission system of Claim 13 wherein the end cap (42) is configured to urge the gear (24) which is configured to urge the leadscrew (26) toward the bearing surface of the thrust plate (30).

16. The transmission system of Claim 14 wherein the end cap (42) comprises a central aperture through which the leadscrew (26) is configured to extend.

17. The transmission system of Claim 16 wherein the second end of the leadscrew (26) is configured to optimally contact the bearing surface of the thrust plate (30).

18. A method of minimizing axial play in an actuator for converting rotary motion into linear motion, the actuator comprising: an electric motor (15), producing rotation of a motor output shaft (16) extending therefrom, the motor output shaft (16) having a transmission worm (20) thereon; a transmission housing (22) secured to the electric motor (15), surrounding the motor output shaft (16) and transmission worm (20), the housing (22) carrying a helical gear (24) engaging a leadscrew (26) at an angle to the motor output shaft

(16), the transmission worm (20) engaging the helical gear (24) to produce rotation of the leadscrew (26), the leadscrew (26) having a threaded distal portion; and a drive bracket (14) engaged by the threads of the threaded distal portion of the leadscrew (26), whereby rotation of the leadscrew (26) via the transmission worm (20) and helical gear (24) produces linear movement of the drive bracket (14); wherein the housing (22) comprises: a bearing surface against which a proximal end of the leadscrew (26) locates; an opening through which the leadscrew (26) extends; and a housing end cap (42) installed across the opening, the transmission housing

(22) and the housing end cap (42) having complementary threads, the housing end cap (42) having a central aperture through which the leadscrew (26) extends to expose the threaded distal portion of the leadscrew (26), the housing end cap (42) urging the leadscrew (26) towards the bearing surface; the method comprising positioning the housing end cap (42) to a position where the proximal end of the leadscrew (26) optimally contacts the bearing surface, thereby minimizing axial play.

19. The method as recited in claim 18, wherein optimal contact of the proximal end of the leadscrew (26) with the bearing surface of the thrust plate (30) is determined by operating the motor (15) and monitoring current draw of the motor (15) while rotating the housing end cap (42) into position, and stopping the rotation when current draw increases, indicating that clearance has been reduced to zero and that friction is increasing.

20. The method as recited in claim 18, wherein optimal contact of the proximal end of the leadscrew (26) with the bearing surface of the thrust plate (30) is determined by measuring torque applied to the housing end cap (42) during its installation, and stopping rotation when a predetermined optimum torque is achieved.

21. The method as recited in claim 18, wherein optimal contact of the proximal end of the leadscrew (26) with the bearing surface of the thrust plate (30) is determined by actual measurement of the amount of axial play.

22. A method of minimizing linear movement in a transmission for converting rotary motion into linear motion, comprising a leadscrew (26), a gear (24) engaging the leadscrew, a drive bracket (14) configured to engage the leadscrew (26), a housing (22) having a thrust plate (30) with a bearing surface against which the leadscrew (26) is configured to engage and an end cap (42) configured to urge the leadscrew (26) toward the bearing surface of the thrust plate (30), the method comprising: determining a position where the leadscrew (26) optimally contacts the bearing surface of the thrust plate (30); and positioning the end cap (42) to such position where the leadscrew (26) optimally contacts the bearing surface of the thrust plate (30); wherein the optimal contact of the leadscrew (26) with the bearing surface of the thrust plate (30) minimizes linear movement of the leadscrew (26) relative to the housing (22).

23. The method as recited in Claim 22, wherein determining a position where the leadscrew (26) optimally contacts the bearing surface of the thrust plate (30) comprises operating a motor (15) and monitoring current draw of the motor (15) while rotating the housing end cap (42) into position, and stopping the rotation when current draw increases.

24. The method as recited in Claim 22, wherein determining a position where the leadscrew (26) optimally contacts the bearing surface of the thrust plate (30) comprises measuring torque applied to the end cap (42) during installation, and stopping rotation when a predetermined optimum torque is achieved.

25. The method' as recited in claim 22, wherein determining a position where the leadscrew (26) optimally contacts the bearing surface of the thrust plate (30) comprises actual measurement of the amount of linear movement.

26. The method as recited in claim 22, further comprising fixing the end cap (42) to the housing (22) to inhibit movement of the end cap (42) relative to the housing (22).

27. The method as recited in claim 26, wherein fixing the end cap (42) to the housing (22) further comprises at least one of ultrasonic welding, screwing, wedging, adhering, and heat staking.

28. A transmission system for converting rotary motion into linear motion, comprising a leadscrew (26), a gear (20, 24) engaging the leadscrew (26), a drive bracket (14) configured to engage the leadscrew (26), a housing (22) having a thrust plate (30) with a bearing surface against which the leadscrew (26) locates and an end cap (42) configured to urge the leadscrew (26) toward the bearing surface of the thrust plate (30), comprising: means for determining a position where the leadscrew (26) optimally contacts the bearing surface of the thrust plate (30); and means for locating the housing end cap (42) to such position where the proximal end of the leadscrew (26) optimally contacts the bearing surface of the thrust plate (30); wherein the optimal contact of the leadscrew (26) with the bearing surface of the thrust plate (30) minimizes linear translation of the leadscrew (26) relative to the housing (22).

29. The transmission system as recited in Claim 26, wherein the means for determining the position where the leadscrew (26) optimally contacts the bearing surface of the thrust plate (30) comprises a system for monitoring a motor (15) and for monitoring current draw of the motor (15) while rotating the housing end cap (42) into position and for stopping the rotation when current draw increases.

30. The transmission system as recited in Claim 26, wherein the means for determining the position where the leadscrew (26) optimally contacts the bearing surface of the thrust plate (30) comprises a system for measuring torque applied to the end cap (42) during installation and for stopping rotation when a predetermined optimum torque is achieved.

31. The transmission system as recited in Claim 26, further comprising a mounting bracket (4) configured for coupling the housing (22) to a track (3) of a seating system.

32. The transmission system as recited in Claim 29, wherein the gear (20) is a two-start gear having a worm thread.

33. The transmission system as recited in Claim 30, wherein the gear (20) having the worm thread is configured to mesh with a gear (24) having a helical thread.

34. The transmission system as recited in Claim 31 , wherein the gear (24) having the helical thread comprises at least about 32 teeth.

35. The transmission system as recited in Claim 31, wherein the gear (20) having the worm thread is configured to mesh with the gear (24) having the helical thread at a gear ratio of about 16:1.