Özkan Kayhan, 030990095, 3rd Week Answers

1) Parametric Design (CAD)

(Old)

Parametric design is a method of linking dimensions and variables to geometry in such a way that when the values change, the part changes as well – hence the dimension-driven capability. This implies that the CAD system treats all dimensions as variables that can be changed any time and almost anywhere, be it in the modelling mode or drawing mode. The geometry is of course governed by these dimensions in the parameter form.

(INTEGRATING ADVANCED COMPUTER-AIDED DESIGN, MANUFACTURING, AND NUMERICAL CONTROL:PRINCIPLES AND IMPLEMENTATIONS-1st Edition-Xun Xu-Chapter 1-P.19)

(New and Better)

The parametric design methodology can be described by the following terms: parameters, dependencies, constraints, requirements, and fixes. Parameter values can be selected from the set of admissible values for particular parameter or computed by means of particular parameter dependencies dk i.e., the following holds pk=dk(pi, pj, ...). Parameters can be limited by constraints ci in the form of ci(pi)<= 0, and/or by requirements rn in the form of rn(pi) <= 0. In case of violated constraint or requirement, particular fix fm is applied to find the sufficient value for the parameter, i.e. pi = fm(pi). The goal is to find and assignment of values to all the parameters such that no constraint is violated, all requirements are satisfied if any of the constraint is violated, i.e. the value of the left hand side of the constraint expression is greater than 0 or any of the requirements is not satisfied during the design procedure progress than the appropriate fix is applied.

(Knowledge-Based Intelligent Information Engineering Systems and Allied... Ernesto Damiani, Pg. 270 )

2) Horizontal Machining Centers (CNC)

(Old)

Also called horizontal-spindle machining center, these are suitable for large as well as tall workpieces that require machining on a number of their surfaces. The pallet can be swiveled on different axes to various angular positions. Another category of horizontal-spindle machines is turning centers, which are computer-controlled lathes with several features.

(Kalpakjian S., Schmid S.R., Manufacturing engineering and technology, Ed. 5th, p. 765,766)

(New and Better)

Horizontal CNC Machining Centers are also categorized as multi-tool and versatile machines, and are used for cubical parts, where the majority of machining has to be done on more than one face in a single setup.

There are many applications in these areas. Common examples are large parts, such as pump housings, gear cases, manifolds and engine blocks and so on. Horizontal machining centers always include a special indexing table and are typically equipped with a pallet changer and other features.

Because of their flexibility and complexity, CNC Horizontal Machining Centers are priced significantly higher than Vertical CNC Machining Centers.

From the programming point of view,there are several unique differences, mainly relating to the Automatic Tool Changer, the indexing table, and -in some cases to the additional accessories, for example, the pallet changer. All differences are relatively minor. Writing a program for the horizontal machining centers is no different than writing a program for vertical machining center.

(CNC Programming Handbook: A Comprehensive Guide to Practical CNC Programming, Peter Smid, p. 9-10)

3) Variational Design (Mathematics, CAD)

(Old)

In variational design, the entire system of constraints for a part or parts is solved simultaneously with a constraint solver (e.g., Newton-Raphson). Variational design systems offer several advantages including the ability to solve problems whose dimensions cannot be calculated with a single algebraic expression as well as subsuming most of the capabilities of parametric design systems. An entire design sequence in a parametric design system can be thought of as a system of constraints in a variational design system.

(A Mathematical Theory of Design, Dan Braha, p 388)

(New and better)

Many solid modelling systems implement a design paradigm in which no longer a specific solid shape is designed, but a parametrized class of potential shapes in which a specific shape is then instanced. Figure 3 illustrates this for 2 dimensional shapes: A quadrilateral with a rounded corner has been defined.

Some of the lengths have been prescribed, as well as that two sides should be perpendicular and the rounding arc tangent to the two adjacent edges. By varying the lengths or angles, different rounded quadrilaterals are obtained from the same underlying definition schema. Moreover, this definition is descriptive rather than procedural because there are no requirements on the sequence in which the constraints should be elaborated. This descriptive definitional style is often termed variational in the solid modelling literature.

(Applied Computational Geometry: Towards Geometric Engineering, Volume 114, Ming C. Lin, p.4 )



4) Sweep Representation (CAD)

(Old)

A set of points moving in space may sweep a one-, two-, or three- dimensional object, which can be represented by the moving set plus the trajectory. Sweep representations for modeling solids are easy to understand and execute yet offer a fertile field for development. Basically there are two kinds of sweep representation: translational sweeping and rotational sweeping.

(Xue, Q., World Scientific Series in Robotic and Automated Systems - Vol. 3, Intelligent Robot

(New and better)

Sweeping an object allow a path through space defines a new object called a sweep. Sweep representations are useful where axial symmetry is present. For example, the water tank in Figure 11.13 is symmetrical about the vertical axis. Only 5 points are required to define the shape of the structure. Sweeping the curve about the vertical axis generates the entire volume.

There are  several ways of creating sweeps. Extrusion or translation sweeps, are made by sweeping a polygon along a straight line normal to the polygon. The trajectory is not perpendicular to the plane of the polygon oblique sweeps.Rotational sweeps are made by rotating about an axis. General sweeps are made by sweeping along an arbitrary curve. The object that is swept need not be two dimensional.

(Fundamentals of Computer-Aided Engineering, Benny Raphael, Ian F. C. Smith, p. 238)

5) The Vacuum Sensor (Sensors)

(Old)

Vacuum sensor is designed as a gauge pressure sensor, but the output terminals are reversed as compared to a gauge configuration to provide an increasing output with the increasing vacuum (decreasing pressure). At ambient pressure, the vacuum sensor indicates a zero output with a full-scale output produced at a full vacuum. Output is not dependent on a barometric pressure.

(Soloman S., Sensors Handbook, pg.1064)

(New and better)

This sensor measures gas pressures below atmospheric pressure by measuring their pressure dependent thermal conductivity. At very low pressures, when the mean distance between collisions of molecules is much larger than the distance between two surfaces, heat is transferred between the surfaces by individual molecules; and the rate of heat transfer is therefore proportional to the rate with which molecules hit the surface, which is the absolute pressure.

(Smart Sensor Systems, Vol 10, Gerard C. M. Meijer, p 174)