History of Computer and Numerical Control
CNC Historical Past
1942 – John Parsons uses perforated card tabulation equipment to produce coordinate tables for helicopter blade wing profile contour layouts.
1948 – Parsons and Frank Stulen calculate three-axis airfoil curve knowledge and acquire contract to design servomechanisms for a computer tool for use to follow this knowledge.
1952 – A vertical-spindle Cincinnati Hydrotel was once programmed making use of punched paper tape to participate in three-axis slicing-software movements
1954 – Numerical manage was introduced to the general public
1976 – The difficult-wired MCU (machine manage unit) was once replaced with the aid of the whole CNC thought.
WHAT NUMERICAL manipulate IS
- Operation of a machine using a sequence of numbers, letters, and symbols.
- Symbols are translated into electrical alerts that investigate the process of actuators three. Instructions are geared up to have the perfect outcome of finishing a particular venture, comparable to machining a workpiece.
WHAT NUMERICAL manipulate IS no longer
- It is not a machining approach – any machining sequence that a machinist can perform can be positioned under numerical manage.
- The computers driving statistical manage display no concept, evaluation, judgment, or actual adaptability.
- Numerical control does now not add any machining potential to the desktop.
- Statistical manage systems are not able to appreciate human language – the person has got to understand the language of the computer manage unit.
NC and CNC switch the competencies wanted to laptop an element from the store floor (machinist) to the place of the job (programmer)
– phase processing potential – laptop capability talents – mathematical competencies – machining expertise
The phase programmer has got to logically conceive and clearly state all computer actions guide (non-pc-assisted) part programming requires intimate advantage of the traits of each every precise machine operation and the control code indispensable to influence it computer techniques (CAD back-ends, submit processors, tool course routers, and so forth.) permit the programmer to suppose at a higher level about the phase programming.
CNC REPRESENTS A CULTURAL other Axes of movement
right hand rule:
1. Prolong thumb, index, and center fingers of the right hand in three orthogonal guidelines 2. The middle finger must factor in the direction of retracting spindle 3. The thumb must point in the direction of the longest travel 4. +x – course of thumb +y – course of the index finger +z – a path of the middle finger
a, b, and c represent angular (rotary) motions about x, y, and z axes (or axes parallel to the x, y, and z axes) If the proper thumb facets within the path of the confident linear axis, the fingers will curl around within the way of the optimistic angular/rotary axis d and e designate designated angular or rotary movement both parallel to a, b, or c, or round specified axes e is also used to designate a secondary feed function and d a tertiary feed function
Secondary/tertiary linear axes
u, v, and w are secondary axes parallel to x, y, and z p, q, and r are tertiary axes parallel to x, y, and z If no longer used and no longer needed for linear axes, these letters could also be used to designate targeted axes no longer parallel to x, y, and z
The designations above expect the workpiece is constant and the chopping software strikes.
If the workpiece moves, the axis is specified employing a main, and the optimistic workpiece is in a path reverse to that wherein the instrument would transfer
The phase programmer need not fear in regards to the top designation in the usual programming – a +x transfer, for example, will motive the instrument to be sent via the workpiece within the most extended dimension from left to proper, as viewed looking in the path of +y
rough-wired vs Gentle-wired – (CNC implies smooth-wired, mini-pc or onboard microprocessor)
Incremental, absolute, or both – measure to which switching can take place
input media – EIA 244 punched tape, EIA 358 punched tape, floppy disk, the direct communications link
factor-to-point, continuous route, or each
Inch, metric, or each
variation committed to precise areas of software
Closed vs Open Loop
Rotary resolvers – rotary transformer the place amplitude of the triggered voltage is proportional to angular displacement – depend on pulses to examine the number of revolutions
Linear scale suggestions – two printed circuit boards, one constant the other movable, furnish the variable coupling.
Optical encoder – circular disk with gray-coded positions furnish a digital encoding – so long as the journey isn’t too rapid so that a complete rotation is overlooked.
—Or use safe stepper motors, and build an open-loop process
Flash converter – fast, but steeply-priced Single-ramp – inexpensive, however gradual, unequal time intervals twin-slope – moderate in price, lengthen in effect availability
using a D-A converter
monitoring – low cost,however,constrained in frequency response Successive approximation – reasonable, reasonably fast, some trouble in the upper frequency
major MCU aspects
MDI – manual data enter
application edit with program replica
Preparatory codes / miscellaneous functions
G (preparatory) – make alterations in the way dimensional knowledge is processed interpolation – linear, round, helical, cubic dimensions – inch or metric knowledge – absolute or incremental feedrate M (miscellaneous) – define a desktop or manipulate the auxiliary function stopping the cycle defining the top of the section program effecting a software alternate
General-Purpose Computer Programs
Workpiece Complexity Categories
1. Point-to-point and straight cuts (2-1/2 D)
– repetitive and simple point-to-point operations
– straight milling in one plane
– point-to-point rectangular pattern operations
– translation of patterns along one axis of the workpiece
2. Non-formula-defined curves
contour profiling limited to
– straight lines tangent to circles and arcs
– circles intersecting circles
– straight lines intersecting circles
all motions on a single plane
3. Repetitive cuts and family of parts
– translation and rotation of patterns
– pocket milling in a single plane with straight cuts
– families of parts in which the configurations are the same but the dimensions may be different
4. Curves and straight lines (2-1/2 D)
-repetitive point-to-point operations over a skewed pattern- repetitive point-to-point activities irregularly spaced around a circle- repetitive actions at translated and rotated pattern post
– automatic pocket milling using a clockwise or counterclockwise motion from the proximity of the center
– splined curve tangent to a circle
formula curves such as an ellipse
Workpiece Complexity Categories (Cont.)
5. Controlled rotary motion
– curve fitting such as following a curve defined by a series of points in either polar or rectangular coordinates
– pocket milling of irregular pockets when points are described
6. Inclined planes and patterns
– pocket cleanouts at various depths
– drilling on an inclined plane
– rapid traversing to a point above the plane
– machining an inclined plane
– repetitive cuts along a surface
– rotation or translation of repetitive pockets
7. Sculptured surfaces
– three-dimensional sculpturing of surfaces (e.g., dies)
8. Swarf cut, formula-defined, and regular surfaces
– cutting a formula-defined surface in 3-D
– cutting a non-formula-defined cavity in 3-D
– moving a cutter with a radius end to a canted plane
– swarfing apart at a constantly changing angle
Highest Workpiece Complexity Category
9. Multiaxis, including five simultaneous motions
– straight cut with the axis of cutter normal to a canter surface
– constant angular rotation of a cutter with tool axis normal to the workpiece surface
– swarfing cut along a path of irregularly varying angle in which the angular change is evenly distributed between two cross-sectional points
– rotate a cutter about a point in one plane and rotate a cutter in two planes
– three-axis simultaneous motion with cutter axis tilted – axis of the cutter to remain parallel to a canted surface
simultaneous control and motion of either four or five axes
OSI / ISO / MAP Communication Protocol
|OSI Layer||ISO Function||MAP 2.1 Protocol|
|7 Application||Provides all services directly comprehensible to applications programs||ISO Case Kernel, FTAM, MMFS/EIA 1393A|
|6 Presentation|| Restructures, data to/from standardized |
the format used within the network
|5 Session|| Name/address translation, access security,|
and synchronize/manage data
|ISO Session Kernel IS 8327|
|4 Transport||Provides transparent, reliable data transfer from the end node to end node||ISO Transport Class IS 8073|
|3 Network||Performs message routing for data transfer between nodes not in the same LAN||ISO Internet DIS 8473 CLNS|
|2 Datalink||Provides the means to establish, maintain and release logical data links between systems, transfer data frames between nodes in the same LAN, and detect and correct errors||IEEE 802.2 Link Level Type 1, Control Class 1|
|1 Physical||Encodes and physically transfers messages between adjacent nodes||IEEE 802.4 Token access on broadband media|