Computer and electronic communication developments have led to the improvement of mfg process efficiency. This development also has led to (CIM) computer integrated manufacturing. In this chapter we will study one segment of CIM: process automation. The following aspects are related to automation: (Simulation, material handling, robotics, group technology, and flexible mfg systems). SIMULATION Simulation Simulation is the process of developing mathematical models of a real system to evaluate the behaviour of the system parameters at the output. Depending on the computer program, used to simulate mfg processes, simulation can be out of the following types:
1.Discrete Event Simulation: It is accomplished by random sampling from probability distribution. 2.Dynamic Simulation: is time-based evaluation of the system behaviour (with respect to time). 3.Continuous Process Simulation: For continuous processes that have no discrete events (e.g. Chemical industry, and pumps). AUTOMATION Automation involves 1) automatic handling between machines and 2) continuos automatic processing at the machines. Combining two or more automatic operations on one machine does not constitute an automated system. Machines are considered automated only when they are mechanically joined for continuous automatic handling and processing: Example: An automatic lathe machine that is joined to a robot to load and unload parts from and to a conveyor.
Purposes for Automation 1.Direct labour costs are reduced 2.Uniform quality is obtained because operator fatigue and boredom. 3.Safety (less accidents) 4.Shop efficiency is improved (automatic distribution of parts during loading, unloading and inspection). 5.Use of standard tools instead of specially designed tools (tools are located in carousels) Part and Process Design Part and process design should be related to each other so part designers and process designers should have close cooperation. The aim of that is to provide the highest possible flexibility and efficiency of the process, and to avoid excessive cost of the automatic process design as a result of excessive accuracy of the part design.
This cooperation helps to decide on the following issues: 1.Power Source: (electrical, hydraulic, and pneumatic) Selection of power source depends on amount of power, space and speed requirements. 2.Transfer Equipment: (Mechanical loading by robots, conveyors, and mechanical arms). 3.Parts Orientation: Important in automatic assembly lines. ROBOTS robot A robot is a reprogrammable multifunctional manipulator designed to move materials, parts or tools through variable programmable motions for the performance of variety of tasks. Robots are used in light and heavy mfg, foundry, automotive, electrical, and aerospace industries. (Typical jobs for robots: spraying, grinding, deburring, welding, packaging, searching, loading and unloading, and tool positioning).
Robot Components: 1.Manipulator: consists of main frame (arm) + wrist + end effector (e.g. spray gun, welding head, gripper). 2.Controller: is the brain of the robot. It stores data and directs movements. The controller functions: a) initiates and terminates motions of the manipulator in a desired sequence; b) stores position and sequences data in memory; c) interface with other mfg operations 3.Power supply. Classification of Robots: 1.Manual Manipulator (worked by an operator). 2.Fixed- sequence Robot: The manipulator performs repetitive operations according to a predetermined pattern of motions that cannot be changed 3.Variable-sequence Robot: In this case, the pattern of motion may be changed
4. Playback Robot: This report stores information into its memory. Desired information will be recalled when required. 5.NC Robot: uses numerical data (e.g. punched data). 6.Intelligent Robot: has sensors for vision and touch senses. Types of Robot Controllers (Classification of Robots according to Controllers Types): 1.Non-servo controlled Robots: (end point, pick-and-place, bang bang, and limited-sequence robots). Their arms travel only at one speed and can stop only at the end point of their axes. (+)High speed, good repeatability, low maintenance, and low cost, (-) Less flexible, limited application. 2. Servo-controlled Robots: have servomechanisms that allow the arm to change direction in mid-air without having to trip a mechanical switch. They can vary speed at any point. (+)ability to move heavy loads, flexible (uses more than one program).
Robot Paths Servo-controlled robots are further classified as: 1.Point to point path: for tool and part handling 2.Continuous path. The robots are taught to perform these paths by moving the robot manipulator through separate points (point to point path) or through a path (continuous path). Coordinate Systems (Degrees of Freedom) for Robots (Fig.29.17) 1.Cartesian Coordinate Robots: Motions travel in right angle (no radial motions). 2.Cylindrical Coordinate Robots: A horizontal rotating shaft goes in and out and rides up and down on a vertical rotating shaft. 3.Jointed Spherical Coordinate (Jointed Arm) Robots: Can perform similar actions to a human ’ s shoulder, arm, and elbow.
4.Spherical (Polar) Coordinate Robots: The arm moves in and out, and is raised and lowered through an arc while rotating about the base. The work envelop of the robot forms the outline of a sphere. Note: Envelope is the area in space the robot can touch. Robotic Sensors (for Intelligent Robots) By means of sensors robots can have humanlike capabilities (vision, eye- hand coordination, touch, and hearing). 1.Vision Sensors: (video camera, light sources, image processing) 2.Tactile Sensors: provide the robot with the capability to respond to contact forces between itself and other objects by defining various sensations (pressure, shape, temperature). 3.Voice Sensors: By defining voice and sound recognition the robot is able to define malfunction (air leaks, abnormal vibrations).
FLEXIBLE MFG SYSTEMS (FMS) Flexible mfg systems are arrangements of individual workstations, machining cells, and robots under the control of a computer. Workpieces are mounted on pallets, which move through the system transferred by conveyors. Most of mfg processes are combined in a FMS. Equipment, machine tools, and mfg cells are located along the material transfer highway. The parts transferred along this highway do not need all the equipment or cells. Pallet transfer to and from machines is done by automatically guided vehicles (AGVs = self controlled vehicles that follow specified paths in a plant floor to move materials, tools, and other items). In FMSs, it is necessary to clean chips away (continuous control and cleaning if chips). FMSs are integrated with computer-aided design (CAD) and manufacturing (CAM).