Abstract:
A roller skate which includes a frame, a structure for fixing the frame to a person&#39;s foot, and at least two balls, which are freely rotatably supported by concave rollers. Axes of rotation of the rollers extend in a horizontal direction, transversely to the longitudinal direction of the frame. A roller is located between the two balls which are arranged side by side. The roller bears against both balls during operation.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a roller skate comprising a frame, means for fixing said frame to a person&#39;s foot, and at least two balls, which are freely rotatably supported by concave rollers, whose axes of rotation extend in a direction, transversely to the longitudinal direction of the frame and in use parallel to a rolling surface. 
     2. Discussion of the Background 
     With a similar roller skate, which is known from US patent U.S. Pat. No. 4,076,263, each ball is supported by one roller positioned vertically above said ball and two rollers positioned in front of and behind the central roller respectively. Said rollers are concave. The roller skate is supported on the road surface by means of said balls, whereby the presence of the balls leads to an improved road behaviour in comparison with that obtained with conventional axle-supported, barrel-shaped rollers which roll on the road surface. In particular when braking, said balls exhibit better road behaviour, because the balls can also rotate i-n a direction transversely to the direction of transport. The concave rollers thereby exert a force on the balls, as a result of which the balls are gradually brought to a standstill. One drawback of the known roller skate is the fact that, due to the presence of the relatively large rollers on either side of the balls, the number of balls to be mounted under the frame is limited. This has an adverse effect on the rolling behaviour of the roller skate. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to provide a roller skate wherein the balls can be positioned a relatively small distance apart. 
     This objective is accomplished with the roller skate according to the invention in that a roller is present between two balls which are arranged side by side in the longitudinal direction of the frame, which roller bears against both balls during operation. 
     The diameter of the roller can be selected practically independently of the distance between the two balls which are arranged side by side, so that an optimum freedom of design is obtained. 
     Another embodiment of the roller skate according to the invention is characterized in that the number of rollers less the number of balls equals 1. 
     Since the number of rollers is only 1 higher than the number of balls, a relatively simple and inexpensive construction of the roller skate is obtained. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be explained in more detail hereafter with reference to the drawings, wherein: 
     FIG. 1 is a side view of a first embodiment of a roller skate according to the invention; 
     FIG. 2 is a cross-sectional view of the roller skate shown in FIG. 1, in the direction indicated by arrows II—II; 
     FIG. 3 is a cross-sectional view of the roller skate shown in FIG. 1, in the direction indicated by arrows III—III; 
     FIG. 4 is a side view of a second embodiment of a roller skate according to the invention; 
     FIG. 5 is a side view of a third embodiment of a roller skate according to the invention; 
     FIGS. 6-9 show several concave rollers abutting against balls. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Corresponding parts are indicated by the same numerals in the figures. 
     FIG. 1 is a side view of a roller skate  1  according to the invention, which comprises a frame  2  and a shoe  3 , which is fixed to frame  2 . Frame  2  is provided with two flanges  3 ,  4  extending in the longitudinal direction of frame  2 , which are connected at an angle to a baseplate  5  of the frame. Axles  6  are present between flanges  3 ,  4 , which axles extend horizontally and transversely to the plane of FIG.  1 . Concave rollers  8  are mounted on axles  6  via a pair of ball-bearings  7 . Balls  9  are positioned between said rollers  8 , with a roller  8  present between two balls  9  arranged side by side bearing against both balls  9 . Ball  9  has a radius RI, whilst the radius of curvature of concave rollers  8  is R 2 . Preferably, the radius of curvature R 2  of concave rollers  8  is larger than the radius of curvature R 1  of ball  9 , so that ball  9  only bears against roller  8  via a point contact  10 . Frame  2  is furthermore provided with a number of barrel-shaped rollers  11 , which extend parallel to axles  6  and which are rotatably supported in arms  12  connected to flanges  3 ,  4 . Barrel-shaped rollers  11  are present on a different side of an axis of balls  9  than rollers  8 . The distance between two rollers  11  arranged side by side is smaller than the diameter of balls  9 . Thus, rollers  11  prevent balls  9  from falling out of frame  2 . As is clearly shown in FIG. 1, balls  9  are spaced a relatively small distance apart, which makes it possible to use a relatively large number of balls  9 . Because a single roller  8  is provided between two balls  9  arranged side by side, which roller bears against both balls  9 , it is possible to select a relatively large diameter for roller  8 . 
     The operation of roller skate  1  is as follows. Roller skate  1  is moved by the user in the direction indicated by arrow PI, whereby balls  9  rotate in a direction indicated by arrow P 2 . Since balls  9  are in contact with rollers  8 , rollers  8  will be rotated in the direction indicated by arrow P 3 . As a result of the relatively large diameter of rollers  8 , the number of revolutions of rollers  8  will be relatively limited thereby. If a user of roller skate  1  wishes to brake, he will move his foot in a direction transversely to the drawing, thus causing balls  9  to rotate in that direction as well. Rollers  8  will come to a standstill, and rollers  8  will exert a friction force on balls  9 , as a result of which balls  9  will gradually be brought to a standstill. 
     FIG. 4 shows in side view a second embodiment of a roller skate  20  according to the invention, which is provided with three balls  9  arranged side by side, which are supported by four rollers  8  arranged beside and between balls  9 . On a side remote from rollers  8 , balls  9  are prevented from falling out of frame  2  by barrel-shaped rollers  11 . Preferably, rollers  11  are detachably connected to frame  2 , so that the balls  9  surrounding a roller  11  can be removed from the frame, and subsequently be replaced, by removing said roller  11 . 
     FIG. 5 shows in side view a third embodiment of a roller skate  21  according to the invention, which is provided with two balls  9 , which are supported by three rollers  8 . At the front side and the rear side, roller skate  21  is provided with conventional rollers  22 , which are rotatably connected to frame  2  by means of horizontally extending axles  23 . 
     Rollers  22  are positioned some distance above the ground surface, whereby one of the rollers  22  comes into contact with the ground surface by tilting the roller skate forward or backward. 
     FIG. 6 shows a concave roller  8 , which abuts against ball  9  at a single location or point contact  10 . 
     FIG. 7 shows a roller  30 , which comprises two cone-shaped elements  31 , which are connected near cone tips  32 . Concave roller  30  abuts against ball  9  near two locations  10 . Locations  10  are positioned symmetrically with respect to the centre of ball  9  and roller  30 . Since ball  9  makes contact with roller  30  at two locations  10 , the force being exerted at a location  10  has been halved in comparison with the situation which is shown in FIG. 6, wherein the force of ball  9  is transmitted to roller  8  via a single location  10  or point contact only. 
     FIG. 8 shows another embodiment of a roller  33 , which abuts against ball  9  at two locations  10 . Roller  33  comprises two concave surfaces  34 , which touch each other near the centre  35 . 
     FIG. 9 shows another embodiment of a concave roller  36 , which comprises a bridge portion  37 , which is connected to cone-shaped segments  38  at both ends. Each cone-shaped segment  38  abuts against ball  9  via a point contact at location  10 . 
     The diameter of the balls preferably ranges between 58 mm for stunt riders and 82 mm for competition riders. The larger the ball, the greater the speed that can be obtained with roller skate  1 .