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need to create 0 to 30 pounds linear force

i need something like a solenoid which can generate 0 to 30 pounds of
linear force. it needs to be easily controllable, i.e. have a
proportionate response to voltage or current as it will be used in a
closed loop system.

i think solenoids are ruled out because they dont generate force in a
nice proportionate way to voltage/current? am i wrong about that?

it also needs to be fast responding, i.e. 0 to 30 pounds in less than
100ms

hmm a solenoid does sound like the right thing..but why do i think
they are on/off?
 
i need something like a solenoid which can generate 0 to 30 pounds of
linear force. it needs to be easily controllable, i.e. have a
proportionate response to voltage or current as it will be used in a
closed loop system.

i think solenoids are ruled out because they dont generate force in a
nice proportionate way to voltage/current? am i wrong about that?

it also needs to be fast responding, i.e. 0 to 30 pounds in less than
100ms

hmm a solenoid does sound like the right thing..but why do i think
they are on/off?
 
i need something like a solenoid which can generate 0 to 30 pounds of
linear force. it needs to be easily controllable, i.e. have a
proportionate response to voltage or current as it will be used in a
closed loop system.

i think solenoids are ruled out because they dont generate force in a
nice proportionate way to voltage/current? am i wrong about that?

it also needs to be fast responding, i.e. 0 to 30 pounds in less than
100ms

hmm a solenoid does sound like the right thing..but why do i think
they are on/off?

Over what kind of distance does force generator have to generate this
force?

Speaker coil design trades off force against travel - the force
produced by the interaction of the cylindrical speaker coil and the
permanent magnet does vary as the coil moves with respect to the
permanent magnet, but you can trade off force against throw.

There is a solution to to this problem in the linear stepping motor -
which has two or three sets of coils which translate across an array
of permanent magnets. Two coil motors are usually designed so that as
you move the coils along the magnet array, the voltages induced in the
coils vary as the sine and cosine of the displacement;
drive the right currents into the coils at any given position and you
can generate whatever force you want (up to the limits set by coil
dissipation and demagnetisation).

The Sawyer motor is the best known example

http://www.nano.pe.u-tokyo.ac.jp/pdffiles/chen102 P5.12.pdf

If you don't need much travel the solenoid/speaker coil approach can
be fine. Force will vary as the coil moves with trespect to the
permanent magnet, and as the permanent magnet heats up, but you can
monitor temperature and position and correct for both.
 
B

Benj

Jan 1, 1970
0
i need something like a solenoid which can generate 0 to 30 pounds of
linear force. it needs to be easily controllable, i.e. have a
proportionate response to voltage or current as it will be used in a
closed loop system.

But you haven't bothered to tell us what the travel (if any) required
is. I"ll assume you just need a force and the actuator doesn't move at
all!
i think solenoids are ruled out because they dont generate force in a
nice proportionate way to voltage/current? am i wrong about that?

Yes you are. Solenoids don't generate a nice linear force with respect
to POSITION. they are fairly linear with respect to drive current. OF
course 30 pounds is a LOT of force and that implies an iron core
solenoid and that means that the iron will hae hysteresis that will
reduce linearity even of drive current.
it also needs to be fast responding, i.e. 0 to 30 pounds in less than
100ms

Fast could also be a problem speakers (moving coil) are fast because
the moving parts are light. High forces are a problem. Such things are
made (to drive shake tables and the like) but $$$$. Iron core
solenoids get lots of force but the linearity problems and the mass of
the iron cores can reduce response speed.
hmm a solenoid does sound like the right thing..but why do i think
they are on/off?

YOU are thinking of solenoids that PULL things. IN other words they
are not only providing force but motion as well. It is the force/
position curve that is way nonlinear in a solenoid. That is why they
are rarely used when linear positioning is needed. For example, large
hard disk head positioners used to be of the speaker type (only MUCH
larger).
 
B

Bob Eld

Jan 1, 1970
0
i need something like a solenoid which can generate 0 to 30 pounds of
linear force. it needs to be easily controllable, i.e. have a
proportionate response to voltage or current as it will be used in a
closed loop system.

i think solenoids are ruled out because they dont generate force in a
nice proportionate way to voltage/current? am i wrong about that?

it also needs to be fast responding, i.e. 0 to 30 pounds in less than
100ms

hmm a solenoid does sound like the right thing..but why do i think
they are on/off?

You have not mentioned how far it has to travel. If it is just a few
milli-meteres its one thing, if it is a foot, it's quite another.
Furthermore, the mass you need to push will be important in the response
time.

You are correct about solenoids, they are non-linear devices who's force is
a strong function of the distance pulled in as well as current in the coil.
However, they can provide the high forces in the range you require and are
cheap.

One possibility is to use a solenoid, either a pusher or a puller depending
on the direction you want with feedback from a force sensor to linearize and
control the force. You did mention closed loop. A simple strain gauge force
transducer or load cell provides the the force sensing feedback. This is
applied to an ampifier to deliver current to the solenoid. A Pulse Width
Modulation scheme, PWM, may be in order to keep power dissipation in check.

As mentioned in other posts, a voice coil actuator would probably be the
best, though expensive choice. Force can be quite linear over a moderate
throw distance and the direction depends on the polarity of the drive
current. Lower mass makes it fast compared to a solenoid. Feedback can also
be applied here to improve performance.

A piezo electric (ceramic) transducer would probably be the cheapest way to
do it but the throw distance is very short. But, it can be very fast.
Ultrasonic tranducers work this way.

Yet another way is the linear induction motor. Basically it is like a
transformer with a shorted single turn secondary free to move. AC current in
the primary causes the shorted secondary to repel away. Forces can be vary
high. Depending on design, mass can be relatively low, but accurate force
would have to be controlled with feedback. Throw distance can be as long as
you want. Maglev trains work on this principle.

A small DC or other motor working on a ball screw, jack screw or rack and
pinion may be the simplest and and relatively cheap method of getting the
motion you want. With proper design, the speed reqirement can probably be
met. Again throw distance must be considered in determining speed, motor
size and gear ratios.
 
T

Tim Wescott

Jan 1, 1970
0
You have not mentioned how far it has to travel. If it is just a few
milli-meteres its one thing, if it is a foot, it's quite another.
Furthermore, the mass you need to push will be important in the response
time.

You are correct about solenoids, they are non-linear devices who's force
is a strong function of the distance pulled in as well as current in the
coil. However, they can provide the high forces in the range you require
and are cheap.

One possibility is to use a solenoid, either a pusher or a puller
depending on the direction you want with feedback from a force sensor to
linearize and control the force. You did mention closed loop. A simple
strain gauge force transducer or load cell provides the the force
sensing feedback. This is applied to an ampifier to deliver current to
the solenoid. A Pulse Width Modulation scheme, PWM, may be in order to
keep power dissipation in check.

As mentioned in other posts, a voice coil actuator would probably be the
best, though expensive choice. Force can be quite linear over a moderate
throw distance and the direction depends on the polarity of the drive
current. Lower mass makes it fast compared to a solenoid. Feedback can
also be applied here to improve performance.

A piezo electric (ceramic) transducer would probably be the cheapest way
to do it but the throw distance is very short. But, it can be very fast.
Ultrasonic tranducers work this way.

Yet another way is the linear induction motor. Basically it is like a
transformer with a shorted single turn secondary free to move. AC
current in the primary causes the shorted secondary to repel away.
Forces can be vary high. Depending on design, mass can be relatively
low, but accurate force would have to be controlled with feedback. Throw
distance can be as long as you want. Maglev trains work on this
principle.

A small DC or other motor working on a ball screw, jack screw or rack
and pinion may be the simplest and and relatively cheap method of
getting the motion you want. With proper design, the speed reqirement
can probably be met. Again throw distance must be considered in
determining speed, motor size and gear ratios.

Yea verily -- almost.

Not all linear motors are linear induction motors -- there are linear
brushless motors, and I wouldn't be surprised at a linear brushed motor.

The OP wants a force, and a 100ms response time. He may be able to do
this with a very free-moving rack and pinion (it depends on just how much
parasitic force he can stand), but I'd approach this option carefully.

Other respondents have mentioned that voice coil actuators are $$$ --
they are, but if you wind your own coil and place your own magnets the
purchase price is low. The _labor_ is high; that plus the fact that
voice coil actuators are generally low-volume items* is what drives up
the price, but rolling your own is a quite viable option.

* Except for disk drives, but those are in-house items.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html
 
B

Brendan Gillatt

Jan 1, 1970
0
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Hash: SHA1

[email protected] wrote:
| i need something like a solenoid which can generate 0 to 30 pounds of
| linear force. it needs to be easily controllable, i.e. have a
| proportionate response to voltage or current as it will be used in a
| closed loop system.
|
| i think solenoids are ruled out because they dont generate force in a
| nice proportionate way to voltage/current? am i wrong about that?
|
| it also needs to be fast responding, i.e. 0 to 30 pounds in less than
| 100ms
|
| hmm a solenoid does sound like the right thing..but why do i think
| they are on/off?

If you have the know-how and someone with experience (certainly not me)
you could try using a pneumatic system with feedback to control the
pressure exerted. I would assume (I'm no expert) that you could create
the 30lbs of pressure with a large enough bore ram and a well geared air
pump.

It's probably a fairly bulky system though cheaper than the voice coil
systems others have mentioned because of the off the shelf parts.
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D

Daniel A. Thomas

Jan 1, 1970
0
i need something like a solenoid which can generate 0 to 30 pounds of
linear force. it needs to be easily controllable, i.e. have a
proportionate response to voltage or current as it will be used in a
closed loop system.

i think solenoids are ruled out because they dont generate force in a
nice proportionate way to voltage/current? am i wrong about that?

it also needs to be fast responding, i.e. 0 to 30 pounds in less than
100ms

hmm a solenoid does sound like the right thing..but why do i think
they are on/off?


Try Google on "linear actuators".
Lots of options.
Dan Thomas
 
J

Jamie

Jan 1, 1970
0
i need something like a solenoid which can generate 0 to 30 pounds of
linear force. it needs to be easily controllable, i.e. have a
proportionate response to voltage or current as it will be used in a
closed loop system.

i think solenoids are ruled out because they dont generate force in a
nice proportionate way to voltage/current? am i wrong about that?

it also needs to be fast responding, i.e. 0 to 30 pounds in less than
100ms

hmm a solenoid does sound like the right thing..but why do i think
they are on/off?
stroke/displacement length?
 
OKAY:

sorry i left out the throw

i imagine the throw will be less than 5mm..

let me explain the application:

i want to make a programmable adjustable fuel pressure regulator for a
car

you take a normal fuel pressure regulator, which is basically a ball
and spring valve where the spring sets the pressure

if you were able to push on the spring, then you can further increase
the regulated pressure

SO, my regulator will have a spring to set the MINIMUM pressure, and
some kind of electrically controlled "force" which will push on the
spring to increase the pressure to whatever it needs to be

the "closed loop" will measure the RESULTANT fuel pressure, NOT the
force of the actuator

my application would require a minimum pressure of about 30 lbs, with
the ability to go up to 60 lbs, so the spring will give me the
minimum, and this electrically controlled "force" device will supply
the remainder, as needed

pneumatic systems arent an option because they add too much complexity
to the system

i thought about using a normal rotary motor but it seemed like it
would be too slow...i could be wrong though. a motor connected to a
threaded rod in a tube might work, but i dont know how much torque the
motor would need and it might need to be geared down, and it might be
slow....but it MIGHT WORK..i may have to look into that
 
D

Don Lancaster

Jan 1, 1970
0
OKAY:

sorry i left out the throw

i imagine the throw will be less than 5mm..

let me explain the application:

i want to make a programmable adjustable fuel pressure regulator for a
car

you take a normal fuel pressure regulator, which is basically a ball
and spring valve where the spring sets the pressure

if you were able to push on the spring, then you can further increase
the regulated pressure

SO, my regulator will have a spring to set the MINIMUM pressure, and
some kind of electrically controlled "force" which will push on the
spring to increase the pressure to whatever it needs to be

the "closed loop" will measure the RESULTANT fuel pressure, NOT the
force of the actuator

my application would require a minimum pressure of about 30 lbs, with
the ability to go up to 60 lbs, so the spring will give me the
minimum, and this electrically controlled "force" device will supply
the remainder, as needed

pneumatic systems arent an option because they add too much complexity
to the system

i thought about using a normal rotary motor but it seemed like it
would be too slow...i could be wrong though. a motor connected to a
threaded rod in a tube might work, but i dont know how much torque the
motor would need and it might need to be geared down, and it might be
slow....but it MIGHT WORK..i may have to look into that

A stepper with a lead screw might work.
But pneumatics are probably the cheapest and simplest.



--
Many thanks,

Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email: [email protected]

Please visit my GURU's LAIR web site at http://www.tinaja.com
 
G

Greg Neill

Jan 1, 1970
0
OKAY:

sorry i left out the throw

i imagine the throw will be less than 5mm..

If it were a really small throw then a piezo
stack motor might have been an interesting
choice. But I suspect that 5mm would be
pushing it (sorry about the pun) for such
devices.
 
T

Tim Wescott

Jan 1, 1970
0
OKAY:

sorry i left out the throw

i imagine the throw will be less than 5mm..

let me explain the application:

i want to make a programmable adjustable fuel pressure regulator for a
car

you take a normal fuel pressure regulator, which is basically a ball and
spring valve where the spring sets the pressure

if you were able to push on the spring, then you can further increase
the regulated pressure

SO, my regulator will have a spring to set the MINIMUM pressure, and
some kind of electrically controlled "force" which will push on the
spring to increase the pressure to whatever it needs to be

the "closed loop" will measure the RESULTANT fuel pressure, NOT the
force of the actuator

my application would require a minimum pressure of about 30 lbs, with
the ability to go up to 60 lbs, so the spring will give me the minimum,
and this electrically controlled "force" device will supply the
remainder, as needed

pneumatic systems arent an option because they add too much complexity
to the system

i thought about using a normal rotary motor but it seemed like it would
be too slow...i could be wrong though. a motor connected to a threaded
rod in a tube might work, but i dont know how much torque the motor
would need and it might need to be geared down, and it might be
slow....but it MIGHT WORK..i may have to look into that

Why do you need the 100ms response speed? If not for that, a geared-down
motor driving the spring position my just be the bee's knees.

An even better way may be a mondo-big fuel injector valve feeding into an
accumulator -- that way you'll be using known-good technology instead of
inventing from fresh.

You may want to do a web search on industrial remote-controlled pressure
regulators: I'm sure they're out there to inspect & dissect.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html
 
B

Bob Eld

Jan 1, 1970
0
OKAY:

sorry i left out the throw

i imagine the throw will be less than 5mm..

let me explain the application:

i want to make a programmable adjustable fuel pressure regulator for a
car

you take a normal fuel pressure regulator, which is basically a ball
and spring valve where the spring sets the pressure

if you were able to push on the spring, then you can further increase
the regulated pressure

SO, my regulator will have a spring to set the MINIMUM pressure, and
some kind of electrically controlled "force" which will push on the
spring to increase the pressure to whatever it needs to be

the "closed loop" will measure the RESULTANT fuel pressure, NOT the
force of the actuator

my application would require a minimum pressure of about 30 lbs, with
the ability to go up to 60 lbs, so the spring will give me the
minimum, and this electrically controlled "force" device will supply
the remainder, as needed

pneumatic systems arent an option because they add too much complexity
to the system

i thought about using a normal rotary motor but it seemed like it
would be too slow...i could be wrong though. a motor connected to a
threaded rod in a tube might work, but i dont know how much torque the
motor would need and it might need to be geared down, and it might be
slow....but it MIGHT WORK..i may have to look into that

So for openers, you are talking about pressure, not force. The actual force
is probably far less than a pound depending on the orifice area where the
ball seats, right? No way do you need 30lb of force as originally claimed.

Simple solution: Place a screw behind the spring to adjust the force on the
spring. Attach a gear to the screw. Drive the screw gear with a small DC
motor with a pinion gear on its shaft. The pinion engages the screw gear.
The purpose of the gear and pinion is to give a gear ratio to increase the
motor torque on the screw keeping the motor small and the system simple.

When there is no current in the motor, the pressure will remain at it's
setting and can remain forever consuming no power. Motor current in one
direction will drive the screw toward higher pressure while current in the
other direction will drive the screw to lower pressure.

Connect the motor in your pressure control loop with appropriate
amplification and compensation using pressure as the control variable as you
state.

Privide two limit switches on the screw travel to keep the screw from
bottoming out and stalling the motor at each end of travel.

Don't make this a bigger deal than it needs to be.
 
J

Jamie

Jan 1, 1970
0
OKAY:

sorry i left out the throw

i imagine the throw will be less than 5mm..

let me explain the application:

i want to make a programmable adjustable fuel pressure regulator for a
car

you take a normal fuel pressure regulator, which is basically a ball
and spring valve where the spring sets the pressure

if you were able to push on the spring, then you can further increase
the regulated pressure

SO, my regulator will have a spring to set the MINIMUM pressure, and
some kind of electrically controlled "force" which will push on the
spring to increase the pressure to whatever it needs to be

the "closed loop" will measure the RESULTANT fuel pressure, NOT the
force of the actuator

my application would require a minimum pressure of about 30 lbs, with
the ability to go up to 60 lbs, so the spring will give me the
minimum, and this electrically controlled "force" device will supply
the remainder, as needed

pneumatic systems arent an option because they add too much complexity
to the system

i thought about using a normal rotary motor but it seemed like it
would be too slow...i could be wrong though. a motor connected to a
threaded rod in a tube might work, but i dont know how much torque the
motor would need and it might need to be geared down, and it might be
slow....but it MIGHT WORK..i may have to look into that
replace the current spring in the regulator with one that'll give you
60 SPI and control the fuel pump instead.
 
the reason i need 100ms response time is that this regulator is for a
turbocharged car and the fuel pressure must increase immediately in
response to boost or the mixture will lean out with catastrophic
results.

100ms is just a guess..the faster the better.

controlling the fuel pump sounds interesting but i'm not sure if it
could be controlled fast enough to respond to boost changes..



GOOD POINT:

whoever said that I dont really need 30 psi...you are probably right.
i will do an experiment and see how much force it really takes on the
spring to increase the regulated pressure...this may mean I could use
a much smaller/cheaper/faster/easier solenoid!
 
W

WJLServo

Jan 1, 1970
0
i need something like a solenoid which can generate 0 to 30 pounds of
linear force. it needs to be easily controllable, i.e. have a
proportionate response to voltage or current as it will be used in a
closed loop system.

i think solenoids are ruled out because they dont generate force in a
nice proportionate way to voltage/current? am i wrong about that?

it also needs to be fast responding, i.e. 0 to 30 pounds in less than
100ms

hmm a solenoid does sound like the right thing..but why do i think
they are on/off?

How about using a rotary motor with an eccentric cam? You can make a
quite good, low loss cam using a collar bearing with a center plug
having an off-center hole bored in it to accept the motor shaft. Use
Loctite cement (RC680) to attach center plug to motor shaft and to
inside race of bearing, and have bearing outer race press against load
point. Should be able to get the force you need with a modest sized
motor. Force will not be linear with displacement, but, will be quite
repeatable. And, since the motor only needs to rotate 90 degrees or
so, response should be fast.

W Letendre
 
R

Rich Grise

Jan 1, 1970
0
the reason i need 100ms response time is that this regulator is for a
turbocharged car and the fuel pressure must increase immediately in
response to boost or the mixture will lean out with catastrophic
results.

100ms is just a guess..the faster the better.

controlling the fuel pump sounds interesting but i'm not sure if it
could be controlled fast enough to respond to boost changes..

GOOD POINT:

whoever said that I dont really need 30 psi...you are probably right.
i will do an experiment and see how much force it really takes on the
spring to increase the regulated pressure...this may mean I could use
a much smaller/cheaper/faster/easier solenoid!

When I was a kid, we retired our old Bendix washer and my two brothers,
my sister, and I got to take it apart in the vacant lot next door. It
had some 115V solenoids about the size of your fist, with a T-shaped
armature. When we energized it, it went "CLACK!" I presume it was for
some water valve or motor clutch or something.

I have no idea if they make them that big any more, or in 12V, or anything.

If you use a 6V solenoid with a resistor in series that's equal to the
solenoid's DC resistance, it pulls in a lot snappier, but won't burn up:
see T = RL or whatever it is. ;-)

Or heck, just adapt an injector!

Have Fun!
Rich
 
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