Flexible mounting of a motor secondary in a linear induction motor for driving elevator car doors

A linear induction motor for opening and closing elevator car doors in an elevator system includes a motor primary fixedly attached to a door hanger and a motor secondary flexibly mounted to a header bracket of the elevator car. A pair of swivel joints secure the ends of the motor secondary to the header bracket. The swivel joints compensate for misalignment and twisting of the elevator car doors by allowing multi-dimensional movement of the motor secondary relative to the header bracket.

CROSS-REFERENCE TO RELATED APPLICATIONS 
This application is related to commonly owned co-pending applications filed 
on the same day herewith having U.S. patent application Nos.: 08/746,274 
(OT-2660) and 08/746,281. 
TECHNICAL FIELD 
The present invention relates to elevator systems and, more particularly, 
to high performance linear induction motors driving elevator car doors 
therefor. 
BACKGROUND OF THE INVENTION 
In conventional elevator systems, elevator car doors are selectively opened 
and closed by a rotary electric motor driving mechanical assemblies which 
typically include a plurality of moving parts such as gear boxes, a set of 
drive arms, and linkages. The major drawback to existing elevator car door 
systems is their susceptibility to misalignments, which necessitate 
adjustments and result in high maintenance costs. Also, the misalignments 
degrade the performance of the system such that the doors' opening and 
closing functions are not consistently smooth. 
Linear motors potentially can provide an alternative to conventional door 
operating systems by eliminating the mechanical linkages and problems 
associated therewith. Linear motors typically include a motor primary unit 
and a motor secondary unit. However, despite the fact that the use of 
linear motors on door systems has been disclosed in various patents, 
including U.S. Pat. No. 1,881,014 to Ayers and U.S. Pat. No. 5,172,518 to 
Yoshino, many problems arise that make implementation of linear motors on 
doors unattractive. One problem encountered with linear motors used on 
elevator car doors is the difficulty in maintaining constant and small 
clearances between the motor secondary and the motor primary. The 
difficulty of maintaining these constant clearances is aggravated by the 
tendency of the elevator car doors to misalign and twist. Since one part 
of the linear motor is usually attached to the elevator car door or its 
hanger and the other part of the linear motor is attached to the elevator 
car, when the doors twist or move relative to the elevator car, the 
clearance between the parts of the motor changes. 
U.S. Pat. No. 1,881,016 to Rose issued on Oct. 4, 1932 and entitled "Door 
Operating Mechanism" shows a linear motor having a motor primary and a 
motor secondary. The patent describes a flexible connection between the 
motor secondary and the door. Although the connection allows two 
dimensional flexibility such as limited pivoting of one end of the motor 
secondary in the vertical direction relative to the elevator car door, the 
pivot still does not compensate for any twisting motions of the door that 
may occur. Thus, if the Rose configuration is used in elevator car door 
systems, any twisting motion of the doors would jeopardize the proper 
operation of the linear motion since the linear motor would not be able to 
conform to the twisting motion of the doors. Therefore, in order to 
implement linear motors on elevator car doors, a mechanism for allowing 
flexibility and relative motion between the linear motor and the elevator 
car door is required. 
Disclosure of the Invention 
It is an object of the present invention to improve the performance of a 
linear induction motor used for opening and closing elevator car doors in 
an elevator system. 
It is an object of the present invention to compensate for misalignment and 
twisting of elevator car doors in an elevator system using a linear 
induction motor for opening and closing elevator car doors. 
According to the present invention, a linear induction motor for opening 
and closing elevator car doors in an elevator system includes a motor 
primary disposed on a door hanger and moving therewith and a motor 
secondary attached onto a header bracket of the elevator car by means of a 
plurality of swivel joints. The motor secondary extends the length of the 
door travel with the swivel joint securing each end of the motor secondary 
to the elevator car. The swivel joints allow multi-dimensional flexibility 
of the motor secondary to compensate for possible misalignment and 
twisting of the elevator car doors and of the motor primary attached onto 
the elevator car door hangers. Therefore, even during misalignment and 
twisting of the elevator car doors, the motor secondary and the motor 
primary maintain constant clearances therebetween. 
One benefit of the present invention is that the swivel joints, disposed 
centrally at each end of the motor secondary, allow centralization of 
thrust forces applied from the motor primary to the motor secondary 
without producing a moment about the motor secondary. 
The foregoing and other advantages of the present invention become more 
apparent in light of the following detailed description of the exemplary 
embodiments thereof, as illustrated in the accompanying drawings.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring to FIG. 1, an elevator car door operating system 10 for opening 
and closing a pair of elevator car doors 12 that are suspended from a pair 
of door hangers 14 includes a pair of motor primaries 16 fixedly attached 
to the pair of door hangers 14 and a motor secondary 18 attached to a 
header bracket 24 secured to a cab facia 26 of the elevator car (not 
shown). 
Referring to FIG. 2, each of the motor primaries 16 includes a primary 
winding 28 and a backiron 30 spaced apart from the primary winding 28 by a 
plurality of motor spacers 32. The primary winding 28 includes a primary 
iron 34 unit with winding 36 wrapped around it and a primary surface 38 
facing the backiron 30. The backiron 30 includes an iron plate 40 having a 
backiron surface 42 facing the primary winding 28. A magnetic air gap is 
defined between the primary surface 38 and the backiron surface 42. 
Each motor primary 16 is fixedly attached to the door hangers 14 by means 
of a plurality of bolts 48 passing through the backiron 30 and the motor 
spacers 32. 
The motor secondary 18 extends the length of the elevator car door travel 
and fits between the backiron 30 and the primary winding 28 as the motor 
primaries 16 move during opening and closing of the elevator car doors 12. 
Referring to FIG. 3, the motor secondary 18 comprises a substantially flat 
plate having a first and a second faces 56, 58 bounded by a top and a 
bottom longitudinal edges 60, 62 extending the length of the motor 
secondary 18 and by a first and second vertical ends 64, 66. A secondary 
guide 72 is placed over each longitudinal edge 60, 62 of the motor 
secondary 18. 
The motor secondary 18 is movably attached to the header bracket 24 at two 
ends 64, 66 and at the center thereof, as best seen in FIG. 1. The motor 
secondary 18 is mounted to the header bracket by means of swivel joints 76 
allowing the motor secondary to move in and out of plane and to rotate 
about the joints 76, as best seen in FIGS. 1 and 5. The swivel joints 76 
also function as standoffs to allow the backiron 30 to travel between the 
header bracket 24 and the motor secondary 18. 
Referring to FIG. 4, the swivel joint 76 assembly includes a shaft 78, one 
end of which is fixedly secured to the header bracket 24. A swivel ball 80 
rides along the shaft 78, as best seen in FIG. 5. A mounting bracket 82 
includes a central opening 84 with a rounded flange 86 for fitting over 
the swivel ball 80 and a plurality of holes 88 for securing the swivel 
joint 76 to the motor secondary 18 by means of plurality of bolts 89. An 
opening 90 formed within the motor secondary 18 is in register with the 
central opening 84 of the mounting bracket 82 and allows the shaft 78 to 
pass therethrough. A bolt 92 passes through the center of the shaft 78 
with a nut 94 securing the swivel joint 76 assembly onto the header 
bracket 24 and the motor secondary 18. The swivel joint 76 shown herein is 
of standard type and is readily available from various manufacturers 
including Triangle Manufacturing Company of Oshkosh, Wis. 
Referring to FIG. 5, the swivel joints 76 allow movement of the motor 
secondary 18 with respect to the header bracket 24. As the swivel ball 80 
rides along the shaft, the motor secondary 18 can move in and out of the 
plane defined by the motor secondary 18. As the rounded flange 86 of the 
mounting bracket 82 fits over the swivel ball 80, the motor secondary 18, 
attached to the mounting bracket 24, can rotate about the three swivel 
joints. The only restricted motion is the horizontal motion, in the 
direction of thrust, within the plane defined by the motor secondary. 
When the doors 12 open and close, the swivel joints 76 isolate the motor 
from possible misalignment or impact. If the doors are either misaligned 
or impacted, such misalignments and impacts are transmitted to the door 
hangers 14 and also to the motor primary 16 that is fixedly attached to 
the door hanger 14. When the motor primary 16 moves in and out of plane, 
or is twisted, the motor secondary 18 also moves about the swivel joints 
76 so that the running clearances between the motor primary 16 and the 
motor secondary 18 remain constant. 
Another benefit of the present invention is that the swivel joints 76 are 
disposed centrally between the top longitudinal edge 60 and the bottom 
longitudinal edge 62 at each end 64, 66 of the motor secondary 18 and 
allow centralization of thrust forces applied from the motor primary 16 to 
the motor secondary without producing a moment about the motor secondary. 
Referring to FIG. 6, an additional benefit of the present invention is that 
if the door travel is too long for a single motor secondary, a pair of 
motor secondaries can be used with the central swivel joint being used as 
a joining mechanism. Two bolts 89 of the mounting bracket 82 can attach to 
one motor secondary and two bolts 89 can attach to the other motor 
secondary. 
While the present invention has been illustrated and described with respect 
to a particular embodiment thereof, it should be appreciated by those of 
ordinary skill in the art, that various modifications to this invention 
may be made without departing from the spirit and scope of the present 
invention. For example, the best mode embodiment described herein depicts 
a central opening biparting two door system with two motor primaries, a 
motor secondary and three swivel joints. For a single door configuration 
with a single motor primary, only two swivel joints on each end of the 
motor secondary would be used.