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
Examples of successful robot installations (Time magazine)
A robot drills 550 holes in the vertical tail fins of an F-16 fighter in 3 hours in General Dynamics. It used to take 24 worker hours to do the job manually.
Examples of unsuccessful robot installations
This configuration allows for extremely dextrous positioning such as it required for automobile spot welding or painting.
Advantage - rich capability.
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.
This is a variant of the cylindrical arm configuration however the work volumes between 2&3 are different.
Advantage - rich capability.
Cartesian coordinate configuration
This is the most limited configuration for a robot.
Used for a part assembly operations.
Advantage - better repeatability motion.
The robot's movements can be divided into two general categories:
arm and body motions
Types of joints used in robots
Input link involve a sliding or translational
motion of the connecting links
Degrees of Freedom Associated with the Arm and Body Motions
Degrees of Freedom Associated with the Wrist
Robot Drive Power
Very powerful, used for heavy payloads
Able to deliver large forces directly to the robot joints
Require pump and reservoir for the fluid
Low accuracy and breakdown problems
High cost (30,000 - 200, 000)
Noisy, dirty, and space intrusive
Spray - paint operations
Automobile industry (spot welding)
Heavy forging and die casting
Least expensive and more practical robots for pick and place operations
Very efficient for on/off cyclic control
Hard to control, especially for delicate positioning
Quit, small on space utilization
Excellent accuracy for relatively light loads
Driven by discrete dc voltage pulses
High accuracy, therefore mostly open loop type
DC servo motors
Feedback loop type
Making possible a smoother and continuously controllable movement.
Precision of Movements
Precision of movements - f(Spatial resolution, Accuracy, Repeatability)
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.
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 refers to a robot's ability to position its wrist end at a desired target point within the work volume.
Accuracy - f(spatial resolution)
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 µr, 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.
Axis Limit (Two position control)
The individual joints can only be moved to their extreme limits of travel (robot axis typically has two extreme points).
Controlled by setting limit switches or mechanical stops to establish the endpoints of travel for each of their joints.
No feedback is associated with the limited sequence robot to indicate that the desired position is achieved.
Pneumatic drive - the type most commonly employed.
Applications - machine loading and unloading.
Point to Point
The user can select any point in space in the robot work envelope and move an end effector directly to that point.
The path and speed of movement to the destination point are both uncontrollable.
Applications - component insertion, hole drilling, spot welding, and crude assembly application.
The entire path is continuously or nearly continuously controlled.
Accomplished by making the robot move through a series of closely spaced points that describe the desired path.
The individual points are defined by the control units rather than the programmer.
It is an application of contouring. not a separate class of motion.
Accomplished by programmer which specifies the starting point and the end point of the path, and the control unit calculates the sequence of individual points that permit the robot to follow a straight-line trajectory.
Applications - spray coating, arc welding.
A gripper is used to grasp an object, and hold it during the robot work cycle.
Holding can be done:
Mechanically - with fingers or jaws or even antropomorphically shaped hands.
Magnetically - as long as the objects being hold are metallic and not destroyed by magnetic fields
By vacuum- as long as vibration shock when the object jumps to the gripper is not a problem.
By piercingwhich punctures the component, as in clothing operation.
By adhesion using sticky tape or another adhesive.
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.
Used to allow the robot to interact with its environment.
Tactile sensors - these are sensors which respond to contact forces with another object.
Proximity and range
When the distance between the objects can be sensed, the device is called a range sensor.
Miscellaneous - include sensors for temperature. pressure, and other variables.
Machine vision - capable of viewing the workspace and interpreting what it sees. Used in robotics to perform inspection, parts recognition.