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SISOM – 2004, BUCHAREST, 20-21 May
POSITIONING CONTROL OF TRANSLATION MODULE USING
INCREMENTAL TRANSDUCERS
Ion Florin POPA, Mihăiţă ARDELEANU, Cornel MARIN, Mihaela VOICU
VALAHIA University of Targoviste, [email protected]
Abstract: The scope of the present paper is the presentation of a possibility to positioning control of a
translation module using to this purpose incremental transducers, PC LPT Port Interface Circuit, a
PC, and a software application written in Turbo Pascal program. In this paper, the mode of work with
parallel port of computer (LPT), the control way of pin group for incremental command and
checking of DC motor which actuates the translation module.
1. DEPICTED APPLICATION
The developed application kept to check and measure the movement of a translation module from the
industrial robot constitution using the following hard resources: a translation module actuated by an
incremental motor, a PC (for the factors computation which interfere, the program flow designed in Turbo
Pascal, data storage receiving and displacement transmission orders), an order electronic block and an
incremental transducer. Interface of translation module of PC has been done by using the LPT Parallel Port
(LPT).
1.1. The transducer is component element of an automatic system by which the output function from
the automated process is measured and converted into a signal able to be compared to the reference input..
TRANSDUCER
fig.1 General scheme of transducer
The used transducer consists of:
- a sensitive element, ES, named also sensor, detecting instrument or captivater which perceives the
variations of physical value x and transforms it into a intermediate value x01, of the other physical
character (usually a linear or angular displacement or of electrical nature: e.m.f. or the resistance,
capacity or inductiveness variation);
- a bonding element, ELT, which can also be a converter, which provides the signal transmission x01 as a
transformed value x02 to the adapter;
- an adapter, A, which converts the signal received and adjusts it to claims required of its usage in the
automation scheme. The signal y from the output of the adapter is, as a rule, a unified signal;
Ion Florin POPA, Mihăiţă ARDELEANU, Cornel MARIN, Mihaela VOICU
378
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an external source of energy SAE, necessary to the adapter A to convert the signal and sometimes also
necessary to the sensitive element ES to detect and convert the measured value x.
The incremental transducer can be photoelectric, inductive or pneumatic. It uses the relative
measurement method and has as a work rule the steps transformation (quanta) of displacement of moving
element in electric pulse signals, which are summarized in an electronic computation.
The component elements of a transducer and the way of interconnection of these ones are presented in
fig.1.
1.2. The personal computer (PC) used is one of a Pentium ll generation; the signals transmission
from PC to command electronic block and data receiving from the incremental transducer is carried out by
parallel port of PC (fig.2)
fig. 2. Parallel port of PC
a. The LPT D group consists of pin set 2 ÷ 9 by which data bits simbolized as D0 ÷ D7 are transmitted.
b.The LPT K group consists of pin set 1, 14, 16 and 17, these ones being bidirectional, the PC having
the possibility of transmitting command bits and receiving control bits or replying from initiated process.
It is specified that pin 1, 14, and 17 are '' denied ", namely the central logical unit of PC transmits to these
pins signals " YES ", but on the path these are denied, finally getting "NO". As a conclusion, these pins
function on inverse logic. Pin 16 functions on direct logic.
c. The LPT S group consists of pin set 10 ÷ 13 and 15. On these pins, bits (signals) are intercepted from
external devices of PC with which this one is interconnected. These pins are unidirectional, their direction
being that of receiving the bits from outside.
d. The GROUNG group consists of pin set 18 ÷ 25, which are bounded to the electric mass, therefore
they will have all the time the potential 0V.
1.3. The translation module is actuated by means of a unipolar DC motor, the displacement
transmission from motor is made by means of a gear belt band transmission which operates a balls - nut
screw assembly. The nut makes a unified body with a slide which displaces linear guided by a guidance
system with 8 rollers (fig.3)
fig. 3. Translation module
2. ADJUSTING CONTROL OF SLIDE POSITION ON THE DISPLACEMENT AXIS
In fig.4., as a block scheme, the adjust way of translation axis position is presented.
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Positioning control of translation module using incremental transducers
Where the elements significance which occur on the scheme is as follows: PC computer –
programmable automaton; EC – comparison element, B.E.C.C. - command electronic block of motor; M –
synchronous motor of actuating of leading screw; SP - driving screw of slide; T – incremental transducer; r reference input; i – input quantity in the electronic block; y – rotations number made of screw: ym – rotations
number measured by transducer; u – command quantity given by B.E.C.C.; m – making quantity; e –
adjusting error, e – i =ym.
fig. 4. Adjusting and control system of slide position
The command signals are produced by special routine which include the command way of motor, this
routine will be iterated for each step necessary to the motor to displace the slide. The transducer produces
signals on which the computer should receive and beginning with a desired value (initialized variable) it
increments the content of control variable ym. The control interferes by a mathematical relation of an
inequality type, as follows:
ym ≤ r
where it is found to be:
ym – control variation;
r – value which depends on the linear displacement assessed in the initial data of program.
Admitted maximum speed/rotative speed is cured both by mechanical part and by electronic part of
transducer. For the choosen rotating sensor, mechanically, the admission maximum rotative speed is a
characteristic of sensor, being pointed out in the parameters table of this, but also a characteristic to used
coupling. In point of electric and electronic, the maximum rotative speed is limited both by the maximum
frequency of photodetectors commutation, fF [KHz], pointed out in season catalogue and also by the
maximum frequency fP [KHz] of processing electronic circuit (register, bistable, logical gates etc).
The connection relationship between the maximum rotative speed and the maximum frequency of
photodetectors commutation is:
f F [ KHz ] 3
n Fmax = max
⋅ 10 ⋅ 60 [ rot/min ] ,
N
where:
nFmax – maximum rotative speed in point of photodetector;
fFmax – admitted maximum frequency of photodetector;
N – division number of disc.
Respectively:
f P [ KHz ] 3
P
nmax
= max
⋅ 10 ⋅ 60 [ rot / min ]
i⋅n⋅ N
where:
nPmax – admitted maximum rotative speed in point of electronic part of processing;
fPmax – admitted maxximum frequency of electronic part of processing;
i – interpolation factor;
n – factor of exploitation faces.
It will be chosen the lowest rotative speed, which complies with all mechanical and electrical
restrictions.
The transducer resolution is determined first by the number N of divisions (gaps) of divider element
(disc). It may be increased " i " times by interpolation of signals supplied by transducer and " n " times by
exploitation of more signals faces.
Ion Florin POPA, Mihăiţă ARDELEANU, Cornel MARIN, Mihaela VOICU
380
For rotative sensor, the resolution, when directly measures the movement of mobile element is
expressed as:
3600
R=
[ grade]
i⋅n⋅ N
In the studied case, the resolution is R = 100, for i = 1, n = 1, N = 36 gaps.
fig. 5. Schematic diagram of transducer
To verify and control the slide displacement, an incremental transducer consisting of phototransistor, a
light source (led), a transistor for the signal amplification, two resistors and one condenser has been devised.
L these electronic elements belong to a mouse, which is considered in its turn an incremental transducer. The
element, which lies between the light source and phototransistor is a disc with gaps fitted on the leading
screw of slide.
At output of phototransister, electrical impulses determined by optical radiation supplied by led arise,
transformed in their turn into impulses by the gaps disc.
A schematic diagram of this transducer is presented in fig. 5, the elements significance noted on figure
being: 1. leading screw; 2. supporting rod of disc; 3. light source; 4. gaps disc; 5. phototransistor.
The transducer will send to computer information (data) on the angular position of leading screw by
which the linear displacement of slide will be calculated, as follows:
d = p ⋅ Nr
where:
d– linear displacement [mm];
p– leading pitch screw [mm];
Nr – recorded rotation number.
The rotation number (Nr) is real as it can contain also decimals. The positioning accuracy comes out
from exactness by which the transducer supplies the number nr, the more accurate this is, the higher the
element resolution (4) is. The resolution of this element is defined by the gaps number made on it.
In this case, a such device is used of which resolution is found to be:
R = 100 for a interpolation factor i = 1 and the exploitation factor of fronts n = 1.
The determination accuracy is given by the following relation:
δ = psc ⋅ pu + jsp
where:
psc – leading screw pitch;
pu – angular pitch of transducer (resolution);
jsp – functional margin from screw - nut coupling.
The accuracy is determined by:
- errors of incremental disc divisions;
- interpolation errors;
- dividing plate run – out from the rotation axe.
In fig. 6, the functional connections between computer and the translation module, on the one hand,
between B.E.C.C. and the incremental motor, and on the other hand the transducer connection on PC,
respectively.
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Positioning control of translation module using incremental transducers
The power unit of motor is connected to B.E.C.C.
fig. 6. Command and control of translation module
Connections significance between the blocks which compound scheme is as:
a - represents the path by which PC sends command bits to electronic block and parallel receives data
from transducer;
b - represents the path by which B.E.C.C. commands the incremental syncronous motor;
c - represents the path by which the transducer sends signals to PC, at the same time it energizes;
d - represents the path by which is delivered the power – supply to motor.
3. PORT PARALLEL COMMAND OF COMPUTER
The carried out application in Turbo Pascal program allows the work with the parallel port of
computer, allows accession, transmission and receiving data which circulate between the incremental
transducer and PC, respectively.
The accession commands of parallel port areas, depicted prior to are as follows:
• for accession of group LPT D:
- ,,port[$378]:=<combination>”;
• for accession of group LPT K:
- ,,port[$37A]:=<combination>”; (for data transmission)
- ,,<program variable>:=port[$37A]”;
• for accession of group LPT S:
- ,,<program variable>:=port[$379]”;
It will be sent on LPT D the decimal "64" and on LPT S, the decimal " 0 ". Application source carried
out in Turbo Pascal program is given below.
program test_control;
uses crt;
const A=64; B=0;
begin
clrscr;
port[$378]:=A;
port[$379]:=B;
end.
4. COMMAND OF INCREMENTAL MOTOR
Command of incremental motor is carried out by the agency of an application carried out in Turbo
Pascal program. Four work way in Turbo Pascal program have been carried out, as follows:
1. pre–established program;
Ion Florin POPA, Mihăiţă ARDELEANU, Cornel MARIN, Mihaela VOICU
382
2. setting – parameters program;
3. manual operation of module;
4. be out of program.
The input data for application: rotative speed (integer number), sense, time (integer number, ms).
4.1. Pre – established program contains: left procedure, right procedure.
The left procedure has as input variable the delay (t), a certain value for variable which represents time
( in practice t = 300 ms used) is initiated. The decimal value 5 is sent on port, The Turbo Pascal compiler
automatically changes it in binary value. The time t is waited for, then it is repeated for decimal values 9, 10
and 6.
The right procedure is developed after the same algorithm, but in inverse course (it is begun with the
decimal value 6).
4.2. Setting–parameters program has been carried out to be profiled better the system parameters: linear
rate and course. These are manually introduced from keyboard after that they are processed by computer and
sent as bits packets for the transistors command from the command and control electronic block of
incremental motor.
4.3. Module manual command. For this transmission procedure f bits on port by means of which motor is
sequencely operated; for each step on which is wanted to be worked out by motor having need by
acknowledge from keyboard. The course changing of motion is achieved by two distinct keys (S and D). In
this case, data are introduce into program, the motion being controlled for a better positioning by human
operator by means of keyboard.
5. CONCLUSION
The depicted procedure for the control and command of a moving element displacement so as carried
out simple as programmed simple, it could be also used in other type of moving elements, being only a
question of moving control of an incremental motor. Depending on the application nature, which follows to
be carried out, the command program of incremental motor is modified, the control program of parallel port
of PC unchanged remains. In addition, the application can be extrapolated at the control and command of a
two or three moving axes, the question being moving synchronization and compound in the clean work
station of the three axes, the working out found by an introduction some synchronization subroutines,
subroutine which apart from the moving correlation of the two or three axes, compound operations of
moving are carried out.
REFERENCES
1. SZTOJANOV, E. BORCOCI, Applied Mechanics, Technical Publishing House, Bucharest, 1987..
2. HUTTE, Engineering Handbook, Technical Publishing House, Bucharest, 1995.
3. E. DUMBRĂVIŢĂ, O. SOMOLESCU, Driving and Automation, Technical Publishing House, Bucharest, 1974.
4. Internet Resources.