Classification of Automation

Fixed automation is used when the volume of production is very high and therefore it is appropriate to design specialized equipment to process the product effectively and at high production rate.

Example: Automobile industry, steel rolling, paper production.

Programmable automation is used when the volume of production is relatively low and there are variety of products to be made. The production equipment is designed to be adaptable to variations in product configuration. Unique products are made in small batches.

Flexible automation is used for mid volume production size. It possesses some of the features of both fixed automation and programmable automation.

 

Products can be produced in batches as well as several different product styles can be mixed on the system.

Definition of an Industrial Robot

Robot Institute of America:

An industrial robot is a programmable, multifunction manipulator designed to move and manipulate material, parts, tools, or specialized devices through variable programmed motions for the performance of a variety of specified tasks.

The Japanese Industrial Robot Association:

A fixed-sequence robot is a manipulator that repetitively performs successive steps of a given operation according to a predetermined sequence, condition, and position, and where set information cannot be easily changed.

D. J. Todd:

An industrial robot is a manipulator that automatically repeats a cycle of operations under program control. The manipulator is used here to mean any device with an arm bearing a hand or gripper.

The most common tasks are those that require demeaning or drudging effort, frequently on a repeating basis, or tasks performed in hazardous environment.

List of Characteristics that are Essential for a True Robot

  1. A robot must be produced by manufacture rather by biology. (This does not rule out the eventual use of artificial biochemically produced structures such as muscles.
  2. It must be able to move physical objects or be mobile itself.
  3. It must be a power or force source or amplifier.
  4. It must be capable of some sustained action without intervention by an external agent.
  5. It must be able to modify its behavior in response to sensed properties of its environment, and therefore must be equipped with sensors.

Examples of successful robot installations (Time magazine)

Examples of unsuccessful robot installations

  1. Joint arm configuration
  2. This configuration allows for extremely dextrous positioning such as it required for automobile spot welding or painting.

    Advantage - rich capability.

  3. Cylindrical configuration
  4. Limited to applications where there are no obstructions in the work area. Can be used for moving objects from one place to another on a cyclic basis.

    Advantage - load carrying capacity.

  5. Polar or spherical configuration
  6. This is a variant of the cylindrical arm configuration however the work volumes between 2&3 are different.

    Advantage - rich capability.

 

  1. Cartesian coordinate configuration

This is the most limited configuration for a robot.

Used for a part assembly operations.

Robot Motions

The robot's movements can be divided into two general categories:

Types of joints used in robots

Output link

Linear


Input link involve a sliding or translational

motion of the connecting links

 

Degrees of Freedom Associated with the Arm and Body Motions

  1. Vertical traverse - the capability to move the wrist up or down to provide the desired vertical attitude.
  2. Radial traverse - involves the extension or retraction of the arm from the vertical center of the robot.

  1. Rotational traverse - the rotation of the arm about the vertical axis.

Degrees of Freedom Associated with the Wrist

  1. Wrist roll - involves rotation of the wrist mechanism about the arm axis.
  2. Wrist pitch - Given that the wrist roll in the center position, the pitch would involve the up and down rotation of the wrist.
  3. Wrist yaw- Given that the wrist roll in the center position, the yaw would involve the right or left rotation of the wrist.

 

Robot Drive Power

 

  1. Hydraulic

Advantages:

 

Disadvantages:

 

Applications:

 

  1. Pneumatic

Advantages:

 

Disadvantage:

 

  1. Electrical

Advantages:

 

Stepper motors

 

DC servo motors

 

Precision of Movements

Precision of movements - f(Spatial resolution, Accuracy, Repeatability)

 

Spatial Resolution

The spatial resolution of a robot is the smallest increment of movement into which the robot can divide its work volume.

 

Spatial resolution - f(control resolution, mechanical inaccuracies)

 

Control resolution is the controller's ability to divide the total range of movement for the particular joint into individual increments that can be addressed in the controller.

 

Number of increments = 2n

 

where n = the number of bits in the control memory.

EXAMPLE:

Consider a robot with 1 degree of freedom. Assume it has one sliding joint with a full range of 2.0m. The robot control memory has a 8-bit storage capacity. Determine the control resolution for the axis of motion.

 

Number of increments = 28 = 256 or 7.8125mm

The spatial resolution of the robot is the control resolution degraded by mechanical inaccuracies.

Accuracy

Accuracy refers to a robot's ability to position its wrist end at a desired target point within the work volume.

Accuracy - f(spatial resolution)

 

Repeatability

It is concerned with the robot's ability to position its wrist or an end effector at a point in space that had previously been taught to the robot. Repeatability refers to the robot's ability to return to the programmed point when commanded to do so.

with mean r, and variance according to CLT.

The Central Limit Theorem

This theorem asserts that the sum of a large number of independent random variables has a distribution that is approximately normal.

 

Motion Control

  1. Axis Limit (Two position control)

Applications - machine loading and unloading.

 

  1. Point to Point

Applications - component insertion, hole drilling, spot welding, and crude assembly application.

 

  1. Contouring

  1. Line Tracking

Applications - spray coating, arc welding.

 

End Effectors

Grippers:

A gripper is used to grasp an object, and hold it during the robot work cycle.

Holding can be done:

Tools

A tool is used in approaches where the robot is required to perform an operation on the workpart, i.e., spot welding, arc welding, spray painting, and drilling.

 

Robot Sensors

Used to allow the robot to interact with its environment.

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