Patent Publication Number: US-7717770-B1

Title: Expansion joint grinder

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   Not Applicable. 
   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT 
   Not Applicable. 
   FIELD OF THE INVENTION 
   This invention relates to grinding devices, and more particularly to a concrete joint grinder for grinding both the inside surfaces of a concrete joint simultaneously. 
   DISCUSSION OF RELATED ART 
   A wide variety of grinders are used to grind floors and working surfaces in construction and remodeling industry. Conventional grinders are designed for grinding projects involving large working surfaces. Hand held grinders are operated in small proximity of wall surfaces. Hand held grinders require the operator to move along the wall either on the operator&#39;s knees or in bent position. This is tiresome and sometimes causes back or other injury to the operator. A major difficulty posed by the prior art grinders are that they can grind only one surface of a concrete joint at a time. The entire grinding process is time consuming and is expensive. 
   Several prior art devices are known to grind concrete surfaces. For example, U.S. Pat. No. 4,018,012 to Hopkins on Apr. 19, 1977 discloses a method of removing metals from the surface of a metal workpiece such as a steel slab or a billet. The grinding apparatus includes a plurality of grinding wheels about an axis extending transversely of the workpiece surface. The grinding elements are subjected to pressure which depends upon the pressure of a hydraulic fluid supplied from a source. Here the grinder can only grind one upper surface at a time. The grinding process is time consuming. Moreover, additional passes may be made to remove more metal and this is accomplished by reversing the workpiece at each end of its travel and continuing to move it back and forth as many times as necessary. 
   U.S. Pat. No. 4,109,635 to Rossborough on Aug. 29, 1978 discloses a grinder for grooved joints on a hollow concrete cylinder. Here the grooving apparatus includes a track structure centered on the axis of a surface to produce a groove of uniform radius. The track structure is a heavy counter weight which includes a ring gear, a carriage and a motor drive spur gear. The whole apparatus is bulky and difficult to handle, and not well suited for grinding both sides of a concrete joint simultaneously. 
   U.S. Pat. No. 6,786,556 to Due on Sep. 7, 2004 discloses a concrete grinder apparatus. The system uses a detachably mounted hand held concrete grinder with a configuration that mounts a hand-held grinder in either a right-facing orientation or a left-facing orientation. The hand held grinder can be worked only on a single, small surface area and requires the operator to move along the wall either on the operator&#39;s knees or in bent position. This is tiresome and can cause back or other injury to the operator. 
   U.S. Pat. No. 5,882,249 to Ferland on Mar. 16, 1999 discloses a concrete finishing machine. Here a flat rotating disk is held against a concrete surface to be finished and a variable speed control is manipulated by the user to smooth and finish the surface. A handle of the invention extends radially on opposite sides of a power take off and lies within a plane normal to the axis between the motor and the rotating disk. The variable speed control is disposed on the handle to allow the user to vary the revolution speed of the disk. Such a device is not well suited for grinding two surfaces of a concrete joint simultaneously while the operator maintains a relaxed position. 
   Therefore, there is a need for an apparatus that can grind both of the inside surfaces of a concrete joint simultaneously. Such an apparatus would be inexpensive, compact and easy to manipulate. Such an apparatus would be adapted to work on a large surface area with relatively minimal manual effort. The present invention accomplishes these objectives. 
   SUMMARY OF THE INVENTION 
   The present invention is an apparatus for grinding both inside surfaces of a concrete joint simultaneously. The apparatus includes a proximal grinding wheel and a distal grinding wheel. A rotational axis orthogonally intersects the proximal and distal grinding wheels at respective centers thereof. At least one grinding implement is fixed to a distal side of the distal grinding wheel proximate a peripheral edge thereof, and to a proximal side of the proximal grinding wheel proximate a peripheral edge thereof. An internal drive shaft is fixed partially within an external drive shaft, and each are co-aligned with the rotational axis of each grinding wheel and mutually slidably engaged. 
   The internal drive shaft is fixed to the distal grinding wheel, and the external drive shaft is fixed to the proximal grinding wheel. The proximal grinding wheel and distal grinding wheel are selectively moved apart by telescoping the internal drive shaft with respect to the external drive shaft. Preferably a biasing means urges the two grinding wheels apart. The distal grinding wheel and the proximal grinding wheel are mutually rotated by a means for coupling a source of rotational kinetic energy to each of the drive shafts. A wheeled support frame is preferably fixed to the source of rotational kinetic energy 
   The present invention facilitates grinding both of the inside surfaces of a concrete joint simultaneously. Such an apparatus is relatively inexpensive, compact and easy to manipulate. Such an apparatus is adapted to work on a large surface area with relatively little manual effort. Other features and advantages of the present invention will become apparent from the following more detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a top plan view, partially cut away, of the invention; 
       FIG. 2  is a right side elevational view of the invention, illustrating a means for coupling the source of rotational kinetic energy to external drive shaft and internal drive shaft; 
       FIG. 3  is a front elevational view of the invention, shown partially cut away; and 
       FIG. 4  is a partial top plan view of the invention, partially cut away, illustrating an internal and external drive shaft each fixed to a distal and proximal grinding wheel, respectively; 
       FIG. 5  is a partial exploded view of the drive shafts and grinding wheels of the invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  illustrates an apparatus  10  for grinding a pair of inside surfaces  20  of a concrete joint  30  simultaneously. The apparatus  10  includes a proximal grinding wheel  40  and a distal grinding wheel  60 . The proximal grinding wheel  40  includes a proximal side  42 , a distal side  44  and a peripheral edge  46  connecting both sides  42  and  44 . A rotational axis  41  orthogonally intersects proximate the center (not shown) of the proximal grinding wheel  40 . A grinding implement  45 , such as a diamond or carbide cutting element, is fixed to the proximal side  42  of the proximal grinding wheel  40  proximate the peripheral edge  46  thereof. 
   An external drive shaft  50  is co-aligned with the rotational axis  41 . A distal end  52  of the external drive shaft  50  is fixed to the center (not shown) of the proximal grinding wheel  40 , such as with a threaded end and nut arrangement  47 . 
   The distal grinding wheel  60  includes a proximal side  62 , a distal side  64 , and a peripheral edge  66  connecting both sides  62  and  64 . The rotational axis  41  orthogonally intersects proximate the center (not shown) of the distal grinding wheel  60 . A grinding implement  65 , preferably identical to grinding element  45  but not necessarily so, is fixed to the distal side  64  proximate the peripheral edge  66 . An internal drive shaft  70  is co-aligned with the rotational axis  41  and fixed partially within the external drive shaft  50 . A distal end  72  of the internal drive shaft  70  is fixed to the center of the distal grinding wheel  60 , such as with a threaded shaft and nut arrangement  67 . The grinding wheels  40  and  60  can be enclosed within a protective case  67  to prevent debris and dust from being flung into the air during operation. 
   A moving means  80  provides for selectively moving the proximal grinding wheel  40  with respect to the distal grinding wheel  60  by telescopically moving the external drive shaft  50  with respect to the internal drive shaft  70 . The moving means  80  preferably includes a longitudinal slot  85  in the external drive shaft  50  and a pin  86  fixed to the internal drive shaft  70 . The pin  86  extends through the slot  85  of the external drive shaft  50 . An actuator  88  is included to move the pin  86  within the longitudinal slot  85  to change the mutual proximity of the proximal grinding wheel  40  and the distal grinding wheel  60  ( FIGS. 4 and 5 ). 
   The distal grinding wheel  60  and the proximal grinding wheel  40  are rotated by a coupling means  100  that couples the source of rotational kinetic energy  90  to each of the drive shafts  50 , 70 . The source of rotational kinetic energy  90  is preferably a gasoline engine  92  or an electric motor  94  connected to an electric power source (not shown), such as an electrical power receptacle. The coupling means  100  preferably includes a drive belt  102  looped around a motor pulley  104  fixed to the source of rotational kinetic energy  90 , and a shaft pulley  106  selectively coupled to the external drive shaft  50  through a clutch means  108  (what FIG?). 
   The proximal end  55  of the external drive shaft  50  includes a biasing means  110  for biasing the proximal end  75  ( FIG. 5 ) of the internal drive shaft  70  away from the proximal end  55  of the external drive shaft  50 , thereby urging the distal grinding wheel  60  away from the proximal grinding wheel  40  ( FIG. 4 ). 
   A wheeled support frame  120  is fixed to the source of rotational kinetic energy  90 . The support frame  120  further includes a handle  122  having an actuator  124  that controls the means  80  for selectively moving the proximal grinding wheel  40  and the distal grinding wheel  60  ( FIG. 1 ). The grinding wheels  40  and  60  are somewhat conical in shape. 
   In use, the external drive shaft  50  and the internal drive shaft  70  are coupled to the source of rotational kinetic energy  90  to rotate each grinding wheel  40 ,  60 . The grinding wheels  40 ,  60  are then moved close enough together by actuating the moving means  80  so that an arc of both grinding wheels  40 , 60  may be placed into the concrete joint  30 . The grinding wheels  40 ,  60  are then moved apart from each other by releasing the moving means  80  until the grinding implements  45 ,  65  of each grinding wheel  40 ,  60  contact the inside surface  20  of the concrete joint  30 . The wheeled support frame  120  is then rolled along the concrete surface proximate the joint  30 , each grinding wheel  40 , 60  grinding the inside surfaces  20  thereof. 
   While a particular form of the invention has been illustrated and described, it will be apparent that various modifications can be made without departing from the spirit and scope of the invention. Accordingly, it is not intended that the invention be limited, except as by the appended claims.