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'[EE] Mechanical activation of a keypad'
2007\08\10@211435 by Jinx

face picon face
I need to depress buttons on a keypad in order to run proof-of-
concept simulations. The keypad is on a commercial unit, and
opening it is not permitted. Not negotiable. Breaking the seal is
big trouble

Actuation force for the keypad is likely to be < 200g. I've not got
it yet but judging by the previous manual use of ones like it, the
force needed was about "average". I've measured the force for
various remote controls, both button and membrane, and they're
all in the range 100g - 200g. It will be a new unit so not expecting
troublesome keys

First thought was solenoids. Possibly the most sensible, but they
are a touch on the expensive side (cost not really a big issue) and
might be a little bulky to fit a dozen over a small keypad. Although
rods could be attached so they could be staggered height-wise

Second thought was levers operated by cams or pins on a rotatable
drum (like a music box. Playing Dance Of The Sugar Plum Fairy not
necessary ;-)) ). Somehow though the cams/pins would have to be
withdrawn as the drum is rotated to position the cam/pin for the next
key to be pressed

Maybe a combination of both methods. Levers + solenoids

I'd be interested in any other ideas. Still Googling

TIA

===============================================
If you aren't part of the solution, you're part of the precipitate

2007\08\10@212949 by Josh Koffman

face picon face
On 8/10/07, Jinx <spam_OUTjoecolquittTakeThisOuTspamclear.net.nz> wrote:
> I need to depress buttons on a keypad in order to run proof-of-
> concept simulations. The keypad is on a commercial unit, and
> opening it is not permitted. Not negotiable. Breaking the seal is
> big trouble
<snip>
> Second thought was levers operated by cams or pins on a rotatable
> drum (like a music box. Playing Dance Of The Sugar Plum Fairy not
> necessary ;-)) ). Somehow though the cams/pins would have to be
> withdrawn as the drum is rotated to position the cam/pin for the next
> key to be pressed

What about something using RC servos? They are inexpensive and fairly
powerful. Other option might be to make a miniature linear actuator
using a small solenoid and a leadscrew?

There's always the option of a CNC mill with an XY table and a small
rubber tip on the Z axis :)

Josh
--
A common mistake that people make when trying to design something
completely foolproof is to underestimate the ingenuity of complete
fools.
       -Douglas Adams

2007\08\10@214011 by Roger, in Bangkok

face
flavicon
face
I seem to remember reading a long time ago about a Braille output device
which was apparently made up of very tiny solenoids.  It connected to a
computer, the operator 'read' a line of output, then the pins repositioned
for the reading of the next line.  Might be worth Giggling that direction as
well.

Also, there are signboards in airports and elsewhere that use tiny solenoids
(I assume) to flip colored disks.  Should be something in the surplus
markets like that.

Regards/Roger, in Bangkok


On 8/11/07, Jinx <.....joecolquittKILLspamspam@spam@clear.net.nz> wrote:
{Quote hidden}

2007\08\10@215550 by Jinx

face picon face
> I seem to remember reading a long time ago about a Braille
> output device which was apparently made up of very tiny
> solenoids

Hmmm. I have some solenoids out of HDDs (I think they
were for head locking). They're certainly very small, and I
don't know whether the force could be amplified enough by
a lever. The direct force is very light, probably a few grams.
Perhaps those are too small. The Braille concept is kind of
what's needed, only it's one press at a time for a sequence
of number and function keys

2007\08\10@224239 by Jinx

face picon face
> What about something using RC servos? They are inexpensive
> and fairly powerful

Yes, good option

> Other option might be to make a miniature linear actuator using
> a small solenoid and a leadscrew?

I've a few 3.5" FDD steppers that might do that

> There's always the option of a CNC mill with an XY table and a
> small rubber tip on the Z axis :)

Not a daft idea. More than one printer mechanism lying around
here that could be adapted for this simple task. Another pro for
that idea is that the positions for any keys could be programmed
in. The interface I'm wanting to operate is made by a variety of
companies and the layout isn't always the same. A mechanically
robust system using levers and whatnot might not be very easily
altered if I'm asked to use a different keypad

2007\08\10@230445 by Jake Anderson

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face
Jinx wrote:
{Quote hidden}

It would be slow though

2007\08\10@232338 by Jinx

face picon face
> More than one printer mechanism lying around here
> >  
> It would be slow though

Probably. And definitely compared with the preferred/tidier/
not allowed direct electrical input way.  Will have to look into
inter-key timing specs. From experience I believe even a few
seconds would be OK, and a printer mechanism would move
faster than that. Maybe 1s to seek and activate a key I'd have
thought

2007\08\10@232953 by Spehro Pefhany

picon face
At 08:13 PM 8/10/2007, Jinx wrote:
{Quote hidden}

Solenoids would tend to be rough.

Small air cylinders might be smoother. Small single-acting spring-return
cylinders run around $11 each new. Maybe you could rig some kind of calliope
gadget to operate them, in lieu of solenoid valves. ;-)


>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speffspamKILLspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com



2007\08\10@232953 by Spehro Pefhany

picon face
At 08:13 PM 8/10/2007, Jinx wrote:
{Quote hidden}

Solenoids would tend to be rough.

Small air cylinders might be smoother. Small single-acting spring-return
cylinders run around $11 each new. Maybe you could rig some kind of calliope
gadget to operate them, in lieu of solenoid valves. ;-)


>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
.....speffKILLspamspam.....interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com



2007\08\10@233553 by Peter Todd

picon face
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On Sat, Aug 11, 2007 at 08:40:09AM +0700, Roger, in Bangkok wrote:
> Also, there are signboards in airports and elsewhere that use tiny solenoids
> (I assume) to flip colored disks.  Should be something in the surplus
> markets like that.

I just bought about 2,000 of those little units actually... They're a
really neat design, a coil is wrapped around a partial loop of iron. The
flip element is then a small magnet, same material as fridge magnets,
suspended in the cut-away portion of the loop. The trick is that with a
sufficidently strong current pulse the loop is partially magnatized, so
the final element is bi-stable and requires no power to maintain it's
position.

Totally useless for hitting keys though. :(


These guys are the only people I know of who still make them:

http://www.scoretronics.com/components/


If you know of any other suppliers I'd be interested.

- --
http://petertodd.org
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2007\08\10@235058 by Jake Anderson

flavicon
face

> Solenoids would tend to be rough.
>
> Small air cylinders might be smoother. Small single-acting spring-return
> cylinders run around $11 each new. Maybe you could rig some kind of calliope
> gadget to operate them, in lieu of solenoid valves. ;-)
>  
Lego technic ;->

2007\08\11@004838 by Russell McMahon

face
flavicon
face
>I need to depress buttons on a keypad in order to run proof-of-
> concept simulations. The keypad is on a commercial unit, and
> opening it is not permitted. Not negotiable. Breaking the seal is
> big trouble


Solenoids with levers potentially viable.
I MAY have a number of solenoids that you could borrow.

Apart from cost, use of R/C servos would be good.

While it may seem a bizarre solution, a potentially very workable one
would  be to suspend suitable weights in requisite positions and have
them lowered by geared motors. This could be open loop by having the
motor arm come up against a stop in each direction and add a series
resistor or run off a low enough voltage that the stall current was
acceptable. Motor would be operated "long enough to be sure" for up
and down directions. Use of cheap geared motors from toys or new ones
intended for hobbyists would keep the price reasonable. A suitably
thick guide (no doubt routed from MDF :-) ) would allow precision
placement of plungers onto selected keys. Pulleys or even just a nail
as a right angle guide would allow motors to be off to one side. This
would look bizarre but should work perfectly.
Surplustronics may have some motorised geared toy mechanisms. I MAY
have a few in my dungeon.

Suitably geared you could also place an arm on the output shaft and
operate the key directly.
The lowered weight has the advantage of easily adjustable keyforce and
rate can then be adjusted with PWM motor voltage or changing common
supply voltage for all motors. Software PWM would allow easy PWM on as
many PIC pins as required.


These are new from Jaycar - $8.50/1 with trade card and $7.50 / 5s.
Motor and gearbox ready to go. 233:1 gearing. Almost ideal for this
task.

       http://www.jaycar.co.nz/productView.asp?ID=YG2725&CATID=&keywords=gearbox&SPECIAL=&form=KEYWORD&ProdCodeOnly=&Keyword1=&Keyword2=&pageNumber=&priceMin=&priceMax=&SUBCATID=


Slightly prettier and $12.30/1, $10.90/5 trade card
Gearing can be adjusted to 4^N:1   for 1<=N<=6
so max ratio is 4096:1


       http://www.jaycar.co.nz/productView.asp?ID=YG2730&CATID=&keywords=gearbox&SPECIAL=&form=KEYWORD&ProdCodeOnly=&Keyword1=&Keyword2=&pageNumber=&priceMin=&priceMax=&SUBCATID=


Jaycar have some other motor-gearbox sets but the above should be good
enough.

They also have solenoids.

Hobby stores will also have similar and other units.



       Russell

{Quote hidden}

> --

2007\08\11@023529 by Tony Smith

picon face
> > I seem to remember reading a long time ago about a Braille output
> > device which was apparently made up of very tiny solenoids
>
> Hmmm. I have some solenoids out of HDDs (I think they were
> for head locking). They're certainly very small, and I don't
> know whether the force could be amplified enough by a lever.
> The direct force is very light, probably a few grams.
> Perhaps those are too small. The Braille concept is kind of
> what's needed, only it's one press at a time for a sequence
> of number and function keys


Those solenoids are great, I wish I'd scanvenged more of them.

They have 2 coils, one (or both) to actuate, and a smaller one to hold, thus
using less current.  Brain-dead use is to energize both coils, wait a bit
and then turn one off.  Beats stuffing about with PWM.

Pinball machines use them too appaerntly.

Tony

2007\08\11@023531 by Tony Smith

picon face
> Second thought was levers operated by cams or pins on a
> rotatable drum (like a music box. Playing Dance Of The Sugar
> Plum Fairy not necessary ;-)) ). Somehow though the cams/pins
> would have to be withdrawn as the drum is rotated to position
> the cam/pin for the next key to be pressed
>
> Maybe a combination of both methods. Levers + solenoids


I've done this before with cams.

You only need a motor and a microswitch.  Put the microswitch in series with
the motor.  Locate the microswitch so at the 'home' position it is off (and
so is the motor).  This could be a hole drilled in the cam, or a pin
sticking out, above the key etc.

Put something in parallel with the microswitch to short it out (Mosfet etc).
Power that up briefly, long enough so the cam moves and the microswitch
turns 'on'.  The motor will keep running, and switch off by itself when the
cam returns to 'home'.

As usual, there's a bit of buggering about making sure the cam isn't
spinning too fast so it overshoots and re-enagages the microswitch, etc.

As a bonus, it impresses people when they watching it running.  (Ok, so it
impresses the nerds, scares off the womenfolk and amuses the rest
momentarily.)

Tony

2007\08\11@033731 by Robert Rolf

picon face

Tony Smith wrote:

>
> As usual, there's a bit of buggering about making sure the cam isn't
> spinning too fast so it overshoots and re-enagages the microswitch, etc.

The way to handle this is to use a SPDT microswitch that shorts the motor when
it turns off (which stops the motion quicker).
You wire the short through the turn-on relay (can't use a FET here,
unless its a SPDT photmos) so that it's removed at turn on.

Or put a ballast resistor across the motor so that it gets damped when the
power gets turned off.

R

2007\08\11@034353 by Jake Anderson

flavicon
face

>
> Suitably geared you could also place an arm on the output shaft and
> operate the key directly.
> The lowered weight has the advantage of easily adjustable keyforce and
> rate can then be adjusted with PWM motor voltage or changing common
> supply voltage for all motors. Software PWM would allow easy PWM on as
> many PIC pins as required.
>
>
> These are new from Jaycar - $8.50/1 with trade card and $7.50 / 5s.
> Motor and gearbox ready to go. 233:1 gearing. Almost ideal for this
> task.
>  

Taught on a similar line. You could "precision" bend a bit of
coat-hanger or something to make up something like a crank shaft.
suspend all your weights off that and run through your sequence.
Provided your sequence is fixed (which the "music player" styles seem to
indicate) you should be up and running pretty darn quick. Go a XU-1 from
bunnings or some such as your motor and sit the other end of the cam in
a notch.

2007\08\11@043324 by Tony Smith

picon face
> > As usual, there's a bit of buggering about making sure the
> cam isn't
> > spinning too fast so it overshoots and re-enagages the
> microswitch, etc.
>
> The way to handle this is to use a SPDT microswitch that
> shorts the motor when it turns off (which stops the motion quicker).
> You wire the short through the turn-on relay (can't use a FET
> here, unless its a SPDT photmos) so that it's removed at turn on.
>
> Or put a ballast resistor across the motor so that it gets
> damped when the power gets turned off.


Now you're making it complicated.

You don't need more parts, you just change how the microswitch interacts
with the cam.  If it works detecting a hole cut in the cam, then just make
the hole a bit bigger, extending the time the microswitch stays off.

A resistor to act a brake would be nice, except it complicates getting the
motor started again.

Tony

2007\08\11@101018 by John Ferrell

face picon face
Automotive door lock actuators are motor driven and available fro
Alltronics, BG, and others for about $5.

John Ferrell    W8CCW
"Life is easier if you learn to plow
      around the stumps"
http://DixieNC.US

{Original Message removed}

2007\08\11@115957 by Bob Axtell

face picon face
Jinx wrote:
{Quote hidden}

For this application, I think solenoids with nylon or delrin probe ends
would be the best
approach. To ease the problem of closeness, I'd either use a X-Y table
to move the probe, or
make two probe stations, and only probe 1/2 at one time.

For some reason, there are millions of solenoids available on the
surplus market. Many are on EBay, but others can be found at All
Electronics and other surplus companies. I was looking yesterday and
found a lot of 50 small solenoids for less than $1 each, as an example.

--Bob A

2007\08\11@130930 by Bob Blick

face picon face


Jinx wrote:
> I need to depress buttons on a keypad in order to run proof-of-
> concept simulations. The keypad is on a commercial unit, and
> opening it is not permitted. Not negotiable. Breaking the seal is
> big trouble


Hi Jinx,

Does this need to be a random-access unit, or are you just testing
durability of the keypad?

If you are testing durability, what are your requirements for pressure
and tolerance(in other words, 400g +50% -20%)

How much travel?

Cheerful regards,

Bob

2007\08\11@132324 by Cedric Chang

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face

On Aug 11, 2007, at 9:59 AM, Bob Axtell wrote:

Jinx wrote:
> I need to depress buttons on a keypad in order to run proof-of-
> concept simulations. The keypad is on a commercial unit, and
> opening it is not permitted. Not negotiable. Breaking the seal is
> big trouble
>

A motor driven cam might work and possibly allow variable depression and
release rates.  In addition, small solenoids could engage and  
disengage cams
on a long drive shaft.  Let me know if you want me to expand on the  
idea.

Cedric

2007\08\11@155223 by Victor Fraenckel

flavicon
face
Get a small CNC mill such as a Taig. You can program it for any type of
keypad you come across and control the z-axis (up and down) to within
0.001 thus controlling the pressure. Write a general purpose g-code
program and then mod it for each type of keypad.

Just a thought!

Vic
--

*____________________________________________________________________________________________*

*Victor Fraenckel
KC2GUI
victorf ATSIGN windreader DOT com**
*


2007\08\11@163147 by Cedric Chang

flavicon
face
great idea Vic

Cedric


On Aug 11, 2007, at 1:47 PM, Victor Fraenckel wrote:

Get a small CNC mill such as a Taig. You can program it for any type of
keypad you come across and control the z-axis (up and down) to within
0.001 thus controlling the pressure. Write a general purpose g-code
program and then mod it for each type of keypad.

Just a thought!

Vic
--  

*_______________________________________________________________________
_____________________*

*Victor Fraenckel
KC2GUI
victorf ATSIGN windreader DOT com**
*


2007\08\11@191606 by Jinx

face picon face
> Does this need to be a random-access unit, or are you just
> testing durability of the keypad?

Bob, the 'fingers' have to simulate a person using the device

A PIC will take serial data from a PC and activate the keys

After a chat with the other principals last night, they suggested I keep
it simple. Which, given my work load, I'm inclined to go along with

What we're doing will be demonstrated to interested parties and
should be kept as compact as possible. So that ruled out air and
XYZ actuators and all the other great contributions

I've also been told that there are some (slightly important) timing
specs involved and that pretty much means solenoids

2007\08\11@205709 by Recon

picon face
Jinx wrote:

{Quote hidden}

The solenoid method sound good but would be hard IMHO to control the
pressure applied to the key.

What I would suggest is to make fingers of steel that a would be the
weight of the pressure you need to apply. Then wind an electro magnet
that would lift the steel finger off the key.  It would be a bit of a
power hog  being all electromagnets would be energized when no keys were
pushed .  But it would have the advantage of being able to change the
key pressure by just adding or removing weight to the finger.  The
finger would really only need to move just enough to activate the key.
Say 1/8" to 1/4" maybe.

Also for this to work the key pad would have to be positioned  so the
finger would be verticle.

Just out of curiosity what size is the keybord and number of keys?  IE  
4 X 5 , 1/2" SQ keys.

RECON

2007\08\11@221640 by Russell McMahon

face
flavicon
face
> After a chat with the other principals last night, they suggested I
> keep
> it simple.

> should be kept as compact as possible. ...

> I've also been told that there are some (slightly important) timing
> specs involved and that pretty much means solenoids

Motorised cams or levers, or  motor controlled drop weights will meet
the above specs and MAY be simpler than solenoids turn out to be.

I've long ago actually done what you describe for the reasons that you
are doing it, albeit with only two keys. I used solenoids. It wasn't
exactly "simple" in the event, but it worked.




       Russell

2007\08\11@223948 by Jinx

face picon face
> Just out of curiosity what size is the keybord and number of keys?

15 keys, a little variability in layout (it's not 4x4) and size, but
generally
about 15-20mm between keys

2007\08\12@062527 by Tony Smith

picon face
> > Does this need to be a random-access unit, or are you just testing
> > durability of the keypad?
>
> Bob, the 'fingers' have to simulate a person using the device
>
> A PIC will take serial data from a PC and activate the keys
>
> After a chat with the other principals last night, they
> suggested I keep it simple. Which, given my work load, I'm
> inclined to go along with
>
> What we're doing will be demonstrated to interested parties
> and should be kept as compact as possible. So that ruled out
> air and XYZ actuators and all the other great contributions
>
> I've also been told that there are some (slightly important)
> timing specs involved and that pretty much means solenoids


Simulating a 'real' keypress is harder than it looks.  I remember seeing a
documentary once where they were building a robot piano player (as you do).
Cams, air, solenoids etc were all tried, they ended up with a combination of
air & solenoids.

Someone earlier had a good idea, use car door lock actuators.  These are
quite cheap (~$25 a set of 4), although I got 12 packs off eBay once for
$50.  $1 each!

Suspend them above the keypad in a 4x4 grid, add dowels to the end to reach
the keypad, and a piece of perspex with guide holes drilled in it above the
keypad.  The 'fingers' will be on a angle depending on how you arrange the
actuators, and how far above.  (Using levers overcomes this.)

This is simpler than motors, cams & levers, but you can't vary the force of
each keypress, and timing could be a problem.

Failing that, small children work cheap, but have poor long-term
reliability.

Tony

2007\08\12@082240 by Jake Anderson

flavicon
face
Tony Smith wrote:
{Quote hidden}

To get a "force" just put a spring on the end of your solenoid something
like a ball point pen spring would do. Compress the spring by X amount =
Y force. Should be close enough for government work.

2007\08\12@114441 by Tony Smith

picon face
{Quote hidden}

Doesn't work as well as you'd hope.  It can 'soften the blow' that solenoids
often have, but putting the spring on the other side, so that the solenoid
pulls against it works a bit better.

It depends on what the client defines as a keypress, being hard, soft, slow,
fast, rapid presses, multiple presses, etc.  And when you've finished
explaining the options, the answer is 'yes, all of that, thanks'.  (Gosh,
that sounded a bit cynical.)  As the piano-playing robot folk found out,
it's not that easy.  Even with solenoids, you really don't get that much
control, just different flavours of 'thump'.  Voicecoils, that's the ticket.

Tony

2007\08\12@144046 by Robert Rolf

picon face


Tony Smith wrote:
>>To get a "force" just put a spring on the end of your
>>solenoid something like a ball point pen spring would do.
>>Compress the spring by X amount = Y force. Should be close
>>enough for government work.
>
> Doesn't work as well as you'd hope.  It can 'soften the blow' that solenoids
> often have, but putting the spring on the other side, so that the solenoid
> pulls against it works a bit better.
>
> It depends on what the client defines as a keypress, being hard, soft, slow,
> fast, rapid presses, multiple presses, etc.  And when you've finished
> explaining the options, the answer is 'yes, all of that, thanks'.  (Gosh,
> that sounded a bit cynical.)  As the piano-playing robot folk found out,
> it's not that easy.  Even with solenoids, you really don't get that much
> control, just different flavours of 'thump'.  Voicecoils, that's the ticket.

As long as they have position feedback.
We use one from an ancient disk drive (4" diameter 6" long) to pull muscles in
a research lab. 2kg of force with 1kHz response (for stiffness measurements).

Speaker horn drivers work reasonably well too, but their throw range is about 3mm max.

You can add position sensing to a solenoid with IR/LED pair reflecting off the back
side of the core.

There are even commercial IR units with digital output that have cm range,
in the $10 range. Roboticists use them all the time in their summo combat
robots.


Robert


2007\08\12@152905 by William \Chops\ Westfield

face picon face

On Aug 12, 2007, at 11:40 AM, Robert Rolf wrote:

>> Voicecoils, that's the ticket.
>
> We use one from an ancient disk drive (4" diameter 6" long)
> to pull muscles in a research lab.

Heh.  Sudden vision of an engineer "let's use voice coils from
mainframe disk drives; they're Cheap Off-the-Shelf technology,
and we'll ALWAY be able to pick up as many as we need from the
surplus market because of the way disk technology is improving!"

Oops.

BillW

2007\08\13@044139 by Alan B. Pearce

face picon face
>> Not a daft idea. More than one printer mechanism lying around
>> here that could be adapted for this simple task.
>
>It would be slow though

Still likely to be faster than human fingers - and probably a heap more
accurate at hitting the buttons ;)

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