Fundamentals of CAD / CAM

CAD
Computer Aided Design is the process of creating, modifying and refining using digital computers which accepts data in the binary form.
Example:
stress-strain analysis,
Heat transfer problems,
 Von mises stress.

The person one who enters command to the system to perform specific operation is called as programmer.
As the person enters commands to the system, the CPU calculates required calculations with the help of automatic logic unit.

After the calculation it is represented on the screen through CRT. in inorder to perform CAD operations, it is essential to have some hardware and softwares.
A software which allows programmer to give command and represent it as an object on the screen is called as CAD package.
Example: Catia, AutoCAD, Pro-E, Solidworks, Solid edge, Ansys, Hypermesh.

CAM
Computer Aided Manufacturing makes use of digital computers to make process planning, production scheduling, routing, MRP-1, MRP-2, floor control and etc.,

CAM applications are of 2 types as follows:
(a) Process monitoring and
(b) Controlling
In this, computers are used directly with the manufacturing or production location.

Process monitoring: It is a single way communication system where information flows takes place from production location to the monitoring location.
Here, even though monitoring is done with the computer but controlling actions taken by the human being.

Process controlling: it is a two way communication channel where information flows takes place from manufacturing space to monitoring space. but, one more element is provided to take control action to the process if any error occurs.


Functions of CAM:
Process planning,
Production scheduling,
Bill of material
Manufacturing resource planning (MRP-1),
Material requirement planning (MRP-2),
NC control,
CNC control,
DNC control,
Record file control,
System aided applications (SAP),
Routing.

Performance Characteristics in Instrumentation and Control Systems

Performance characteristics
(a) static characteristics.
(b) dynamic characteristics.
  • Speed of response and measuring lag,
  • Fidelity and dynamic error,
  • overshoot,
  • Dead time and dead zone,
  • Frequency response.

(a) Speed of response and measuring lag:
Speed of response is defined as quick with which an instrument responds to change the value of quantity which is being measured.
Measuring lag refers to the delay in the response of an instrument to change in the input value.

(b) Fidelity and dynamic error:
Fedility is defined as the degree of closeness with which the instrument indicates or records the signal.
Dynamic error is defined as the difference between the indicated quantity and true value.

(c) Overshoot:
It is defined as the maximum amount by which the pointer moves behind the steady state.

(d) Dead time and Dead zone:
The time is defined as the time required for the instrument to begin to respond change the measure point.
Dead zone is defined as a largest change of the measuring to which the instrument does not respond.

(e) Frequency response:
Maximum frequency of the measuring variable of a instrument is capable of following the error.
Frequencies of the measured variable should not exceed 60% of the natural frequency of measuring instrument.

Generalized measuring systems and its functional elements


Generalized measuring systems and its functional elements.
(a) Primary sensing element
(b) Transducer element
(c) Data manipulation element
(d) Data transmitter element
(e) Data process element
(f) Data presentation element


(a) Primary sensing element:
The element that is sensitive to the measuring variable. The sensing element senses the condition and process the variable by extracting a small part of energy and producers and output which is proportional to the input.

(b) Transducer element:
The element that converts signal from one physical form to another form without changing the information contained.
Example: bourdon tube and bellows which transfers pressure into displacement.
Rack and pinion which converts Rotary into linear vice versa.

(c) Manipulation element:
This element modifies the director signal by amplification (increase the power /strength) and filtering (removing unwanted noise and signals)., So that desired output is produced.

(d) Data transmission element:
An element that transmits the data or signal from one location to another location without changing the information contained.
The data may be transmitted over long distance (from one location to another location( or short distance (from test centre to the nearby computer)

(e) Data processing element
An element that modifies the data before it is displayed or finally recorded.
If any corrections or errors occur in the data the processing element modifies the data.

(f) Data presentation element.
An element that provides recorded data or indication of output from the data processing element.


 Tags: ICS, Instrumentation, control systems, control system, measurement

Introduction to Instrumentation and Control Systems

Measurement:
It is defined as the study of physical and chemical parameters of any object by comparing with standards.
The word measurement is used to tell us the length, weight, temperature, colour or change in any physical parameters of the material.

Instrumentation:
It is a technology of using instrument to measure and control physical and chemical parameters/properties of the material.

Methods of measurement:
(a) Direct and indirect measurement.
(b) Primary secondary and tertiary measurement.
(c) Contact and non contact type measurement.


(a) direct and indirect measurement
Direct measurement: the value of physical parameters is determined by comparing it directly with different standards.
Indirect measurement: the value of physical parameters is determined by indirect comparison with secondary standard calibration.

(b) Primary secondary and tertiary measurements:
Primary measurement:
In this measurement the physical parameters is determined by Reference standards.

Secondary and tertiary measurement:
The secondary and tertiary measurement are indirect measurements involving 1 transmission are called secondary measurements. And those involving two transmissions are called tertiary measurement.
Example: temperature is measured by a mercury in a class.
Pressure is measured by boundary tube.


(c)Contact and non-contact measurements:
Contact measurement:
Sensing element of a measuring device as contact with the medium.
Example: thermometer.

Non-contact measurement:
Sensing element of a measuring device does not have physical contact with the medium.
Example: laser


 Tags: ICS, measuremt, measuring,instrumentation