Imagine a simple fractional hp DC gearmotor with a torque limiter or torque
limiting clutch that powers a small machine at 60 or so RPM. Lets say the
machine jams and the torque limiting device kicks out. How can I cheaply,
easily sense this condition and turn off the motor?

This is a personal project and when I get it running it will amaze and
astound!

Buerste wrote:

machine jams and the torque limiting device kicks out. How can I cheaply,
easily sense this condition and turn off the motor?


Are you going to make your torque limiter? If so, make one that's noisy
when operating. I had an industrial sewing maching with a safety clutch
in the form of a spring-loaded ball in the driven member, engaging with
a detent hole in the driven half of a coupling. It made a nice racket
when the machine jammed.

Jordan

On 2009-07-06, Buerste wrote:
Imagine a simple fractional hp DC gearmotor with a torque limiter or torque
limiting clutch that powers a small machine at 60 or so RPM. Lets say the
machine jams and the torque limiting device kicks out. How can I cheaply,
easily sense this condition and turn off the motor?

use an appropriately sized breaker?

This is a personal project and when I get it running it will amaze and
astound!

"Ignoramus18221" wrote in message
...
On 2009-07-06, Buerste wrote:
Imagine a simple fractional hp DC gearmotor with a torque limiter or
torque
limiting clutch that powers a small machine at 60 or so RPM. Lets say
the
machine jams and the torque limiting device kicks out. How can I
cheaply,
easily sense this condition and turn off the motor?

use an appropriately sized breaker?

But once the limiter trips, will the motor draw enough overage to pop a
breaker?

On Jul 6, 8:05*am, "Buerste" wrote:
Imagine a simple fractional hp DC gearmotor with a torque limiter or torque
limiting clutch *that powers a small machine at 60 or so RPM. *Lets say the
machine jams and the torque limiting device kicks out. *How can I cheaply,
easily sense this condition and turn off the motor?

You could put a photo sensor on the gear motor and the part of the
machine that stops turning when the terque limiter kicks out. Use
these to set and reset a flipflop. Integrate the output of the
flipflop. When the torque limiter kicks out the reset would no longer
occur, and the voltage from the integrator will go to high. Use this
to turn off the motor.
Dan

wrote in message
...
On Jul 6, 8:05 am, "Buerste" wrote:
Imagine a simple fractional hp DC gearmotor with a torque limiter or
torque
limiting clutch that powers a small machine at 60 or so RPM. Lets say the
machine jams and the torque limiting device kicks out. How can I cheaply,
easily sense this condition and turn off the motor?

You could put a photo sensor on the gear motor and the part of the
machine that stops turning when the terque limiter kicks out. Use
these to set and reset a flipflop. Integrate the output of the
flipflop. When the torque limiter kicks out the reset would no longer
occur, and the voltage from the integrator will go to high. Use this
to turn off the motor.
Dan
Good idea.

" wrote:

On Jul 6, 8:05 am, "Buerste" wrote:
Imagine a simple fractional hp DC gearmotor with a torque limiter or torque
limiting clutch that powers a small machine at 60 or so RPM. Lets say the
machine jams and the torque limiting device kicks out. How can I cheaply,
easily sense this condition and turn off the motor?

You could put a photo sensor on the gear motor and the part of the
machine that stops turning when the terque limiter kicks out. Use
these to set and reset a flipflop. Integrate the output of the
flipflop. When the torque limiter kicks out the reset would no longer
occur, and the voltage from the integrator will go to high. Use this
to turn off the motor.
Dan


'A missing pulse detector' not only detects a complete stop, but if
the speed is off.


--
You can't have a sense of humor, if you have no sense!

On Jul 6, 4:23*pm, "Buerste" wrote:

Good idea.

Probably better if there are multiple reset pulses per revolution of
the output and only one set pulse on the motor. That would assure the
flipflop is reset shortly after being set regardless of the relation
of the two shafts.

Dan

On Jul 6, 4:23*pm, "Buerste" wrote:

Good idea.

Better if there are multiple reset pulses per rev and only one set
pulse per rev. That would ensure the f/f got reset right after it got
set. Regardless of the phase between the two shafts.

Dan

Buerste wrote:
Imagine a simple fractional hp DC gearmotor with a torque limiter or torque
limiting clutch that powers a small machine at 60 or so RPM. Lets say the
machine jams and the torque limiting device kicks out. How can I cheaply,
easily sense this condition and turn off the motor?

This is a personal project and when I get it running it will amaze and
astound!



This is a maybe, since I don't have details of the application. Use a
PTC thermistor (fuse type) limiter for the motor. Let the PTC perform
the torque limiting. Put the LED (properly current limited) of an
optocoupler across the thermistor. When the thermistor goes high
resistance, there will be enough voltage across the optocoupler input to
turn it on. The output of the optocoupler goes back to your office, or
wherever.


Kevin Gallimore

On Mon, 06 Jul 2009 18:29:03 -0400, axolotl wrote:
Buerste wrote:
Imagine a simple fractional hp DC gearmotor with a torque limiter or
torque limiting clutch that powers a small machine at 60 or so RPM.
Lets say the machine jams and the torque limiting device kicks out.
How can I cheaply, easily sense this condition and turn off the motor?

This is a personal project and when I get it running it will amaze and
astound!

This is a maybe, since I don't have details of the application. Use a
PTC thermistor (fuse type) limiter for the motor. Let the PTC perform
the torque limiting. Put the LED (properly current limited) of an
optocoupler across the thermistor. When the thermistor goes high
resistance, there will be enough voltage across the optocoupler input to
turn it on. The output of the optocoupler goes back to your office, or
wherever.

Seems like there's just one complicated solution after another
so far in this thread, that all involve adding a bunch of parts.
Here's one that uses *fewer* parts: Take out the torque limiting
device; couple the motor straight through to the machine; take
out the motor mounting bolts; fasten the motor in place with a bit
of string or duct tape. When the machine jams, the motor spins
and its power leads wind up and twist off, stopping the motor.

--
jiw

simple electronic way. Have a magnet on the rotating part. Place a reed
switch near enough that it closes every time the magnet comes by. Have a
timer you set to two seconds. Reset the timer when you presss "start", and
every time the reed switch is closed by the magnet. You can make this timer
from a 555 chip, or just buy a timer. If the timer expires, drop out a
relay to de-energize the motor.



"Buerste" wrote in message
...
Imagine a simple fractional hp DC gearmotor with a torque limiter or
torque limiting clutch that powers a small machine at 60 or so RPM. Lets
say the machine jams and the torque limiting device kicks out. How can I
cheaply, easily sense this condition and turn off the motor?

This is a personal project and when I get it running it will amaze and
astound!

"Bill Noble" wrote in message
...
simple electronic way. Have a magnet on the rotating part. Place a reed
switch near enough that it closes every time the magnet comes by. Have a
timer you set to two seconds. Reset the timer when you presss "start",
and every time the reed switch is closed by the magnet. You can make this
timer from a 555 chip, or just buy a timer. If the timer expires, drop
out a relay to de-energize the motor.


You'll never be able to sell your brain for much...it's USED!
Thanks Bill.

"Buerste" wrote in message
...
Imagine a simple fractional hp DC gearmotor with a torque limiter or
torque limiting clutch that powers a small machine at 60 or so RPM. Lets
say the machine jams and the torque limiting device kicks out. How can I
cheaply, easily sense this condition and turn off the motor?

This is a personal project and when I get it running it will amaze and
astound!

We had a machine at work where the motor was mounted to allow it to rotate
against a spring. There was an adjustable limit switch so that at a certain
torque, the spring would compress far enough to trip the switch and stop the
motor. Simple and cheap.

RogerN

On 2009-07-06, wrote:
On Jul 6, 8:05*am, "Buerste" wrote:
Imagine a simple fractional hp DC gearmotor with a torque limiter or torque
limiting clutch *that powers a small machine at 60 or so RPM. *Lets say the
machine jams and the torque limiting device kicks out. *How can I cheaply,
easily sense this condition and turn off the motor?

You could put a photo sensor on the gear motor and the part of the
machine that stops turning when the terque limiter kicks out. Use
these to set and reset a flipflop. Integrate the output of the
flipflop. When the torque limiter kicks out the reset would no longer
occur, and the voltage from the integrator will go to high. Use this
to turn off the motor.

Or -- set up a retriggerable one-shot which times out a bit
slower than the optical sensor pulses so it keeps getting reset as long
as things are running at normal speed. When the shaft slows down, the
one-shot finally reaches the end of its time and triggers the motor stop
circuit. And it could be done with magnetic pickups as well if dust is
a problem with a optical sensor. For that matter -- if there are steel
or iron gears involved, a magnetic pickup near the teeth of the gear
could be used to generate the pulses.

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

On Mon, 6 Jul 2009 03:05:21 -0400, "Buerste" wrote:

Imagine a simple fractional hp DC gearmotor with a torque limiter or torque
limiting clutch that powers a small machine at 60 or so RPM. Lets say the
machine jams and the torque limiting device kicks out. How can I cheaply,
easily sense this condition and turn off the motor?

This is a personal project and when I get it running it will amaze and
astound!


The torque of a DC motor is proportional to current, and vise versa.
You can limit torque by limiting current. If you want the motor to
turn off the motor at some torque level, simply turn it off if
current draw reaches a predetermined level. Any additional torque
limiting would be redundant unless there are dynamic considerations
you didn't mention.

Jordan wrote:
Buerste wrote:

machine jams and the torque limiting device kicks out. How can I
cheaply, easily sense this condition and turn off the motor?


Are you going to make your torque limiter? If so, make one that's noisy
when operating. I had an industrial sewing maching with a safety clutch
in the form of a spring-loaded ball in the driven member, engaging with
a detent hole in the driven half of a coupling. It made a nice racket
when the machine jammed.

Jordan

Put a magnet on each half of the limiter, detect both magnets, if one
comes around without the other, shut off, sound alarm.

Requires limiter with only one "Drive" position.

Stuart

On Mon, 6 Jul 2009 03:05:21 -0400, "Buerste" wrote:

Imagine a simple fractional hp DC gearmotor with a torque limiter or torque
limiting clutch that powers a small machine at 60 or so RPM. Lets say the
machine jams and the torque limiting device kicks out. How can I cheaply,
easily sense this condition and turn off the motor?

This is a personal project and when I get it running it will amaze and
astound!

Several have suggested sensing drive and driven parts but left the
signal processing details as an exercise.

I'm in dialup-land just now so it'd be tedious to download a
datasheet, but I'm pretty sure the CD4046 CMOS phaselocked loop would
work well here. It would produce an output signal if the frequency of
(digital) inputs differ, as they would here. I'd suggest something
like Allegro hall-effect geartooth sensors with integral magnets
because they're so easy to apply. They could easily sense screwheads
on the drive and driven parts. The CD4046 costs less than a buck and
will accept supply voltages from 3 to 18 volts DC.

You'll find a datasheet at www.ti.com Search for CD4046B.

Ping me if you're interested in this approach. I'll be back in town
tomorrow.

"Don Foreman" wrote in message
...
On Mon, 6 Jul 2009 03:05:21 -0400, "Buerste" wrote:

Imagine a simple fractional hp DC gearmotor with a torque limiter or
torque
limiting clutch that powers a small machine at 60 or so RPM. Lets say
the
machine jams and the torque limiting device kicks out. How can I cheaply,
easily sense this condition and turn off the motor?

This is a personal project and when I get it running it will amaze and
astound!

Several have suggested sensing drive and driven parts but left the
signal processing details as an exercise.

I'm in dialup-land just now so it'd be tedious to download a
datasheet, but I'm pretty sure the CD4046 CMOS phaselocked loop would
work well here. It would produce an output signal if the frequency of
(digital) inputs differ, as they would here. I'd suggest something
like Allegro hall-effect geartooth sensors with integral magnets
because they're so easy to apply. They could easily sense screwheads
on the drive and driven parts. The CD4046 costs less than a buck and
will accept supply voltages from 3 to 18 volts DC.

You'll find a datasheet at www.ti.com Search for CD4046B.

Ping me if you're interested in this approach. I'll be back in town
tomorrow.

if you are going to build your own timer, I would strongly recommend the
555 - set the timer to 2 seconds, hit the reset with the reed switch I
recommended, and wire the output to a 2n2222 in open collector mode to drive
a relay (or if a small relay, drive directly, just don't forget the
suppression diode) - minimal parts count, very cheap, easy to hook up - just
follow the schematic in the application handbook

On Tue, 07 Jul 2009 13:32:50 -0700, Bill Noble wrote:

"Don Foreman" wrote in message
...
On Mon, 6 Jul 2009 03:05:21 -0400, "Buerste" wrote:

Imagine a simple fractional hp DC gearmotor with a torque limiter or
torque
limiting clutch that powers a small machine at 60 or so RPM. Lets say
the
machine jams and the torque limiting device kicks out. How can I
cheaply, easily sense this condition and turn off the motor?

This is a personal project and when I get it running it will amaze and
astound!

Several have suggested sensing drive and driven parts but left the
signal processing details as an exercise.

I'm in dialup-land just now so it'd be tedious to download a datasheet,
but I'm pretty sure the CD4046 CMOS phaselocked loop would work well
here. It would produce an output signal if the frequency of (digital)
inputs differ, as they would here. I'd suggest something like Allegro
hall-effect geartooth sensors with integral magnets because they're so
easy to apply. They could easily sense screwheads on the drive and
driven parts. The CD4046 costs less than a buck and will accept
supply voltages from 3 to 18 volts DC.

You'll find a datasheet at www.ti.com Search for CD4046B.

Ping me if you're interested in this approach. I'll be back in town
tomorrow.

if you are going to build your own timer, I would strongly recommend the
555 - set the timer to 2 seconds, hit the reset with the reed switch I
recommended, and wire the output to a 2n2222 in open collector mode to
drive a relay (or if a small relay, drive directly, just don't forget
the suppression diode) - minimal parts count, very cheap, easy to hook
up - just follow the schematic in the application handbook

Had I bothered jumping in on this thread earlier this is pretty much what
I would have recommended. National called it a "pulse omission detector"
in their data sheets, although I don't know if Fairchild will have as
rich a selection of circuits as the 1980 National Linear Databook.

--
www.wescottdesign.com

Don Foreman wrote:
On Mon, 6 Jul 2009 03:05:21 -0400, "Buerste" wrote:

Imagine a simple fractional hp DC gearmotor with a torque limiter or torque
limiting clutch that powers a small machine at 60 or so RPM. Lets say the
machine jams and the torque limiting device kicks out. How can I cheaply,
easily sense this condition and turn off the motor?

This is a personal project and when I get it running it will amaze and
astound!

Several have suggested sensing drive and driven parts but left the
signal processing details as an exercise.

I'm in dialup-land just now so it'd be tedious to download a
datasheet, but I'm pretty sure the CD4046 CMOS phaselocked loop would
work well here. It would produce an output signal if the frequency of
(digital) inputs differ, as they would here. I'd suggest something
like Allegro hall-effect geartooth sensors with integral magnets
because they're so easy to apply. They could easily sense screwheads
on the drive and driven parts. The CD4046 costs less than a buck and
will accept supply voltages from 3 to 18 volts DC.

You'll find a datasheet at www.ti.com Search for CD4046B.

Ping me if you're interested in this approach. I'll be back in town
tomorrow.

How about this, Assuming a spring loaded ball type limiter, keyed to
input and output shafts. Leave the keys long, place a roller limit
switch (spdt) against each shaft so the keys trigger the switch.
Install one dpdt relay in the power line to the motor. Wire it so power
flows to the motor in the NC position.

The drive limit roller is wired so it passes power when the key rolls
under it. The driven side is wired NC from the output of the drive
switch, if it hits the key, it opens. This circuit goes to the relay
coil. Giving the driven side a longer dwell might be helpful.

When both are running normally, the drive switch tries to shut off the
motor every revolution, but the series wired driven switch stops the
signal from getting to the relay. If the limiter slips, the driven side
is out of line with the drive phase, and the relay kicks, then run the
second pole of that relay to latch it until reset.

2 switches (or sensors), 1 relay, 1 control transformer (unless motor
voltage matches relay coils), 1 reset switch (in latching loop).

On Jul 7, 7:04*pm, Stuart Wheaton wrote:
Don Foreman wrote:
On Mon, 6 Jul 2009 03:05:21 -0400, "Buerste" wrote:
How can I cheaply,
easily sense this condition and turn off the motor?

How about this, Assuming a spring loaded ball type limiter, ...

Two (or more) radially opposed balls between plates, the driven plate
free to slide axially against a spring and adjusting nut. Cut a
shallower circular groove or lip, slightly outside the ball recesses,
that will retain them but let the plates turn independently, at a
greater axial separation. Arrange your limit switch to detect the
shifted, stalled plate.

The trick is resetting it. Perhaps have a short spiral track the ball
follows out when tripped and back into place when either shaft is
reversed. The noise of the ball dropping into the slightly deeper
outer end of the spiral groove is the audible trip indicator.

jsw

Bill Noble wrote:

simple electronic way. Have a magnet on the rotating part. Place a reed
switch near enough that it closes every time the magnet comes by. Have a
timer you set to two seconds. Reset the timer when you presss "start", and
every time the reed switch is closed by the magnet. You can make this timer
from a 555 chip, or just buy a timer. If the timer expires, drop out a
relay to de-energize the motor.

That'll work until the output shaft stalls with the magnet over the reed
switch, holding the 555 timer in a reset state permanently.

Google "watchdog timer", or go to maxim-ic.com and search on that term.
There are one chip solutions that handle this (and other) gotchas.

--
Paul Hovnanian
------------------------------------------------------------------
It's easier said than done.
.... and if you don't believe it, try proving that it's easier done than
said, and you'll see that it's easier said that `it's easier done than
said' than it is done, which really proves that it's easier said than
done.

What's that Lassie? You say that Stuart Wheaton fell down the old
rec.crafts.metalworking mine and will die if we don't mount a rescue
by Tue, 07 Jul 2009 19:04:38 -0400:


On Mon, 6 Jul 2009 03:05:21 -0400, "Buerste" wrote:

Imagine a simple fractional hp DC gearmotor with a torque limiter or torque
limiting clutch that powers a small machine at 60 or so RPM. Lets say the
machine jams and the torque limiting device kicks out. How can I cheaply,
easily sense this condition and turn off the motor?

This is a personal project and when I get it running it will amaze and
astound!

Several have suggested sensing drive and driven parts but left the
signal processing details as an exercise.

I'm in dialup-land just now so it'd be tedious to download a
datasheet, but I'm pretty sure the CD4046 CMOS phaselocked loop would
work well here. It would produce an output signal if the frequency of
(digital) inputs differ, as they would here. I'd suggest something
like Allegro hall-effect geartooth sensors with integral magnets
because they're so easy to apply. They could easily sense screwheads
on the drive and driven parts. The CD4046 costs less than a buck and
will accept supply voltages from 3 to 18 volts DC.

You'll find a datasheet at www.ti.com Search for CD4046B.

Ping me if you're interested in this approach. I'll be back in town
tomorrow.

Don Foreman wrote:
How about this, Assuming a spring loaded ball type limiter, keyed to
input and output shafts. Leave the keys long, place a roller limit
switch (spdt) against each shaft so the keys trigger the switch.
Install one dpdt relay in the power line to the motor. Wire it so power
flows to the motor in the NC position.

If you have a spring loaded ball type limiter, then you could mount a
roller lever switch to trip when the ball/plate rides up.

--

Dan H.

"Paul Hovnanian P.E." wrote in message
...
Bill Noble wrote:

simple electronic way. Have a magnet on the rotating part. Place a reed
switch near enough that it closes every time the magnet comes by. Have a
timer you set to two seconds. Reset the timer when you presss "start",
and
every time the reed switch is closed by the magnet. You can make this
timer
from a 555 chip, or just buy a timer. If the timer expires, drop out a
relay to de-energize the motor.

That'll work until the output shaft stalls with the magnet over the reed
switch, holding the 555 timer in a reset state permanently.

Google "watchdog timer", or go to maxim-ic.com and search on that term.
There are one chip solutions that handle this (and other) gotchas.

--
Paul Hovnanian
------------------------------------------------------------------

so, just capacitively couple to the reset pin - one part, no problem.

On Tue, 07 Jul 2009 18:50:18 -0800, "Paul Hovnanian P.E."
wrote:

Bill Noble wrote:

simple electronic way. Have a magnet on the rotating part. Place a reed
switch near enough that it closes every time the magnet comes by. Have a
timer you set to two seconds. Reset the timer when you presss "start", and
every time the reed switch is closed by the magnet. You can make this timer
from a 555 chip, or just buy a timer. If the timer expires, drop out a
relay to de-energize the motor.

That'll work until the output shaft stalls with the magnet over the reed
switch, holding the 555 timer in a reset state permanently.

Google "watchdog timer", or go to maxim-ic.com and search on that term.
There are one chip solutions that handle this (and other) gotchas.
Don't use a reed switch - use an inductive pickup - passing the
magnet GENERATES a pulse, instead of switching one.

Or just put a capacitor in series with the reed switch (assuming you
are using DC - which is pretty well a given connecting to a 555 timer)
that will limit the duration of the pulse.

Don Foreman wrote:

On Mon, 6 Jul 2009 03:05:21 -0400, "Buerste" wrote:

Imagine a simple fractional hp DC gearmotor with a torque limiter or torque
limiting clutch that powers a small machine at 60 or so RPM. Lets say the
machine jams and the torque limiting device kicks out. How can I cheaply,
easily sense this condition and turn off the motor?

This is a personal project and when I get it running it will amaze and
astound!

Several have suggested sensing drive and driven parts but left the
signal processing details as an exercise.

I'm in dialup-land just now so it'd be tedious to download a
datasheet, but I'm pretty sure the CD4046 CMOS phaselocked loop would
work well here. It would produce an output signal if the frequency of
(digital) inputs differ, as they would here. I'd suggest something
like Allegro hall-effect geartooth sensors with integral magnets
because they're so easy to apply. They could easily sense screwheads
on the drive and driven parts. The CD4046 costs less than a buck and
will accept supply voltages from 3 to 18 volts DC.

You'll find a datasheet at www.ti.com Search for CD4046B.

Ping me if you're interested in this approach. I'll be back in town
tomorrow.


The old LM567 tone detector chip would work, too.


--
You can't have a sense of humor, if you have no sense!