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Which is better for tight quarters - Ping))) or Sharp GP2D12 Analog Distance Se — Parallax Forums

Which is better for tight quarters - Ping))) or Sharp GP2D12 Analog Distance Se

OakGraphicsOakGraphics Posts: 202
edited 2005-07-04 20:02 in BASIC Stamp
I have a need to measure the distance of a motorized slide that moves a total of 12 inches inside a tight area.
The slide is about 18" x 6" target· in a shaft about the same size.· I would like to measure how far the slide is in the shaft.· Looking at measurment assessories - i see Ping))) and the Sharp GP2D12 Analog Distance Sensor may be good for this, but was wondering if the close-quartiers would muck with them too much.
·I would basically like an LCD readout from a BS1 or BS2 showing the distance in in/cm/whatever.
Anybody have any ideas on this?·rolleyes.gif

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-07-01 20:48
    Hello,

    ·· The answer to your question depends highly on what type of surface the sensor would be looking at, it's reflectivity and/or angle and how the sensor would be mounted with respect to the assembly.· It also matters if the sensor needs to detect accurately sudden changes in motion, since the PING))), for example, wouldn't be able to do that.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • OakGraphicsOakGraphics Posts: 202
    edited 2005-07-01 22:06
    Good questions Chris - let me see if I can elaborate:

    Reflectivity: whatever is needed. I can even put a reflector on it - since this is hidden inside a shaft. I can even paint the rest non-reflective black if that helps. Whatever is best.

    Angle - straight on I would think. So the reflector would be in direct line of sight and height with te sensor

    Mounting: Sensor would be mounted at the top of the shaft pointing downwards. Probably off-center since there is a piston pulling/pushing the slide in the shaft.

    Speed: pretty slow. About 4 to 5 seconds to travel the 12 inches. Not much faster then that as this is heavily geared.

    Does that help?
  • Bruce BatesBruce Bates Posts: 3,045
    edited 2005-07-01 22:31
    OakGraphics -

    See if either of these techniques will do what you need to do:
    http://www.tpub.com/doeinstrument/instrumentationandcontrol40.htm

    Regards,

    Bruce Bates
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-07-02 01:43
    Hello,

    ·· You have definately provided the much needed information.· Based on that, I guess it's really just a matter of preference.· The PING))) sounds like it would probably work.· Each sensor has a minimum distance it can detect, so that's another thing to keep in mind.· For the Sharp sensor it's 10cm.· Anything closer gives incorrect readings.· The PING))) can see down to 2cm.· This may be a consideration.· The PING))) would seema better choice?



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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • OakGraphicsOakGraphics Posts: 202
    edited 2005-07-02 03:00
    The Ping))) does seem to be the better choice with the limitation of the other's 10cm minimum reach.
    Could it be possible to 'pinpoint' the ping))) by using tubes in front of it, so it doesent see things closer then say - oh 5 degrees? That would help a bit I think. smile.gif
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-07-02 19:24
    ·· I highly doubt it would work properly by doing that.· You would be affecting the acoustics of the device, used in it's measuring.· I would say it would probably have an adverse affect.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • Philip GamblinPhilip Gamblin Posts: 202
    edited 2005-07-04 09:28
    Remember the Ping is ultrasound as opposed to IR with the Sharp. So the reflectivity issues are different.
  • OakGraphicsOakGraphics Posts: 202
    edited 2005-07-04 19:08
    So what would be the best detectable surface for the ping))) ?
    And for that matter - what would be the worse?

    Thinking of sound - I imagine any hard surface will work. I would guess foam panels would be the worse But since I will be pointing the ping))) straight on the target, I don't think I will get any interferance from the pieces in the shaft around it, since the target will still be the closest thing.

    How accurate is ping))) anyways? Within a cm?

    Thanks for all the advice, I am ordering up on today! [noparse]:)[/noparse]
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-07-04 20:02
    ·· Many of the questions you're asking are answered within the documentation, which is located at the link below.· You should use a surface perpendicular to the plane of the sensor's FOV.

    http://www.parallax.com/detail.asp?product_id=28015

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
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