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Файл:The design of the exoskeleton. Monograph
.pdf
71
* primary, provoked by Autonomous sources. Such, except for passing
cars, of turbulence, of the incident in the first place are the motor and
drivetrain elements;
• secondary. The sound waves coming from the noise sources pass
through the materials that isolate the car interior: the metal parts of the
body (motor shield, "tunnel", wheel arch, etc.), the Components of the car
control, as well as the plastic elements of the finishing and dashboard. They
all resonate, creating structural noise. This contributes not only to the
transmission of primary noise, but also provokes its own vibration
vibrations (most of all in the joints of these parts).
That is why the sound insulation of the engine compartment ‒ perhaps
the first point, which begins with high-quality sound insulation of the car.
Of course, the engine or transmission to paste sound insulation materials,
we can not. Processed are:
* motor shield with internal and external parties (the partition that
separates the car and the underhood compartment);
• the internal cavity of the instrument panel;
• hood;
• interior part of wheel arches, side panels;
• "tunnel", near which the exhaust system, and in cars with rear-wheel
drive or all-wheel drive and gimbal transmission.
4.3.2. Materials for desiccation
Noise insulation of the car engine is carried out by three classes of
materials.
* vibration damping-composition based on bitumen and foam rubber.
It has a viscoelastic structure and is used to convert mechanical vibrations
into thermal energy. In practice, the tight fit of the material allows to
extinguish resonant vibrations of metal and plastic elements. The vibration
absorber forms the base layer. It is most effective at insulation of thinwalled metal surfaces (up to 3 mm).
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• Soundproof material has a special structure. It reflects not only
sound but also heat waves.
• Noise absorbers ‒ fibrous or porous material in which a large number
of interconnected cavities (in some models with a dense insulating layer on
the front side). The open structure retains and disperses the noise.
4.3.3. Selection of materials
If different models of the material have the same composition and
structure, but different thickness, you can follow the rule - the thicker, the
better. In this case, the effectiveness also depends on the method of
combination and the area of pasting. Not for all materials and areas of the
vehicle, the percentage of covered area is directly proportional to
efficiency.
Among manufacturers, experts recommend:
• STP and Shumoff, which are recognized leaders in the domestic
market;
• Vikar;
• Noisebuster;
• SGM.
4.3.4. Cable
To implement the developed method of torque transmission, it is
necessary, taking into account the working forces, to select the cables of
the required strength.
The strength of the steel cable is one of the main criteria for its
evaluation. The permissible load of steel cables depends on the strength
of the product, which is determined by its thickness, design and method of
manufacture.
This in turn will certainly affect a large number of parts, which,
depending on the diameter of the selected cable will have the appropriate
elements are made taking into account this parameter.
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4.3.5. Couplings
It is obvious that in the design without the use of couplings can not do
at least to ensure alignment between the motor rotor and the gear shaft,
so consider the most popular types of couplings and analyze them.
Rigid couplings are the simplest type. Rigid couplings have an all-metal
housing made of steel, aluminum or other metal, which causes their
special strength, that is, such couplings are able to transmit a significant
moment without deformation. Rigid couplings, for example, BA series
(aluminum), are characterized by high rigidity and low cost. However, the
stiffness has a reverse side - BA couplings are unable to compensate for
misalignment of the shafts and absorb vibration, so that can only be used
in machines with precisely manufactured structural parts and high build
quality.
Spiral couplings, as well as rigid couplings BA series, are made of a
single piece of aluminum alloy, but have a significant difference - the
Central part of the coupling has a precise cross-cutting. These cuts are
made so that the flexible spiral couplings are easily bent within certain
limits, but the torsional rigidity of the coupling does not change - it still
transmits the moment synchronously, without gaps and elastic
deformations. However, the moment itself is transmitted at the same time,
of course, much - 4-8 times less than that of rigid couplings, because the
cuts reduce the strength of the aluminum rod. Such a fee for the main
advantage ‒ flexibility (at high budget), which makes it possible to connect
the shafts ‒ so, the angle between the shafts for couplings of the DR series
can reach 2 degrees, and the minimum center distance - 0.2 mm.
These couplings (BF series) are collapsible ‒ Cam. Between the two
integral parts of the coupling is inserted a cushioning polyurethane gasket
- on the one hand, the polyurethane has enough hardness to transmit the
moment synchronously, on the other, enough elastic and binding to
absorb some of the shock vibrations. As a result, BF couplings, on the one
hand, are able to transmit significant torque, several times more than in
spiral clutches (which brings them closer in this property to the rigid BA
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couplings), and on the other - are able to slightly compensate for
misalignment of the shafts (angle up to 1 degree) and absorb vibration,
which is useful when using stepper motors. Of the minuses it is worth
noting that the polyurethane gasket is subject to normal wear-over time,
the material is gradually deformed, and there is a gap, and then there is a
need to replace the clutch.
Membrane couplings are also collapsible flexible couplings, and
represent a more advanced solution than spiral ‒ membrane couplings are
also used when you need to connect the shafts, which can be at an angle.
Application of steel membrane in the capacity of transmitting torque
element allows to eliminate the main weakness of the spiral coupling, small
load capacity. Membrane couplings are able to transmit absolutely
synchronously the moment equal to and even greater than the rigid
couplings BA, and their flexibility (due to the excellent elasticity of the steel
membranes) at the same time exceeds the flexibility of the spiral couplings
DR - the angle between the shafts can reach 2.5 degrees, the center
distance ‒ 0.2 mm. the Only aspect in which the membrane couplings are
inferior to the spiral is the speed of rotation, but the maximum speed of
the membrane couplings in 10000-14000 rpm will satisfy the vast majority
of practical tasks. Membrane couplings are used wherever the strength of
the spiral clutch is not enough (there is a possibility of damage to the
clutch), as well as in cases where the spring properties of the spiral
couplings are undesirable. Thus, membrane couplings are desirable to use
with powerful engines ‒ stepper motors with flange NEMA 34 and more, as
well as servo motors.
The final selection of the coupling that will be applied in the
development will be carried out only for the finished final design, which will
determine the specific operating conditions and requirements.
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Summary
Thus, after analyzing the previous information, it became obvious that
to date, undoubtedly the entire system will be subject to the control of the
microcontroller (of the most common and available is the Arduino
development platform). NEMA series 23 and 34 stepper motors will be
used from a number of engines (Annex 6). However, despite the presence
to date in the relatively free access of electromyographic sensors, it was
chosen for the first prototype to still rely on the concept of a simpler and
primitive control, namely the placement of control buttons on crutches,
which not only will not be problems with noise, but will allow people to use
the device whose limbs are absent at all.
In the process of working on the project, it became obvious that it is
necessary that the conditions for stopping the supply of power to the
drives, the mobility in the hinges is blocked. This would save energy and in
case of problems or simply the end of the battery / fuel, fix the design
statically, which is very important given the potential application of the
product. It was decided to develop special brakes-clamps to the rotor of
the engine, which are reduced by tension springs and diluted with
electromagnets.
Designs with the use of ballscrews brakes would not need, which
makes the option of using them quite attractive in view of the fact that to
obtain the necessary effort would be enough engines 2-2.7 Nm, which
would also affect the power consumption for the better, as well as the total
weight of the displacement blocks. However, ballscrew designs are well
known and do not require additional consideration. They can be applied to
the development with the involvement of a minimum number of nonstandard elements. Therefore, further work will be carried out with the
development of blocks for the created methods of torque transmission on
structures 2 and 3 in this section.
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5. SIMULATION OF THE MOTION OF BIPEDAL EXOSKELETON
WITH FIVE AXES
5.1. Control of the electric drive of the exoskeleton based on a
high-torque motor with permanent magnets
The control system of the brushless motor with permanent magnets
was implemented in The Matlab – Simulink environment. Figure 5.1 shows
a General diagram of a DC brushless motor control system with a rotor
position sensor.
Figure 5.1 Diagram of the control system
The operation of the voltage inverter is based on switching the DC
power supply to periodically change the polarity of the voltage. The
switching frequency is set by the control signals generated by the control
circuit (control hysteresis unit).
Hysteresis control method is used to suppress noise and to improve
the dynamic characteristics of engines [11]. The principle of operation of
the hysteresis of single-phase current control A is set out in figures 5.2 and
5.5.
VDC
Hyteresis
current control
d
θ
/
dt
PI
1 / Kt
ω
ref
ω
r
PI
PI
PI
- + +
+
- - +
-
I
ref
I
a
I
b I c
LED
BDPT
77
Figure 5.2 – Principle of operation of the control hysteresis
Figure 5.3 – Scheme of implementation of management
From the hysteresis unit, the control pulses are fed to the voltage
inverter unit to turn on (turn off) the corresponding phase switches
according to the characteristics specified in table 5.1.
Table 5.1 – Signs of key inclusion
The angle of
rotation of
the rotor
Hall sensor
output
Inclusion
Phase current
H1
H2
H3
A
B
C
0 – 60
1
0
0
T1
T4
+ia
-ia
выкл
60 – 120
1
1
0
T1
T6
+ia
выкл
-ic
78
120 – 180
0
1
0
T3
T6
выкл
+ib
-ic
180 – 240
0
1
1
T3
T2
-ia
+ib
выкл
240 – 300
0
0
1
T5
T2
-ia
выкл
+ic
300 – 360
1
0
1
T5
T4
выкл
-ib
+ic
Figures 5.4, 5.5, and 5.6 show the components of the model
brushless DC motor. It contains the following blocks: the block of
electromotive force, the block of calculation of phase currents, the block of
creation of laws of phase inductances, the block of calculation of speed,
the electromagnetic moment and a turn angle.
Figure 5.4 – speed, electromagnetic torque and rotation calculation
Unit
79
Figure 5.5 – phase current calculation Unit
Figure 5.6 – Block of the laws of the phase inductances
Figure 5.7 shows the block used to convert signals from the Hall
sensor:
80
Figure 5.7 – Unit conversion of the signals from the Hall sensor
For simulation were chosen the following parameters of motor: 40
watts, the number of pairs of poles 4, phase resistance 0.7 Ohm phase
inductance: 5.1 mH, vzaimoinduktivnosti: 1.5 mH, the ratio of the
electromotive force 40V/rpm, supply voltage Vdc = 120V, the coefficient of
reciprocity: 0.1.
The current regulator is set to optimum modulo, and the speed
regulator to symmetrical optimum.
The simulation results are shown in figure 5.8:
Figure 5.8 – simulation Results
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