Robotic sensors – Fundamentals of robotics technology

A robot is a multi-functional, programmable manipulator designed to move materials, parts, tools, or devices using several pre-programmed motions for the performance of a variety of tasks.

An industrial robot consists of several rigid links connected by joints of different types, controlled and monitored by a computer.

A robot uses several power sources to perform action. It can gain power mainly from hydraulic drives, designed to actuate linear or rotational joints. They give a robot high speed and strength, whereas electric drive provides a robot with less speed and strength, making them ideal for smaller robots.

But, robots supported by electric drive systems are more accurate, exhibit better repeatability, and are cleaner to use. Pneumatic drive, on the other hand, is useful for smaller robots with fewer degrees of freedom but can carry out simple pick-and-place material handling operations.

Robotic sensors

A robot needs sensing to be an active participant in the environment. The sensor constitutes a robot’s window to the environment. Each sensor works based on the transduction principle, i.e., a conversion of energy from one form to another. Sensors measure a physical quantity; they do not provide the state.

Sensors are devices for sensing and measuring geometric and physical properties of robots and the surrounding environment, such as position, orientation, velocity, acceleration, distance, size, force, moment, temperature, luminance, weight, etc.

Robot sensors can be classified into two groups: Internal sensors and external sensors. Internal sensors obtain information about the robot itself, such as its position, velocity, acceleration, etc., while external sensors collect the information in the surrounding environment.

  • Position sensors monitor the position of a robot’s joints, and the position data is fed back to the control systems for determining the accuracy of movements.
  • Range sensors assess the distances from a reference point to another. Range sensing is accomplished by means of television cameras or sonar transmitters and receivers.
  • Velocity sensors estimate the speed with which a manipulator is moved. Variations in acceleration during movements give rise to the dynamic nature of the manipulator. These sensors monitor and control inertial forces (which occur due to changes in acceleration), damping forces (which occur due to changes in velocity), and spring forces (that occur due to elongation, caused by gravity and the weights carried), to fine-tune the manipulator’s dynamic performance.
  • Proximity sensor sense and indicate the presence of an object within a specified distance or space without any physical contact.
  • Gyroscopes are heading sensors that keep the orientation to a fixed frame.
  • Accelerometers measure accelerations concerning an inertial frame.

The hand of a robot

The hand of a robot is an end-effector, mounted on the wrist to enable the robot to perform specific tasks. There are various types of end-effectors, designed for the same robot to make it more flexible and versatile.

For instance, grippers grasp and hold an object and place it at the desired location. Grippers are classified as mechanical grippers, magnetic grippers, vacuum or suction cups, adhesive grippers, hooks, scoops, etc.

A robot manipulates a tool to operate on a work part. Here the tool acts as an end-effector. Typical examples of tools used as end-effectors are spot-welding tools, arc-welding tools, spray-painting nozzles, and rotating spindles for drilling and grinding.

Robot movement and precision

The speed of response and stability are two crucial characteristics of a robot’s movement. The speed defines how quickly the robot arm moves from one point to another, while stability refers to a robot’s motion with the least amount of oscillation. The precision of the robot movement is defined by essential features like the spatial resolution, which is the smallest increment of movement into which the robot can divide its work volume. The spatial resolution depends on the system’s control, resolution, and the robot’s mechanical inaccuracies.

A robot joint is a mechanism that permits relative movement between parts of a robot arm. Some of the basic movements required for most industrial robots are (1) rotational movement which enables the robot to place its arm in any direction on a horizontal plane; (2) radial movement which allows the robot to move its end-effector radically to reach distant points and (3) vertical movement which enables the robot to take its end-effector to different heights.

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