DESCRIPTION 
     1. Technical Field 
     The present invention relates to a concrete floor finishing machine for finishing concrete floor surfaces after concrete is deposited, and more particularly to a concrete floor finishing machine comprising a vehicle body including a pair of propelling devices, and a finishing device for smoothing out concrete floor surfaces in half-set state. 
     2. Background Art 
     A known finishing machine of this type comprises a vehicle body including a pair of propelling devices, and a finishing device rotatable about the vehicle body as disclosed in Japanese patent application laid open under No. 60-47159 for example. This known finishing machine having the finishing device rotatable about the vehicle body has great practical advantages in that it is capable of finishing a large area in one run compared, for example, with a machine having a finishing device drawn by a vehicle body, and that its propelling devices leave no traces on the concrete floor surfaces regardless of the running direction of the propelling devices. 
     However, since the finishing device rotates about the vehicle body, its radius of rotation tends to be large and the entire finishing device itself must be large. This renders the finishing device heavy and accordingly requires large and heavy bearings and motor. As a result, the entire finishing machine becomes complicated and heavyweight. During a finishing operation, therefore, the propelling devices tend to mar the concrete floor surfaces to excess. Further, since this known finishing machine cannot readily make a small sharp turn and its finishing device has a large radius of rotation, it inevitably leaves large unfinished parts in corners of the concrete floor. This machine is unsuitable for finishing a small area of concrete floor in particular, and leaves room for improvement in this respect. 
     DISCLOSURE OF INVENTION 
     The present invention has been made having regard to the above-noted disadvantages of the prior art, and its object is to provide a compact and lightweight concrete floor finishing machine retaining the advantages of the known finishing machine and yet capable of finishing a small area of concrete floor also. 
     In order to achieve this object a concrete floor finishing machine according to this invention is characterized in that finishing devices are provided one for each of the propelling devices to be driven to revolve around the propelling devices, respectively. 
     Since the finishing devices are driven to revolve around the propelling devices, respectively, the finishing devices themselves are substantially reduced in size and weight compared with the known finishing device rotatable around the vehicle body although the number of finishing devices is twice. As a result, bearings, motors and other components are also reduced in size and weight, rendering the entire finishing machine itself compact and lightweight. Moreover, these finishing devices have a substantially diminished radius of rotation thereby to greatly reduce unfinished parts left in corners of the concrete floor. 
     It will be understood from the above description that the concrete floor finishing machine according to the present invention retains the advantages of the known finishing machine noted at the outset of this specification and yet is compact and lightweight to perform a finishing operation leaving only small unfinished parts in corners of the concrete floor. Therefore this finishing machine is capable of finishing a small area of concrete floor by making full use of its ability to make small sharp turns and without marring the floor surfaces to excess. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     The drawings illustrate concrete floor finishing machines embodying the present invention, in which: 
     FIG. 1 is a plan view of a concrete floor finishing machine, 
     FIG. 2 is a partly broken away front view of the finishing machine, 
     FIG. 3 is a sectional view taken on line III--III of FIG. 2, and 
     FIG. 4 is a partly broken away front view of a modified finishing machine. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     An embodiment of the invention will now be described referring to FIGS. 1 through 3. A concrete floor finishing machine shown therein comprises a frame member 1 and a tubular member 2 constituting parts of a vehicle body3. The vehicle body 3 includes a pair of right and left propelling devices 4a and 4b in a lower portion thereof. As shown in detail in FIG. 3, each of the propelling devices 4a  and 4b includes a pair of fore and aft pulleys 6 and 7 supported by a frame 5 and a crawler 8 formed of rubber extending between the pulleys 6 and 7. The propelling device is driven backward and forward by a motor 10 through a sprocket 9 fixed to the rear pulley 7, a sprocket 11 fixed to the motor 10 and a chain 12 extending between and in mesh with the two sprockets 9 and 11. The frames 5 of the respective propelling devices 4a and 4b provide support for vertical tubular members 13a and 13b whose upper ends are operatively connected to the frame member 1 through clutches 14a and 14b. The tubular members 13a and 13b carry gear cases 16a and 16b fixed thereto which support motors 15a and 15b, respectively. 
     Each of the gear cases 16a and 16b houses a pulley 17 fixed to the motor 15a or 15b, a pulley 18 relatively rotatably mounted on the tubular member13a or 13b, and a belt 19 extending between the two pulleys 17 and 18. The pulley 18 mounted on the tubular member 13a or 13b includes a plurality ofpins 20a or 20b depending therefrom. These pins 20a or 20b respectively extend into perforations formed in a flange 22a or 22b of a rotatable tubular member 21a or 21b relatively rotatably and slidably fitted on the tubular member 13a or 13b. Each of the rotatable tubular members 21a and 21b carries a bracket 24a or 24b fixed to a lower position thereof and including an arm 23a or 23b projecting downwardly from an extreme end of the bracket 24a or 24b. Each rotatable tubular member 21a or 21b carries aself-aligning bearing 25a or 25b at or adjacent a lower end thereof throughwhich a finishing device 28a or 28b is attached to the rotatable tubular member 21a or 21b. The finishing device 28a or 28b includes a total of four trowel members 26a or 26b for smoothing out a concrete floor A in half-set state, and support members 27a or 27b for supporting the trowel members 26a or 26b, respectively. The finishing device 28a or 28b is rotatable about the tubular member 13a or 13b, with the arm 23a or 23b abutting against one of the support members 27a or 27b. As seen from FIG. 1, the finishing devices 28a and 28b have respective extreme ends thereof movable on paths of revolution Ca and Cb overlapping each other in plan view. 
     The rotatable tubular members 21a and 21b each carry a bevel gear 29 fixed to an intermediate position thereof and meshed with a bevel gear 30 fixed to an end of a rotary shaft 31 mounted in the tubular member 2, whereby the two rotatable tubular members 21a and 21b are operatively interconnected and, as described later, the two finishing devices 28a and 28b  are driven in synchronism. A linear motor 32 is fixedly mounted on the frame member 1 for rotating a screw shaft 33 in mesh with a threaded bore, not shown, defined in the frame member 1, the screw shaft 33 carrying a plate 34 at a lower end thereof. The tubular member 2 carries ashaft 36 pivoted thereto and including a plate 35. A load sensor 38 is attached to a tubular member 37 relatively slidably fitted on the shaft 36. The load sensor 38 is elastically pressed against the plate 34 on the screw shaft 33 by a compression spring 39 mounted between the plate 35 andthe tubular member 37. 
     The foregoing concrete floor finishing machine operates as follows. For carrying out a finishing operation, the clutches 14a and 14b are locked torigidly connect the two tubular members 13a and 13b to the frame member 1, and the motors 10 rotate the right and left crawlers 8 to propel the vehicle body 3 backward or forward. At the same time, the other motors 15aand 15b rotate in opposite directions, causing rotation of the pulleys 17, belts 19, and pulleys 18. This causes the right and left pins 20a and 20b to revolve and the two rotatable tubular members 21a and 21b to rotate in opposite directions. Then, through the brackets 24a and 24b the arms 23a and 23b are caused to revolve into contact with one of the support members27a and one of the support members 27b, respectively, thereby rotating the finishing devices 28a and 28b about the propelling devices 4a and 4b in opposite directions. The trowel members 26a and 26b at extreme ends of therevolving support members 27a and 27b smooth out surfaces of the concrete floor A. In other words, as shown in FIG. 1, the finishing devices 28a and28b rotate in opposite directions indicated by arrows a and b while the vehicle body 3 advances in the direction of arrow F. 
     Since the finishing devices 28a and 28b are driven to rotate around the propelling devices 4a and 4b, respectively, each finishing device has a small radius of rotation well suited for finishing corners of the concretefloor A. And since the finishing devices 28a and 28b are driven to rotate in opposite directions, reactions acting on the finishing devices 28a and 28b offset each other to prevent a zigzag movement of the vehicle body 3. However, it is not absolutely necessary to rotate the finishing devices 28a and 28b in opposite directions. The reactions acting on the finishing devices 28a and 28b may be offset, for example, by differentiating speeds of the right and left propelling devices 4a and 4b, to permit the finishing devices 28a and 28b to rotate in the same directions. 
     During the finishing operation, the load sensor 38 constantly detects the reactions acting on the finishing devices 28a and 28b, and in response to the detections the linear motor 32 is reversed to control pressing forces of the finishing devices 28a and 28b with respect to the concrete floor A.This assures uniform finish over an entire area of the concrete floor A. Furthermore, since the two rotatable tubular members 21a and 21b are operatively connected and synchronized with each other by the bevel gears 29 and 30 and the rotary shaft 31, the extreme ends of the finishing devices 28a and 28b have the mutually overlapping paths of revolution Ca and Cb and do not leave unfinished floor surfaces. The left trowel members26a and the right trowel members 26b are placed out of phase beforehand andare never shifted into collision with each other even if a great load acts on either the left trowel members 26a or right trowel members 26b. 
     For changing the traveling direction of the vehicle body 3, the linear motor 32 is rotated to lift the propelling devices 4a and 4b, the clutches14a and 14b are disengaged in this state and the two motors 15a and 15b arerotated. Then the motors 15a and 15b revolve with the tubular members 13a and 13b about axes of the tubular members 13a and 13b, respectively, thereby turning the propelling devices 4a and 4b. Since the propelling devices 4a and 4b are lifted when their traveling direction is changed, the concrete floor surfaces are not marred by the propelling devices 4a and 4b. 
     The concrete floor finishing machine operates as described above. This finishing machine may have the drive mechanisms operable by remote controlor may be automatically controllable by means of a microcomputer. 
     While in the described embodiment the finishing devices 28a and 28b are driven by the motors 15a and 15b provided separately, the two finishing devices 28a and 28b may be driven by a single motor as shown in FIG. 4. This embodiment includes a motor 15c fixed to a substantially middle position of the tubular member 2 for driving a bevel gear 40, and a rotaryshaft 31 mounted in the tubular member 2 and carrying a bevel gear 41 fixedthereto and meshed with the bevel gear 40. 
     According to this embodiment, therefore, the motor 15c rotates the rotary shaft 31 through the bevel gears 40 and 41, and the rotary shaft 31 in turn rotates the rotatable tubular members 21a and 21b in opposite directions through the bevel gears 30 fixed to opposite ends of the rotaryshaft 31 and the bevel gears 29 fixed to the rotatable tubular members 21a and 21b. The other power transmitting elements function in the same manneras in the preceding embodiment, and the finishing devices 28a and 28b rotate in opposite directions about the propelling devices 4a and 4b, respectively. This feature, as in the preceding embodiment, assures excellent finishing work adjacent corners of the concrete floor A, prevents a zigzag movement of the vehicle body 3, and prevents the finishing devices 28a and 28b from colliding with each other even though the extreme ends thereof are movable on the mutually overlapping paths of revolution Ca and Cb. In addition, this embodiment requires only one motor15c though the motor 15c may somewhat be large, and accordingly dispenses with the gear cases 16a, 16b, pulleys 17, 18 and belts 19, which has the advantage of rendering the entire machine lightweight. Since the other constructional and functional features of this embodiment are the same as those of the preceding embodiment, like references are affixed to like elements and explanations thereof are not repeated. 
     INDUSTRIAL APPLICABILITY 
     As described, the concrete floor finishing machine according to the presentinvention is suited for efficiently smoothing out concrete floor surfaces in half-set state.
This disclosure relates to a concrete floor finishing machine for smoothing a concrete floor surface while the placed concrete is in a semi-hardened state, and enables a floor finishing machine to be laid directly on the smoothed concrete floor. This concrete floor finishing machine includes finishing units which are arranged on the outer sides of a pair of left and right travelling means provided on a wheel unit. These finishing units consist of a plurality of trowels, respectively, which are arranged radially around the travelling means, respectively, these trowels being adapted to be turned around the travelling means.