Editorial Feature

Robotic Arms for Testing and Inspection

Research on automated limb structures has contributed efforts to help design robotic arms that have similar functions to that of a human arm. A typical robotic arm is linked by joints to form a kinematic chain that allows translational displacement or rotational motion.

The end of the kinematic chain is known as an end effector and is similar to the human hand. The robotic arm is of several types that include the following:

  • Cartesian robot - It has three prismatic joints with axes that coincide with a Cartesian coordinator. This robotic arm is designed mainly for assembly operations, sealant application and handling machine tools.
  • Cylindrical robot - This robot is used for spot welding, handling die casting machines and other assembly operations.
  • Spherical robot - Designed with a polar coordinate system, this robot is used for fettling machines, spot welding, handling machine tools, arc welding and gas welding.
  • SCARA robot - An automated arm used for pick and place work, assembly operations, machine tool handling and sealant applications.

The motion of the robotic arm is controlled through the application of kinematics to imitate the movement of the human arm at a high degree of repositional precision.

Acceleration, velocity, and position of movement of the robotic arm are all determined by trajectory planning. The movements are translated into joint movements through inverse kinematics. The movement of a robotic arm with respect to different torque and forces is established through inverse dynamic equations.

Image Credits: Photos.com

Design of Robotic Arm

Larger robotic arms employ pneumatics or hydraulics instead of motors. Step motors move in proper increments, unlike ordinary motors.

This approach enables the computer to move the arm precisely thereby repeating the same movement again and again. It also features motion sensors to ensure that it moves at exact increments.

On the other hand, an industrial robot consists of six joints that are analogous to a human arm. In this robot, the shoulder is fixed to a stationary base structure instead of a movable body. It has six degrees of freedom, whereas the human arm has seven degrees of freedom.

How a Robotic Arm Works?

  • Cartesian robot - The robotic arm has three arms that operate along linear axes of control. Each of the arms is perpendicular to other two which enables them to reach various points in a three-dimensional space. These arms can vary in size based on the application of the robot. Also, this robotic arm has the potential to telescope, which enables it to access and interact with other objects.
  • Cylindrical Robot Arm - It consists of a cylinder attached to a base. The cylinder rotates on the base to enable the robot arm to interact with the environment across all directions. It has a long metal shaft connected to the cylinder and another metal shaft through elbows. These elbows can bend through the internal mechanism screw jacks or gears. A rack and a pinion system operated by a grooved gear and a long, grooved strip controls the rotating functions of a robotic wrist. The strip moves along a direction to turn the gear through friction generated by the grooves present on the strip and gear.
  • Spherical Robot Arm - This robot includes two pivotal joints comprising rings that turn on pivots. It also features a prismatic joint that includes a rectangular object sliding inside a larger rectangular object. All these joints are enclosed within a spherical structure to which the robotic arm is attached. The two pivotal joints are fixed perpendicular to enable the arm to rotate up, down, left and right. The prismatic joint enables the arm to stretch and interact with the environment.
  • SCARA Robot Arm - This arm includes Z-shaped joints having axes on both ends. It also includes a pivotal joint on both ends of the Z-shaped structure, and another pivotal joint in the middle. The bottom of the robot arm is attached to a pedestal.

Advantages

The key benefits of a robotic arm include the following:

  • Simple kinematic model.
  • It can easily access machine openings and cavities.
  • Rigid structure.
  • Maximum flexibility.
  • Easy to visualize.
  • A spherical arm can bend down to pick objects up off the floor and covers a large volume through a central support.

Products on the Market - Advancements

Several robotic systems designed for clinical laboratory automation are commercially available now. These devices equipped with supporting software and analytical hardware will likely reform the laboratory testing field. Certain robotic arm systems that have been introduced particularly for automating laboratory testing include the following:

Mitsubishi Robotic Arms

Developed by AB Controls, these robotic arms have the potential to control up to three robots per system. This system includes a single programming software package for all types of robots. It enables both SCARA and vertically articulated robots to be configured on a single platform. It features built-in collision detection technology and multi-task programming that ensures easy separation and programming of tasks.

The major benefits of Mitsubishi robotic arms include the following:

  • Robustness
  • Ease of use
  • Efficient program development
  • High precision and speed
  • Compliance control.

Harmonic Arm™

AAI Canada, Inc. offers Harmonic Arm™, a high-quality programmable robot arm equipped with sensors, controller, built-in simulation software and an additional joint. It also features custom grippers that can be mounted on the forearm at an angle of up to 90°, based on the applications. It can be directly controlled through a serial interface via a programmable logic controller or a personal computer.

The key benefits of Harmonic Arm™ include the following:

  • Intelligent control
  • High precision
  • Quick movement
  • Minimizes backlash
  • It can be used stand-alone on a linear axis or on a mobile robot.

WAM™ Arm

The WAM™ Arm developed by Barrett Technology, Inc. is a naturally backdrivable manipulator available in two main configurations including four and seven degrees of freedom. Integration of advanced electronics with backdrivable cable results in flexible motions.

The major advantages of the WAM™ Arm include the following:

  • It is independent of torque or mechanical force sensors
  • Highly dexterous
  • Power-efficient
  • Very small, weighing only 43 g.

Sources and Further Reading

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