Abstract:
A gripping device comprising: a house; at least one gripper configured with at least one claw, the claw being configured with a pair of first phalanxes linked to the house at a first joint, and a pair of second phalanxes linked to the first phalanxes at a second joint; a first actuator arranged on the first joint; a second actuator arranged on the second joint; and a motor configured to enable the first and the second actuators co-operate so as to push the second phalanxes off a gripping substrate, or to push the second phalanxes back to the gripping substrate.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 61/511,800 filed Jul. 26, 2011, which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     Preventing trees from falling is important to protect human life and property in urban areas. Most trees in urban areas require regular maintenance. To reach upper parts of a tree to perform such maintenance, workers need to climb the tree. However, tree climbing is dangerous, and thus a tree-climbing robot is developed to assist or replace tree climbers in their work. 
     Several robots have been designed to climb trees. WOODY2006 as proposed by Y. Kushihashi, et al. in “Development of Tree Climbing and Pruning Robot, Woody-1-Simplification of Control using adjust Function of Grasping Power” is a climbing robot designed to replace human workers in removing branches from trees. The robot climbs by encircling the entire tree trunk. The size of the robot is thus proportional to the circumference of the trunk. WOODY2006 avoids branches by turning its body and opening the gripper, but it requires an almost straight tree trunk. 
     Kawasaki 2008 as proposed by H. Kawasaki, et al., “Novel climbing method of pruning robot” also developed a climbing robot for tree pruning. It uses a gripping mechanism inspired by lumberjacks, and uses a wheel-based driving system for vertical climbing. It encircles the entire tree trunk for fastening on a tree. It cannot avoid branches when the fastening mechanism cannot be opened. 
     SUMMARY OF THE INVENTION 
     In one aspect, there is provided a ripping device comprising:
         a house;   at least one gripper configured with at least one claw, the claw being configured with a pair of first phalanxes linked to the house at a first joint, and a pair of second phalanxes linked to the first phalanxes at a second joint;   a first actuator arranged on the first joint;   a second actuator arranged on the second joint; and   a motor configured to enable the first and the second actuators co-operate so as to push the second phalanxes leave off from a gripping substrate, or to push the second phalanxes back to the gripping substrate.       

     According to one embodiment, the motor may comprise a linear motor configured to have an extension operation stage and a contraction operation stage, wherein, the linear motor operates to enable the first and the second actuators co-operate so as to push the second phalanxes leave off from a gripping substrate in the extension operation stage, or to push the second phalanxes back to the gripping substrate in the contraction operation stage. For example, the first actuator may comprise a first pre-compressed spring and the second actuator may comprise a second pre-compressed spring. During the extension operation stage, the linear motor compresses the first pre-compressed spring and releases the second pre-compressed spring so as to push the second phalanxes leave off from the gripping substrate; and during the contraction operation stage, the linear motor compresses the second pre-compressed spring and releases the first pre-compressed spring so as to push the second phalanxes back to the gripping substrate. 
     In a further aspect, there is provided a ripping device comprising:
         a house;   at least one first phalanx linked to the house at a first joint;   at least one second phalanx linked to the first phalanx at a second joint, wherein there is provided a first pre-compressed spring and a second pre-compressed spring in the first and the second joint, respectively; and   a linear motor arranged on the house,   wherein the linear motor is configured to further compress the first spring and release the second spring so as to push the second phalanx leave off from a gripping substrate during the linear motor extends, and to compress the second spring and release the first spring so as to push the second phalanx back to the gripping substrate during the linear motor contracts.       

     In a further aspect, there is provided a manipulator, which may comprise:
         a plurality of plates;   a plurality of springs arranged to pass though the plates;   a plurality of actuators mounted in one of the plates, each of the actuators includes a motor to control lengths of the third springs between each two of the plates independently, such that the manipulator performs bending and extension motions.       

     According to one embodiment, the springs and the actuators co-operate such that the manipulator performs said bending and extension motions in a plurality of Degree of Freedom (DOF). For example, there may be 3 springs and 3 actuators, and the actuators cooperate with the springs such that the manipulator acts in 3 Degree of Freedom (DOF). In addition, the manipulator may further comprise a plurality of passive spacers arranged at middle of the manipulator to ensure the springs in constant distance through the entire manipulator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates functional blocks for a gripping device according to one embodiment of the present application. 
         FIG. 2   a  illustrates a cross-sectional view of the gripping device (contraction operation stage) as shown in  FIG. 1 . 
         FIG. 2   b  illustrates a cross-sectional view of the gripping device (extension operation stage) as shown in  FIG. 1 . 
         FIG. 3   a  illustrates a top view of the proposed manipulator as shown in  FIG. 1 . 
         FIG. 3   b  illustrates a side view of the proposed manipulator as shown in  FIG. 1 . 
         FIG. 3   c  illustrates an exemplary configuration for the actuator in the proposed manipulator as shown in  FIG. 3   b.    
         FIG. 4  illustrates a complete climbing gait of a gripping device according to one embodiment of the present application (moving forward). 
         FIG. 5  illustrates a part of climbing motions to avoid an obstacle on a tree. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  illustrates functional blocks for a gripping device  1000  according to one embodiment of the present application. As shown in  FIG. 1 , the structure of the gripping device  1000  comprises two parts, i.e. a gripper  100 , such as an omni-directional tree gripper, and a continuum manipulator  200 . For example, there may be two grippers  100 , each of which has a first end and a second end. The first end is connected to ends of the continuum manipulator  200 , respectively. The grippers  100  can adhere on a tree surface tightly while the continuum manipulator  200  acts as maneuver mechanism to move the second end of the gripper to a target position. Hereinafter, the configurations of the gripper  100  and the manipulator  200  will be discussed in reference to  FIGS. 2 and 3 , respectively. 
     Omni-Directional Tree Gripper  100   
       FIG. 2   a  illustrates a cross-sectional view of the gripping device  100  during the contraction operation stage according to one embodiment of the present application, and  FIG. 2   b  illustrates a cross-sectional view of the gripping device  100  during the extension operation stage according to one embodiment of the present application. There are many innovative approaches to provide adhesive force such as vacuum suction, magnetic attraction, elastomeric adhesive, electro adhesive and fibrillar adhesive. Those methods work well on urban settings such as vertical walls and glass windows that are smooth and flat. However, they are not applicable on tree surface, as the nature of trees is totally different from urban settings. Claw climbing method is widely used in tree living animals such as squirrels and birds. Through an observation of the tree living animals, the claw gripping is reliable on a tree surface. As a result, the claw gripping method is adopted to provide adhesive force. The design of the proposed gripper  100  aims at providing adhesive force on a wide range of gripping curvature such that the gripper  100  is able to adhere on tree trunks and branches. The gripper  100  is designed to be omni-directional along its principal axis  60  so that no additional orientation actuator and control is needed about its principle axis and hence keeps the device  1000  in lightweight and simple. 
     The gripper  100  may, for example, comprise four claws equally separated by 90 degrees. As shown in  FIGS. 2   a  and  2   b,  each claw is formed by two parts (a first Phalanx  10  and a second Phalanx  20 ) and has surgical suture needles  210  installed at the tip. The adhesive force of the gripper is generated by the spine penetration. 
     The claws adopt two bar linkages mechanism to generate optimal direction of acting force. As shown in  FIG. 2 , all claws in a gripper are actuated by a linear motor  30  arranged on a house  50 . A pushing plate  40  is mounted at the end of the linear motor  30 . When the linear motor  30  extends, the plate  40  pushes all the phalanxes  10  and  20  and hence makes the phalanxes  10  and  20  upward. A pair of first pre-compressed springs  70  arranged on a pair of first joints  701  (joints A, one for each spring  70 ) are further compressed. A pair of springs  80  arranged on a pair of second joints  801  (joints B, one for each spring  80 ) are released at the same time. This motion pulls the spines off from a gripping surface  90  like a tree trunk. When the linear motor  30  contracts, the compressed springs  70  and  80  on joints A and B generate a force to push claws back to the gripping surface and at the same time the springs on joint B will further be compressed. Since the gripping force is generated by the preloaded springs only, the static gripping with zero energy consumption can be achieved. The constant force spring (a flat spiral spring) is adopted to ensure that the force is independent to the claw traveling angle. In addition, since the moving mechanism of each claw is independent, it allows the claws to travel in different angle. This ensures that all of the claws penetrate into the gripping substrate, even if it has an irregular shape, to generate the maximum force. 
     Manipulator  200   
     There are many types of continuum manipulators, such as wire-driven and pneumatic-driven. Most of them are able to bend in any direction and some are even able to extend to a certain extent. Most current research uses the continuum structure in robot arms, but few researchers have realized that it can also be applied to maneuvering. The continuum mechanism is a compliant structure, as it does not contain fixed joints. In one embodiment, the continuum mechanism may utilize the same or similar physical structure as disclosed by G. Robinson, J. B. C. Davies. Please refer to “Continuum Robots—A State of the Art”, Proceedings of the 1999 IEEE International Conference on Robotics and Automation, Detroit, Mich., May 1999. 
     Its inherent passive compliance is particular benefit for maneuvering in an arboreal environment, as it can often eliminates the need for complex force sensing and feedback control. For climbing purposes, the manipulator must be compact and lightweight. There are many types of continuum manipulator, but none of them fulfills all of these requirements. Existing continuum manipulators need to connect to large external boxes that contain wire, drivers, motors, or air pumps. Although some pure wire-driven continuum manipulators have the potential to be more compact and lightweight, the manipulators are not extendable. Extendibility is important. 
     Due to these limitations, a novel design of continuum manipulator  200  to maneuver with both bendable and extendable functionalities is proposed. The proposed continuum manipulator is a self-contained module that actuators  207  are integrated and hence no external control box is required. It makes the proposed continuum manipulator  200  compact and lightweight. In addition, the special driving mechanism allows superior extension ability that the existing designs cannot achieve. 
       FIGS. 3   a  and  3   b  shows the proposed manipulator  200  according to one embodiment of the present application. It is formed by, for example, three mechanical springs  203 ,  204  and  205  that are connected in parallel. The distance between the center of the continuum manipulator  200  and springs are equal and the springs are equally separated by 120 degrees. One end of spring is fixed on a plate  201 , while the other end does not have any fixed connection. The springs pass through a plate  202  in which there is arranged three actuators  207 . As shown in  FIG. 3   c , each of actuators  207  includes one motor  2071  (for example, DC motor) to control the length of springs between two of the plates independently. Through the control of the length of each spring, the continuum manipulator  200  can perform bending and extension motions. 
     Commonly, the number of actuators required in each section of continuum manipulator is more than the number of admissible degrees of freedom. However, in the proposed structure, only three (for example) actuators are used but it can provide 3 Degree of Freedom (DOF). This structure provides maximal DOF with minimal actuators. The actuation mechanism is similar to rack and pinion mechanism which allows unlimited extension of the continuum manipulator theoretically. In practice, it is limited by the length of the springs only. The spring can be treated as a bendable rack. The spring should only be allowed to bend in any direction but not able to compress or extend so as to keep a constant gap distance for pinion  2072  ( FIG. 3   c ) to drive. On top of that, keeping the springs in constant distance through the entire manipulator is important to keep a uniform shape. As a result, several passive spacers  206  are installed at the middle of the manipulator to constrain the distance among springs. The maximal distance between constraint plates are constrained by wires. 
     Motion of Device 
     A. Locomotion of the Device  1000   
     The locomotion of the device as described in the above is similar to inchworms which is a kind of biped locomotion.  FIG. 4  shows a complete climbing gait of the locomotion. It is composed of a plurality of (for example, six) climbing steps. The square colored in grey represents the closed gripper that is attached on the substrate while the square colored in white represents the opened gripper that detached on the substrate. The order of motion in the figure represents the locomotion of moving forward. The locomotion of moving backward is just in reverse order. 
     The device  1000  is able to change a moving direction in three-dimensional space by bending the continuum manipulator. It allows the device  1000  to climb along a curved shape of tree or avoid obstacles such as non-passing through branches. This ability makes the device  1000  have high maneuverability that surpass the existing tree climbing robots.  FIG. 5  shows part of climbing motions to avoid an obstacle on a tree. The device  1000  can first adjust the direction of the bottom gripper and then climb along this direction to avoid the obstacle. This method is also applicable for turning to another side on a branch or selecting a branch to climb. 
     B. Control of the Device  1000   
     In this state, the device  1000  is a remote control robot. The control input of the gripper is simply an on/off command to make grippers fully open or close. As for the control of the continuum manipulator, since it has three DOF, three channels of input are needed. One way is to directly input the length of each spring. However, it is not an intuitive way for human manipulation. Human being always has a perspective of the direction of motion when controlling something, i.e., the concept of left, right, front and back. As a result, to make an intuitive controller, we define three control inputs, i.e., S input , κ input   FB  and κ input   LR . S input  controls the length of virtual backbone, κ input   FB  controls the magnitude of front and back bending while κ input   LR  controls the magnitude of left and right bending. The concept of front is defined as the direction of positive x-axis while the concept of left is defined as the direction of positive y-axis. The mapping from the control inputs to the posture of the continuum manipulator are: 
               [         S           κ           ϕ         ]     =     [           S   input               min   ⁡     (             κ   input   FB     2     +       κ   input   LR     2         ,     κ   max       )                 atan   ⁢           ⁢   2   ⁢     (       κ   input   LR     ,     κ   input   FB       )             ]               where               S   input     ∈     [     0   ,     S   max       ]               and               κ   input   FB     ,       κ   input   LR     ∈       [       -     κ   max       ,     κ   max       ]     .             
Experiments and Results
 
     Numerous experiments have been conducted to evaluate the performance of the device  1000  in different aspects, i.e., Gripping force of the tree gripper, Climbing on different species of trees; Transition motion; Turning motion; and Slope climbing. 
     1) Gripping Force of the Tree Gripper 
     In the experiments, the gripper first gripped the tree without any external force being applied. An external pull-out force was then applied normal to the gripping surface to test how much force was needed to pull the gripper out of the tree. The maximum pull-out force was limited to 40N to avoid breaking the gripper. Eighteen types of trees with different surface curvatures were tested. The curvature of the trees, bark textures, and the maximum pull-out force with different gripping orientations are summarized in Table 2. In the table, O 1 , O 2 , and O 3  represent gripping different orientations, respectively. The curvature of tree (C) may be obtained by: 
             C   =     1     D   /   2             
where D is the diameter of tree.
 
     Table 2 shows that on the first ten types of trees (No. 1-10), the performance was excellent. The gripper was able to generate over 40N of pull-in force in any gripping orientation. However, the results also reveal that the gripper does not work well on some types of trees, and particularly those with bark that peels off easily. In such cases, when a large pull-out force was applied, the gripper was pulled out as the bark peeled off (No. 11-15). Further, for soft trees the pull-out force broke the bark (No. 16-18). 
     The experimental results indicate that on most of the trees, the maximum pull-in force of the gripper in all gripping orientations is similar, and matches the analytical results as reported. The only exception is tree No. 13. This is because the bark of this tree peels off easily and its surface is not smooth, but rather has many vertical grooves. Gripping orientation will be better if it can create a pair of claws oriented perpendicular to the vertical groove, which allows the claws to penetrate deeper into the tree to generate a larger force. 
     As mentioned previously, the gripping curvature affects the pull-in force of the gripper. This phenomenon is clearly demonstrated by the experimental result for tree No. 10, where the generated pull-in force with a 6.2 m −1  surface curvature is larger than that with a 4.8 m −1  surface curvature. However, the result for tree No. 11 does not match the analytical result. This is because the tree with a 6.0 m −1  surface curvature was older, and its bark will be peeled off easily, whereas the tree with a 11.2 m −1  surface curvature was younger and its bark will not be peeled off easily. 
     In the experimental results, and especially those for trees No. 16-18, it is clear that using gripping orientation  3  generates the largest pull-in force, which matches the analytical results. 
     
       
         
               
             
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Maximum pull-in force on different types of trees. 
               
             
          
           
               
                   
                 C 
                 Pull-in force (N) 
               
             
          
           
               
                 No. 
                 Trees 
                 Texture 
                 (m −1 ) 
                 O1 
                 O2 
                 O3 
               
               
                   
               
             
          
           
               
                 1 
                 
                   Bombax malabaricum 
                 
                 Rough 
                 4.4 
                 &gt;40 
                 &gt;40 
                 &gt;40 
               
               
                 2 
                 
                   Acacia confuse 
                 
                 Smooth 
                 5.6 
                 &gt;40 
                 &gt;40 
                 &gt;40 
               
               
                 3 
                 
                   Ficus microcarpa 
                 
                 Smooth 
                 4.6 
                 &gt;40 
                 &gt;40 
                 &gt;40 
               
               
                 4 
                 
                   Livistona chinensis 
                 
                 Fissured 
                 8.4 
                 &gt;40 
                 &gt;40 
                 &gt;40 
               
               
                 5 
                 
                   Callistemon viminalis 
                 
                 Ridged 
                 6.3 
                 &gt;40 
                 &gt;40 
                 &gt;40 
               
               
                   
                   
                 and 
               
               
                   
                   
                 Furrowed 
               
               
                 6 
                 
                   Bauhinia variegata 
                 
                 Smooth 
                 8.1 
                 &gt;40 
                 &gt;40 
                 &gt;40 
               
               
                   
                 var.  candida   
               
               
                 7 
                 
                   Bauhinia variegate 
                 
                 Smooth 
                 8.8 
                 &gt;40 
                 &gt;40 
                 &gt;40 
               
               
                 8 
                 
                   Araucaria 
                 
                 Banded 
                 7.2 
                 &gt;40 
                 &gt;40 
                 &gt;40 
               
               
                   
                 
                   heterophylla 
                 
               
               
                 9 
                 
                   Bauhinia blakeana 
                 
                 Smooth 
                 6.7 
                 &gt;40 
                 &gt;40 
                 &gt;40 
               
               
                 10 
                 
                   Roystonea regia 
                 
                 Smooth, 
                 6.2 
                 &gt;40 
                 &gt;40 
                 &gt;40 
               
               
                   
                   
                 shallowly 
                 4.8 
                 15 
                 15 
                 20 
               
               
                   
                   
                 fissured 
               
               
                 11 
                 
                   Taxodium distichum 
                 
                 Fibrous, 
                 11.2 
                 29 
                 30 
                 30 
               
               
                   
                   
                 exfoliating 
                 6.0 
                 12 
                 10 
                 10 
               
               
                 12 
                 
                   Casuarina 
                 
                 Slightly 
                 6.9 
                 11 
                 13 
                 12 
               
               
                   
                 
                   equisetifolia 
                 
                 exfoliating 
               
               
                 13 
                 
                   Cinnamomum 
                 
                 Ridged 
                 5.2 
                 20 
                 12 
                 5 
               
               
                   
                 
                   camphora 
                 
                 and 
               
               
                   
                   
                 furrowed, 
               
               
                   
                   
                 exfoliating 
               
               
                 14 
                 
                   Khaya senegalensis 
                 
                 Blocky, 
                 4.0 
                 10 
                 10 
                 10 
               
               
                   
                   
                 exfoliating 
               
               
                 15 
                 
                   Melaleuca 
                 
                 Sheeting, 
                 4.5 
                 5 
                 5 
                 5 
               
               
                   
                 
                   quinquenervia 
                 
                 exfoliating, 
               
               
                   
                   
                 soft 
               
               
                 16 
                 
                   Delonix regia 
                 
                 Smooth 
                 6.7 
                 24 
                 24 
                 25 
               
               
                 17 
                 
                   Mangifera indica 
                 
                 Shallowly 
                 4.1 
                 20 
                 22 
                 25 
               
               
                   
                   
                 fissured 
               
               
                 18 
                 
                   Eucalyptus citriodora 
                 
                 Smooth, 
                 4.1 
                 18 
                 16 
                 20 
               
               
                   
                   
                 soft 
               
               
                   
               
             
          
         
       
     
     2) Climbing on Different Species of Trees 
     The tree climbing tests have been implemented on thirteen species of trees. The device  1000  is commanded to perform vertical climb up motion. The species of trees, diameters and the number of total trials and successful climbing gaits are summarized in Table 3. Results show that the device  1000  performs well on a wide variety of trees. It can be noticed that the range of successful climbing diameter of tree is wide, from 64 mm to 452 mm. However, the device  1000  will fail on several species of trees, i.e.,  Melaleuca quinquenervia, Cinnamomum camphora  and  Bambusa vulgaris  var.  Striata . The reason of fail climbing on  Bambusa vulgaris  var.  Striata  is that the tree surface is very hard that the spine on gripper is difficult to penetrate. As for the  Melaleuca quinquenervia  and  Cinnamomum camphora , their barks can be peeled off easily. By the experimental results, it can be concluded that the device  1000  performs well on the trees that the surfaces are not very hard and have less exfoliation. 
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Climbing performance on different species of trees 
               
             
          
           
               
                   
                   
                 Diameter 
                 No. of steps 
               
               
                   
                 Tree 
                 (mm) 
                 (Success/Total) 
               
               
                   
                   
               
               
                   
                 
                   Bombax malabaricum 
                 
                 452 
                 20/20 
               
               
                   
                 
                   Callistemon viminalis 
                 
                 315 
                 20/20 
               
               
                   
                 
                   Delonix regia 
                 
                 309 
                 20/20 
               
               
                   
                 
                   Bauhinia blakeana 
                 
                  80, 207 
                 20/20 
               
               
                   
                 
                   Bauhinia variegate 
                 
                 258 
                 20/20 
               
               
                   
                 
                   Roystonea regia 
                 
                 325 
                 20/20 
               
               
                   
                 
                   Acacia confuse 
                 
                 229 
                 20/20 
               
               
                   
                 
                   Grevillea robusta 
                 
                 159 
                 20/20 
               
               
                   
                 
                   Bambusa ventricosa 
                 
                 64, 95 
                 20/20 
               
               
                   
                 
                   Araucaria heterophylla 
                 
                 277 
                 20/20 
               
               
                   
                 
                   Cinnamomum camphora 
                 
                 210, 293 
                 13/20 
               
               
                   
                   Bambusa vulgaris  var.  Striata   
                  99 
                 1/5 
               
               
                   
                 
                   Melaleuca quinquenervia 
                 
                 446 
                 0/5 
               
               
                   
                   
               
             
          
         
       
     
     3) Transition Motion 
     In order to verify the maneuverability of the device  1000 , a transition motion from a trunk to a branch has been tested. An experiment has been implemented on a  Bauhinia blakeana . The diameter of the initial gripping trunk is 280 mm and the slope is about 45 degrees while the diameter of the target gripping branch is 118 mm and the slope is about 90 degrees. It shows that the device  1000  succeeded to leave the trunk and completely climbed on the branch. This transition motion takes three climbing gaits within three minutes. 
     4) Turning Motion 
     A turning motion has also been performed to evaluate the maneuverability of the device  1000 . The experiment was implemented on a trunk of a  Bauhinia blakeana  with diameter 207 mm. From the experiment, it can be seen that the device  1000  moved from the front side to the back side. This motion takes five climbing gaits around five minutes. The compliance was succeeded to make the gripper normal to the tree surface so that the device  1000  can perform the turning motion successfully. 
     5) Slope Climbing 
     This experiment examined the maximal climbing slope of the tree climbing robot. It has been implemented on a  Bauhinia blakeana  with diameter 172 mm. The climbing angle is about 103 degrees. It can be seen that the device  1000  climbed up the tree successfully. There is no over slope climbing effect appeared in the experiment. 
     While the present application has been illustrated by the above description and embodiments or implementations, it is not intended to restrict or in any way limit the scope of the appended claims hereto.