2.1 DESIGN CONSIDERATION:

Figure 1: Design Overview of Robotic Arm.

The following were put into consideration in the design process.

i. Electrical actuators DC servo are chosen instead of hydraulic and pneumatic actuators because of the little power requirement and its light weight which is suitable for this design.

ii. Materials used for the fabrication were locally sourced from available materials.

iii. The materials which will be used for the design will be light in weight so as to reduce the weight concentration on the base and the shoulder.

iv. Rectangular sheets instead of blocks are chosen for the links because of their light weight and stability and to reduce the weight of the arm.

v. A continuous path controller was chosen (PIC microcontroller was used).

vi. The torque is fully balanced by the inertia of the electric motors.

2.2 SELECTION OF DEGREE OF FREEDOM (DOF):

The number of independents movements that an object can perform in 3D space is termed as the number of degree of freedom (DOF). Thus, a rigid body free in space has six degree of freedom – three for positions and three for orientations. For our application 4 DOF are suitable.

2.3 MATERIAL SELECTION:

The most suitable material to fabricate the structure of the arm has to be light and strong. Otherwise, the servo motor will not be able to pull up the arm and to perform the desired turning degree. Among the materials that can be considered to fabricate the structure are aluminum, Perspex, plastic polymer and carbon fiber. In choosing the fabrication materials, the aspect of availability of the materials, the overall cost and the flexibility to be shaped, should also be taken into consideration. Thus among the four materials considered, the aluminum is the most ideal material to be chosen as fabrication material.

2.4 SPECIFICATIONS OF ROBOTIC ARM:

The robot arm for this project is the revolute type that closely resembles the human arm. Shoulder that mounted on base can move the arm through 180 degrees, from horizontal to vertical on each side. The shoulder uses large-scale servo, provide the torque needed to lift the rest of the arm, as well as any object that it may be grasping. Attached to the shoulder piece is an elbow that can move through 180 degrees, also powered by a large-scale servo. The wrist is made up of one standard servo and can move through 180 degrees, in vertical direction. Attached to the wrist is a two-fingered gripper that utilizes a unique design built around a single standard servo.

Table no. 4.6: Specification of robotic arm.Table No.1: Specification of robotic arm

Specification Value

Number of axes 4

Horizontal reach 230 mm

Vertical reach 130 mm

Drives 4 servo motors

Configuration 4 Axes plus gripper.

All axes completely independent.

All axes can be controlled simultaneously.

Work Envelope (a) Shoulder Rotation -150 degrees

(b) Elbow Rotation -180 degrees

(c) Wrist Rotation -180 degrees

(d) Gripper Rotation -90 degrees

3. CAD MODELLING OF ROBOTIC ARM

Considering the all points in designing, CAD model (Creo software) is used for robotic arm design. Various component of robotic arm is shoulder, elbow, wrist, grippers. The purpose of utilizing this Creo software is because Creo can provide a detail, real images and walk through overviews for demonstrating design. The 3D views of various parts of robotic arm are shown in fig. 2-8.

4. INVERSE KINEMATICS ANALYSIS

In order to control the position and orientation of end- effector of a robot arm to reach its object, the inverse kinematics solution is more important. In this project, inverse kinematics problem is solved by RoboAnalyzer 3D Model Based Robotics Learning Software. RoboAnalyzer is developed in the Mechatronics Lab, Department of  Mechanical Engineering at IIT Delhi, India under the guidance of Prof. S. K. Saha.

Figure 9: Initial and final position of Robotic arm.