[rescue] Vector Plotters

Dave McGuire mcguire at neurotica.com
Mon Oct 5 14:34:02 CDT 2015

  While vector displays are indeed capable of continuous positioning, as
opposed to discrete positioning, the vast majority of vector displays
are driven from digital things, via a D/A converter.  So there are
discrete steps in there anyway.

  That's going to be the case with most anything...you will have a very
hard time getting away from discrete positioning.  You could build a
positioning system with DC servo motors, but at some point you'll be at
the mercy of their own resolution, which will give you the same sorts of
difficulties, but less predictably.


On 10/05/2015 01:48 PM, Justin Haynes wrote:
> Thanks!  Actually for #2 I meant to say 'vector' not 'raster'.  How does
> the mechanism work such that perfectly true curves (or lines) can be made?
> I understand with analog computers or analog electronic music synthesis,
> Voltages can correspond to values.  In a sense, calculations can happen
> with electrons taking the place of numbers.
> How then do we go from digital math to curves being represented smoothly?
> Is there a notion of a matrix which lines can be drawn smoothly between?
> What should I read?
> -Justin
> On Mon, Oct 5, 2015 at 12:21 PM, Carl R. Friend <crfriend at rcn.com> wrote:
>> On 10/05/2015 12:56 PM, Justin Haynes wrote:
>>> 1. Do any plotters exist with a mechanism for moving the pen in a smooth
>>> line rather than across a grid of discrete locations?  The pen still makes
>>> a relatively smooth movement, but this is simply a desirable artifact.
>>    If any such devices exist, they'll almost certainly be very old
>> and long-obsolete.  The accepted methodology for getting smooth curves
>> now is to reduce the step-size either through better stepper-motor
>> technology or gearing.  Also at play in this is that the tip of the
>> pen is likely some multiple of the smallest step size -- you won't
>> notice the stepping action, especially with felt-tipped pens.
>> 2. In raster displays, lines look smooth, but I'd guess the line is still
>>> being created with many discrete movements, and they blend together for a
>>> similar reason as the pen on a plotter does - the electron beam cannot
>>> change directly quickly enough to make such tiny jagged edges.  Do raster
>>> displays exist which can accomplish an actual straight line?
>>    Raster displays, by nature, can only produce steps; get out a
>> magnifying-glass to see for yourself.  This is best viewed on a
>> monochrome display which won't have the colour-producing artefacts
>> present in colour tubes -- or worse -- LCDs.
>>    Vector CRTs, however do exist and typically, but not always,
>> make use of storage-tubes for the display.  These are capable of
>> producing perfectly true curves, but are long obsolete.
>> 3. Finally, I think this has interesting applications for 3d Printers.
>>    3D printers will unquestionably use stepper motors with the
>> absolute precision down to motor-technology and gearing.  They
>> are too new for anything else.
>> 4. I have no idea how a CDC machine accomplishes curves, but I suppose when
>>> you have a lathe or similar tool capable of smoothing edges it isn't
>>> critical.
>>    The answer is fine-grain steppers and large gear-ratios (lots of
>> turns on the stepper to produce one turn of the screw that moves the
>> tool).  In machining, time is not so much of the essence, but precision
>> is, and cutting metal happens in small increments anyway.
>>    Cheers!
>> --
>> +------------------------------------------------+---------------------+
>> | Carl Richard Friend (UNIX Sysadmin)            | Boylston            |
>> | Minicomputer Collector / Enthusiast            | Massachusetts, USA  |
>> | mailto:crfriend at rcn.com                        +---------------------+
>> | http://users.rcn.com/crfriend/museum           | ICBM: 42:20N 71:43W |
>> +------------------------------------------------+---------------------+
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Dave McGuire, AK4HZ
New Kensington, PA

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