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filedate 1975-02-26 generic text, type C, neo UTF8
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C00002 00002 A DISSERTATION PROPOSAL
A DISSERTATION PROPOSAL
December 31, 1973
The automated machine shop. Two possible routes, both
viable, one a lot more ambitious than the other. The more immediate
sort of automated machine shop- the interactive machine shop. The
more ambitious type of shop- the completely automated shop. I will
discuss my thinking on these two proposal alternatives.
The interactive machine shop.
Presently, most prototype machining is done manually with no
numerically controlled machines being employed. The prime reason
given is not economics, but the fact that the machinist must really
be there to make the first part. N.C. machine programming methods
today require an average of 3 rounds of iteration to make a
successful part. Thus, for short runs, the N.C. machine-programming
debugging operation offsets the advantages of the machine's high
speed and errorless machining ability.
Generally, programming of these N.C. machines is not done by
the machine operator, but by a programmer who usually happens to be
either an engineer, or an ex-machinist who has had special training.
The operation works like so. The shop recieves a print from the
engineering department. The foreman looks the print over and decides
how to make the part. If the quantities are large enough, he may
decide that n.c. machining may be the best way. In this case, he
will turn the drawing over to a programmer who will use either a
Flexowriter, or in larger establishments a mini-computer and the APT
programming language to create a program tape for the n.c. machine. A
part will be attempted. Only in rare cases will the first part be
completely successful, as even the best programmeers have difficulty
n picking the proper machining speeds for all cuts, or accounting for
part or tool deflection, or insuring that no interferences occur in
the cutting sequence. In just about every case, the programmer ends
up watching the first and second and thrid part goo thru the machine
while making corrections to the program. Frequently as many as ten
iterations are required to successfully make a part.
My first proposal is for a more interactive approach to this
machining operation, involving more computer use with a standard n.c.
machine. Here is what I envision. Think of the following layout.
You have a prototype machine shop- execpt it is equipped with n.c.
machine tools (in addition or instead of the conventional manuallly
controlled tools). A computer terminal from a large timeshare
computer also is in the shop. In addition there is a machinist. This
fellow may not be too skilled a programmer, but merely a person
capable of taking instructions and making judgements about what is
good machining practice, and who also knows what his machines can do
and what they can't do.
In the full blown version of this interactive shop, a
part gets designed by an engineer sitting in front of a display
console. Here he has the ability to manipulate geometric shapes and
call in subroutines of fixed configurations, to create a part which
he then wishes to make. Maybe he will design a complete device
consisting of several parts, some purchased, some made, and some
modified pruchased parts. Each part can be detailed separately on
the screen, and then dimensioned so that it will fit into the whole
system, using a computer aided dimensioning system which would have
knowledge of standard machining tolerances, and practices. The
program would also have knowledge of other constraints, such as
dimensions or shapes of purchased components which fit into th
system. By making several passes at the program and reviewing the
finalized assembly and dimensioned drawings, the engineer can operate
interactively with the computer to produce a system with all the
proper component tolerances, dimensions, and configurations which
satisfies him, and also represent a reasonable machining task.
Next, the engineer "sends" the layout and drawings to the
machine shop. This means that the computer makes up a machining tape
per the design drawings, and supplies a list of required material to
the shop. Here the machinist has a say of what the shop has in
stock, and what kinds of jigs and fixtures to hold the parts the shop
may have. His input is back to the computer in the form of
answering questions put to the shop by the computer. These questions
await simple replies, such as the stock dimension, or the location of
a corner of the stock or part on the mill table, or the size of
cutters available. Based on this information and a built in program,
the computer creates a first pass n.c. tape. The machinist, who may
have a reference set of drawings at hand so that he can spot obvious
errors, sets up the machine per the instructions, and then starts the
operation. Rough cuts are performed and unless the operator notes
any fatal errors, the machining sequence proceeds with the computer
giving the machine AND the operator new instructions from time to
time. Feedback from the operator is accepted and computer updates
in the machining operation are made as needed. Typical feedback
information will be in the form of answers to various questions posed
by the computer- such as cutting speed ok? or can I take a deeper
cut?, etc. The response will be in the form of simple Y and N or
number type answers. Requests for dimension measurement may come as
the part nears the finished dimensions. Here the computer will
request that the operator measure the thickness of a part, or the
diameter of a bore, or the taper of an edge. The data is fed back to
the computer and serves to update the program to accomodate for the
particular errors inherent in the machine, or the setup. Furthur
instructions such as requesting a statement of the surface finish, or
requesting that an edge be deburred, or requests that a cutter be
changed, or that a hole be hand tapped, or even that the operator do
a particularly sensitive cut where extra careful observation of the
cutting operation may be required. These commands would all come to
the operator through the remote trminal which could be a teletype or
In a more advanced sort of system, the data link
between machine and computer could be improved with the incorporation
of direct force feedback, so that cutter forces, or cutter
temperature could be fedback to the computer. Even sounds and some
special purpose sensor outputs could be used to furthur improve the
speed and accuracy of the prototype machining operation.
This completes an outline of a proposed development of an
interactive prototype and short run machine shop. I consider it a
very realistice type of proposal. Several parts of this proposal
could be implemented quickly right here at Stanford. I have talked
to some of the people in the Department of Chemistry, and they have
expressed interest in a project of this sort. Their shop is
presently just about the best shop on campus, but it lacks any n.c.
machines. In fact, I doubt that there are any n.c. machine tools at
Stanford University, with the possible execption of SLAC. With
machine shop costs of $12 per hour and up, it appears that this
interactive approach is a viable way to speed up the production of
prototype and short run production parts, at a large savings in cost.
Back to the Chemistry Dept. Besides having the best shop on campus,
(machines and facilities), they also have some of the most capable
machinists, one of whom is a trained operator of n.c. equipment from
a previous postion at Hewlett-Packard. Because of this quality
shop, the Chemistry Dept. has a very positive attitude towards
acquisition of new equipment and thus there are funds available for
the purchase of an n.c. milling machine(for example). Here is a
really good chance for several graduate theses, in the Computer
Science , Mechanical Engineering and Interdepartmental Fields.
A DISSERTAION PROPOSAL
December 31, 1973
A continuation of Prop2.
The totally automated machine shop.
The concept of the totally automated machine shop was brought
removed and placed in a shear or saw very easily by a manipulator.
up in Prop1. This earlier discussion outlined some of my thinking
regarding the possibilities of developing a completely automated
machine shop in which the operator would be a computer and a
mechanical arm. The input would be an interactively created design
and the output a finished part or eventually a product manufactured
to the description created by the designer.
As a starting point, I will give a brief description of how I
see the general prupose shop working. First lets look at the layout.
Imagine that we have a large timeshare computer, and a high data rate
link to a machine shop. In this shop are a number of machines all
n.c. type or else powered such that either electrical switching or at
the most low mechanical forces are required to make them perform all
tasks. They are all located in known locations, and each has a well
stocked accessory holder. A stock room with a good supply of stock
material is near the tools. This stock is stored so that it can be
Besides these machines there exists one or more mechanical
manipulators which can move around to all of the machines and perform
various operational tasks on these machines, just as a human operator
does. The machines, the manipulators, and the associated
accessory and sensing devices are all interfaced to the computer so
that they are directly controlled (thru a mini-computer if
Now lets look at a typical sequence of operation. An
engineer sits down at a graphics display console. His task is to
create a working device of some sort. This device is part of a
system. There are several parts to the device, some purchased,
others made from purchased stock, and still others modifications of
purchased completed components. These parts must all fit together
and operate as a device, and the device must operate properly in the
completed system. Using GEOMED or a similar interactive
display-graphics program, the engineer can reate shapes and structure
on his console and manipulate these developed bodies at will. As
engineer are generally rather realism oriented people, the graphics
program will probably be oriented to display shapes and forms in a
manner which is easily interpreted by the design engineer. A
library of pruchased component dimensions and specifications along
with standard engineering dimensions and details can also be called
by the designer or directly by the computer, as would be the case
when placing screw holes, or selecting screw or shaft sizes.
Assume that the design is done, the designer looks over what
he has created on the screen and sees that everything is correct; the
program has picked the proper screws, has matched up all the bolt
patterns properly, and has chosen the right tolerances. Now a
manufacturing operations program can be called in. This gives the
operator a list of the proposed machining operations and a list of
the stock required, and the estimated time and cost. A breakdown
gives the details, so that the designer can change dimensions or
specifications to reduce costs, or get around difficult or impossible
operations. Once this iterative operation is completed, the required
setup list and stock list is compared with the shop inventory. If
they are complete, the machining can begin.
Following the computer generated sequence commands the
machining operations are performed. The individual machines are
directly controlled by the computer using position feedback and
feedback from permanently mounted motor current and temperature
sensors, force sensors, etc. Setting up each machine, changing
tools, and transferring material are the mechanical manipulators.
These arms serve the same purpose as the human operator in the
typical n.c. machine shop. In addition, they provide the computer
with a device for positioning measuring instruments, checking on
surface finishes, and making all the necessary observations that are
required of a human macchine operator. This information is fed
directly back the computer for updating of the machining sequences.
In this way, the shop need not be a very precisely set up layout.
Real machines setup almost casually can be used in such a situation
where feedback is sufficient.
The task is complete when the finished parts are delivered to
the output box, just like line printer output. Possibly, even
assembled into a complete assembly, properly inspected, tested,
documented and certified.
Certainly, the development and execution of a complete,
general purpose system such as has just been described is no
overnight task. A number of man years effort is involved, both in
the programming and the engineering of such a system. The execution
of such a problem is beyond the cope of a single PhD thesis
dissertation, but a thorough study of the problems and approach to
such a project may very well be a good thesis topic. But, as an
alternative to a paper study of such a general purpose completely
automatic system, it seems reasonable to attempt the development of a
special purpose automatic shop as a more realistic initial goal.
What follows are some thoughts on a special purpose completely
The automated sheet metal shop.
Prototype sheet metal parts are very expensive relative to
production quantities. As an example, it is frequent to find that
the cost of just two of a kind is only 5% more than the initial one
piece. Why is this so. Well, there has never been much automating of
sheetmetal processes, other than blanking and stamping which are
restricted to large production runs. Other than n.c. punches and
n.c. stops on hand fed shears, there are no other really automatic
machines used in this field. It has been considered a hard to
automate field, because of the types of machines used and the need to
do a lot of manipulating of the material which can frequently be
large floppy sheets, of varying thicknesses, yield strength, and