Re: Digest Number 2321

Hello,

Another tip from the old days:

The Underwriter's Laboratories "cheese cloth test" may be used for identifying unacceptable hot spots on circuit board components. This method is for testing only. A piece of cheese cloth is placed over the electronic components. The equipment under test is powered for 24 hours with typical loading and all enclosure covers in place. After 24 hours, any signs of discoloration of the cheese cloth will indicate the location of unacceptable temperature levels. The cheese cloth should be removed after testing due to potential fire hazzards.

More modern methods include the use of marking components with pens that disperse heat sensitive ink and the use of miniature heat sensitive adhesive labels that are affixed to the components.
Of course infrared optical pyrometers and conventional thermocouples are also widely used.

For mounting components to heat sinks in power electronic circuits, we use fully torqued allen machine screws with hardened hex nuts in conjunction with silicon grease to achieve maximum heat exchange and to prevent component failures.

Ned

--- In CAD_CAM_EDM_DRO@y..., "Paul Weber" <pbweber@j...> wrote:
> Hello list,
> I thought I would pass on a tip from the old days. I you mount heat sinks
> to the power fets, transistors with nylon screws it makes troubleshooting
> easier. When the smoke comes out the part gets hot. A melted mounting
> screw is a sure sign of over heating.
> Paul
> ----- Original Message -----
> From: <CAD_CAM_EDM_DRO@y...>
> To: <CAD_CAM_EDM_DRO@y...>
> Sent: Saturday, May 18, 2002 9:41 AM
> Subject: [CAD_CAM_EDM_DRO] Digest Number 2321
>
>
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> > ------------------------------------------------------------------------
> >
> > There are 3 messages in this issue.
> >
> > Topics in this digest:
> >
> > 1. Re: Digest Number 2320
> > From: Ray Henry <rehenry@u...>
> > 2. Re: CNC robotic welding arms
> > From: "rainnea" <rab@r...>
> > 3. Software for sale on the list Slight change in Prcedure.
> > From: wanliker@a...
> >
> >
> > ________________________________________________________________________
> > ________________________________________________________________________
> >
> > Message: 1
> > Date: Sat, 18 May 2002 08:18:54 -0500
> > From: Ray Henry <rehenry@u...>
> > Subject: Re: Digest Number 2320
> >
> >
> > Jon, Babar
> >
> > I disagree but not violently. The names of all five files can be changed
> and
> > still make a working system. As Jon points out you change the ini file
> name
> > in the run file. The others are changed in the ini file. What Jon may be
> > thinking of is trying to change a file name while the EMC is running.
> > Several of us have fallen into that trap at one time or another.
> >
> > By way of example, I want to use a custom .nml file if I plan to run or
> view
> > machine progress over a network. When I do several different small lot
> parts
> > I save .tbl files and name them along with the part program file. I also
> use
> > the var file to save parameters and variables from one run to the next.
> For
> > one project here I engrave serial numbers and keep the last one as a
> variable
> > in a specific ini. In general, I keep a separate specific personality for
> > the EMC under each major project. This includes all five of these files.
> >
> > HTH
> >
> > Ray
> >
> > > From: Jon Elson <elson@p...>
> > > Subject: Re: How to setup STG-II?
> > <s>
> > > But, the other files, (xxx.var, xxx.nml, xxx.tbl) should have the names
> > > emc.var, emc.nml, emc.tbl to be used by emc. (In general, you shouldn't
> > > need to modify these files outside of EMC anyway, so using the standard
> > > names shouldn't cause much of a problem.) My understanding, unless
> > > things have been changed (possible, since I still use an old version of
> > > EMC) is that these files are always used as emc.var, emc.nml, and
> emc.tbl
> >
> >
> > ________________________________________________________________________
> > ________________________________________________________________________
> >
> > Message: 2
> > Date: Sat, 18 May 2002 13:49:50 -0000
> > From: "rainnea" <rab@r...>
> > Subject: Re: CNC robotic welding arms
> >
> > Thanks for the info on the EMC files.
> > As I understand it, EMC can handle all these calculations and would
> > be the ideal method in theory, but has some rotational velocity
> > issues in practice ?
> > I'd imagine that it may just be easier and provide more flexibility
> > to use a 3D animation program designed and perfected to handle very
> > complex kinematics (and able to visualise them) to work out all of
> > the joint / axis movements and then from there, output the
> > coordinates that each axis has to move to in order for the toolpoint
> > for follow a subdivided toolpath.
> > >From this, the CNC controller would be able to handle the translation
> > of these axis movement coordinates into step and direction signals
> > while being totally unaware of the configuration of the machine if
> > (and this is the problem) it could determine how fast each axis
> > should travel for each move.
> >
> > One method that kind of works is to set a maximum feedrate per axis,
> > for example, when using a 3-axis controller to do rotary machining
> > where the Y-axis controls the rotation of the part and the controller
> > doesn't know how far the toolpoint is really moving but calculates
> > the feedrate based on the maximum feedrate set for the Y-axis as if
> > it were a linear axis. This at least gives smooth and predictable
> > movement but the axis feedrates would be the same whether the tool
> > was cutting near the centre or at the outer radius of a rotary part,
> > giving very different toolpoint velocities.
> >
> > Another method, not without its disadvantages, but that may be very
> > effective is tagging the distance that the tool tip is actually
> > moving relative to the material onto each line of G-Code containing
> > the axis movements (as opposed to the tool movement). The distance
> > value would be used to calculate feedrate or it could even be
> > replaced with a feedrate or time value. Would this be enough for the
> > controller to generate proper constant velocity movement at the
> > toolpoint?
> >
> > For example, take a hexapod machining over a cusp or sharp point of a
> > surface where the tool is changing angle rapidly but the toolpoint is
> > actually moving very little in relation to the material. Using the
> > above method would mean a series of six-axis coordinates for the six
> > hexapod struts to move to, along with corresponding values that
> > correspond to the distance that the toolpoint is actually moving. The
> > controller would move the hexapod struts, coordinating their
> > acceleration / deceleration, target and max velocity not knowing or
> > caring about the physical arrangement of the machine, but just how
> > long these axis movements should take. The same should hold true for
> > other 4 and 5 axis arrangements.
> > Could / should this method work ?
> >
> > Rab
> >
> >
> >
> >
> > ________________________________________________________________________
> > ________________________________________________________________________
> >
> > Message: 3
> > Date: Sat, 18 May 2002 11:09:45 EDT
> > From: wanliker@a...
> > Subject: Software for sale on the list Slight change in Prcedure.
> >
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> > bill,
> > List Mom
> > List Owner
> >
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