Abstract:
A motor assembly for a telescopic leg includes a drive shaft extending therefrom and at least one mounting pin extending from the motor assembly in a direction generally parallel to and spaced from the shaft. A base to which the motor assembly is mounted includes an aperture having a polymeric grommet positioned therein for receiving the pin for providing a noise isolating interconnection of the motor assembly to the base. In a preferred embodiment, a plurality of spaced pins are provided and extend through a plurality of aligned polymeric grommets in the base.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims priority under 35 U.S.C. § 119(e) on U.S. Provisional Application No. 60/253,920 entitled MOTOR MOUNT, filed on Nov. 29, 2000, by James E. Doyle and Jonathan D. Bruin, the entire disclosure of which is incorporated herein by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates to a motor mounting assembly for a linear actuator and particularly to one used for actuating telescopic table legs.  
           [0003]    Telescopic table legs are commonly used in work places for adjusting the table height for a variety of uses, such as positioning the work surface of a table for standing or various sitting positions. Electrically driven linear actuators are frequently employed to control the height of a table with telescopic legs. Such actuators includes a reversible motor and drive gear assembly coupled to a power screw which extends concentrically within a telescopic leg assembly and couples to a drive nut for extending or retracting one leg with respect to another. Typically, the motor housing is coupled by threaded fasteners to a cap on the top of the inner leg and, as the motor is actuated, the metal-to-metal connection transmits undesirable motor vibration and resonant frequencies through the linear actuator support structure. This noise and vibration is also transmitted through the support structure and legs of the table. Efforts to reduce such noise and vibration in a work place environment have included providing motor mounting pads which extend from a motor housing to a support plate for the motor, however, it remains necessary to prevent shifting of the motor with respect to the driven member during actuation of the motor and a mechanical interconnection is required to prevent movement of the motor drive assembly about the axis of the drive screw when actuated. Thus, a source of transmission of vibration and noise remains with such a system.  
         SUMMARY OF THE INVENTION  
         [0004]    The system of the present invention overcomes the noise and vibration transmission of the prior art by providing a motor mounting assembly in which a motor includes a motor and gear housing having a drive shaft extending therefrom and at least one mounting pin extending from the motor housing in a direction generally parallel to and spaced from the drive shaft. A base to which the motor is to be mounted includes an aperture having a polymeric grommet positioned therein for receiving the pin of said motor housing and providing a noise isolating interconnection of the motor housing to the base. In a preferred embodiment of the invention, a plurality of spaced pins are provided on the motor or motor housing and extend through a plurality of aligned polymeric grommets in the base.  
           [0005]    By providing a pin extending in the direction of the drive screw which is captively received in a grommet, the motor is effectively isolated along two axes, the longitudinal axis of the motor drive shaft and an axis orthogonal thereto by the extension of a pin through a receiving grommet. Accordingly, with the system of the present invention, a noise and vibration isolation motor mount is provided which is relatively easily assembled, inexpensive, and effective in preventing the transmission of noise and vibration from a drive motor in a linear actuator system employed for telescopic legs of a work table.  
           [0006]    These and other features, objects and advantages of the present invention will become apparent upon reading the following description thereof together with reference to the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is a fragmentary perspective exploded view of a telescopic leg for a table including a motor and base assembly of the present invention;  
         [0008]    [0008]FIG. 2 is a fragmentary perspective view of the table leg and base coupled thereto;  
         [0009]    [0009]FIG. 3 is a vertical cross-sectional view of the motor mounting assembly shown in FIGS. 1 and 2; and  
         [0010]    [0010]FIG. 4 is a vertical cross-sectional view of an alternative embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0011]    Referring initially to FIG. 1, there is shown a telescopic table leg assembly  10  which is employed to raise and lower a work surface  12 , shown schematically in FIG. 1, of a table to be raised and lowered to different use positions. The table leg assembly includes an inner leg  14  and an outer leg  16  (FIG. 3) telescopically receiving the inner leg with an interface cap  15  (FIG. 3) extending along the top of the fixed lower leg  16 , which extends to a support surface such as a floor (not shown). Although the invention is described in connection with a two-piece telescopic leg assembly including inner leg  14  and outer leg  16 , it is to be understood that other multiple telescopic legs may also incorporate this invention.  
         [0012]    The mounting system, as best seen in FIGS. 2 and 3, includes a base  20  having a peripheral flange  22  including apertures  21  (FIG. 2) for securing the base to the undersurface of table  12  as seen in FIG. 1. The base includes a central aperture  24  through which the end  26  of drive screw  26  extends with the lower end of the drive screw being conventionally supported at the lower end in coaxial aligned relationship with legs  14  and  16  through a drive mounted to the outer leg  16  and threadably receiving drive screw  26  such that rotation of the drive screw  26  extends and retracts the inner leg  14  with respect to outer leg  16  in a conventional manner. The drive screw  26  is supported on a lower side  23  of base  20  by means of a thrust bearing  30  (FIG. 3) and washer  32 . The lower side  23  of base  20 , which is made of stamped steel, is welded to the end of inner leg  14  at junction  25  to fix base  20  to leg  14  with base  20 , in turn, fixing leg  14  to table surface  12 . The base  20  could also be made from plastic or die cast metal.  
         [0013]    A reversible electrical drive motor  34  includes a right angle gear box  36  and motor mounting plate  38  secured to gear box  36  by means of fastening screws  40 , which extend through apertures  39  in motor mounting plate  38  into a gear box housing  36 . The end  26 ′ of drive screw  26  includes a threaded aperture  28  for receiving a fastening screw  29 . Thus, end  26 ′ of drive screw  26  is rotatably received in an aperture  37  of gear box housing  36  and is rotatably and vertically held within aperture  37  by fastening screw  29  and washer  31  (FIG. 3). Gear box  36  conventionally includes an internal drive gear (not shown) which engages drive gear  42  fixedly mounted to end  26 ′ of drive screw  26  for rotating the drive screw  26  in response to actuation of motor  34  in opposite directions for extending and retracting the inner leg  14  with respect to the outer leg  16 .  
         [0014]    The motor mounting plate  38  includes in a preferred embodiment shown, three equidistant downwardly extending pins  50 ,  52 , and  54  which are axially aligned and spaced from the screw jack end  26  and extend downwardly, as seen in FIGS. 1 and 3, and are received by three equally spaced elastomeric members, such as grommets,  60 ,  62  and  64  mounted in apertures  70 ,  72 , and  74  formed in surface  23  of base  20  as best seen in FIG. 2. Pins  60 ,  62 , and  64  are preferably tapered at an angle of up to about 10°, as seen in FIG. 3, to readily fit in the apertures of polymeric grommets  60 ,  62  and  64  for positioning, aligning, and holding the motor mounting plate  38  in alignment with base  20  with the coupling of end  26 ′ to the gear box  36  securing the motor assembly in a vertical direction, as seen in FIG. 3, with respect to the base  20 . Thus, motor  34  is lockably attached to end  26 ′ of drive screw  26  and its mounting plate  38  is radially fixed with respect to base  22 , such that when actuated, the motor torque is transmitted through drive screw  26  and thrust nut  16  and held in position by pins  70 ,  72 , and  74  within grommets  60 ,  62 , and  64  against rotation. The commercially available grommets are typically made of a rubber compound to provide isolation of the motor assembly with respect to base  20  and table legs  14  and  16 , thereby greatly reducing the transmission of noise and vibration from the motor to the legs. Although rubber grommets are employed in the embodiment shown, other elastomeric sleeves or grommet-like elements could be employed as long as they receive and locate the pins in base  20  and provide acoustical isolation between the pins and the base.  
         [0015]    In an alternative embodiment of the invention as seen in FIG. 4, instead of three equidistant (i.e., 120° spacings) pins, the motor  34  and its plate  38  may include a single pin  80  extending through a grommet  82  in base  20  with sides opposite shaft end  26 ′ including one or more resilient pads  84  extending between the lower surface  37  of motor mount  38  and the upper surface  27  of base  20 . Pin  80  locates and locks motor  34  from rotation as does drive screw  26 , while pad(s)  84  also acoustically isolate motor plate  38  form base  20  with the remaining mounting of the motor being identical to that seen in FIGS.  1 - 3 .  
         [0016]    In either embodiment, one, two, or three pins can be employed or a combination of one pin and one or more pads  84 , as shown in FIG. 4, to provide a stable noise isolation mount for the motor assembly  34  to the telescopic leg assembly. In some embodiments, the mounting pins can be integrally formed on the motor housing or gear box  36  eliminating the necessity of a motor mounting plate. Thus, this invention includes structure in which the interconnection of the motor drive assembly with a telescopic leg includes a pin and an isolating elastomeric grommet-like member.  
         [0017]    It will become apparent to those skilled in the art that various modifications to the preferred embodiment of the invention as described herein can be made without departing from the spirit or scope of the invention as defined by the appended claims.