Apparatus for finishing flat surfaces
FIELD OF THE INVENTION 
     The invention relates to an apparatus for finishing flat surfaces such as floors of stone, concrete or similar hard materials. The apparatus includes a frame equipped with a number of wheels and on which a power unit is mounted for driving a finishing tool. The finishing tool is mounted on a vertical shaft so as to be capable of rotation. 
     BACKGROUND OF THE INVENTION 
     Apparatus of the kind referred to above is disclosed in U.S. Pat. No. 4,317,314 and does not include means for laterally inclining the tool. Also, the apparatus is dependent on external forces for its propulsion usually by the operator pushing or pulling the apparatus in the desired direction, which especially in the case of large cutting depths requires considerable effort and so constitutes a major ergonomic inconvenience. 
     In similar apparatus in other areas, for example, sweeping machines of the type disclosed in U.S. Pat. No. 2,978,719, it is known that by angling the two brush shafts in a vertical plane at right angles to the direction of motion of the apparatus, and consequently also the brushes in relation to the floor, a certain driving force in a forward or rearward direction can be obtained. 
     The disadvantage of this latter solution is that the angling device is comparatively complicated and sensitive to damage and is scarcely suitable for heavier machines like grinders or millers where high contact pressure on the floor is required. Above all, the angling device becomes complicated when applied to grinding machines of the kind described in the above-mentioned Swedish patent with facilities for varying the contact pressure of the grinding or milling tool against the floor. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a concrete surface grinding apparatus which can be self-propelled in a simple manner without the disadvantages associated with apparatus such as the sweeping apparatus described above. 
     According to a feature of the invention, the finishing tool can be tilted transversely with respect to the longitudinal axis of the apparatus so that it is at an angle with respect to the floor. As a result, when the apparatus is parallel with the floor, the frictional force between tool and floor during rotation of the tool gives rise to forces relative to the longitudinal axis of the apparatus which are of equal magnitude in both forward and rearward directions; and, when the apparatus is angled with respect to the floor, a force resultant occurs in either the forward or rearward directions, depending upon whether the tool is inclined to the right or to the left. Consequently, with the aforementioned lateral inclination of the tool, the apparatus is caused to propel itself either forwards or rearwards at a speed which can be varied according to the magnitude of the lateral inclination. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The invention will now be described with reference to the drawing wherein: 
     FIG. 1a is a front elevation view of a grinding apparatus according to the invention moving in a forward direction; 
     FIG. 1b is a plan view of the grinding apparatus of FIG. 1a; 
     FIG. 2a is a front elevation view of a grinding apparatus according to the invention moving in a rearward direction; 
     FIG. 2b is a plan view of the grinding apparatus of FIG. 2a; 
     FIG. 3 is a schematic showing how tilting of the grinding apparatus is accomplished by adjusting the height of its wheels; and, 
     FIG. 4 is a side elevation view of a machine for working and smoothing an even surface of the kind which can be equipped with means for tilting the frame thereof laterally to achieve motion in a straight-line direction. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
     The frame of the grinding apparatus is identified by reference numeral 1. The apparatus is fitted with two non-steerable wheels 6a, 6b positioned on respective sides of a rotating grinding or milling disc 2 on a vertical shaft 3 to which a grinding or milling tool 5 is resiliently mounted. In addition, the frame is fitted with a steerable wheel 11 (FIG. 4). The shaft 3 is journalled in a bearing housing which, by means of a system of links in the form of tierods, is mounted in the frame in a manner permitting it to be raised and lowered. An apparatus of this kind is shown in U.S. Pat. No. 4,634,188 which is incorporated herein by reference and includes a rearward steerable wheel. 
     The bearing housing can be loaded with a number of weights 4 corresponding to the grinding pressure it is desired to achieve without causing a change in the normal forces acting on the wheels and the steerable wheel, respectively. 
     According to a feature of the invention, wheels 6a and 6b are affixed to the respective hydraulic cylinders 7a and 7b shown in FIG. 3. The other ends of the cylinders are secured to frame 1. The hydraulic cylinders 7a and 7b communicate via hydraulic oil lines 8 with a double-acting hydraulic cylinder 10 actuated by a lever 9. 
     By operating lever 9, the wheels 6a and 6b are raised and lowered so that the desired tilting of frame 1 is achieved, causing the normal pressure of the grinding or milling tool 5 against the floor to differ on the right and left side as viewed in the direction of the longitudinal axis of the apparatus; this causes a resultant force to develop which moves the apparatus in forward or rearward direction depending upon whether it is tilted to the right or to the left. 
     The same effect can of course also be achieved by arranging weights 4, which load the bearing housing, in an adjustable asymmetric manner in relation to the right-hand and left-hand side of the longitudinal axis of symmetry of the apparatus. 
     It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.