COMMENT ⊗   VALID 00003 PAGES
C REC  PAGE   DESCRIPTION
C00001 00001
C00002 00002			COMPUTER CONTROL CONNECTOR
C00004 00003		COMMENTS ON INTERFACING THE M.I.T. MODEL ARM
C00018 ENDMK
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		COMPUTER CONTROL CONNECTOR

1	Pot +Voltage Common (+10 vdc max)
2	Ground common
3	Pot -Voltage Common (-10 vdc max)
4	Ground
5	CC Reset (momentary gnd. to disable arm)
6	Ground
7	CC Set (momentary gnd. to enable arm)
8	Gnd
9	Pot #1 Wiper-output 
10	Tach. #1 output
11	CC Motor #1 (+-10 v range)
12	CC Brake #1 (gnd. to enable)
13	spare
14	spare
15	P2 wiper
16	Tach 2
17	CC Motor #2
18	CC Brake #2
19	spare
20	spare
21	P3 wiper
22	T3
23	CC M3
24	CC B3
25	spare
26	spare
27	P4- wiper A
28	T4
29	P4- wiper B
30	CC M4
31	CC B4
32	Spare
33	P5 wiper
34	T5
35	CC M5
36	CC B5
37	spare
38	spare
39	P6- wiper A
40	T6- 
41	P6-wiper B
42	CC M6
43	CC B6
44	spare
45	P7 
46	T7
47	CC M7
48	spare
49	CC M7-hammer mode
50	Overtemp sig.(high =hot)

	COMMENTS ON INTERFACING THE M.I.T. MODEL ARM

	First a few words on the system setup. 

	The arm package consists  of three units, the arm,  the power
supply, and the  manual controller.  The manual controller plugs into
the power supply, and the arm  connects to the power supply thru  the
50 conductor 3M flat cable provided.  One end plugs into the arm, the
other into  the ARM connector on the power supply.  As one end of the
cable is polarized, it is not possible to plug it in wrong-so long as
you dont try to force things.   The best way is to lead the cable out
of the power supply underneath the  carrying handle.  This acts as  a
strain relief should the cable recieve an unintentional pull.  

	The manual controller permits computerless remote movement of
individual joints of the arm.  It also selects the operating mode.  

	There are 5 brake switches on this control.  They control the
brakes on joints 1 thru  5.  (joint 6  and the hand have no  brakes).
Joint numbering  starts at the  base (#1) and  works out to  the hand
(#7).  These switches absolutely  turn their proper brake  off.  They
AND to  turn  their proper  brake  on.   The  arm can  be  physically
positioned  using  only  the  brake  switches  (MODE  switch  in  any
position, including OFF is OK).  Just turn a joint brake off and move
that joint with your hands. 

	The MODE  switch selects the  function.   OFF means only  the
brake switches function  (Both OFF positions are the same).  COMPUTER
means that  the computer  controls the  ARM.   The numbered  and HAND
positions refer to the manual control mode where turning the VEL knob
+  and - makes the selected joint move +  or -.  Turning the VEL knob
does two things.  It first turns off the selected  joint brake and at
the same time commands a  joint velocity.  This commanded velocity is
proportional to the knob displacement, but also dependent on  gravity
and load torques on the particular joint.  To properly use this mode,
keep the  brake switches in ON position, as  their off position is an
absolute OFF. 

	There are  two more  buttons  on this  controller.   The  RED
button is the  stop button when operating in COMPUTER  mode.  Pushing
it  momentarily will disable the  arm.  This means  the arm will stop
where it is and the brakes will turn on.  To re-  enable the arm, see
the section  under computer control.  The  BLACK button is the impact
mode on the hand.   Pushing this button  WHILE turning the VEL  knob,
with HAND mode selected will cause the hand to see a rectangualr wave
drive   signal  whose  duty   cycle  is  proportional   to  VEL  knob
displacement.  This will either cause the hand to tighten its grip on
an  object,  or else  release  its  grip.    CAUTION- use  this  mode
sparingly,  as it heats the motor up  and also causes more rapid hand
screw wear.  

	Some observations on the manual operation of the  arm.  Under
manual control,  the maximum speeds of  the arm are  much slower than
the  maximums  under  computer  control.    In  addition,   the  joint
strengths are slightly reduced.  Do not hold a joint against its stop
too  long.  If  no motion  is taking place,  let the VEL  knob center
itself.   This reduces motor  heating.   The power  supply has  motor
temperature  sensors in  it.   If you  do keep  a joint  on too  long,
especially  at high current levels, the  overtemp sensor will disable
the arm until the motor cools a bit.  The hot joint will be indicated
by its  correspondingly numbered LED on  the power supply.   DONT run
the arm into its stops too  frequently.  The arm stops are  primarily
to keep the joints from winding up.  Properly operated the arm should
never run  into its stops.   Just like with a  person- its painful to
move a joint to its limits of motion, expeciall at high speed.   This
caution is very improtant under  computer control where maximum joint
velocity is much higher. 

	COMPUTER CONTROL

	The other 50 pin 3M connector comming out of the power supply
is  for  connection  to  a  computer  interface,  or  other  external
hardware.   The accompanying pin chart lists  the pin assignments for
this connector.   A  summary  follows.   Pot  voltage means  the  pot
reference supply terminals.   Customer must supply his  own precision
supply.   This should be  compatible with the A/D  used.  Typically a
+-10 vdc supply is used.  This supply should be capable  of supplying
at least 250  ma.  Ground or Gnd. or  Ground Common terminals are all
tied  together and represent  the ground  terminals.  CC  refers to a
Computer  Command  terminal.   These  are  Motors  (M1,  etc)  Brakes
(B1,etcc.), and Enable  and Disable.  The Motors accept  a +- 10 vdc.
signal range at  10 ma. max.   This corresponds  to full  scale motor
current.  The power supply contains current  amplifiers.  These amps.
output  a motor current  proportional to  the voltage input  from the
computer on the  CC M1 (etc.)  terminal.   The Brake input  terminals
accept a high (can  be TTL or floating) or Low (TTL low  or GND) at 1
ma.  to trun  the brakes  on or off.   LOW  means the  brakes are ON.
There is  also the CC  SET and  CC RESET  leads.  These  are used  to
enable or disable  the arm (all joints at a  time).  Grounding CC SET
enables the arm, while grounding CC RESET disables the arm.  This can
be done  with TTL logic,  and only requires  a momentary pulse.   The
reset  function is ORed  with the RED  button on  the manual control.
Its a good idea to trun the brakes on with the computer  before doing
your first ENABLE  or else the arm may fall.   Also, its advisable to
have a timeout on the ENABLE so that if the program dies the arm will
stop.  Thus a 100 ms. timeout is a good thing.  The software can give
enables every  100 ms. and a  hardware timer can be set  to trigger a
RESET in 100 ms.  if no new RESET is recieved. 

	On the  output side,  The Pot  Wiper terminal  are the  joint
position signals comming directly from the pots on each joint.  Their
rande  will be about  90% of the  Pot supply voltage,  execpt for the
hand which is only about 20% at present.  On joints 4 and 6 there are
two wipers spaced about 180 degrees apart.  This allows for more than
about 340 degrees of joint motion as one wiper is always in an active
region on the pot element.   The computer must have an  algorithm for
selecting the proper wiper to  use.  Starting algorithms must also be
carefully t out if both  wipers are to be  properly used.  Of  course
many useful tasks can  be done with the more  limited motion resolved
by just a single wiper.  The pots are not highly linear devices. This
doesnt matter  if  Unimate type  of  operation  is desired,  but  for
computer planned motions, a table  lookup procedure must be sotred in
the computer. 

	Joints 1  thru 5 have mechanical tachometers.  Joints 6 and 7
have electronic tachometers.   In all cases, the output  signals have
been  amplified inside  the power:supply.   This  scaling  results in
larger than raw output. Due to ellectronic circuitry constraints, the
tach readings will be  affected by turning the VEL knob  even when in
COMPUTER mode.   Thus, keep your hands off this know when reading the
tachs, or running in computer mode.   Joints 6 and 7 have  electronic
tachometers.   These are  electronic circuits which  measure the back
EMF  of the  motor  and attempt  to cancel  out the  armature losses.
Unfortunately, this is not too accurate a process, but  it does serve
its  purpose of providing  a damping  signal for use  improving servo
stability.  The output of these electronic tachometers is about +-  3
volts full scale.  The other tachs have 6-10 volt full scales.  

	The CC M7 Hammer lead refers to the input for the hand hammer
mode.   The  hammer mode  duty  cycle is  proportional to  the signal
amplitude.  Actually,  it is  probably better to  operate the  hammer
mode from software directly into the CC  M7 input.  This way the duty
cycle  and frequency can  be program changed easily.  One less output
channel is needed too.  Remember, take it easy in using this mode. 

	The joint hot output is  normally low.  it will go  high when
the arm is hot and has  stopped because of a hot motor.  This is just
a status bit so the computer can keep track of what has happened.  As
with all other digital inputs, it is TTL compatible.