Types of Robots
A Robot is officially defined by the Robot Institute of America as "A re-programmable, multi-functional manipulator designed to move materials, parts, tools, or special devices through variable programmed motions for the performance of a variety of tasks" .
Many different variations of robots are available for use in industrial applications and are used to carry out repeated actions highly accurately and without variation. Robots require a control program to govern its velocity, direction, acceleration, deceleration and distance of movement at any time.
An Industrial robot consists of several links connected in series by linear, revolute or prismatic joints. At one end the robot will be fixed to a supporting base while the other is manipulated into position and equipped with a tool allowing it to perform a task.
Industrial robots are composed of the following parts:-
A processing unit is connected to every industrial robot to regulate robot components, provide system networking, dynamic user control and program/teach.
This is the main moving part of the robot which is manipulated to deliver the end effector to the correct location.
The source of power to the arm motors/pumps.
- End Effector
The device on the end of the robot which is suitably equipped with tools required to perform a specific task once the arm has delivered it to the correct position. i.e., grippers, scalpel, spray gun, vacuum or even a vision camera.
Relay information about axis position, end effector orientation and surrounding environment.
There are a number of parameters which describe a robot as follows:-
- Number of Axis
Two axis are required to reach any point in a plane (x,y) and three axis are required to reach any point in space (x,y,z). Further axis of roll, pitch and yaw are required to control the orientation of the end of the robot.
- Kinematics (Motion)
The physical arrangement of rigid members and joints in the robot defining its possible motions.
- Working Envelope
The region of space within physical reach of the robot.
- Carrying Capacity
How much weight a robot can lift or move.
How quickly the robot can position itself as required.
How closely the robots position can be achieved.
- Motion Control
Whether a robot need repeatedly move between pre-programmed positions as it sees best or be continuously controlled in orientation and velocity to follow a predetermined path in space.
- Power Source
Be it electric motors or hydraulic actuators.
Motors can be geared to the joints or direct drive.
Cartesian Coordinate Robot
A Cartesian Coordinate Robot has three linear axes of control (x,y,z). Cartesian coordinate robots with the horizontal member supported at both ends are sometimes called Gantry robots and can be quite large in size.
A Cylindrical Robot has two linear axis and one rotary axis around its origin.
Spherical / Polar Robot
A Spherical or Polar Robot has one linear axis and two rotary axes.
SCARA (Selective Compliance Assembly Robot Arm) is a particular robot design developed in the late 1970's in Japan. The basic configuration of a SCARA is a four degree-of-freedom robot with horizontal positioning accomplished by a combined Theta 1 and Theta 2 motion, much like a shoulder and elbow held perfectly parallel to the ground. SCARA robots are known for their fast cycle times, excellent repeatability, good payload capacity and large workspace.
Picker / Delta Parallel Robots
Picker or Delta Parallel Robots use three parallelograms to build a robot with three translational and one rotational degree of freedom. The parallelograms ensure consistent orientation of one end of the arm with respect to the other, while the rotational axis is provided at the end effector. As the arms are parallel with each other, the weight of the load is distributed over all three arms and similarly any errors are averaged over the legs instead of built up as with serial robots. However the rotational and positioning capabilities are closely linked complicates the delivery and orientation of the end effector.
Articulated / Jointed-Arm Robots
Articulated or Joint-Arm Robots are the most versatile robots available closely mimic the natural form of the human arm. There are two variations of these robots based on the number of axis used. A three axis jointed arm has three rotary axis, one around the base and on each of the joints (A1,A2 & A3). In terms of a human arm this can be compared to the shoulder, bicep and forearm but without the use of a wrist. A six-axis robot does include the axis of the wrist (A4, A5 & A6), known as pitch, roll and yaw. With these extra axis this robot can deliver the end effector to any point in space in any orientation.
Snake Arm Robots
Snake Arm Robots are flexible manipulators that get their name from their ability to follow the front of the robot around and through obstacles in a snake-like fashion. They gain access to areas otherwise in accessible to allow operations such as inspection, welding and positioning to take place. They are constructed in much the same way as the human spine via a number of interconnected vertebrae. Drive wires are used like tendons, terminating at different points along the length providing the ability to pull the body in a certain direction, individually adjusting the curvature of the section where the wire terminates. The length of the wires is controlled by a series of servo-actuators within the drive unit at the base of the robot arm.
The robot can be controlled in three modes:-
- Joystick Path Following
The operator controls the head of the robot and the controller computes the wire tensions required to make the body follow the path of the head.
- Cartesian Tip Motion
The operator moves in the Cartesian Coordinate Space taking care that the body of the robot does not hit any obstacles previously passed by the head.
- Joint Mode
The operator can independently control the robots individual joints to fine tune a position or camera view.