Due to the limited financial support of this project, the content of the robot hardware design is not completely new, but a restructured version of an existing mobile robot. We modified the mechanism to get rid of the existing drawbacks, to ensure the new mobile robot can fit for these requirements of the current project.
錯誤 錯誤 錯誤
錯誤! 找不到參照來源找不到參照來源找不到參照來源找不到參照來源。。。。 is the overview of the mobile robot. There are a total of four driving wheels, two on the each side of the robot. This enables this robot to move forward, backward and turning around.
Furthermore there are two degrees of freedom at the bottom of the chassis. These components can be used to maintain balance when walking on an uneven terrain. This robot has two arms and hands. Left and right arms are the original designs from an existing mobile robot. Both left and right hands are the new version of the design. A stereo vision system is installed on the top of the robot. The head can rotate up and down, also left and right. In addition, a computer and motor drivers are installed inside the Robot’s chassis. All of the motor drives are connected by series communications with RS-232.
Fig. 1 Overview of the armed mobile robot
The detail specification is shown in Table 1. The height of robot is 140 ~ 150 cm. There are totally 34 degrees of freedom. DC servo motors are used to actuate the robot, while harmonic drivers and pulleys are used to reduce the speed. The camera used as the eye is a Logitech webcam 5000. Maximum loading is 650 grams by the hand. There are seven degrees of freedom in each arm. 錯誤錯誤錯誤錯誤! 找不到參照來源找不到參照來源找不到參照來源找不到參照來源。。。 shows the 。 rotating range of each degree of freedom.
Because the gripping ability of the older hand is very limited, it needs to re-design a new one. The degree of freedom of the new robotic hand takes reference to the real human hand. There are 5 degrees of freedom on the new hand as shown in 錯誤錯誤錯誤錯誤! 找不到參照來源找不到參照來源找不到參照來源。找不到參照來源。。。. It’s a simplified model from the humans. DOF-1~2 for the finger’s joint, these joints can change the direction and angle of fingers. DOF-4~5 are for opening and closing three fingers.
5 Table 1 Specification of the robot
Height 140~160 cm Actuators DC Servo Motor Reduction
Mechanism
Harmonic Drive Gear Timing-Belt/Pulley Camera Webcam ×2 Maximum Load 650g (Hand)
Table 2 Moveable range of two arms Movable Range of Arm
Fig. 2 Arrangement of 5 DOF of hand
Most important part is the ability of grapping. By clever arrangement of the 5 degrees of freedom of hand, this robotic hand can hold on objects like cube, bottle, cylinder, square column, slice and wand. The maximum load of this robotic hand is 650g.
Cube Bottle-1 Bottle-2 Cylinder-1 Cylinder-2
Cylinder-3 Square column Bar Screw Key
Fig. 3 Simulation results of grasping different objects
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After the three finger hand design, we designed a new type of five fingers hand. Because of the objects for the robot to grasp are all things in human’s daily, we want the robot hand to best resemble the real human’s hand. Furthermore, we wish that the robot hand size is closer to the real human so that the robot hand can grasp the target items with higher confidence. The simulation results of grasping using the three finger hand can be seen in Fig. 3. mechanisms: fingers bent/straighten mechanism, thumb twisting/bending mechanism and fingers outreach/contract mechanism.
Table 3 Degrees of freedom and the joint definitions DOF Joint DOF Joint
1 J1,1 5 J2,2+J2,3+J2,4
2 J1,2 6 J3,2+J3,3+J3,4
3 J1,3 7 J4,2+J4,3+J4,4
4 J2,1+J4,1+J5,1 8 J5,2+J5,3+J5,4
Fig. 4 Free body diagram
Fingers bent and straighten mechanism
The index finger, middle finger and ring finger share the same mechanism design. 錯誤錯誤錯誤錯誤! 找不到參照來找不到參照來找不到參照來找不到參照來 源
源 源
源。。。。 shows the mechanism design of the index finger. Motor are embedded in a first knuckle and the helical gears are used to turn 90 degrees from the output axis. A coordinated motion of the two sets of four-bar
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linkage mechanism shown in 錯誤錯誤錯誤! 找不到參照來源錯誤 找不到參照來源找不到參照來源找不到參照來源。。。。, achieves a degree of freedom bending motion of three joint chain.
Fig. 5 Finger mechanism design
Fig. 6 Linkage mechanism diagram
With the same movement principle of the little finger and index finger, the motor is embedded within the first knuckle and uses two sets of four-bar linkage mechanism to drive the chain bending joints. The length and the strength of human little finger are usually smaller than those of the other four fingers, therefore you can use a smaller torque, smaller length and smaller outer diameter, and a smaller DC motor to drive the mechanism. 錯誤錯誤錯誤! 找不到參照來源錯誤 找不到參照來源找不到參照來源。找不到參照來源。。。 shows such little finger mechanism design.
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Fig. 7 Little finger mechanism design Thumb twisting and bending mechanism
Accounting for the many important activities of the hands, we set each of three joints as an independent degree of freedom, and it needs a larger torque than the other fingers.
And also we use worm gears reducer mechanism to increase the reduction ratio. Since this mechanism has a self-locking function, the worm gears will not reversely rotate when the thumb bents resistant objects.
The motor embedded in the last knuckle uses a helical gear to drive as shown in 錯誤錯誤錯誤錯誤! 找不到參照來源找不到參照來源找不到參照來源找不到參照來源。。。. 。
Fig. 8 Thumb bending mechanism design
The twisting joint design is co-axial to the motor 1, and is fitted with a spur gear. Motor 1 and the bending mechanism rotate on the axis, and avoid interference linkage as shown in 錯誤錯誤錯誤錯誤! 找不到參照來源找不到參照來源找不到參照來源。找不到參照來源。。。.
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Fig. 9 Thumb twisting mechanism design
Fingers outreach and adduction mechanism
Outreach and contraction mechanisms of the index finger, ring finger and little finger use the seven-bar mechanism to drive. The middle finger due to a small swing angle is fixed in the palm base. The motor with worm gear drives the ring finger linkages with the maximum swing angle14° and the index finger and the little finger the maximum angle 13° and 21°, respectively. The fingers outreach and adduction mechanism is shown in 錯誤錯誤錯誤錯誤! 找不到參照來源找不到參照來源找不到參照來源找不到參照來源。。。. 。
Fig. 10 Fingers outreach and adduction mechanism design
The mechanism design and the real manufactured palm is shown in 錯誤錯誤錯誤錯誤! 找不到參照來源找不到參照來源找不到參照來源找不到參照來源。。。。 and 錯誤錯誤錯誤! 錯誤 找不到參照來源
找不到參照來源 找不到參照來源
找不到參照來源。。。。, respectively. The major structural dimensions comparison is shown in 錯誤錯誤錯誤錯誤! 找不到參找不到參找不到參找不到參 照來源照來源
照來源照來源。。。. 。
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Fig. 11 The whole robot hand mechanism design
Fig. 12 Real robot hand mechanism assembly
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Fig. 13 Robot hand mechanism dimensions
After we assemble and install robot hand, we performed some robot hand mechanism actuation test as show in Table 4. And also did the robot hand object handling tests as show in Table 5.
Table 4 Robot hand mechanism actuation test
Motion 1: stone Motion 2: OK motion
Motion 3: number 3 Motion 4: number 5
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Table 5 Robot hand mechanism crawl and hold the test
Catch the ball Grasping disc Grasping notebook
Grasping a box Grip PET bottle Grip the cup
Holding the phone Grip plier Clip business card
The experiments shows that the mechanical hand can grasp a tennis ball (sphere), a disc (disk), a rectangular box (box), a plastic bottle, a cup (cylinder), a telephone, and a pair of pliers. Also shown in 錯誤錯誤錯誤錯誤!
找不到參照來源 找不到參照來源 找不到參照來源
找不到參照來源。。。。, the robot hand can also pinch the business card between the fingers and thumb clip.
Because we have designed the new robot hand, we make a comparison between the 3 fingers and the 5 fingers hand designs as shown in 錯誤錯誤錯誤! 找不到參照來源錯誤 找不到參照來源找不到參照來源。找不到參照來源。。。.
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Table 6 Design compare list about robot hand
Design type/item 3 fingers 5 fingers
Finger number Three Five
Degree of freedom 5 DOF 8 DOF Driving mechanism Built-in actuator
Slider and linkage
Built-in actuator Slider and linkage Finger motion Under-actuated Under-actuated
Hand size(cm) 12(L) x 10(W) 18(L) x 16(W)
Maximum load 650g 535g
In order to increase the work space of the hands and the practicality of the robot, we set two degrees of freedom on the body. The first degree of freedom can make the robot stoop, with the two arms degrees of freedom, significantly increasing the working space. The second degree of freedom can change the robot’s height, which is useful and convenient when the robot picks up the object on different height. The chassis was originally designed by Professor Nakajima, the Department of Advanced Robotics, Chiba Institute of Technology [21]. We modified their original design so as to integrate with the upper body mechanisms. There are 2 degrees of freedom at the front and rear chassis’ mechanism. It helps the robot move on uneven terrain as shown in Fig 14.
Fig. 14 (left) Body’s degrees of freedom. (right) The chassis’ degrees of freedom
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