Kinematic Analysis Of Manipulator Arm For Cutting Of Hazardous Material Using Abrasive Water Jet

Kinematic Analysis Of Manipulator Arm For Cutting Of Hazardous Material Using Abrasive Water Jet

Prof V Kumar1, P W Deorankar2, Purnanand3,

1 :Prof MechEngg AISSMSCOE Pune, 2: PG Scholar, AISSMSCOE Pune 3: Scientist R&DE(E)DRDO Pune

Abstract

Remotely operated vehicles (ROV) are found to be of great utility in military application. ROVs have been developed to deal with Improvised Explosive devices (IEDs). IEDs are small in size and has limited weight which can be rendered safe by disturbing the circuitry of these small bombs. However it cannot handle large size of explosive stores like bombs dropped from aircraft. Unexploded explosives becomes dangerous to handle and poses threat to nearby area i.e. personnel and equipment. In order to obviate the danger to human life in disposing the unexploded, suspected bombs an Unmanned Ground Vehicle (UGV) is being developed. This UGV will be used to meet the various requirements involved in diffusing and disposing an unexploded bomb. A manipulator arm is being developed and integrated on the vehicle to undertake defusing operation and safe disposal of bombs. The manipulator arm has been designed to hold and handle the nozzle used to impinge abrasive jet on the bomb. This arm will have adequate degrees of freedom to move and access the bombs from various angles. This manipulator will also be remotely controlled. A detail kinematic analysis of the manipulator arm has been carried out to approach the bomb from various angles. This arm is designed for cutting the bomb surface of various radius and lying in different orientation.

Keywords:ROV,Manipulator, Direct kinematics, DH parameters, Work Volume

1. Introduction

   Worldwide more and more tons of war zone explosives, terrorist explosive devices and chemical weapons are being found on land and under water. The opening up and deactivation of these bombs, grenades and mines, and also the cutting up and apportioning of solid rocket propellants, place ever higher requirements on the safety of the bomb technicians.Unexploded Ordnance (UXO) becomes dangerous to handle and poses threat to nearby area i.e. personnel and equipment. Till date disposal of these unexploded Ordnance or bombs is being undertaken manually

   by armed forces. In order to obviate the danger to human life in disposing the unexploded, suspected bombs it is desired to use Unmanned Ground Vehicle (UGV) for handling these hazardous material. A remotely operated UGV basically a

   Skid Steer Vehicle is being developed to meet the various requirements involved in diffusing and disposing a unexploded bomb. The main arm of skid steer will be used for handling the UXO. A secondary arm or manipulator needs to be developed and integrated on the vehicle to undertake diffusing operation and safe disposal of bomb.

   Figure 1 Manipulator Arm Assembly

   The manipulator needs to be developed to hold and handle the nozzle used to impinge abrasive jet on the explosive. This arm needs to have adequate degrees of freedom to move and access the explosive from various angles. This manipulator will also be remotely controlled.

   The articulated manipulator arm with 5 rotary joint and one prismatic joint has been used for different jointsrefer figure 1. Matlab 6.1 has been used for simulation for Direct kinematics. Direct kinematics is a method to compute the position and orientation of the manipulators end- effector relative to the base of the manipulator as a function of the joint variables. The position of end- effector has been found by transformation matrix from base to the end effector by the use of D- H parameters, using symbolic computation of Matlab. The work space of the manipulator arm has been generated.

2. Manipulator Design

   For cutting an unexploded bomb lying in different orientation, manipulator has to be designed keeping various paths to be traced by the manipulator as per the requirement.Following cases of bomb orientation are considered :-

   1. Unexploded bomb is lying on the surface.

   2. Nose of the unexploded bomb is buried in the soil and only tail portion is visible.

   3. Entire unexploded bomb is buried under the soil.

   After giving a thought to various paths that manipulator will have to traverse on the bomb surface. We have finalized the concept of manipulator as depicted in fig 2. 1 is the angle of rotation of the turret. The back arm is connected to turret and back arm will have pitch movement 2. Further forearm 1 is connected to back arm and will have pitch movement at 3. Forearm 2 is connected to forearm 1 at 4 and will have pitch movement. At the other end of forearm 2 we have rotational movement at 5 where a linear table with nozzle is attached.

   Figure 2 Schematic of Manipulator Arm

   For cutting a circular template on bomb surface we have to tilt the forearm 2 at 4 by 90 and then give roll at 5 so that nozzle traces a circular path on the bomb surface. Rotary actuators are selected for actuation of all joints. Torque requirement of motors were calculated considering the payload and the link weights refer figure 3. Since the end effector nozzle has to follow various paths for cutting with precision, design of arm was stiffness based and deflection of the links has been kept within the acceptable limits. [4] For metal cutting application the system with high stiffness and low weight provide better accuracy. Cross sections of the links were finalized keeping the stiffness requirement in view.Bending moment is calculated with the loads as shown in figure 3. Bending moment was calculated as 282.75 N-m for back arm, 102.750 N-m for forearm 1 and 23.25 N-m for forearm 2. FE analysis of the links was carried out using abaqus CAE 6.10-1. Deflection was found to be 0.0858 mm for back arm, 0.184 mm for forearm 1 and 0.0139 mm for forearm 2.

   Figure-3Load Diagram for arm with link weights and actuator weight

   2.1 Realisation of prototype Manipulator

   Figure 4 Schematic of mini Manipulator

   A Scale down prototype of manipulator arm was modeled for realization refer figure 4. The aim of developing a prototype arm was to prove the concept of various approaches for cutting a bomb. Motors were selected based on the torque requirement adequate to sustain the weight of the actuator, payload and the mounting attachment.

   Dynamixel actuators MX-106 and RX-64 are used for prototype manipulator arm. The actuators are supplied with standard attachment frames and horns for forming various links of the arm. In spite of the compactsize, it generates relatively big Torque by way of the efficient speed reduction. It can read the current position and speed. It is easy to wire since it is connected with Daisy chain. The main body is made of engineering plastic to withstand against strong external force. Since a bearing is used at the last axis of the gear, the amount of efficiency reduction is minimal even if strong external force is applied to the axis.

3. Manipulator Kinematics

   In this section the articulated manipulator arm with 5 rotary joints has been simulated for different joint variables. Matlab 6.1 has been used for simulation for Direct kinematics. Direct kinematics is a method to compute the position and orientation of the manipulators end-effector relative to the base of the manipulator as a function of the joint variables. The position of end-effector has been found by transformation matrix from base to the end effector by the use of D- H parameters, using symbolic computation of Matlab. The work space of the manipulator arm has been generated.

   1. <3>Denavit-Hartenberg (D-H) Parameters for manipulatorarm

      Figure5: Schematic of Mini Manipulator Withjoints and link numbers

      Figure6 Attachment of frames to the various links

      Figure 5 and 6 shows Schematic of Manipulator with joints and link numbers and reference frames for finding D-H parameters of the manipulator arm respectively.Denavit-Hartenberg parameters (D-H parameters) for the manipulator are listed below in table 1 where I is the joint number, is linktwist, a is link length, d is link offset and is joint angle.

      Table 1

      i	i 1	ai – 1	di	i
      1	0	0	d1	1
      2	90	0	0	2
      3	0	a2	0	3
      4	0	a3	0	4
      5	90	0	d5	5

      Here the values of link parameters are d1 =150 mm, a2= 800 mm, a3 = 600 mm, d5 = 300 mm

      L = d1 + a2+ a3 +d5 = 1850mm. Joint variables Variation of different joint angles are as follows

      1 varies from 0 to 360 degree.

      2 varies from 0 to 180 degree

      3 varies from 0 to 270 degree

      4 varies from 0 to 270 degree

      5 varies from 0 to 360 degree

   2. Direct Kinematics

      0T5 = 0T1 x 1T2 x 2T3 x 3T4 x 4T5

      So, we will get a 4 x 4 matrix, which is a combination of rotation matrix, position vector, prospective and scaling factor for frame 5 with respect to frame 1. The first 3×3 matrix is the rotation matrix and the first three entries of the last column is the position vector in terms of Cartesian Co-ordinates i.e. [ xy z ]T.

      Where

      r11 = Cos1[Cos (2 +3)+ 4]Cos5 + Sin1Sin5 r12 = -Cos1[Cos (2 +3)+ 4]Sin5+ Sin1Cos5 r13 = Cos1Cos5[Cos(2+3+4)+ Sin1Cos5

      r14 = Cos1[300Sin(2+3+4)+4 + 600Cos(2+3)

      +800 Cos2] r21=Sin1Cos(2+3+4)Cos5 Cos1Sin5 r22=-Sin1Cos(2+3+4)Sin5 Cos1Cos5 r23=Sin1Sin(2+3+4)

      r24=300Sin1Sin(2+3+4)+600Sin1Cos(2+3)

      +800 Sin1Cos2] r31=Sin1(2+3+4)Cos5 r32=-Sin1(2+3+4)Sin5 r32=-Cos(2+3+4)

      r34=-300Cos(2+3+4)+600Sin(2+3)+800

      Sin2+d1]

      From this, we get the position vector of the end effector in Cartesian co-ordinates in terms of the joint variables. These are derived from matlab calculation

      px = 300*(cos(t1)*cos(t2)*cos(t3)- cos(t1)*sin(t2)*sin(t3))*sin(t4)- 300*(-cos(t1) *cos(t2)*sin(t3) – cos(t1) * sin(t2) *cos(t3))

      *cos(t4) + 600 * cos(t1)

      *cos(t2)* cos(t3) -600* cos(t1)

      *sin(t2)* sin(t3) + 800 * cos(t1)

      *cos(t2)

      py = 300*(sin(t1)*cos(t2)*cos(t3)- sin(t1)*sin(t2)*sin(t3))*sin(t4)- 300*(-sin(t1) * cos(t2)*sin(t3)- sin(t1) *sin(t2)*cos(t3)) *cos(t4)

      +600 *sin(t1)* cos(t2)*cos(t3)-

      600 *sin(t1)* sin(t2)*sin(t3)

      +800 *sin(t1) *cos(t2)

      pz =

      300*(sin(t2)*cos(t3)+co

      s(t2)*sin(t3))*sin(t4)-300*(- sin(t2) *sin(t3)

      +cos(t2)*cos(t3))*cos(t4)+600*si n(t2)*cos(t3)+600*cos(t2)*sin(t3

      )+ 800*sin(t2)+d1

   3. Work Space Envelope

      The work space i.e. effective area within which the arm can effectively function, is shown in figure7 and8 respectively. The existence and nonexistence of a kinematic solution defines the work space of the manipulator. Work Space is plotted for the manipulator arm using auto CAD is as below :-

      Figure 7Work space in vertical plane

      Figure 8 Range of reach for each link

      Figure 9 Realization of mini manipulator

4. Conclusion

   The manipulator has been designed by considering the different orientation of UXO. The designed manipulator is able to achieve various paths at different angles. Further cross section of the links has been selected to achieve deflection within acceptance limits. FE analysis of the links has been completed. Realisation of mini manipulator has been completed using servo motors. Kinematic analysis has been completed.Realised mini manipulator is shown in figure 9. The manipulator is thus suitable for the task of handling and diffusing of unexploded bombs.

5. Acknowledgement

   We would like to thank respected Dr S Guruprasad(director, R & DE(Engrs)),Shri AK Patel(GD-ASG, R & DE (Engrs), Shri AA Mukherjee (Gp Head-ASG, R&DE(Engrs) for their consistent support and morale boost and allowing us to carry out our design and analysis.

6. References

1. Craig JJ Introduction to Robotics, Pearson Education.

2. Kinematic Analysis and synthesis of mechanism by AK Malik, A Ghosh and GuntlerDittrich.

3. Innovative design for 6 degree of manipulator arm at national seminar on UGV at VRDE Ahmadnagar by MK Pathak R&DE (Engrs)

4. Stiffness Analysis of a parallel Kinematic Manipulator AC Pankaj, SK Pradhan, DK Biswas and J Basu CMERI, Durgapur.