Re: Encoders
Posted by
Ted
on 1999-06-28 22:20:44 UTC
rtr@...
Ted Robbins
The best way, easiest if you have a schematic, is to probe the wires from
one of the encoders to the pc board. There are probably four to six wires
coming out of the encoder.
One of them, probably black, will stay at ground when you turn the encoder.
This wire is probably the power ground wire. It may also be the signal
ground wire if there are only four wires coming out of the encoder.
Another wire, probably red, will stay at the applied positive voltage,
usually five volts, even when you turn the encoder. This is the positive
voltage source which is paired with the common or negative voltage source
wire described above. Sometimes it is higher, between 6 and 15 volts.
This often means there is a voltage regulator within the encoder, helping
make it more noise immune.
The remaining two wires will usually be the two square waves coming out.
This will be easy if there are only two wires remaining. One will be
channel A and the other will be channel B. Remember, channel A leads
Channel B by 90 degrees when turned clockwise like a clock (WIth luck).
Just synch or trigger on one of the square waves and note whether the other
square wave goes positive or negative 90 degrees after the positive trigger
of the first wave.
For those of you who are better machinists than me, but worse electronics
nerds, a full 360 degree cycle of one of the waves is one positive going
and one negative going square wave. If one wave leads another by 90
degrees, or a quarter of a full cycle, the lagging wave will go to its
positive voltage just after the first, or leading wave. If the second wave
goes down, usually to zero, just aftert the triggering wave goes up, then
the second wave really is the leading, or signal A, not signal B.
Now for the hard part, the other wires. Often there are one or two signal
ground or signal common wires. These two terms really mean the same thing
here. They are often twisted around the wires with the square waves on
them and running beside the square wave traces on the circuit board. They
are seperated from the power ground to keep the electrical noise on the
power ground from affecting the square wave signals.
Sometimes there is also an index signal, another track on the disk that has
only a single slot so you know where the home position of the disk is.
There is always a single wire with this signal, seen when you turn the disk
more than a full turn. It may share the signal ground with the A and B
channels, or it may have a signal ground of its own. It is sometimes
labeled channel C and sometimes labled channel Z and sometimes labled
Index.
Getting the resolution of the encoder, ie; how many slots per turn.
Mark the shaft of the encoder so you will know when it makes a complete
turn. Turn the encoder one full trun slowl, counting the positive going
transitions, You can do all of this with a multimeter if it isn't a real
fine resolution encoder. Look for numbers on the encoder, usually the last
few of the string of numbers you may be lucky enough to find. These
numbers should agree with your count. Typically, they will be a decimal
number like 50 or 125 or 1000, or a binary number like 128, 512, or 1024.
Sometimes there will be four channels to provide direct english and metric
information, for instance one channel pair might have some multiple of
1000 while another channel pair might have a multiple (Or submultiple, of
course) of 2400 to make the metric, english information readily available.
Such an encoder would not be found on a printer.
Niether would absolute encoders with many channels, each coded to a coarser
reading than the outermost channel to provide direct information of the
encoder's position, even when power fails and is turned back on. Multi
turn encoders are built for the same safety information over applications
that require an encoder to make many turns and still give good location
information after power failure. Again a printer doesn't need such an
expensive encoder. It can be programmed to reset its reference zero
position by moving back to its limit of travel when the printer power is
applied.
With this information and some luck it should be possible to figure out the
wires coming from the encoder while it is in its original circuit. Since
the output circuit in the encoder may be an unterminated transistor when
the encoder is removed from the circuit, you will want to trace out the
transistor or IC that the wires from the encoder go to. Usually, the
circuit has a pull up resistor or totem pole transistor built right in,
but don't bet on it.----------
Good luck, and I do a lousy job of threading.
Ted Robbins
The best way, easiest if you have a schematic, is to probe the wires from
one of the encoders to the pc board. There are probably four to six wires
coming out of the encoder.
One of them, probably black, will stay at ground when you turn the encoder.
This wire is probably the power ground wire. It may also be the signal
ground wire if there are only four wires coming out of the encoder.
Another wire, probably red, will stay at the applied positive voltage,
usually five volts, even when you turn the encoder. This is the positive
voltage source which is paired with the common or negative voltage source
wire described above. Sometimes it is higher, between 6 and 15 volts.
This often means there is a voltage regulator within the encoder, helping
make it more noise immune.
The remaining two wires will usually be the two square waves coming out.
This will be easy if there are only two wires remaining. One will be
channel A and the other will be channel B. Remember, channel A leads
Channel B by 90 degrees when turned clockwise like a clock (WIth luck).
Just synch or trigger on one of the square waves and note whether the other
square wave goes positive or negative 90 degrees after the positive trigger
of the first wave.
For those of you who are better machinists than me, but worse electronics
nerds, a full 360 degree cycle of one of the waves is one positive going
and one negative going square wave. If one wave leads another by 90
degrees, or a quarter of a full cycle, the lagging wave will go to its
positive voltage just after the first, or leading wave. If the second wave
goes down, usually to zero, just aftert the triggering wave goes up, then
the second wave really is the leading, or signal A, not signal B.
Now for the hard part, the other wires. Often there are one or two signal
ground or signal common wires. These two terms really mean the same thing
here. They are often twisted around the wires with the square waves on
them and running beside the square wave traces on the circuit board. They
are seperated from the power ground to keep the electrical noise on the
power ground from affecting the square wave signals.
Sometimes there is also an index signal, another track on the disk that has
only a single slot so you know where the home position of the disk is.
There is always a single wire with this signal, seen when you turn the disk
more than a full turn. It may share the signal ground with the A and B
channels, or it may have a signal ground of its own. It is sometimes
labeled channel C and sometimes labled channel Z and sometimes labled
Index.
Getting the resolution of the encoder, ie; how many slots per turn.
Mark the shaft of the encoder so you will know when it makes a complete
turn. Turn the encoder one full trun slowl, counting the positive going
transitions, You can do all of this with a multimeter if it isn't a real
fine resolution encoder. Look for numbers on the encoder, usually the last
few of the string of numbers you may be lucky enough to find. These
numbers should agree with your count. Typically, they will be a decimal
number like 50 or 125 or 1000, or a binary number like 128, 512, or 1024.
Sometimes there will be four channels to provide direct english and metric
information, for instance one channel pair might have some multiple of
1000 while another channel pair might have a multiple (Or submultiple, of
course) of 2400 to make the metric, english information readily available.
Such an encoder would not be found on a printer.
Niether would absolute encoders with many channels, each coded to a coarser
reading than the outermost channel to provide direct information of the
encoder's position, even when power fails and is turned back on. Multi
turn encoders are built for the same safety information over applications
that require an encoder to make many turns and still give good location
information after power failure. Again a printer doesn't need such an
expensive encoder. It can be programmed to reset its reference zero
position by moving back to its limit of travel when the printer power is
applied.
With this information and some luck it should be possible to figure out the
wires coming from the encoder while it is in its original circuit. Since
the output circuit in the encoder may be an unterminated transistor when
the encoder is removed from the circuit, you will want to trace out the
transistor or IC that the wires from the encoder go to. Usually, the
circuit has a pull up resistor or totem pole transistor built right in,
but don't bet on it.----------
Good luck, and I do a lousy job of threading.
> From: TADGUNINC@...determine
> To: CAD_CAM_EDM_DRO@onelist.com
> Subject: Re: [CAD_CAM_EDM_DRO] Encoders
> Date: Monday, June 28, 1999 8:10 PM
>
> From: TADGUNINC@...
>
> Another quick question,
> I have several older commercial printers, is there any way to
> the number of slots, cpr? I have a scope and a means of powering them up.discussion of shop built systems in the above catagories.
> Tracey
>
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