Abstract:
A human assisted walking robot formed by a motor, a cargo bin, a pair of legs mounted to the carrier; and a stabilizing support mounted at its proximal end to the carrier and having a wheel rotatably mounted to the distal end. The motor drives the first and second leg members resulting in a walking motion. Each leg is formed by a thigh link and a shank link. A four-bar linkage is coupled between the motor and the thigh and shank of each leg so that rotational motion generated by the motor produces a walking motion by the legs.

Description:
FIELD OF THE INVENTION 
     This invention relates to the field of robotics, specifically how robots can aid humans in transporting heavy loads over rough terrain. 
     BACKGROUND OF THE INVENTION 
     The task of transporting heavy objects over rough terrain has previously been solved by the use of wheeled and treaded vehicles. These vehicles include jeeps, motorcycles, tanks, and All-Terrain-Vehicles (ATV). The limitations of these devices are the types of terrain that they can operate on, and their maneuverability on that terrain. On roads or other relatively smooth terrain, these devices are successful. But when the terrain is very irregular, as in jungles, these devices become useless. Another limitation of these devices is due to their size. The size problem has been solved by a class of inventions called motorized wheelbarrows and carts (as in U.S. Pat. Nos. 5,465,801; 5,284,218; 5,211,254; and 4,811,988). These inventions all use wheels as the means to contact the ground and provide the locomotion. On smooth roads, wheel devices provide suitable means for locomotion. On very rough and irregular terrain wheeled devices consume a significant amount of power, provide poor ride quality, damage the terrain, and encounter problems with traction. Often, these wheeled devices cannot even traverse the rough terrain. 
     The solution to providing means for locomotion on rough and irregular terrain comes from legged robots and machines. Legged versus wheeled locomotion has the advantages of requiring less energy, attaining higher speeds, greater mobility, better isolation from terrain irregularities, and less environmental damage (Bekker 1960; Song and Waldron 1989). The problem with having legged machines navigate through rough terrain is the technology is such that it cannot support a fully autonomous legged machine. A few six-legged machines have been built that can walk on irregular terrain (Adaptive Suspension Vehicle built by Ohio State University, Song and Walkron 1989; MECANT I, Hartikainen et. al 1992) but they are large, bulky, and move slowly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The objects and advantages of the Human Assisted Walking Robot (HAWR) will become apparent from the following detailed description of preferred embodiments thereof in connection with the accompanying drawing in which like numerals designate like elements, and in which: 
     FIG. 1 is an isometric CAD drawing showing the entire HAWR as viewed from the front right side of the HAWR. 
     FIG. 2 is an isometric CAD drawing showing the HAWR as viewed from the top right side of the HAWR. The cargo bin has been removed for a better view of the underlying components. 
     FIG. 3 is a schematic for the controller circuit. 
     FIG. 4 is an isometric CAD drawing showing only the transmission and the double four-bar linkage for the right leg of the machine. The components associated with the left leg of the machine have been omitted for clarity. 
     FIG. 5 is an isometric CAD drawing showing the rigid frame of the machine. 
     FIG. 6 is an isometric CAD drawing showing the HAWR as viewed from below on the front left side of the HAWR. The left leg and its driving hardware and the cargo bin are not shown so that the right leg and its driving hardware can be viewed more easily. 
     FIG. 7 is an isometric CAD drawing showing the HAWR as viewed from the front right side of the HAWR. The left leg and its driving hardware are not shown so that the right leg and its driving hardware can be viewed more easily. 
     FIG. 8 is an isometric CAD drawing showing the shank leg assembly. 
     FIG. 9 is a plot of the path of the foot in the vertical plane. 
    
    
     SUMMARY OF THE INVENTION 
     The present invention solves the problems inherent in wheeled transport vehicles and legged robots by providing a human assisted walking robot formed by a motor, a cargo bin, a pair of legs mounted to the carrier; and a stabilizing support mounted at its proximal end to the carrier and having a wheel rotatably mounted to the distal end. The motor drives the first and second leg members resulting in a walking motion. Each leg is formed by a thigh link and a shank link. A four-bar linkage is coupled between the motor and the thigh and shank of each leg so that rotational motion generated by the motor produces a walking motion by the legs. 
     The present invention has other objects and advantages which are set forth in the Description of the Preferred Embodiment. The features and advantages described in the specification, however, are not all inclusive, and particularly, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification and claims herein. 
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Depicted in FIG.  1 . is a Human Assisted Walking Robot (HAWR) designed to transport loads over rough terrain. The HAWR uses two legs, a right leg  1  and a left leg  2 , to support the load, carried in a cargo bin  3 , The human operator grasps the HAWR at a set of handles  4  in FIG. 2 to provide stabilizing forces and navigate the HAWR. By grasping the handles  4 , the operator can provide stabilizing forces needed to keep the machine balanced upright. A wheel  5 , or multiple wheels, can be used to help the operator stabilize the robot. In the preferred embodiment no wheel is used. The user controls a power unit  6  by means of an apparatus  7  which then controls the walking speed of the robot. Power unit  6  can be any type of motor, with the preferred type being an internal combustion engine. 
     In general there are two ways to control the speed of the HAWR: 
     In the first method, the direct control, apparatus  7  directly adjusts the flow of power from power unit  6 . For example if power unit  6  is an internal combustion engine, then apparatus  7  controls the engine throttle and therefore the torque output of the engine. Or if power unit  6  is an electric motor, then the apparatus  7  could be a device, such as a potentiometer or rheostat, that controls the output torque of the motor. 
     In the second method, indirect control, a feedback controller  8  in FIG. 3 is employed to regulate the walking speed of the HAWR similar to cruise control in automobiles. The input to controller  8  is directly assigned by the operator via a transducer  9 . Transducer  9  can be a speed setting switch, a force sensor, or any other transducer device that is able to get the operator&#39;s input. In the preferred embodiment, the transducer  9  is a multiple position switch, where each position corresponds to a different speed. A tachometer, encoder, or any other device which can determine the speed of the walking robot is employed as the speed sensor  10 . In the preferred design, the speed sensor  10  is a tachometer. Also in the preferred design, feedback controller  8  is a microprocessor, but it could be an electronic circuit instead. An electronic amplifier  36  is used to amplify the command from the computer  8 . This amplifier, in return, drives a small DC motor  37 . Motion of the DC motor  37  allows for adjustment of the engine throttle. The engine  6  then drives the HAWR mechanism through a centrifugal clutch  38 . 
     The following describes the mechanism of HAWR. The power to the walking mechanism of the robot is provided by the onboard power unit  6  in FIG. 2. A clutch is used to disengage the power unit  6  from the rest of the system. This clutch, in many cases is integrated with the power unit. Many two-stroke internal combustion engines are available with centrifugal clutches, which is the preferred design. Depending on the output speed of the power unit  6 , a transmission system may be necessary to modulate the rotational speed of the power unit. Because the typical speed of two-stroke internal combustion engines is around 8000 rpm, a transmission  11  is employed to reduce the engine speed. The preferred transmission is a gear type, but it could also be a hydrostatic having a continuous gear ratio with the possibility for forward and reverse settings. The transmission  11  has two output shafts, one to power the left leg  2  of the walking robot, and the other to power the right leg  1  of the walking robot. The power unit  6  and transmission  11  are mounted to rigid frame  12  in FIG.  5 . From this point on, the left and right sides of the walking robot are identical, and thus the left leg will be omitted in FIGS. 4,  6 , and  7  so that the components can be more easily viewed. The right side of the output shaft of the transmission  11  is used to drive the double four-bar linkages  13  which governs the movement of the right leg  1 . The connection between transmission  11  and double four-bar linkage  13  is through a chain and sprocket system  14 . A transmission sprocket  15  in FIG. 7 is rigidly connected to the right side of a transmission output shaft  35 . A drive chain  16  connects transmission sprocket  15  and a driver sprocket  17 . Driver sprocket  17  is rigidly connected to a thigh driver-link  18  and a shank driver-link  19 , such that thigh driver-link  18  and shank driver-link  19  rotate with the same speed of driver sprocket  17 . This indicates that when the transmission output shaft  35  rotates, both thigh driver-link  18  and shank driver-link  19  rotate also. The angular speed of the thigh driver-link  18  and the shank driver-link  19  depend on the relative size of transmission sprocket  15  and driver sprocket  17 . The thigh driver-link  18  and the shank driver-link  19  are considered the inputs to the double four-bar linkage  13 . The double four-bar linkage  13  consists of two four-bar linkages: 
     A thigh linkage  20  which consists of three moving links: the thigh driver-link  18  (input to the linkage  20 ), a thigh coupler-link  22 , and a thigh rocker-link  23  (output of the linkage  20 ). A full rotation of thigh diver-link  18  causes thigh rocker-link  23  to rock back and forth. In other words the thigh linkage  20  governs the trajectory of the rocking motion of thigh rocker-link  23  in response to continuous rotation of thigh driver-link  18 . 
     A shank linkage  21  which consists of three moving links: the shank driver-link  19  (input to the linkage  21 ), a shank coupler-link  24 , and a shank rocker-link  25  (output of the linkage  21 ). A full rotation of shank diver-link  19  causes shank rocker-link  25  to rock back and forth. In other words the thigh linkage  21  governs the trajectory of the rocking motion of shank rocker-link  25  in response to continuous rotation of shank driver-link  19 . The rocking motion of shank rocker-link  25  is transferred to a shank leg  26  as described below. Rigidly connected to shank rocker-link  25  is an upper sprocket  27 . Rigidly connected to shank leg  26  is a lower sprocket  28 . A leg chain  29  connects upper sprocket  27  and lower sprocket  28 . As shank rocker link  25  rocks, it rotates upper sprocket  27 , which rotates lower sprocket  28 , which rotates shank leg  26 . 
     The foot  30  is mounted to the end of shank leg  26 . Therefore the motion of foot  30  is governed by the double four-bar linkage  13 . The two four-bar linkages  20  and  21  (in double four-bar linkage  13 ) work in conjunction to form a suitable trajectory for the position of foot  30  in FIG. 9, in the vertical plane. The designers must arrive at the proper lengths of the double four-bar linkage links such that a proper trajectory is generated for foot  30 . 
     FIG. 9 shows the preferred trajectory for foot  30  relative to rigid frame  12  where it is similar to how humans walk. Imagine the path that a walking human&#39;s foot traces out relative to a fixed point on the body, e.g. the hip. The path is relatively flat during the time that the foot was in contact with the ground. If the path we not relatively flat, then it would mean that the human&#39;s hips are moving up and down a significant amount during walking. As we know from watching other people walk, the hips stay relatively level during walking, meaning the foot path is relatively flat while the foot is in contact with the ground. When the foot reaches the end of the flat part, i.e. the human&#39;s leg is fully extended behind the body, it is time for the foot to come off the ground and move forward for the next step. The path that the foot takes to return forward must lie above the flat portion, or else the foot would bump into the ground. In other words, one must lift one&#39;s foot off of the ground while bringing it forward. Referring to FIG. 9, we see that the machine&#39;s foot  30  lifts off of the ground as it moves from point B to point A. Also note that the path reaches a height of about 10 inches above the flat portion. This rise corresponds to the lifting of foot  30  10 inches off of the ground. The reason for this rise is so that the machine can step over objects, such as rocks, or onto objects, such as stairs. 
     As mentioned previously, the designer of the HAWR must arrive at a proper trajectory for the path of foot  30 . A proper trajectory has two main properties: 
     1. For 180 rotation of the input—thigh driver-link  18  and shank driver-link  19 , foot  30  travels from A to B and for remaining 180 degree rotation, foot  30  travels from B to A. This means that if the input—thigh driver-link  18  and shank driver-link  19 —rotates at constant speed, the time it takes for the foot  30  to go from A to B is the same as the time for the foot  30  to go from B to A. 
     2. This trajectory must be such that the foot  30  is in contact with the ground from A to B (on the relatively flat portion of the trajectory). And that the return path (from B to A) lies above the flat portion so that the foot does not bump into the ground. 
     The motion of the foot  30  (end point of right leg  1 ) has been described. The trajectory of the end point of left leg  2  is identical to that of the end point of the right leg because the motion generating mechanisms are identical for both sides. However the left foot double four-bar linkage is 180° out of phase with the motion of the right double four-bar linkage. The means that when the foot  30  of the right leg  1  is at point A, the foot of the left leg will be at point B. The opposite is also true; when the left leg is at point A, the right leg will be at point B. This is similar to human walking; the left leg is basically doing the same thing as the right leg, except half a step (180° of the cycle) out of phase. 
     To produce walking we need to have at least one foot on the ground. This is guaranteed by having the left foot be at point A Oust striking the ground) when the right foot is at point B Oust stepping off of the ground). The next requirement for walking is that the machine is propelled forward. If we look back at FIG. 9 we see the path of the foot relative to the rigid frame  12  or the body of the machine. When the foot is on the ground (i.e. between points A and B), if the foot is moving horizontally backward relative to the body of the machine, then the machine is moving horizontally forward relative to the foot. Because the foot is in contact with the ground, we can extend our observation to conclude that the body is moving horizontally forward relative to the ground. This only covers what happens while the foot is on the path between points A and B. However, recall that when one foot reaches point B, it lifts off of the ground, and the other foot (which is at point A) becomes the ground contact foot. Therefore, because the contact foot is always between points A and B, the motion of the machine relative to the ground must be horizontally forward. 
     This machine offers a significant advantage over other types of rough terrain walking machines that have been previously mentioned. It will be appreciated that this walking robot has only one powered degree of freedom and can traverse many different types of terrain. The simplicity of such a device allows it to be reliable and low, cost. It will also be appreciated that legged means of locomotion provides for a significant advantage over wheeled means enabling a wider range of terrain to be traversed. 
     To reduce the vibrations transferred to the cargo and the operator a fluid filled shock absorber  31  is incorporated in the leg design. The shock absorber  31  provides damping and compliance to the relative motion between a bottom-half shank leg  32  and a top-half shank leg  33 . Extending from bottom-half shank leg  32  are three slide-shafts  34 . Drilled in top-half shank leg  33  are three corresponding holes. The three slide-shafts  34  fit into the holes of top-half shank leg  33 . Top-half shank leg  33  and bottom-half shank leg  32  can only slide axially, relative to each other. The shock absorber  31  in FIG. 4 is mounted to the top-half shank leg  33 . The other end of the shock absorber  31  contacts the bottom-half shank leg  32 . The foot  30  is mounted to the end of bottom-half shank leg  32 . The foot  30  has a rubber bottom surface, which provides increased traction with the ground. 
     From the above description, it will be apparent that the invention disclosed herein provides a novel and advantageous human assisted walking robot. The foregoing discussion discloses and describes merely exemplary methods and embodiments of the present invention. One skilled in the art will readily recognize from such discussions that various changes, modifications and variations may be made therein without departing from the spirit and scope of the invention. Accordingly, disclosure of the present invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims.