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BACKGROUND OF THE INVENTION 
     The present invention relates to an excavation machine and more particularly to an excavation machine which is ideal for hard rock mining and can be readily automated. 
     There exists in the hard rock mining industry a long felt need for mechanized evacuation techniques to take the place of drill and blast hard rock mining operations. The advantages of mechanized evacuation techniques and their adaptability to automation are well recognized. 
     PRIOR ART 
     Attempts to provide mechanical machines for hard rock mine excavation include road headers, continuous miners and modified versions of tunnel boring machines, or TBMs, as they are often referred to. Unfortunately, too date, these attempts have not been successful. These machines have suffered from maintenance problems, unacceptable bit wear and resulting high excavation costs. In addition, tunnel boring machines are still best suited for excavating long, relatively straight paths and do not have the capability to negotiate the tight turns necessary to follow ore veins. 
     In addition, these machines have been extremely costly and massive in size, weighing hundreds of metric tons. Lacking the desired mobility and versatility to follow desired mineral veins they are unable to avoid the excavation of rock which does not contain the desired minerals. 
     SUMMARY OF THE INVENTION 
     The basic object of the present invention is to provide an excavation machine which is relatively inexpensive, is mobile and versatile, is relatively light in weight (weighing no more than eight metric tons including power and control units and equipment for automation) and has the ability to make tight turns in any direction to follow a mineral vein and thereby avoid needless evacuation of undesired rock. 
     Another object of the invention is to provide an excavation machine for hard rock mining operations which use a cutter and reaming head mounted on a boom with two activator or rocker cylinders and excavates by applying a large impact or crushing cutting force in a repetitive manner, generally known as impact ripping. 
     Another object of the invention is to provide a “walking” mining machine with a partial face hard rock cutting reamer working member. 
     Yet another object of the present invention is to provide an excavating mining machine with adjustable bits in which operating space is provided to adjust the bits. 
     Still another object of the present invention is to provide new and improved composition drag bits for hard rock mining. 
     The present invention is a electro-hydraulic powered machine which can be easily automated and remotely controlled so as to significantly reduce the health and the safety risks associated with hard rock mining operations. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top view of the excavation machine of the present invention minus the power and control units. 
     FIG. 2 is a side sectional view taken along A—A in FIG.  1 . 
     FIG. 3 is a rear end view of the excavation machine of the present invention shown in FIG. 1 minus the conveyors for removing rock and muck. 
     FIG. 4 is a perspective view of the cutting head of the present invention cut away to show the slots for the insertion of the drag bit holder mountings. 
     FIG. 5 is a cut away view of one of the drag bit holder mountings of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in FIG. 1, the present invention incorporates two shield frame members. A front shield frame member  10  and a rear shield frame member  12 . Each of the shield frame members is approximately 1140 mm high, 1225 mm wide, and 1120 mm long. 
     The shield frame members  10  and  12 , in addition to carrying the impact and cutting mechanisms and power control units and automation equipment serve to protect the equipment from any falling debris. 
     Each of the shield frame members,  10  and  12 , is mounted on a pair of steel skids  14  and  16 , respectively. While additional hydraulic grippers may be employed, the front shield frame member  10  has at least two horizontal hydraulic thrust extending grippers, one  18 , extending to the left and the other  20 , extending to the right to engage and grip adjacent side walls. Likewise, while additional hydraulic thrust extending grippers may be employed, the back shield frame member  12  has at least two horizontal hydraulic thrust extending grippers, one  22  extending to the left and the other  24  extending to the right to engage and grip adjacent side walls. 
     Mounted on the front shield frame member  10  is a boom  26  which carries an impact and cutting reamer head  28 , a device for breaking and cutting into hard rock. The front shield frame member  10  also carries gathering arms or a scoop (not shown) for gathering cut rock and muck and delivering it to a conveyor  30  where it is carried back for excavation. 
     The rear shield frame member  12  in addition to housing a conveyor  32  for carrying rock and muck also houses hydraulic pumps, a water pump, a cable reel for electric cable to connect to a power source, all of the controls necessary to operate the excavation machine and whatever automation equipment that is desired. A control station  34  may be provided on the rear shield frame member  12  for an operator or at a remote site by using conventional robotic control systems (not shown). 
     The boom  26  is mounted on a swivel head  36  having a vertical pin  38  about which it moves laterally left and right and a horizontal pin  40  about which it moves vertically up and down. A hydraulic power cylinder  42  extending from a frame member  44  in front shield frame member  10  to the boom  26  controls the movement of the boom  26  in a vertical direction about the horizontal pin  40 . 
     A hydraulic motor (not shown) or two hydraulic power cylinders,  46  and  48 , connected to front shield frame member  10  and the boom  26  are provided to move the boom left and right about the pin  38 . 
     A hydraulic feed cylinder  50  inside the boom  26  is provided to move the cutter head  26  forward with a force of twelve metric tons into a rock face to be cut. A pair of hydraulic cylinders  52  and  54  on the left and right of the boom  26  are connected to the cutter head  28  to pivot the cutter head  28  left and right about a mounting pin  56  with a cutting and reaming force of seventy metric tons. 
     The front shield frame member  10  and the rear shield frame member  12  are connected together by a pair of hydraulic cylinders  58  and  60 . As illustrated in FIG. 1 rear shield frame member  12  has a spherical plate  62  extending forward therefrom with a longitudinal slot therein for receiving a vertical pin  66  protruding from a spherical plate  68  extending from the rear portion of the front shield frame member  10 . 
     A significant feature of the present invention is employing the concept of raised boring techniques or the use of drag bits in hard rock mining. Previous attempts to use drag bits in hard rock mining were unsuccessful due to the short life of the drag bits and the significant costs incurred in replacing them. 
     In the past the drag bits were welded on the cutter heads and when the bits broke or shattered or wore out it was necessary to replace the complete cutter head which was obviously very expensive. 
     In the present invention the bits are made of a new alloy which is much stronger than previous alloys. A new alloy which has been found to provide desired performance in drag bits comprise generally in % by weight, tungsten-carbide 75%, nickel 5%, cobalt 5%, hafnium 2.5%, uranium 2.5%, tantalum 5%, and niobium 5%. 
     In addition, in the present invention as shown in FIG. 5, the bits are welded to longitudinal extensions  80  having impact proof round threads adapted to engage impact proof round threads in a mounting bit holder member  70 , which enable the bits to be advanced forward to overcome the effects of wear. The mounting bit holder members are welded to the cutter head. 
     As illustrated in FIG. 4 access is provided to the end of these longitudinal extensions in order that the extensions may be manually adjusted advancing each of the bits during periodic maintenance. 
     As illustrated in FIG. 4, the cutting head  28  houses three bit holder members,  70 ,  72 , and  74 , each of which has four bits. For more effective cutting the bits in the center bit holder member  70  have ballistic shaped heads and the bits in the side bit holder members  72  and  74  have dome shaped heads. 
     In operation, the machine of the present invention starts in a conventional starting chamber having a face, a roof, and side walls with the hydraulic grippers  18  and  20  thrust into contact with the side walls securing the front shield frame member  10  firmly in place. Similarly, the hydraulic grippers  22  and  24  are thrust into contact with the side walls and secure the rear shield frame member  12  firmly in place. 
     Through the control of the hydraulic power cylinder  42  the boom  26  moves the cutting head  28  to the bottom of the rock face to be cut. The feed cylinder  50  presses the cutter head  28  forward against the rock face to be cut with a force of twelve metric tons and power cylinders  52  and  54  move the cutter head  28  back and forth left and right about the pin  56  with an impact and cutting force of seventy metric tons so that all of the drag bits cut into the face of the rock. The power cylinders  46  and  48  are used to move the boom  26  left or right to cut a path more to the left or right to initiate left or right turns. 
     Spray nozzles (not shown) are provided in the cutting head  28  for cooling the bits and wetting down the rock dust during the cutting of the rock. After the rock is cut to a depth of approximately 250 mm, the feed cylinder  50  retracts the cutter head  28  from the rock face, the power cylinder  42  moves the boom  26  and the cutter head  28  up 500 mm, the feed cylinder  50  presses the cutter head forward against the face of the rock with a force of twelve metric tons and the power cylinders  52  and  54  again move the cutter head  28  back and forth left and right about the pin  56  whereby the drag bits cut into the face of the rock with an impact and cutting force of seventy metric tons. These steps are repeated until the entire face of the rock has been cut. As the rock is cut it is scooped up and carried by conveyors out the back of the machine. 
     When a complete cut is made of the rock face, the thrust of the hydraulic pressure of the grippers  18  and  20  is reduced releasing the front shield frame member  10  from the side walls, the hydraulic cylinders  58  and  60  then push the front shield frame member  10  forward, the thrust of the hydraulic pressure of the grippers  18  and  20  is again increased to grip the side walls and hold the front shield frame member  10  firmly in place, the thrust of the hydraulic pressure in grippers  22  and  24  is reduced releasing the rear shield frame member  12  from the side walls, and the hydraulic cylinders  58  and  60  move the rear shield frame member forward. The thrust of the hydraulic pressure in the grippers  22  and  24  is then increased to grip the side walls and hold the rear shield frame member  12  rigidly in place while the cutter head proceeds through another cutting cycle. 
     The excavation machine is made to turn to the left by having the cylinders  48  and  46  move the boom  26  and cutter head  28  to the left and concentrate the cutting of the rock on the left. The front shield frame member  10  is made to follow the left cut by decreasing the thrust of the hydraulic pressure of the gripper  18  and increasing the thrust of the hydraulic pressure of the gripper  20 . Likewise, to turn to the right the cutter head  28  cuts more to the right and the thrust of the hydraulic pressure is increased in the gripper  18  and decreased in the gripper  20 . Similarly, since the boom  26  carrying the cutting head  28  can be moved up and down, the machine can proceed upwardly or downwardly along any gradient to follow a vein of ore. 
     Although the invention has been shown in connection with a certain specific embodiment, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention.

Summary:
An excavation machine for hard rock mining which is relatively inexpensive, is mobile and versatile, is relatively light in weight (weighing no more than eight metric tons including power and control units and equipment for automation) and has the ability to make tight turns in any direction to follow a mineral vein and thereby avoid needless evacuation of undesired rock. The machine uses a cutter and reaming head mounted on a boom with two activator or rocker cylinders and excavates by applying a large impact or crushing cutting force in a repetitive manner, generally known as impact ripping.