Spring loaded contact device and rotary connector

A spring loaded contact device having a housing with an internal bore, a spring disposed in the bore, a pin disposed in and extending from the bore, and a dimple formed in the housing that secures the pin in the bore. A first portion of the pin contacts the spring, a center portion of the pin is smaller than the first portion and protrudes from the bore, and a head of the pin is disposed external to the bore and has a rounded cylindrical end. A rotary connector using the spring loaded contact devices has first and second printed wiring boards that rotate relative to each other that are electrically interconnected using a plurality of spring loaded contact devices disposed on the first printed wiring board. The spring-loaded contact devices are used to transfer electrical signals or power to conductive contacts formed on the second printed wiring board.

BACKGROUND OF THE INVENTION 
The present invention generally relates to rotary connectors, and more 
particularly, to an improved spring loaded contact device and spring 
loaded rotary connector having rotatable printed wiring boards 
electrically interconnected by a plurality of the spring loaded contact 
devices that slide on conductive traces. 
The purpose of a rotary connector is to transmit power or signals from a 
stationary object to a moving or rotating object. A conventional slip ring 
connector is a very fragile device. Conventional slip rings are 
impractical and very vulnerable to road hazards for use in automobile and 
transportation vehicles. In harsh environments, such as those encountered 
in aircraft and vehicular use, such slip ring connectors often fail due to 
the fragile nature of brushes and rings used therein. Conventional wire 
wrap connectors are used that exhibit very high failure rates. 
U.S. patent application Ser. 08/680,075, filed Jul. 15, 1996, entitled 
"Spring Loaded Rotary Connector" assigned to the assignee of the present 
invention, discloses a spring loaded rotary connector having rotatable 
printed wiring boards electrically interconnected by a plurality of spring 
loaded plungers that slide on metal tracks. While conceptually simple, the 
design of the spring loaded contact devices is extremely important so that 
optimal contact is achieved between them and the metal tracks formed on 
the rotatable printed wiring boards. Proper design is required to produce 
a long life connector that is reliable and operates smoothly under varying 
loading conditions. 
Therefore, it is an objective of the present invention to provide for an 
improved spring loaded contact device and spring loaded rotary connector 
having rotatable printed wiring boards with conductive traces that are 
electrically interconnected by means of a plurality of the spring loaded 
contact devices. 
SUMMARY OF THE INVENTION 
In order to meet the above and other objectives, the present invention 
provides for an improved spring loaded contact device and spring loaded 
rotary connector employing same. The spring loaded contact device has a 
housing with an internal bore, a spring disposed in the bore, a pin 
disposed in and extending from the bore, and a dimple formed in the 
housing that secures the pin in the bore. A first portion of the pin 
contacts the spring, a center portion of the pin is smaller than the first 
portion and protrudes from the bore, and a head of the pin is disposed 
external to the bore and has a rounded cylindrical end. 
The spring loaded contact device is optimally designed for use in 
constructing a spring loaded connector having a plurality of printed 
wiring boards that rotate relative to each other that are electrically 
interconnected using a plurality of the spring loaded contact devices. The 
spring loaded contact devices are disposed on one printed wiring board and 
transfer electrical signals or power to metallized contacts or conductive 
traces formed on a second printed wiring board. The spring loaded contact 
devices are very rugged and provide for a rotary connector having long 
life. The spring loaded contact devices are sandwiched and sealed between 
the printed wiring boards and can withstand harsh highway or outdoor 
environments. 
The spring loaded contact devices and conductive traces on the printed 
wiring boards provide for a rotary connector that is used to transmit 
power or signals from a stationary object to a moving object. Rotary 
connectors employing the spring loaded contact devices may be used to 
replace slip-ring type connectors currently used in many aircraft and 
vehicle applications. The spring loaded contact devices make the spring 
loaded rotary connector very rugged and it is reliable in harsh outdoor 
environments. Two rotary connectors using the present spring loaded 
contact devices have been built and tested on an auto axle and have met 
all expectations. The present invention may be used in rotary connectors 
designed for use in cars, trucks, motor homes, motorcycles, and aircraft, 
and wherever rotary electrical connectors may be employed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to the drawing figures, FIG. 1 is a cross sectional view of a 
spring loaded contact device 10 in accordance with the principles of the 
present invention. The spring loaded contact device 10 comprises a 
cylindrical housing 11 having an internal bore 12 and a closed first end 
with a hole 14 therethrough. The housing 11 has a first diameter 13a 
adjacent the first end for a portion (about one-third) of the length of 
the housing 11, and a slightly larger diameter 13b for substantially the 
remainder of the housing 11, and a lip 13c formed at a second or opposite 
end of the housing 11 from the first end. A spring 21 is disposed in the 
bore 12 which has one end disposed adjacent the hole 14 in the housing 11. 
A pin 20 is disposed in the bore 12 and has a cylindrical portion 16 that 
is disposed in the bore 12 and contacts the second end of the spring 21. 
The pin 20 has a center portion 17 that is smaller in diameter than the 
first portion 16. The pin 20 is tapered between the first and second 
portions 16, 17. A dimple 15 is formed in the housing 11 that secures the 
pin 20 in the bore 12. The pin has a head 18 that has a cylindrical shape 
that is rounded at its end. The head 18 of the pin 20 is designed to ride 
on metal traces formed on a printed wiring board as shown in FIGS. 2-4. 
The spring loaded contact device 10 is designed so that it is extremely 
long wearing and resilient. The components of the spring loaded contact 
device 10 may be formed from brass, beryllium copper or preferably high 
purity gold, such as from a material known as exotic gold, manufactured by 
Ny Corporation, for example. 
Thus, in its simplest form, the spring loaded contact device 10 comprises a 
housing 11 having an internal bore 12, a spring 21 disposed in the bore 
12, a pin 20 disposed in and extending from the bore 12, and a dimple 15 
formed in the housing 11 that secures the first portion 16 of the pin 20 
in the bore 12. The first portion 16 of the pin 20 contacts the spring 21, 
the center portion 17 of the pin 20 is smaller than the first portion 16 
and protrudes from the bore 12, and the head 18 of the pin 20 is disposed 
external to the bore 12 and has a rounded cylindrical end. 
In a reduced to practice embodiment of the spring loaded contact device 10, 
it had a fully extended length of 0.220 inches, the first diameter 13a of 
the housing 11 was 0.035 inches, the slightly larger diameter 13b was 
0.037 inches, the lip 13c and head 18 had diameter of 0.040 inches, the 
length of the housing 11 was 0.160 inches, the diameter of the hole 14 was 
0.010 inches, the head 18 had a length of 0.030 inches, and the head 18 
had a curved contact surface with a radius of 0.032 inches. The pin 20 had 
a travel of 0.030 inches. The housing 11, spring 21, and pin 20 were made 
from exotic gold to provide a spring loaded contact device 10 having 
excellent electrical conductivity. 
FIG. 2 illustrates a cross sectional side view of a spring-loaded rotary 
connector 30 employing a plurality of spring loaded contact devices 10 
shown in FIG. 1. FIG. 3 illustrates a bottom view of a spring-loaded 
rotary connector 30 of FIG. 2. FIG. 4 illustrates an enlarged view of a 
portion of the spring loaded rotary connector 30 of FIG. 2. The 
spring-loaded rotary connector 30 is illustrated with reference to its use 
in a shaft-type application, wherein its rotatable components are coupled 
to a shaft 33 that rotates relative to a fixed enclosure 31. However, it 
is to be understood that the connector 30 may be designed so that the 
enclosure 31 rotates relative to a fixed shaft 33. 
The exemplary rotary connector 30 is comprised of a enclosure 31 having 
first and second covers 32a, 32b that may be secured to the enclosure 31 
by means of a plurality of screws 41, for example. A rotatable shaft 33 is 
disposed through the center of the enclosure 31, and a disk 36 and collar 
35 extend radially outward from the shaft 33. First and second bearings 
34a, 34b are coupled to the shaft 33 on opposite sides of the disk 36 and 
the collar 35. The first and second covers 32a, 32b secure outer races of 
the bearings 34a, 34b. Thus the shaft 33, disk 36, and collar 35 rotate 
with respect to the enclosure 31 and covers 32a, 32b. 
Referring to FIGS. 2 and 4, a first printed wiring board 37 is secured to 
the disk 36 by means of adhesive 44, such as a thin layer of double sided 
adhesive tape 44, for example. The first printed wiring board 37 has a 
plurality of conductive traces 43 or contacts 43 that are connected to a 
plurality of spring loaded contact devices 10. The spring loaded contact 
devices 10 may be secured in a plurality of plated holes, for example, 
formed in the first printed wiring board 37. The plurality conductive 
traces 43 or contacts 43 are connected (such as by soldering) by way of a 
plurality of wires 45 to a connector 46. The plurality of spring loaded 
contact devices 10 contact a corresponding plurality of electrically 
isolated conductive traces 42 disposed on a second printed wiring board 
39. The second printed wiring board 39 is secured to the enclosure 31. The 
plurality of electrically isolated conductive traces 42 are typically 
connected to a sensor or other device (not shown). A spacer 38 is disposed 
between the first and second printed wiring boards 37, 39. The spacer 38 
is used to control the amount of deflection of the first and second 
printed wiring boards 37, 39, and hence the amount of deflection of the 
spring-loaded rotary connector 30. 
As should be readily apparent, the spring loaded contact devices 10 slide 
on the conductive traces 42 when the first printed wiring board 37 rotates 
with respect to the second printed wiring board 39. The rotation of the 
shaft 33 relative to the enclosure 31 is represented by the arrow in FIG. 
3. Consequently, electrical signals are transferred from the first printed 
wiring board 37 to the second printed wiring board 39 by way of the spring 
loaded contact devices 10 and the conductive traces 42 on the second 
printed wiring board 39. 
The spring-loaded rotary connector 30 permits relative angular movement 
between the shaft 33 and the enclosure 31 that secures the second printed 
wiring board 39. The spring-loaded rotary connector 30 also compensates 
for movement between the first and second printed wiring boards 37, 39 in 
terms of their separation distance. More specifically, if the respective 
planes of the first and second printed wiring boards 37, 39 are not 
parallel, then the pins 20 of the spring loaded contact devices 10 adjust 
for the differences in distance therebetween. This may be caused by 
vibration of a vehicle, for example, or relative movement between the 
components that are connected to the shaft 33 and the enclosure 31 to 
which the second printed wiring board 39 is secured. This might be the 
relative movement between an axle and a wheel of a vehicle, for example. 
The relative motion is compensated for by the rounded shape of the heads 
18 of the spring loaded contact devices 10 which operate to keep 
electrical contact with the respective conductive traces 42 irrespective 
of the relative angular relationship between the first and second printed 
wiring boards 37, 39. 
The rotary connector 10 is shown as comprising flat printed wiring boards 
37, 39 that are designed to engage the shaft 11. However, it is to be 
understood that contoured printed wiring boards 37, 39 such as may be 
provided by cylindrical or spherical printed wiring boards 37, 39, for 
example, may be employed as well as flat printed wiring boards 37, 39. 
Therefore, the connector 30 is not limited to a flat configuration. 
The spring loaded contact devices 10 and the rotary connector 30 employing 
same have been designed to withstand harsh outdoor environments such as 
when the connector 30 is used in conjunction with axles of automobiles and 
trucks, for example. The rotary connector 30 may be used to transmit power 
or signals from a stationary object to a moving object. The rotary 
connector 30 has been developed to replace existing slip-ring type 
connectors conventionally used in many aircraft and vehicle applications. 
The spring loaded rotary connector 30 is rugged and performs well in harsh 
outdoor environments. Two connectors 30 have been built and tested on an 
auto axle, and have performed well. The spring loaded contact devices 10 
and the rotary connector 30 in which they are employed may be used in 
cars, trucks, motor homes, motorcycles, and aircraft, wherever rotary 
electrical connectors are used. 
Thus, an improved spring loaded contact device and spring-loaded rotary 
connector have been described. It is to be understood that the 
above-described embodiments are merely illustrative of some of the many 
specific embodiments which represent applications of the principles of the 
present invention. Clearly, numerous and other arrangements can be readily 
devised by those skilled in the art without departing from the scope of 
the invention.