Integral ball cage for pointing device

An electronic mouse with an integral ball cage. The ball cage in one embodiment has integrally formed extensions having openings for enclosed shaft encoders and a pressure roller. The shaft encoders are preferably made of a single piece of plastic. The ball cage is preferably formed as part of the lower housing of the mouse.

FIELD OF THE INVENTION 
This application relates to pointing devices such as electronic mice or 
trackballs, and particularly relates to the ball cage therein and its 
components. 
BACKGROUND OF THE INVENTION 
Electronic mice are well known for their advantages as pointing devices. 
Basically, an electronic mouse converts the linear movement of the mouse 
over a surface into digital signals to control the cursor of the computer. 
One common type of electronic mouse uses an optomechanical interface, 
whereby the movement of a ball drives at least two shaft encoders. The 
shaft encoders in turn drive an encoding wheel located between a 
photosource and a photodetector. The movement of the encoding wheel causes 
pulses of light to reach the photodetector, which creates a pulse train 
indicative of movement of the mouse. 
To provide accurate correlation between the movement of the mouse and 
movement of the cursor, the ball in an optomechanical mouse must be 
supported within fairly close tolerances. In substantial part, these close 
tolerances are necessary to maintain the ball in constant contact with the 
shaft encoders. In most such mice, a ball cage is provided to maintain the 
ball in proper position, and the shaft encoders are integrated into the 
ball cage. In the past, the ball cage has been a complicated assembly 
comprising in excess of twenty parts, including multiple parts for the 
shaft encoders and related mechanical elements, a pressure roller to 
maintain the ball in contact with the shaft encoders, and the ball cage 
itself. Also, a traction spring with hooks, which is comparatively 
difficult to assemble, has been required by many prior designs. 
Such complicated assemblies increase manufacturing costs and reduce 
reliability. In addition, prior art designs typically do not lend 
themselves to use in automatic assembly. There has therefore been a need 
for a simple ball cage configuration which provides at least equal 
accuracy while reducing complexity and part count and permitting automatic 
assembly. 
SUMMARY OF THE INVENTION 
The present invention substantially overcomes the limitations of the prior 
art by providing an integral ball cage having only six parts which is 
capable of automated assembly. In particular, the shaft encoders are 
formed integrally, as is the pressure roller, and the integrated shaft 
encoder and pressure roller simply clip into the remainder of the ball 
cage. Likewise, the optical elements have been simplified to eliminate the 
need for a mask by building the mask function into the geometry of the 
photosensor, thereby also reducing part count. Finally, the pressure 
roller and its shaft are formed integrally, making assembly much simpler. 
Additionally, the design has been modified to permit use of an 
inexpensive, simple, and more easily assembled compression coil spring. 
Two embodiments, each an improvement over the prior art, are disclosed. In 
the first embodiment, the ball cage is mounted on the printed circuit 
board which supports the logic and the optical elements. In a second 
embodiment, the ball cage can be integrated into the bottom housing rather 
than being mounted on the printed circuit board, further simplifying 
assembly and improving reliability, and also allowing the PCB to be 
reduced in size. 
In either embodiment, the resulting ball cage is, by comparison with the 
prior art, much simpler to manufacture and assemble, thereby improving 
both yield and reliability. Importantly, the new ball cage is adapted well 
to automated assembly techniques. 
It is one object of the present invention to provide an improved 
optomechanical mouse in which the ball cage and remaining elements are 
capable of automatic assembly. 
It is another object of the present invention to provide an optomechanical 
mouse having a highly integrated ball cage. 
It is a further object of the present invention to provide a ball cage 
having a minimal number of moving parts. 
It is a still further object of the present invention to provide an 
optomechanical mouse having a highly integrated ball cage and optical 
elements which can be assembled by machine.

DETAILED DESCRIPTION OF THE INVENTION 
Referring first to FIG. 1, an optomechanical mouse constructed according to 
one embodiment of the present invention, indicated generally at 10, is 
shown in exploded view. For simplicity, only a ball cage for an electronic 
mouse will be shown, although the present invention could be implemented 
in a trackball without major modification. The mouse 10 includes an upper 
housing 20, a printed circuit board 30 to which a ball cage 40 is mounted, 
a lower housing 50, a ball 60, and a belly door 70 which connects into the 
lower housing for retaining the ball within the ball cage 40. 
Alternatively, and as is described in greater detail hereinafter, the ball 
cage 40 could be mounted to another component, and for example could be 
formed integrally, that is, as a single piece, with the lower housing 50. 
The printed circuit board 30 shown in FIG. 1 includes circuitry for 
converting the analog movement of the ball 60 into digital signals. 
Switches 150a-c interact with buttons 180a-c in a conventional manner to 
send user commands to the associated computer system. Depending on whether 
the mouse is a serial device or a bus board device, the printed circuit 
board may include either a microprocessor (for the serial configuration) 
or a simpler logic set (the bus version). The logic on the printed circuit 
board 30 for the serial version is typically equivalent to that included 
in a Logitech N-9 serial mouse, while the logic for the bus version is 
equivalent to that included in a Logitech N-9 bus mouse. Alternatively, 
the logic may be processor based, such as in Logitech's S2 mouse or Combi 
mouse. The particular type of logic found on the PCB 30 will depend on the 
port to which the mouse will be connected. 
Referring next to FIGS. 2a-d, the ball cage of the present invention can be 
better appreciated. Although the ball cage is integrally formed, for 
purposes of illumination the ball cage will be described as a plurality of 
separate parts. The ball cage 40 can be seen to include a central ball 
enclosing section 110 having extensions 120 and 130 extending laterally 
therefrom. The extension 120 and 130 are positioned orthogonally to one 
another and provide support for integrated shaft encoders 140 and 150, 
which are better described in FIG. 6. The ball 60 resides within the 
central section 110. 
The extensions 120 and 130 may be further appreciated by taking FIG. 4 in 
conjunction with FIG. 2a. FIG. 4 shows in cross-section, together with 
FIG. 3, the arrangement by which a shaft encoder 140 is clip mounted into 
retainer member 135 of the ball cage extension 120. A similar arrangement 
is used for the shaft encoder 150 mounted in ball cage extension 130. The 
extensions 120 and 130 may each be seen to include an upper shroud 125 and 
to be formed to include spindle supports for receiving the shaft encoders. 
The central ball enclosing section 110 further supports an integrally 
formed pressure roller housing 160, also seen in cross-sectional view in 
FIGS. 3 and 5. A pressure roller fork 170, formed independently from the 
housing 110, is suspended from an upper portion of the pressure roller 
housing 160, and in turn supports a pressure roller 180. The pressure 
roller 180 includes a pair of spindles 190 which extend into holes or 
slots 200 in the fork 170, best seen in the sectional view of FIG. 5. It 
can be seen that the spindles 190 eliminate the need for a shaft through 
the pressure roller, and thus substantially simplify assembly of the 
pressure roller in the pressure roller fork. The pressure roller fork 170, 
and in turn the pressure roller itself, is urged into engagement with the 
ball 60 by means of a spring 210 which extends between an inside portion 
of the housing 160 and an outside portion of the fork 170. It will be 
appreciated that the spring 210 operates in compression, which simplifies 
assembly. The pressure roller thereby maintains the ball 60 in contact 
with the shaft encoders 140 and 150 to ensure a high level of accuracy in 
translating movement of the ball 60 into movement of the cursor on the 
video screen of the associated computer system. 
Turning to FIG. 6a-d, the shaft encoders 140 and 150 can be better 
appreciated. Each shaft encoder includes an integrally formed slotted disk 
220, a shaft portion 230 and a pair of spindles 240 which extend into 
appropriate receiving holes in the extensions 120 and 130. The shaft 
portion 230 includes a disk support portion 250, a lightweight 
strengthening portion 260 and a cylindrical portion 270. The portion 260 
may be seen from FIG. 6c to have a "+" shaped cross-section in some 
embodiments to maintain constant wall thickness and prevent deformation, 
but in at least some embodiments a cylindrical cross section is 
preferable. The number of slits in the disk 220 can be adjusted according 
to the desired resolution of the mouse in dots per inch. The arrangement 
shown is FIG. 6b is appropriate for 400 dpi resolution. From FIG. 6d, the 
shaft encoder 140 can be seen to be integrally formed, typically of Minion 
11 C1 40 BKB 86 polymer, while the ball cage 40 is typically made from 
DELRIN 500 CL or other suitably stable polymer having a low frictional 
coefficient. 
A key advantage of the present invention is its simplified assembly. The 
integrated shaft encoders 140 and 150 simply clip into the remainder of 
the ball cage 40. The pressure roller 180 simply clips into the pressure 
roller fork 170, and the spring 210 is maintained in compression. As a 
result, these elements are well adapted to conventional automated assembly 
techniques, unlike the prior art. 
Shown in FIGS. 7, 8A-B and 9A-B is an alternative to the the embodiment of 
FIGS. 1-6. In particular, the embodiment of FIGS. 7-9A-B further 
integrates the ball cage into the lower housing, as shown in the exploded 
perspective view of FIG. 7. It will be appreciated that the housing of 
this embodiment can vary significantly from the housing of the first 
embodiment discussed above without altering any aspect of the present 
invention. 
In the arrangement of FIGS. 7-9A-B, the shaft encoders are mounted directly 
onto the lower housing, and the optical elements are mounted on a printed 
circuit board containing the other conventional logic. To properly 
position the PCB over the shaft encoders, the PCB is mounted in an 
inverted position, and the optical elements fit into retainers on the 
lower housing. Such an arrangement permits simplified assembly, and again 
is optimized for automated assembly techniques. 
In particular, and still referring to FIG. 7, a mouse according to the 
present invention is indicated at 700, and includes an upper housing 710, 
a printed circuit board 720, a switch plate 730, a connecting cable 740 
extending between the PCB 720 and the plate 730, a lower housing 750, a 
ball 760 and a belly door 770. During normal operation, the belly door 770 
is interlocked with the lower housing 750 to properly position the ball 
760 into a ball cage 772 on the housing 750. 
For convenience, the PCB 720 is shown in inverted view, with the component 
side up, whereas in normal operation the PCB 720 is mounted with the 
component side down as depicted by the phantom lines 773 in FIG. 7. The 
PCB 720 includes first and second pairs of optical emitters and receivers 
774A-B, typically LEDs and phototransistors. When positioned on the lower 
housing 750, locating pins 776 in the lower housing 750 are inserted 
through holes 778 on the PCB 720. This positioning also places the optical 
emitters and receivers 774A-B into enclosure pairs 780A-B, such that each 
emitter and receiver 774 inserts into an enclosure 780. 
The PCB 720 is locked into position on the locating pins 776 by means of 
the upper housing 710 which includes positioning pins (not shown) on its 
underside and is locked into position relative to the lower housing by 
means of retaining clips 790, which mate with corresponding parts on the 
underside of the upper housing 710. The output of the mouse is provided 
through a cable connection 808, to which may be connected a conventional 
multiwire cable. 
Referring to FIGS. 8A-B and 9A-B, integrally formed shaft encoders 794 and 
796 each insert into retainer pairs 798A-B and 800A-B, adjacent the ball 
cage 772. The ball cage 772 includes openings therethrough, best seen in 
FIG. 9A, to permit the pressure roller portions 804 of the shaft encoders 
794 and 796 to contact the ball 760. In addition, the ball cage 772 
includes an opening 840 (FIG. 8A) for the pressure wheel assembly 806, 
constructed the same as the pressure wheel assembly in the first 
embodiment described hereinabove, to contact the ball 760. The back end of 
the compression coil spring of the pressure wheel assembly 806 seats 
around a pin 842, and the fork of the pressure wheel assembly 806 is 
clipped into retainers 844. The switch plate 730 (FIG. 7) is located on 
spacers 820 and clips into position by means of retaining clips 822. The 
switch plate 730 includes one or more switches 824 for performing control 
or data functions as dictated by the software. 
Referring particularly to FIG. 8B, the belly door clip 828 is retained in 
place on a flange 850, and openings 852 and 854 are provided through the 
bottom of the lower housing to ensure clearance for the shaft encoders 794 
and 796. The position of the pin 842 can also be seen relative to the 
remainder of the ball cage 772. 
One feature of the embodiment shown in FIGS. 7-9A-B is that it permits 
extremely small balls to be used. For example, in the embodiment shown, 
the roller ball 760 can be on the order of 15 mm, and weigh on the order 
of 9 grams, using a steel core with a rubber coating. This provides 
substantially the same weight as the ball in the first embodiment 
discussed above, but with a substantially reduced diameter. 
Referring particularly to FIG. 9B, which shows in detail the enclosure pair 
780B as indicated by the circle labeled "Z" in FIG. 8A, the relative 
locations of the enclosure pair 780B and the opening 852 for the shaft 
encoder 796 can be better appreciated. It can be seen from the Figure that 
one side of the enclosure pair, preferably for the receiver, need not be 
fully enclosed. 
Having fully described a preferred embodiment of the present invention 
together with alternatives, it will be apparent to those of ordinary skill 
in the art that numerous alternatives and equivalents exist which do not 
depart from the invention set forth above. It is therefore to be 
understood that the invention is not to be limited by the foregoing 
description, but only by the appended claims.