US 3814942 A
A human head restraint system for positively restraining the human head in a predetermined position utilizing eccentrically pivoted cams on either side of the predetermined position for engaging various sizes of human heads. The active area of the cam profiles are non-circularly shaped for insuring that the area of actual contact with most human head sizes is close to a line passing through the cam pivot points thus minimizing the effective lever arm available to the restrained head for effecting movement of the restraining cams from the predetermined position.
Description (OCR text may contain errors)
0 United States Patent 11 1 1111 3,814,942
Darden June 4, 1974 1 HUMAN HEAD RESTRAHNT SYSTEM Primary ExaminerArchie R. Borchelt 75 Inventor: Stephen c. Darden, Reston, Va. igg g g Darby &  Assignee: Acuity Systems, Incorporated, cushmm1 McLean, Va.
 Filed: NOV. 10, 1972 57 ABSTRACT PP 305,330 A human head restraint system for positively restraining the human head in a predetermined position utiliz- 52 us. on. 250/456, 351/38 ing eccemfically PFY Cams eithefi Side the 51 1m. (31. G01n 21/00 predetermmed P P for engagmg vanous s1zes of 581 Field of Search 351/38; 250/451, 456; heads- The acme W 9 the Cam P fi are 74/568 F5; 297/39] 392, 404 non-c1rculariy shaped for msurmg that the area of actual contact w1th most human head s1zes 15 close to a  References Cited line paszing tlf1fr0tt1 gh tlhe cam pivot plogits tthutshminim1z1ng e e ec we ever arm ava1a e 0 e re- UNITED STATES PATENTS strained head for effecting movement of the restraining cams from the predetermined position. ea er 4 Claims, 4 Drawing Figures PATENTEDJUN 4:914
/ pw/ae Amy HUMAN HEAD RESTRAINT SYSTEM This invention generally relates to apparatus for restraining a human head in a predetermined position. Such human restraint systems are necessary in many medical and research applications, especially in ophthalmology.
Perhaps the most conventional apparatus for restaining human heads is a simple forehead stop or strap combined with a chin rest. However, such arrangements permit easy lateral movements of the head (from side to side) which are unacceptable for some applications such as with automatic refractometers wherein automatic measurements are carried out for analyzing the optical properties of the human eye. In such types of apparatus it is important that the human head be held to the desired predetermined position within a much higher degree of tolerance than is possible with conventional simple restraint systems.
One prior attempt at solving this problem is disclosed in US. Pat. No. 3,594,072 Feather which attempts to stabilize the head against lateral movement by utilizing two eccentrically pivoted circular disks for engaging either side of the head. In this system, the eccentrically pivoted disks do not rotate freely but rather have sufficient friction to prevent free rotation. While the eccentrically pivoted circular disks permit a single system to fit heads of varying sizes, unless the circular disks are actually very rigidly clamped against further pivoting after being positioned, they do not actually constrain the head. Rather, they merely provide the patient with some tactile feedback when his head does move laterally. That is, in general, the area of contact with the restrained head is so far removed from a line connecting the two pivot points that the head is provided with a significant lever arm for moving the disks as a result of any lateral force which the head may exert thereagainst.
It has now been discovered that a significantly improved human head restraint apparatus results from using specially profiled cams in place of the eccentrically pivoted circular disks utilized heretofor. The cams utilized in this invention are also eccentrically pivoted to permit accommodation of different head sizes by rotating the cams about the eccentric pivot axes. However, once the specially shaped cam profiles actually engage opposite sides of the head, they positively constrain it against lateral movements because any such lateral forces that might be exerted by the head are always directed close to a line passing through the pivot axes. In other words, the area of contact with the human is always maintained relatively close to the line passing through the two pivot points such that there is no significant lever arm available about the pivot point to permit substantial lateral head movements.
Further, positive restrainment of the human head may be obtained by spring biasing the cams for engagement with the human head and damping rotation in the opposite direction with dashpots. Typically, in operation, the subject invention is utilized by placing the subjects head approximately in place with the chin on an appropriate chin rest located between two specially shaped or profiled cams which are pivoted on eitherside of the predetermined position within which the human head is desired to be restrained. Thereafter. the cams are simply released so that they drop into position and engage the head. Because the points of contact are close to'a line passing through the two pivot points, the lever arm available to the subject for attempting to move the cams laterally is very short and thus no substantial movement in a lateral direction is possible. This is especially so with respect to the embodiment where the cams are spring loaded for rotation in the direction towards the subject head and where rotation in the opposite direction is damped.
The many advantages and objects of this invention will become more apparent from the following detailed description of the invention in conjunction with the accompanying drawings of which:
FIG. 1 is a schematic depiction of a prior art head restraint system;
FIG. 2 is a similar schematic depiction of an exemplary embodiment of the human head restraint system of this invention;
FIG. 3 is pictorial representation of the exemplary embodiment of this invention attached to an autorefractometer; and
FIG. 4 is a schematic depiction of the mechanical system attached to one of the cams in the exemplary embodiment of this invention.
Referring to FIG. 1, a prior art technique for restrain ing the human head 10 is depicted. Here, circular disks l2, 14 are pivoted about eccentric axes 16, 18 respectively. Rotation about the eccentric axes causes the circular disks to come into contact with the human head 10 at contact points 20 and 22 respectively. In a typical case as shown in FIG. 1, the contact points 20 and 22 will result in'a significant lever arm (I such that the head i 10 can easily move the disks l2 and 14 by applying lateral forces thereto unless these disks are physically locked in position after engaging the head 10.
An exemplary embodiment of this invention is shown in FIG. 2. Here, specially profiled cams-30, 32 are eccentrically located on either side of the head 38. Because of the specially shaped cam profile 40 and 42, the areas of contact 44, 46 respectively with the head 38 will always lie very close to a line connecting the pivot axes 34, 36. Accordingly, substantially no lever arm is present to permit undesired rotation of the cams 30 and 32 due to lateral head forces exerted by the head 38.
As should now be appreciated, the exact shape of the cam profile 44, 42 can be varied within reasonable limits so long as the resulting areas of contact 44, 46 for the desired range of head sizes 38 lies reasonably close to a line connecting the two pivot points 34, 36. One form of cam profile that will provide such a result is a catenary curve. However, more generally, acceptable results should come from using any cam profile having a rise (i.e., an increase in radius per degree of arc) to radius ratio less than 10' and whose minimum radius exceeds one inch. Such a cam profile will result in contact points with the human head 38 within about 20 of a line connecting the two cam pivot axes 34, 36. That is, as shown in FIG. 2 the contact points 44, 46 will always lie within the arcs a where the magnitude of a will vary somewhat depending upon the particular profile shapes 40, 42 and/or the range of head sizes 38 with which the restraint system is designed to operate successfully.
For many applications, such as for restraining heads in an automatic refractometer system, the system should be designed to accept a range of head sizes which differs by at least 3 inches in lateral dimensions.
Furthermore, the head should usually also be restrained in the other two dimensions (vertically and frontally) so that the nominal line between the pivotal axes 34, 36 intersects the head at approximately 100 to l 30 millimeters behind the vertex of the cornea and approximately to 40 millimeters above the vertex of the cornea. As previously stated, the cam profiles 40 and 42 should be defined to contact the head within an are a that is within approximately 20 of the line connecting the two pivotal axes.
FIG. 3 shows the exemplary embodiment with earns and 32 mounted on an automatic refractometer 50. Here, the eccentric pivotal axes 34, 35 are disposed on either side of the predetermined aperture 52 through which the patient is supposed to look and at which position the patients head is to be restrained. A chin rest 54 is disposed below and between the pivotal axes 34 and 36. A head strap 56 is also provided for approximately positioning the head in the forward direction while the chin rest positions the head in the vertical direction as previously discussed. Restraint of the head in the lateral direction is, of course, achieved by rotating the earns 30, 32 inward into contact with the human head as shown in FIG. 2.
,C am 30 is shown again in FIG. 4 together with a schematic depiction of some attached mechanical apparatus which is preferred in the exemplary embodiment. Specifically, the pivotal axis 34 is seen to comprise a shaft 60 which is rotatably mounted within bearings 62, 64. The shaft 60 is spring biased by spring 66 and lever arm 68 for rotation inwardly in the direction which will result in engagement of the specially shaped cam surface with the human head. At the same time, rotation in the opposite direction is clamped with a dash-pot 70 connected to lever arm 72 as should now be apparent. The spring constant and/or damping characteristics of the particular dash-pot (typically an air dashpot) may be selected for particular applications to result in particular degrees of head restrainment as should now be appreciated by those in the art.
While only one exemplary embodiment of the invention has been specifically discussed in detail above, those in the art will readily appreciate that many modifications may be made in the exemplary embodiment without in any way departing from the spirit and teaching of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention.
What is claimed is:
1. Apparatus for restraining a human head in a predetermined position, said apparatus comprising:
a axis disposed on either side of said predetermined position, and
a cam eccentrically pivoted about each of said axes,
said cams having a non-circular profile for engaging a predetermined range of head sizes at contact points within a 20 are from a line connecting the two axes, and wherein the noncircular profile of each of said cams has a rise (increase of radius from its axis per degree of arc) to radius ratio which is less than l0 and a minimum radius exceeding one inch.
2. Apparatus as in claim 1 further comprising means for spring biasing each of said cams to rotate in a direction causing engagement of the cam profile with a human head when disposed in said predetermined position.
3. Apparatus as in claim 2 further comprising means for damping cam rotation opposite to the said direction of spring biased rotation.
4. Apparatus as in claim 1 further comprising a chin rest disposed below and between said pivotal axes.