Gimbal-mounted virtual reality display system

A compliant structure which includes a sensor for sensing translation and rotation of a top plate is disclosed. The structure is composed of a base plate and three supporting legs. The legs are compliant. The deflections of the structure are substantially in a plane and the translation and twist of the top platform may be measured by the gimbaled sensor assembly attached to one of the legs.

BACKGROUND OF THE INVENTION 
1. Field of Invention 
This invention relates to the art of mechanical structures whose 
deformation can be easily measured. 
2. Description of the Prior Art 
In the field of virtual reality, displays are mounted on structures which 
can be manipulated by a user. The motion of the display is measured and is 
used to control the user's view point in a computer generated world. Such 
devices are exemplified by the art described in U.S. Pat. No. 5,436,638. 
Making a suitable structure for mounting a display on is a challenge, one 
desires that the display be movable with little force. It is also 
desirable that the platform encourages controllable motion which means 
that the perceived stiffness in the left--right directions be matched with 
forward--back and that twist also feels similarly stiff. As detailed in 
U.S. Pat. No. 5,436,638 it is desired that it be possible for the 
structure to facilitate rotations about a user. This invention provides 
that flexibility is a way which is easy to sense and measure. 
SUMMARY OF THE INVENTION 
A structure suitable for holding a display is the object of this invention. 
The platform is supported by three compliant members. One of these members 
is attached to a gimbaled mechanism which facilitates the easy measurement 
of the deflection of the platform as it is moved by the user.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows the front view of the invention. The compliant measured 
structure is composed of a base plate 105 which supports the plate for the 
display 100 on three compliant delrin legs. The front legs 101 and 102 
provide support for plate 100. The rear leg 103 provides support to 100 
and mates with the gimbaled sensor assembly 104. The plate 100 is thus 
supported in a way such that it can be moved forward/back, side to side, 
and rotated about an arbitrary vertical axis. When the plate 100 is moved 
from its rest position, the three legged structure holds it level and the 
legs flex to accommodate the new position. As the legs flex, the display 
will move in the desired direction and will also get closer to the base 
105 by a tiny amount. Deflections of the legs are generally small--in the 
range of about .+-.10 degrees or so. 
FIG. 2 illustrates how the device is put together. The legs 201 and 202 are 
mounted directly onto base plate 205 with each leg being attached with two 
screws to the base plate so the legs 201 and 202 can not rotate in place. 
The gimbaled assembly 204 is also rigidly mounted onto base plate 205. The 
top of the gimbaled assembly is threaded and attaches to leg 203. 
FIG. 3 shows the gimbaled assembly in more detail. The gimbaled assembly is 
mounted on base plate 302. The rear leg 301 is attached to the gimbaled 
assembly and the shaft which is attached to the leg 301 passes through 
block and rotary bearing 307. Rotary joint 303 provides rotation of frame 
306 so that shaft and rotary joint 305 can measure the angle of leg 301 in 
the forward/back plane. The deflection of the leg 301 is transferred 
through block 307 to frame 306 which is measured by an encoder mounted on 
305. The left/right motion of the top plate is transferred to a rotation 
of leg 301 which is transferred to block 307 and is measured by an encoder 
mounted on shaft 304. Thus we can see two of the three degrees of freedom 
of the gimbaled assembly--forward/back motion will appear at shaft 305 and 
left/right motion will appear at shaft 304. 
FIG. 4 shows another view of the gimbaled assembly. Rear leg 401 is 
attached to gimbaled assembly 404 which is mounted on base plate 403. The 
shaft 402 rotates with the rotation of leg 401 since they are attached. An 
encoder mounted on 402 will report the degree of twist of leg 401. Thus, 
as a torque is applied to the display plate 100, the rotation may be 
measured at shaft 402. 
FIG. 5 illustrates how the encoders are mounted onto the gimbaled assembly 
501. The rear leg is attached to threaded shaft 517. Shaft 503 encodes 
left/right motion of the platform and is measured by attachment of the 
encoder disk 509. The mounting plate 508, and reader 516 are mounted onto 
the gimbaled assembly. The cover 510 helps prevent dirt from fouling the 
encoder disk 509. Shaft 502 encodes forward/back motion of the platform. 
This motion is detected by attaching encoder disk 512 onto the shaft. The 
mounting plate 511 and reader 514 are attached to the gimbaled assembly 
and cover 513 prevents dirt from fouling the encoder disk. Twisting the 
platform results in a twist of the rear leg which is attached at 517 and 
appears at shaft 504 which is the other end of the threaded attachment 
point 517. Motion at shaft 504 is measured by attaching encoder disk 506 
to the shaft 504. The base plate 505 and the reader 515 are attached to 
the gimbaled assembly and cover 507 prevents dirt from fouling the encoder 
disk 506. 
FIG. 6 shows how the compliant platform is used. A user 603 looks into a 
display 601 mounted on the invention 602. The user may push the display 
forward and the encoders will register this motion and send it to the 
computer which is generating the images seen in the display 601. This will 
allow the user to move forward in the computer generated world. Pushing 
the display to the left will be measured in a similar fashion and the 
images updated accordingly. Twisting the display will be measured by the 
third encoder of the gimbals and will result in turning in the virtual 
world. Combining these motions lets a user maneuver easily in the virtual 
world. In particular, sliding to the right and twisting to the left at the 
same time results in an orbiting motion which is good for looking at the 
other side of an object. Slightly pushing forward at the same time results 
in a spiral path. 
FIG. 7 shows the details on the construction of the front two legs. The 
main body of the delrin leg 701 joins the two flexible hinge areas 703 and 
702. The leg is mounted with two screws to the base plate at the end 705. 
The end 704 is angled to mate with the mounting play for the display and 
is also attached with two fasteners so the leg can't rotate. The necking 
down 706 is so that a cover does not bind on the man body of the leg at 
maximum deflection. The joint between the hinges 703 and 702 with the main 
body of the leg 701 are radiused as shown at 707. 
FIG. 8 shows the structure of the rear leg. This delrin part is similar to 
the front legs. Main body 801 is attached to the gimbaled assembly by 
threaded hole 803. The plate for mounting the display is attached to the 
leg at the angled end 804. The hinge for the leg is 802 the transition 
from the main body of the leg to the hinge is radiused in a similar manner 
to the front legs. 
The structure is compliant in that the three legs are springy. The top 
plate on which a display may be mounted moves substantially in a plane 
relative to the base plate. This motion is measured by the gimbaled sensor 
assembly at the base of the rear leg. The encoders used to measure the 
motion could be replaced by another sensing means. For example, the 
encoders could be replaced by rotary potentiometers to measure the angles. 
Another alternative would be to use rotary switches. 
In addition to having the leg members including an explicit hinge point, it 
would be possible to design legs where the flexing occurred over the 
entire length of the leg. In this invention, the legs are made on a lathe 
from round stock but making legs whose hinge elements were not symmetric 
about the vertical axis would allow one to adjust the springiness in 
particular directions. By adjusting the cross section of the legs, a 
system could be made in which left--right motion was easy and 
forward--back motion more difficult for example. 
It would be possible to have more than two compliant supporting legs if 
desired. Thus if the display were particularly heavy or for aesthetic 
reasons, a number of additional legs could be introduced without impacting 
the performance of the structure. 
At present, the range of motion of the structure is limited by having a 
cover with three holes mounted part way up the structure. Then when the 
structure is pushed to the limit, the legs bang into the edges of the 
holes in the cover.