RELATED APPLICATIONS  
   This application is a continuation-in-part of prior U.S. patent application Ser. No. 10/236,687, filed Sep. 5, 2002 now U.S. Pat. No. 6,893,096. The prior application is incorporated herein by this reference. 


   FIELD  
   This invention relates to a mechanism for adjustably supporting a headrest relative to a chair back. 
   BACKGROUND  
   In many situations, and particularly in medical and dental chair situations, chairs are provided with a back and a headrest which projects above the back. Attempts have been made to produce a comfortable and easily adjusted headrest, but for the most part these have not provided the range of adjustability and ease of use that may be desired. 
   The headrest often is a somewhat pillow-shaped element spaced from the upper edge of the chair back and needs to be positioned to comfortably cradle the user&#39;s head. The comfort and adaptability of the headrest will be determined in great part by its angular position relative to the chair back, its position relative to the plane of the support surface of the chair back, and its distance from the top of the chair back. Each of these may require different positioning due to the characteristics of the user. 
   Many conventional headrests on chairs, such as dental chairs, are mounted on the chair back through mechanism which provides some degree of adjustability. However, the adjustment may require loosening of a screw-actuated mechanism, adjusting the headrest, and then having to screw the mechanism back to a tightened condition. This often is a two-handed operation and requires more operator time and effort than is desired. 
   A more desirable mechanism would allow the headrest to be locked in a desired position with the mechanism at rest, be able to be released by a single-hand actuation, with release of the actuator then returning the mechanism to a locked condition. 
   Further, for matters of hygiene, a plastic bag, or other covering, often is placed over the headrest and actuator mechanism making it difficult to access screw actuators or other conventional adjustment mechanism. Thus, a mechanism which permits one-handed adjustment and which may be easily operated through such a covering would be desirable. 
   Further, it is desirable to have a headrest support and adjustment mechanism which permits at least two degrees of pivotal freedom. Such would allow the mechanism to be pivoted, or rotated, fore-and-aft relative to the chair back, and then have another adjustment permitting pivoting of the headrest itself relative to remainder portions of the mechanism. 
   In the past, the height adjustment of the headrest above the chair back generally has been permitted only through a major operating stem which is slidable relative to the chair back and then frictionally held in position. There has been little opportunity for minor adjustment of the height of the headrest once the stem is held in place. A need is apparent for some auxiliary slide mechanism allowing simple raising and lowering of the headrest relative to the chair back which may be accomplished either by the operator or the patient/user of the chair. 
   Additionally, it has been found that many headrests and headrest adjustment mechanisms are so thick, when measured front-to-back, that when the chair, headrest and patient are laid back to a nearly horizontal position, with the patient&#39;s head preferably as close to the operator&#39;s (dentist or hygienist) lap as possible, the patient&#39;s head still is elevated some distance above the operator&#39;s lap. This can produce an inconvenient working position for the operator, requiring that their hands and wrists be placed in undesirable positions. It has been found that the lower the patient&#39;s head may be relative to the operator&#39;s lap, the more desirable the angle for the operator&#39;s hands and wrists. Thus, a thinner mechanism and headrest are desirable to allow such. 
   Thus it is desirable to provide headrest adjustment mechanism which can be worked through a covering bag, is easy to clean, is simple to operate, is reduced to as small a package as possible to provide good positioning of the patient for the operator to work on, and is operated with a single hand operated manual actuator which requires a minimal amount of force to release the headrest from a lockup position to permit adjustment, yet when the actuator is released, positive locking for the headrest in a desired orientation is provided. 
   SUMMARY  
   Described herein are embodiments of the headrest support and adjustment mechanism that address many of the disadvantages of the prior art. 
   According to one embodiment, a mechanism for supporting and permitting selected adjustment of the position of a headrest relative to a chair to which the headrest is movably attached comprises a body, a first pivotable connection, a second pivotable connection and a selectively releasable locking mechanism. The body has a first end positionable adjacent the chair and a second end positionable adjacent the headrest. The first pivotable connection is near the first end of the body and adapted to connect to the chair and to allow pivoting of the body relative to the chair. The second pivotable connection is near the second end of the body and adapted to connect to the headrest and to allow pivoting of the headrest relative to the body. The selectively releasable locking mechanism is configured to retain the body in selected angular positions relative to the chair and relative the headrest and is configured to allow one-handed actuation. The locking mechanism can be configured to clamp together interleaving plate members in frictional contact. 
   The mechanism can comprise a set of first plate members pivotally connected adjacent the first pivotable connection and a set of second plate members pivotally connected adjacent the second pivotable connection, with the first plate members extending towards the second plate members with portions of said second plate members being interleaved with portions of the first plate members. The locking mechanism can be configured to clamp the interleaved first and second plate members into locking frictional contact to hold them against movement relative to each other, thereby locking the body in the selected angular positions. 
   Each of the first and second pivotable connections can be independently pivotable relative to the other. 
   The mechanism can comprise a headrest plate extendable from the second end of the body and allowing for the headrest to be selectively translated toward and away from the body. The locking mechanism can be positioned approximately coaxially with the first pivotable connection or the second pivotable connection. 
   The locking mechanism can be a first locking mechanism positioned approximately coaxially with the first pivotable connection, and the mechanism can comprise a second locking mechanism positioned approximately coaxially with the second pivotable connection. 
   The mechanism can comprise a separating member positioned between at least two of the interleaved first and second plate members in at least one location. The separating member can be a washer with an opening sized to receive a shaft of the locking mechanism. 
   The mechanism can comprise a set of plate members having a first set of ends pivotally connected adjacent the first pivotable connection and an opposite set of second ends pivotally connected adjacent the second pivotable connection, the locking mechanism being configured to clamp the plate members into locking frictional contact to hold them against movement relative to each other, thereby locking the body in the selected angular positions. 
   According to another embodiment, a mechanism for supporting and permitting selected adjustment of the position of a headrest relative to a chair to which the headrest is movably attached comprises a body, a first pivotable connection, a second pivotable connection and a selectively releasable locking mechanism with a single actuating member. 
   The body has a first end positionable adjacent the chair and a second end positionable adjacent the headrest. The first pivotable connection is near the first end of the body and adapted to connect to the chair and to allow pivoting of the body relative to the chair. The second pivotable connection is near the second end of the body and adapted to allow pivoting of the headrest relative to the body. Each of the first and second pivotable connections are independently pivotable relative to the other. While the single actuating member is operated, the first pivot connection is released from a locked position, thereby allowing the body to be pivoted relative to the chair, and the second pivot connection is released from a locked position, thereby allowing the headrest to be pivoted relative to the body. When the actuating member is released, the first pivot connection and the second pivot connection are locked in their respective positions. 
   According to another embodiment, a mechanism for supporting and permitting selected adjustment of the position of a headrest relative to a back of a chair comprises a body, a first bracket to which a headrest may be connected, the first bracket being pivotally connected at a first pivot adjacent one end of said body, a second bracket for connecting to a chair back, the second bracket being pivotally connected at a second pivot adjacent an end of the body opposite the one end, a set of parallel first plate members pivotally connected adjacent one set of their ends to the first bracket at a third pivot in a region spaced from the first pivot, the first plate members extending toward the opposite end of the body and movable longitudinally, a set of parallel second plate members pivotally connected adjacent one set of their ends to the second bracket at a fourth pivot in a region spaced from the second pivot, the second plate members extending toward the one end of the body and movable longitudinally, with portions of the second plate members being interleaved with portions of the first plate members, a clamping mechanism operable to clamp the interleaved portions of the first and second plate members into locking frictional contact to hold them against movement relative to each other to hold the first and second brackets in selected angular positions relative to the housing, and a release mechanism manually operable to release the clamping mechanism to permit longitudinal movement of the sets of first and second plate members relative to each other and pivotal movement of the first and second brackets relative to the body. 
   The first plate members can have elongate longitudinally extending first slots formed therein spaced from the third pivot and the second plate members can have elongate longitudinally extending second slots formed therein spaced from the fourth pivot, and the clamping mechanism can comprise an elongate locking member extending transversely of the body and slidably through aligned portions of the first and second slots. 
   According to another embodiment, a mechanism for supporting and permitting selected adjustment of the position of a headrest relative to a back of a chair comprises a body, a first bracket to which a headrest may be connected, the first bracket being pivotally connected at a first pivot adjacent one end of the body, a second bracket for connecting to a chair back, the second bracket being pivotally connected at a second pivot adjacent an end of the body opposite the one end, a set of parallel first plate members pivotally connected adjacent one set of their ends to the first bracket at a third pivot in a region spaced from the first pivot, the first plate members extending toward the opposite end of the body and movable longitudinally, a set of parallel second plate members having portions interleaved with portions of the first plate members, the second plate members extending toward the one end of the body and movable longitudinally, at least one auxiliary link member having a first end pivotally connected to one set of ends of the second plate members and a second end pivotally connected to the second bracket, a clamping mechanism operable to clamp said interleaved portions of the first and second plate members into locking frictional contact to hold them against movement relative to each other to hold said first and second brackets in selected angular positions relative to the housing, and a release mechanism manually operable to release the clamping mechanism to permit longitudinal movement of the sets of first and second plate members relative to each other and pivotal movement of the first and second brackets relative to the body. 
   The locking member has a longitudinal axis and the first, second, third and fourth pivots have pivot axes, and the longitudinal axis and the pivot axes can be mutually parallel with one another. 
   The release mechanism can comprise an elongate lever pivotally connected to the body at a lever pivot and having an operating portion positioned to engage the clamping mechanism and release the clamping mechanism from a locked position. The clamping mechanism can be secured against movement longitudinally of the body to restrict movement of the plate members relative to the body when the clamping mechanism clamps the interleaved portions of the first and second plate members into frictional locking contact. 
   The body can comprise an elongate housing having opposed spaced apart top and bottom walls and spaced apart opposed side walls defining an enclosure. The housing can have a selected width and height, with the width greater than the height. The first and second plate members can be enclosed in said housing. 
   The mechanism can comprise a headrest positioning mechanism connected to the first bracket permitting selected movement of the headrest relative to the first bracket and toward and away from the chair back, the positioning mechanism comprising a connector member adapted to be secured to a rear side of the headrest, and the connector member and headrest support bracket having inter-engaging elements thereon permitting translational movement of the connector member relative to the first bracket. 
   The first bracket or the connector member can have a pair of opposed spaced apart guide portions thereon, and the other of the first bracket and the connector can have a pair of elongate guideways thereon which receive and support the guide portions to permit translational movement of the connector member relative to the first bracket along a path defined by the guideways. There can be a layer of material of reduced frictional characteristic interposed between the inter-engaging elements of the first bracket and the connector member to provide a selected sliding interconnection therebetween. There can be a friction element coupled to the first bracket or the connector member and biasing means yieldably urging the friction element into contact with the other of said first bracket and connector member to provide a selected frictional interconnection therebetween to retain the headrest support bracket and connector member in selected position when no operator force is being applied thereto. 
   According to another embodiment, a mechanism for supporting and permitting selected adjustment of the position of a headrest relative to a back of a chair, comprises a body, a first bracket to which a headrest may be connected, the first bracket being pivotally connected at a first pivot adjacent one end of the body, a second bracket for connecting to a chair back, the second bracket being pivotally connected at a second pivot adjacent an end of the body opposite the one end, a set of plate members pivotally connected adjacent a first set of their ends to the first bracket at a third pivot in a region spaced from the first pivot and pivotally connected adjacent a second set of their ends to the second bracket at a fourth pivot in a region spaced from the second pivot, a clamping mechanism operable to clamp the plate members into locking frictional contact to hold them against movement relative to each other to hold the first and second brackets in selected angular positions relative to the housing, and a release mechanism manually operable to release said clamping mechanism to permit longitudinal movement of the plate members relative to each other and pivotal movement of the first and second brackets relative to the body, wherein the second bracket is adapted to allow translation of the headrest relative to the bracket. 
   These and other features will become more apparent as the following description is read in conjunction with the drawings. 


   
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a rear perspective view of a headrest support according to an embodiment in the invention, illustrated in conjunction with a back of a chair (in dashed lines). 
       FIG. 2  is an enlarged cross-sectional view taken generally along the line  2 — 2  in  FIG. 1 . 
       FIG. 3  is a cross-sectional view of a pivotally adjustable support mechanism portion of the headrest support, with mounting brackets at opposite ends thereof shown in first positions in solid outline and in second positions in dashed outline. 
       FIG. 4  is a view similar to  FIG. 3  with the operating elements therein in reversed operating positions. 
       FIG. 5  is a cross-sectional view taken generally along the line  5 — 5  in  FIG. 4 . 
       FIGS. 6A ,  6 B,  6 C,  6 D and  6 E are schematic side views showing the headrest support in various positions to illustrate its range of motion and use. 
       FIG. 6F  is a schematic view showing the position of the headrest support being adjusted with one hand. 
       FIGS. 7A ,  7 B and  7 C are plan, sectioned elevation and sectioned plan views, respectively, of a variant of the support mechanism similar to  FIGS. 4 and 5 , except the pivot positions have been reversed. 
       FIGS. 8A ,  8 B and  8 C are plan, sectioned elevation and sectioned plan views, respectively, of a variant of the support mechanism similar to  FIGS. 4 and 5 , except the linkage includes additional components and has a different configuration. 
       FIGS. 9A ,  9 B and  9 C are plan, sectioned elevation and sectioned plan views, respectively, of a variant of the support mechanism similar to  FIGS. 4 and 5 , except the linkage has a single set of continuous links rather than two discrete sets of links. 
       FIGS. 10A ,  10 B and  10 C are plan, sectioned elevation and sectioned plan views, respectively, of a variant of the support mechanism similar to  FIGS. 4 and 5 , except the release mechanism is positioned coaxially with one of the pivots instead of between the pivots. 
       FIGS. 11A ,  11 B and  11 C are plan, sectioned elevation and sectioned plan views, respectively, of a variant of the support mechanism similar to  FIGS. 4 and 5 , except there are two independently operable release mechanisms. 
       FIGS. 12A and 12B  are plan and sectioned elevation views, respectively, of a variant of the support mechanism similar to  FIGS. 4 and 5 , except that there are single pivots at the ends and the interleaved members have complimentary curved slots where they overlap in the area of the release mechanism. 
   


   DETAILED DESCRIPTION  
   Referring to the drawings, and first more specifically to  FIG. 1 , at  10  as indicated generally a headrest with a cushion  11  supported above a chair back  12  such as would be used in a dental or other medical style chair to support a patient. The headrest is supported above the chair back  12  by adjustment and support mechanism indicated generally at  14  constructed according to an embodiment of the invention. 
   An elongate slide post, or bar,  18  would be attached to the back of chair  12  by a frictional holding mechanism which allows major raising and lowering of the headrest mechanism. This allows approximate positioning of the headrest but is inconvenient for finer adjustment once the patient is in the chair. 
   The adjustment and support mechanism  14  for the headrest according to the invention includes an elongate housing, or mounting body,  22 . Referring to  FIGS. 3–5 , the housing has a selected length L, a selected height H, and a selected width W which are best adapted to provide the operational advantages of the present device. For example, the width W is greater than height H so that appropriate operating mechanism may be accommodated within the housing while still providing a low profile height H to allow patient&#39;s head on the headrest to be placed as close to the operator&#39;s lap as possible. The support mechanism  14  is show in  FIGS. 3–5  in a substantially horizontal orientation which it may assume when a patient is laid back in the chair. 
   The housing  22  has a substantially planar top wall  24 , a substantially planar bottom wall  26 , spaced therefrom, and a pair of opposed spaced apart side walls  28 , 30 . The top, bottom and side walls define an enclosure which houses the major portion of the operating components of the apparatus. 
   A headrest mounting bracket  34  having a pair of bracket arms  34   a ,  34   b  is pivotally connected through pivot connection, or rod,  36  adjacent one end of housing, or body,  22 . Pivot connection  36  is spaced outwardly from a central region of housing  22  toward said one end. Pivot connection  36  has an axis  36   a  which extends laterally, or widthwise, of housing  22 . Headrest bracket  34  also has a lever arm portion  34   c  thereon which extends laterally from pivot connection  36 . 
   A crossplate, or guide plate,  38  extends across outer edge portions of bracket arms  34   a ,  34   b  and is secured, as by welding, thereto or is cast as a single element with bracket arms  34   a ,  34   b . The crossplate has opposed outer edge, or margin, portions  38   a ,  38   b  which project laterally outwardly beyond bracket arms  34   a , 34   b  and a central portion  38 C as best seen in  FIGS. 2 and 5 . 
   As best seen in  FIG. 2 , cushion  11  of headrest  10  may have a shallow curved configuration to comfortably cradle a patient&#39;s head, indicated generally at  40  in dashed line in  FIG. 2 . A connector plate, or member,  44  may be secured to the back of cushion  11  and, as best seen in  FIG. 2 , has a shallow curved configuration which conforms to, or is complementary to, the curved configuration of cushion  11 . Connector plate  44  has laterally spaced apart parallel guide rail portions  46 , 48  extending longitudinally of the connector plate and forming channels, or guideways,  46   a , 48   b  adapted to slidably receive edge margin portions  38   a , 38   b , respectively, of crossplate  38  therein. Channels  46   a , 48   b  act as guideways to mount connector plate  44  on headrest bracket  34  and permit translational sliding movement relative thereto. Explaining further, a sliding fit is provided between edge margins  38   a , 38   b  and channels  46   a , 48   b  permitting the headrest connector plate  44  and the headrest cushion connected thereto to be slid along crossplate  38  toward and away from chair back  12 . 
   To improve the operation of this translational sliding movement, appropriate materials may be interposed between edge margin portions  38   a ,  38   b  and channels  46   a , 48   b  to provide a selected sliding fit therebetween. The fit should be such that an operator or patient may easily slide the headrest up or down to produce the most convenient or comfortable position desired. A layer of a material such as DELRIN (produced by E.I. Dupont De Nemours) has been found to work well as an interface in the channels between edge margin portions  38   a ,  38   b  and channels  46   a ,  48   b . This, or other material appropriate to provide the desired sliding fit, may be applied either to edge margin portions  38   a ,  38   b  or to the interiors of channels  46   a ,  48   b.    
   Referring still to  FIG. 2 , a cavity  42  is formed in central section  38   c  of crossplate  38  facing toward connector plate  44 . A friction plate  47 , which may be in the form of a block of NYLATRON (produced by Polymer Corporation) is situated in cavity  42  with a spring  49  biasing it outwardly toward connector plate  44 . The biasing force of spring  49  urging friction plate  47  outwardly and against connector plate  44  serves to produce a selected frictional holding of the connector plate relative to the crossplate such that the headrest cushion will be held in a selected position once it is placed as desired by the user. 
   A back support bracket  50  to which post  18  is secured, as by welding or other means, is pivotally connected to housing  22  through a pivot connection, or rod,  52  adjacent the end of housing  22  opposite bracket  34 . Pivot connection  52  is spaced outwardly from a central region of housing  22  toward the opposite end. The pivot connection  52  has an axis  52   a  which extends laterally, or widthwise, of housing  22 . 
   Bracket  50  includes a pair of laterally spaced bracket arms  50   a ,  50   b . Bracket arms  50   a ,  50   b  project outwardly from their associated end of housing  22  through openings defined in housing  22 , as do bracket arms  34   a ,  34   b , at the opposite end of the housing. Bracket  50  has a lever arm portion indicated generally at  50   c  which projects laterally of pivot connection  52 . 
   A plurality of elongate substantially planar parallel plate members, or fingers, also referred to herein as friction plates,  56  are disposed in a set. They are pivotally connected adjacent their outer set of ends at a pivot connection  58 , or rod,  58  to lever arm  34   c  of bracket  34 . The axis  58   a  of the pivot connection extends transversely, or widthwise, of housing  22 . Remainder portions of plate members  56  extend longitudinally through a major portion of the interior of the enclosure provided by housing  22  toward the opposite end of the housing. 
   Elongate slots  56   a  are formed in plates  56  extending longitudinally thereof. These slots extend toward the opposite, or inner, ends of plates  56  spaced from the end portion connected to pivot connection  58 . Plate members  56  and their respective slots  56   a  are aligned transversely, or widthwise, of housing  22 . 
   A plurality of elongate parallel substantially planar plate members, or fingers, also referred to as friction plates,  62  are disposed in a set with their outer ends pivotally connected at a pivot connection, or rod,  64  extending transversely, or widthwise, of housing  22 . The axis  64   a  of pivot connection  64  extends transversely, or widthwise, of housing  22 . Plates  62  are connected to lever arm  50   c  in a region spaced from pivot connection  52  for bracket  50 . 
   Remainder portions of plate members  62  extend longitudinally through the enclosure of housing  22  toward the end occupied by bracket  34 . Plate members  62  have elongate longitudinally extending slots  62   a  formed therein which extend to a region adjacent their inner ends. Plate members  62  and their respective slots  62   a  are aligned transversely, or widthwise, of housing  22 . 
   As best seen in  FIG. 5 , the inner end portions of the sets of plate members, fingers,  56  and  62  are interleaved in a mid-region of housing  22 . 
   In the interleaved region portions of slots  56   a ,  62   a  are aligned. An elongate rod portion  68  of a locking, or clamping, mechanism indicated generally at  70 , extends laterally and slidably through aligned portions of slots  56   a ,  62   a . Rod portion  68  assists in maintaining alignment of the plate members as they move within the housing. Rod  68  has an enlarged cylindrical head portion  68   a  received in a cavity  72  formed in side wall  28 . The opposite end portion  68   b  of rod  68  extends into a throughbore  74  in side wall  30 . 
   An enlarged bearing member, or portion,  76  secured to rod  68  is mounted for reciprocating movement in the direction of arrow  78  and is positioned to bear against a laterally outwardly facing side of one of the plate members. In  FIG. 5 , it bears against an outer facing surface of a plate member  56 . Rod  68  and member  76  are held against movement longitudinally of housing  22 . 
   A plurality of stacked spring washers, or Bellville springs, indicated generally at  80  are interposed between side wall  28  of the housing and bearing member  76 . These urge the bearing member away from wall  28  and into forceful bearing contact with the plate members. This forces the interleaved portions of the plate members into clamping engagement between bearing member  76  and the inner, or abutment, surface  30   a  of side wall  30 . The forceful clamping of bearing member  76  against the interleaved portions of fingers  56 , 62  clamps them into frictional locking engagement such that they are held in the position shown. Since the outer end portions of the plate members  56 , 62  are connected to bracket members  34 , 50 , this frictional locking will hold the brackets in their given positions, thus holding the adjustment mechanism in position relative to slide bar support  18  and holding headrest  10  in selected angular position relative to housing  22 . 
   Depending upon the particular operating requirements, including the number, size, and surface finish of the plate members  56 , 62  and the clamping force that can be applied to them, it may be desirable in some situations to interpose washers or other thin separating structures between adjacent plate members  56 , 62  at least in the area of their overlap where the clamping force is applied. Such a washer  90  or separating structure is shown schematically in, e.g.,  FIG. 7 . In practice, any washer  90  or other separating structure can be quite thin, e.g., even 10% or less of the thickness of the plate members  56 , 62 . 
   Release mechanism including a lever  84  is provided to release the frictional clamping force and allow the plate members, or fingers, to move longitudinally relative to the housing and relative to each other to permit rotation of and changing of the angularity of brackets  34  and  50  relative to housing  22 . 
   The elongate lever  84  is pivotally connected at  86  to housing  22  and has an engaging projection  88  thereon closely adjacent pivot connection  86 . When the lever is in the position illustrated in solid outline in  FIG. 5 , it has substantially no effect on the clamping mechanism and thus the clamping mechanism frictionally locks the plate members in position. Swinging of the lever member to the dashed outline position illustrated in  FIG. 5 , causes projection  88  to engage end portion  68   b  of rod  68  and force the rod and bearing member  76  away from clamping engagement with the plate members against the biasing force of springs  80 . When the clamping force is thus released by swinging movement of the lever, the plate members are released allowing relative sliding movement therebetween. This permits rotational swinging of bracket  34  and bracket  50  relative to housing  22  to change the angular position of headrest  10 . Release of lever  84  returns the mechanism to its locked up position. 
   The range of pivotal movement of brackets  34 , 50  and the commensurate longitudinal shifting of their associated fingers  56 , 62 , respectively, are illustrated in  FIGS. 3 and 4 . 
   Explaining operation of the apparatus, the operator initially places headrest slide support, or rod,  18  in a selected position relative to the back rest. When a patient, or user, enters the chair, the operator may depress lever  84  easily with one-handed operation due to its significant mechanical advantage provided by the long lever arm to release the clamping lock of the fingers. With the clamping lock thus released, the angular positions of portions of the assembly may be easily adjusted to conform to the patient. Release of the lever returns the mechanism to a locked position. 
   When the user, or patient, is seated in the chair their back rests against the plane of the user-engaging surface of the chair back. When the clamping mechanism is released, housing  22  may be swung rearwardly or forwardly about its pivot axis  52  to swing the headrest relative to the plane of the user-engaging surface of the chair back. At the same time, the angle of head rest support bracket  34  may be swung about its pivot axis  36  to a selected angular position relative to housing  22 . This is all permitted by longitudinal movement of plate members  56 , 62  within the housing when the clamping mechanism is released. In this way, the headrest may be positioned as desired for the most comfortable disposition for the user and convenient positioning for the operator. 
   Similarly, once the patient is situated, the slide mechanism connected to the back of the headrest allows the headrest to be easily slid up and down relative to the chair back to obtain desired vertical positioning. 
     FIGS. 6A ,  6 B,  6 C,  6 D and  6 E are schematic side views showing the headrest  10  in various positions to illustrate further its range of motion and use. In  FIG. 6A , the headrest  10  is shown in a compact state with the slide bar support  18  retracted and the headrest positioned to overlap an upper edge of the chair back  12 . In the illustrated implementation, the chair back  12  has curved cross-section terminating in side edges that curve outwardly from the center back area, as shown in the figures. With the headrest  10  in the compact state, the mechanism  14  (which can have a generally enclosed housing) is generally aligned with the slide bar  18  in the illustrated implementation. 
   In  FIG. 6B , the slide bar support  18  has been extended to position the headrest  10  away from the chair back  12 . In addition, the head rest  10  has been translated in the direction of arrow B relative to the mechanism  14 . 
   In  FIG. 6C , the mechanism  14  has been adjusted to position the head rest  10  outward from the plane of the slide bar support  18 . In the illustrated implementation, the head rest  10  has been maintained generally parallel to the slide bar support  18 . 
   In  FIG. 6D , the slide bar support  18  has been partially retracted and the head rest  10  has been translated in the direction of arrow B relative to its position in the compact state. In addition, the mechanism  14  has been adjusted to position the headrest  10  at an angle relative to the slide bar support. 
   In  FIG. 6E , the slide bar support  18  is in approximately the same position as shown in  FIG. 6D . The mechanism  14  has been pivoted to position the head rest  10  generally parallel to the slide bar support  18  and spaced outwardly from the plane of the chair back  12 . 
     FIG. 6F  shows the one-handed operation capability in more detail. Specifically,  FIG. 6F  shows an operator&#39;s left hand depressing the lever  84 , thereby releasing the locking mechanism to allow its body and the headrest  10  attached to the body to be repositioned within the ranges as shown schematically by the arrows in the figure. 
     FIGS. 7A ,  7 B and  7 C show an alternative embodiment of the head rest support mechanism.  FIG. 7A  is similar to  FIG. 5  in that the internal elements of the mechanism  10  are shown, but it is viewed from the opposite side and schematically depicts an arrangement where the pivot connections  36 , 52  are reversed from the relative positions shown in  FIG. 5 . In other words, the pivot connection  52  that connects to the slide bar support is positioned closer to the top wall  24  ( FIG. 7B ) than as shown in  FIG. 5 . Similarly, the pivot connection  36  that connects to the cross plate  38  is spaced closer to the bottom wall  26  ( FIG. 7B ) than as shown in  FIG. 5 . For convenience of illustration, only two plate members  56  and three plate members  62  are shown in  FIGS. 7A and 7C , but of course any number of plate members can be provided depending upon operating requirements. As described above, washers  90  can be provided between adjacent plate members  56 , 62 , particularly in the area of the rod  68 . 
     FIGS. 8A ,  8 B and  8 C show an alternative embodiment similar to  FIGS. 7A–7C , except the linkage includes an additional link  91  ( FIG. 8B ). The link  91  may be comprised of multiple link members  92  ( FIGS. 8A and 8C ), similar to the plate members  56 , 62 . The link members  92  have slots  93  that connect the link  91  and allow it to move relative to a stationary pivot  95 . From right to left in  FIG. 8B , the pivot connection  52  to the slide bar support  18  is stationary or grounded, the pivot connection  64  between the slide bar support  18  and the plate members  62  is free to move, the pivot connection  68  at the inner ends of the plate members  62  to the inner ends of the plate members  56  is stationary, the pivot connection  94  at the outer ends of the plate members  56  to the link  91  is free to move, the pivot connection  58  connecting the other end of the link  91  and the cross plate  38  is free to move, and the pivot connection  36  to the cross plate  38  is fixed. Movement of the link  91  is constrained by the stationary pivot  95  and the length of the slots  93 . The addition of the link  91  provides additional degrees of freedom in positioning the cross plate, and thus the head rest  10 , relative to the chair back attached to the support rod at  18 . Although not illustrated, other embodiments employing additional links are also possible. 
     FIGS. 9A ,  9 B and  9 C show an alternative embodiment similar to  FIGS. 7A–7C , except that the pivot connections  36 , 52  are each positioned closest to the same side of the housing, in this case the bottom wall  26 , and the two sets of plate members  56 , 62  have been replaced by a single set of plate members  56  with curved slots  97 . The curved slots constrain the motion of the plate members  56  relative to the pivot connection  68 . In this embodiment, the positions of the slide bar support  18  and the cross bar  38  are not independent of each other. Although the embodiment of  FIGS. 9A–9C  provides less freedom in positioning the headrest  10  compared to other embodiments in this application, the additional ability to translate the headrest  10  relative to the mechanism allows for sufficient flexibility of positioning for many situations. 
     FIGS. 10A ,  10 B and  10 C show an alternative embodiment similar to  FIGS. 7A–7C , except that the locking mechanism  70  is positioned coaxially with the pivot connection  52  for the slide bar support  18 , rather than between the pivot connections  36 , 52  as shown in  FIGS. 7A and 7B . Of course, in another variation it would also be possible to position the locking mechanism coaxially with the pivot connection  36 . As illustrated, the plate members  62  are constrained only to pivot and, unlike the embodiment of  FIGS. 7A and 7B , they cannot translate relative to the locking mechanism  70 . 
     FIGS. 11A ,  11 B and  11 C show an alternative embodiment similar to  FIGS. 7A–7C , except that in addition to the locking mechanism  70 , there is a second, separate locking mechanism  71 . Also, there is a set of plate members  63 , which are generally stationary in this example, that are interleaved at one set of their ends with the plate members  56  adjacent the pivot connection  36 , and at the opposite set of their ends with the plate members  62  adjacent the pivot connection  52 . Of course, the single set of plate members  63  could be replaced by two shorter sets, with each of the shorter sets having one end interleaved. 
   As shown in  FIGS. 11A and 11B , the locking mechanisms  70 , 71  can be positioned coaxially with the pivot connections  36 , 52 , respectively. With the embodiment of  FIGS. 11A and 11B , adjusting the position relative to the cross plate  38  and adjusting the position relative to the slide bar support  18  requires actuation of the separate locking mechanisms. The actuator handles may be positioned to allow for one-handed actuation of both locking mechanisms  70 , 71 , such as shown in  FIG. 11A . 
     FIGS. 12A and 12B  show an alternative embodiment similar to  FIGS. 4 and 5 , except that there are single pivots at the ends and the interleaved plate members have complimentary curved slots where they overlap in the area of the release mechanism. Specifically, the plate members  56  connected to the cross plate  38  are pivotable about the single pivot connection  36 , and the plate members  62  connected to the slide bar support  18  are pivotable about the single pivot connection  52 . The plate members  56 , 62  have complimenting curved slots  65 , 67 , respectively, positioned near their inner ends. The slots  65 , 67  overlap as shown and define the pivot ranges. The slots  65 , 67  receive and allow the plate members  56 , 62  to move relative to the locking mechanism  70 . Although the embodiment of  FIGS. 12A and 12B  as illustrated may provide slightly less freedom in positioning the headrest  10  compared to other embodiments, particularly those with more pivots, the mechanism provides sufficient flexibility of positioning for many situations. In addition, the positions of the pivots, the lengths of the plate members and the slots and other geometrical relationships can be adapted as necessary to yield a sufficient range of motion. 
   The configuration of housing  22  and the operating mechanism mounted therein for permitting adjustment of the headrest and locking such in a selected position, has a relatively thin profile, or height H, allowing the patient&#39;s head to be placed closely adjacent the operator&#39;s lap. Further, the enclosed housing provides a protective casing for the operating mechanism which permits ease of operation, cleaning, and positioning. Other advantages include the ability to configure the assembly to default to a locked position so the head rest does not move unexpectedly, the ability to operate the mechanism with one hand and while the mechanism is covered, such as with plastic or other sterile covering, the ability to adjust the position while the patient is occupying the chair, and the ability to accommodate patients of all sizes, including children. 
   In the illustrated embodiments, the selective locking into desired positions for use of the headrest is achieved using a locking mechanism that releasably secures interleaved plate members in place relative to each other. Other mechanisms are also possible, including but not limited to belt arrangements and locking members with nesting cone- or hemispherical-shaped elements. It would also be possible to provide the a powered locking force with fluid, electricity, magnetism, etc. 
   While preferred embodiments have been described herein, it should be apparent to those skilled in the art that variations and modifications are possible without departing from the spirit of the invention.
A mechanism for supporting and permitting selected adjustment of the position of a headrest relative to the back of a chair comprises a body, a first pivotable connection, a second pivotable connection and a selectively releasable locking mechanism. The first pivotable connection is near the first end of the body, adapted to connect to the chair and to allow pivoting of the body relative to the chair. The second pivotable connection is near the second end of the body, adapted to connect to the headrest and to allow pivoting of the headrest relative to the body. The selectively releasable locking mechanism is configured to retain the body in selected angular positions relative to the chair and relative to the headrest by clamping together interleaved plate members in frictional contact and to allow for one-handed actuation.