| |
In lugnet.technic, Mark Bellis wrote:
[SNIP]
Hi Mark,
>
> Kevin,
>
> I think "differential output" is what I really meant, though I called it "no
> leak" because the supply never leaks, one output or the other is always
> pressurised and there is never a state where both outputs leak. There is also
> only one place where the leaking output leaks on the XOR and XNOR gates, from
> the single switch - subsequent parity stages have no leaks at all. The idea
> behind it was to have full control of both outputs in all possible states, since
> that is also the goal of a finite state machine. It suits me being a control
> freak :-)
I figured that if you're going to write an article for BrickJournal on pneumatic
basics up through sequencers, you would probably want to talk about the simplest
gates, the single output gates. If not, I'll write up a followup article that
talks about them.
Well, any gate design that leaks the source pressure is a broken. It seems like
you use leak to sometimes mean pressurized. For example here: In my mind, all
leaks are bad.
> one output or the other is always
> pressurised and there is never a state where both outputs leak.
Do you mean both outputs are pressurized?
>
> I use differential output gates because the output is suitable for driving the
> input of the next gate, so these circuits are building blocks. To invert the
> output, swap the output hoses. To invert the input, swap the input hoses.
Yes, NOT is free!
> My differential gates are suitable for driving load-bearing cylinders because
> there will be minimal pressure loss in the gate when the inputs change to
> another state that has the same output. That was another requirement of the
> design, which is helped by using as much flex tube as possible. The
> load-bearing functionality was the main reason for having no leaks.
Mine are also designed to always have pressure available at one and only one
output at a time.
My four switch AND-gate minimizes pressure loss by having the minimum number of
hoses inherint in the gate.
On this aspect of gate design, can you compare and contrast your AND gate and
mine? Should I be concernted about minimal pressure loss? How do your gates
minimizing this?
>
> Another thing was to avoid any gate being transparent. This means, similarly to
> electronic flip-flops, that the input can't go through to the output without a
> proper change of state. In a transparent electronic D-type flip-flop, if the D
> input changed, the Q and !Q outputs would change with it. In a non-transparent
> flip-flop the change of Q and !Q has to wait for the data at D to be clocked
> into the flip-flop, such that it changes state. This avoids logic races in
> electronic flip-flops and it was also something I wanted to avoid in pneumatics,
> in order to be sure of the next state of the system at all times and prevent
> movement into an undesirable or lock-up state.
I understand transparent latches, but I'm not sure I understand how that concept
relates to here.
Can you tell me on my four switch, two output AND gate, how it might allow for
undesirable transparency.
> Another featurge of my designs is that the input need not necesarily be a
> pneumatic function. All that is required is something that moves a set of valve
> switches, so it could be a motor or hand input. I've not yet tried adding
> machines but I could make one on the same basis as a binary full adder from an
> electronics book, using and AND gate and an XOR gate for each of two half adders
> and and OR gate for the summation.
This is a given in my AND, and XOR gate design, and very doable with my OR gate
design.
I have made a half adder based pneumatic/electronic adding machine, and a full
adder based pneumatic/elecronic adding machine. This was was published in
"Mindstorm Masterpieces", a book I coauthored. I used a clock mechanism to save
the carry from bit column to bit column (I pressurized the input switch that
drove the carry piston, and then depressurized it before I changed the inputs.)
I'm sure my most recent gate designs would work even better as a full adder.
Smaller part count, means much cheaper when talking pneumatics.
>
> Don't blame me, I'm just an electronics engineer :-)
I'm a computer engineer, so I have similar understanding. I'm just trying to
understand why you feel six switches are neccessary to make a "differential
output" AND gate.
> I do use single switch ANDing on enable lines, where I need only one pressure
> and not a differential output. I use enable lines to interupt the air supply to
> a set of cylinders, so the enable is a gated air supply to the middle port of a
> switch, such that a cylinder can't move either way if it is not enabled. I
> haven't yet applied an enable line to only one port of a cylinder because the
> system might end up with either pressure on both ports or a leak on both ports,
> both of which I want to avoid. For enable lines I apply the supply to the
> middle switch port and take the output from one side with a stopper on the other
> side. The supply must never leak.
In my walkers I use single output/single switch AND gates all the time (except
SSC1, that used one of my four switch AND gates with differential outout). When
using the single switch AND gates to drive both ports of a cylinder, I work out
in the timing diagram where these can occur, and I eliminate them by ANDing one
of the piston inputs with the NOT of the other piston input.
For the most part, the muscle pistons are also timing pistons. Typically my
circuit is made of only single switch/single output AND gates. There are lock
up problems when a piston does not complete its transition due to outside
forces.
> On the first of your gates, are you feeding pressure A into the cylinder and
> also through a B switch to the AB port?
This A pressure could just as easily be directly from the pump. Pressure never
goes through that switch unless there is pressure at the A input.
>
> Also, you seem to be addressing hose pressures as the objects that have a state.
> I have always used valve positions as the objects that have "0" and "1" states.
Do you want to only look at gate outputs, or are you willing to also look at the
nets that come out of them.
The switch state alone cannot tell you the pressure at either differential
output. You must know the inputs to be able to truly tell.
> This means that, assuming the centre port is pressurised, in state "0" the right
> port is pressurised whilst the left port leaks, and vice versa.
Lets look at the simplest single switch AND gate.
The piston position, controlled by pressure at the pistons expand or contract
port, controls the position of the switch. This alone does not tell you whether
there is pressure at either of the switches right or left ports. You must know
whether there is pressure or not at the center port to truly know if there is
pressure at the right or left port of the switch.
In the single switch/piston design, if I call the piston A, I think of switch
output port closest to the piston as A, and the switch output port farthest from
the piston as NOT A. This is only really true if the center port of the swtich
gets pressure directly from the pump.
If you run pressure from piston B's expand port into the center port of piston
A's switch, the outputs of the switch become A AND B and NOT A AND B, where A
AND B comes out of the port farthest from the piston.
Right and left do not help because you can make mirror images of the gates, get
the proper function, yet all your rights and lefts in descriptions are wrong.
>
> I looked at your 4-switch dual pressure AND gate, assuming that the "B" input is
> from another valve switch, but it appeared to cause both outputs to leak in 0-1
> or 1-0 states, due to the mismatch between the two hoses from the B switch (into
> B and !B ports) and he states of A and B. What parts are used that don't appear
> in the diagram?
You are talking about glitches? I think that the only thing that could cause
glitches is the transition of A from expanded to contracted, and contracted to
expanded. I'm not sure how we can get glitches when there is a large portion of
the handle sweep that the switch is not providing pressure out either port.
Please explain how these can happen.
>
> Solving the 0-1 and 1-0 mismatch was what pleased me most about my AND gate
> design.
>
> Mark
This is fun!
Kev
|
|
Message has 2 Replies:
Message is in Reply To:
32 Messages in This Thread:
  
 
- Entire Thread on One Page:
- Nested:
All | Brief | Compact | Dots
Linear:
All | Brief | Compact
This Message and its Replies on One Page:
- Nested:
All | Brief | Compact | Dots
Linear:
All | Brief | Compact
|
|
|
|
