sensor for diameter of a pencil

[dimas_lilik]

I want to measure the diameter of a pencil. what is the proper sensor for this measurement?
I am using Microcontroller 89S52.
Please help me.

 

[FvM]

The answer depends much on how you want to perform the measurement. A slide gauge can perfectly measure the diameter, you also get types with a data interface for readout. But perhaps you intend a non-contact measurement or the pencil is moving in a specific way? Also the intended resolution and accuracy would be an important point.

 

[kak111]

it is two ways in my mind

-measuring like with caliber with linear scale
-optical sensor system

So measuring length should be 5...10mm
what is the needed resolution

KAK

 

[dimas_lilik]

Hi..FvM,
Measurement accuracy of 0.02 mm, the desired diameter of 8mm on the top, 10mm at the bottom.
Pencil dropped in the hole that is the sensor, sensor readings only the tip of the upper and lower end.

---------- Post added at 18:58 ---------- Previous post was at 18:55 ----------

Hi..Kak111...
May be optical sensor system is good.
Did you suggest me for this sensor?

 

[FvM]

An optical triangulation sensor should be able to achieve the accuracy, but it would require to fix the object in a defined place. Your description of the setup is still vague regarding object placement.

 

[kak111]

Here is some ready to use sensors

GS 754 CCD-Forked
Measuring sensors

Black-Line
Laser Measurement Systems

**broken link removed**

Mechanical Industry - Barline

PBZ Edge Measurement Sensors | Edge Measurement | Measurement Sensors | Control Products | Business Index | Products [azbil - Yamatake Corporation]

Measurement Sensors: LD | Panasonic

and google finds more..........

You can use also so called edge detector types, if the object is positioned
right way on other side

Harder but cheaper way is to us a ccd-camera or cheap hd-cam and make the measuring program yourself. ( Find the edge-pixels in picture and calculate
object width )

Regards KAK

 

[dimas_lilik]

did you have suggest with low price sensor? if i use laser very expensive.

 

[kak111]

Ok, those sensors are not the cheapest one, but they are ready to use and
"easy" to use.

But now i realize that you need cheap as possible optical measurement sensor
with accuracy 20µm in measured width 8 to 10mm.

Pencil dropped in the hole that is the sensor, sensor readings only the tip of the upper and lower end.

This means that pencil falls through measuring sensor about vertical position
( not precise ) and measured value is readed at both ends during fall time.
This means that sensor measuring area should be maybe over 15mm.
and measure time must be very short.

Is this right with your desing.

and more

Is the cross-section of the pencil perfect circle at whole length
Is the side perfect straigth line

KAK

 

[dimas_lilik]

thanks KAK111,

1. Too difficult when the position of the pencil falling (moving)
2. easier if the position of the pencil still.
3. Top of different diameter with the lower end
4. the upper end of a pencil 10 mm. lower end of the pencil 8 mm
Yes, the cross-section of pencil perfect circle at whole length

 

[FvM]

I've asked this before, but as an update to the recent discussion:
-If the object will be still, is it possible to have a defined support respectively reference plane at one side?
-If you have still object and a reference plane, why not using a dial gauge with digital readout?

 

[dimas_lilik]

Hello FvM : can you explain about " dial gauge"?
Please

 

[kak111]

As i wrote 22.05.11.
-measuring like with caliber with linear scale

I drew principle pict. for you
it has two digital calibers with RS-232 or USB
Price about á 30...60€

View attachment Pencil_Measure_01.pdf

Measure movement maybe with small pneumatic cylinder or
small screw with gearbox & motor (or motor with planetary gears )

Comments.......

Regards KAK

 

[arbj]

I drew principle pict. for you
it has two digital calibers with RS-232 or USB
Price about á 30...60€....

excellent idea indeed, I think your idea is quite innovative and viable.

 

[dimas_lilik]

Thank's KAK111, But I have trouble: the upper end of a pencil 10 mm. lower end of the pencil 8 mm,
So If i use motor to moving caliber measure head, the motor will stop when the tip of 10mm were detected. So lower end of the pencil not measurable.

 

[FvM]

So If i use motor to moving caliber measure head, the motor will stop when the tip of 10mm were detected. So lower end of the pencil not measurable.

Depends on the mechanical design. I must confess, I didn't exactly understand how the setup sketched by KAK is meaned to work. In my understanding, the utilized instrument is similar to what I know as a dial gauge, see this explanation Dial indicator - Wikipedia, the free encyclopedia

There are different methods to use it. You can e.g. move the "rail" carrying the dial gauges against a calibrated stop, leaving room for the pencils. The dial gauge tips are layed up the pencil ends and are adjusted to show the height over the base plate.

 

[kak111]

I think , you perceive that my drawnings are only simple
principles , not blueprints of prototype.

New principle...................
View attachment Pencil_Measure_02.pdf

Next should we solve few things
- is system used in vertical or horisontal
- which is to moving part
- where and how to install measuring force springs
- what is the energy source and mechanism for measure movement
- stopper for object, ( stopper movement for dropping object )
- object guide plate
- sensor or microswich for signalling measure ready
-
- etc , etc

Comments............

Regards KAK

PS.
Measure gauge or caliber measure tool however you know what i mean.
this tool is " työntömitta " in finnish.

**broken link removed**

 

[dimas_lilik]

KAK111 thank you
from your principle measurement, i understood, but many mechanics to be made.
I fear the mechanical problem did not finish.
There another way? like ultrasonic or infra red may be?

 

[kak111]

Measurement accuracy of 0.02 mm

Accuracy like 20µm is not possible with ultrasonic devices.

Another acceptable principle for thiskind of measure is optical with
IR- or visible light.

1. use laser scanner or fork as it was ......

22-05-11, 21:50
kak111

Re: sensor for diameter of a pencil
Here is some ready to use sensors

2. use CCD Line Camera ( can be made by yourself ???? )
( needs programming )
example............

Spectronic Devices - CRONIN LINE CAMERAS using photo-diode-arrays

Read PDF´s for array data sheet too in that site.

3. use HD-webcam with added optics
( needs programming like machine vision to find objects edge in picture)
example..............

Camera Measure Home Page - Measure via webcam

Tell your opinion about these.

Regards KAK

 

[dimas_lilik]

Hi KAK111,
I try with ultrasonic, but not able to 0.02mm accuracy
may be you know about ultrasonic?
how many accuracy for ultrasonic?

 

[kak111]

I cant see any realistic easy or economical wise ways to use
ultrasonic measure in this case.

1. Sound speed in air is 330m/s = 0.33 mm / 1µs
-if you can find echo from pencil which is round shaped ( not good reflector)
and separate that from other reflections ( surrounding surfaces and parts )
so that is the coefficient for resolution .

2. If standard piezo is used frequency is 50...200kHz
ie. one cycle of sound wave is 6.6...1.6 mm long in air.
There gonna be big problem to find and separate echo from pencil
for timing calculations.

How you think to do this measure.

Regards KAK

---------- Post added at 22:56 ---------- Previous post was at 22:19 ----------

I have one more idea with cheap HD-webcam.

If you put new optic ( one lens ) front to cam
you can take a picture of pencil, using white background
so that pencil fills allmost the picture area

and then calculate how width is the pencil in picture measured in pixels
then calibrate pixel to real measure ( in mm´s )

Cheap cam´s are 720p (1280 × 720pixels)

ie. you get for example 10mm = 1000pixels (+/- 10)
so accuracy is 0.01mm (+/- 0.1)

Better cam´s are 1080p (1920 × 1080pix´s )

Or you can take a picture of 1/2 or 1/4 pencil width for better accuracy
when pencil fixed in holding device

KAK