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Файл:The design of the exoskeleton. Monograph
.pdf
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Figure 5.17 – Results of single-support phase modeling
2. Two-point phase
Figures 5.18 show the change in the coordinates of the links in time,
the angles between the vertical and the hip, the vertical and the Shin, as
well as the dependence of the reactions of the supports and internal forces
on time in the single-support phase:
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Figure 5.18 – simulation Results of the bi-support phase
Figure 5.19 presents the results of modeling the full step consisting of
two-support – one-support - two-support phases:
Figure 5.19 – simulation Results of a full step
The light of the interaction of the dynamics of the movements of the
exoskeleton's degrees of freedom allows to build the dynamic model of
walking, like walking. This model will make it possible to implement
effective control of the exoskeleton, including control in statically unstable
positions.
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Summary
The simulation showed the effectiveness of the proposed approach to
the construction of a computer model of the dynamics of the active
exoskeleton, taking into account the previously considered features.
As a result of the simulation, unacceptably large pulsations of the
engine torque were obtained. Compensation of pulsations is possible by
means of adaptive control, while linear regulators are not effective enough
to solve this problem in the entire range of exoskeleton movements. The
model is implemented by means of the Matlab package, using the rich
features of libraries.
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6. PROJECT IMPLEMENTATION
All design work was performed by means of the automated
SolidWorks software. Also, in some cases, Autodesk Inventor was used.
6.1. Designed modules. Travel units
Box 1:
Description: a Collection of equipped motor Nema 34 for transmitting
torque to the shaft of the winder rope and braking system for fixing the
position of the shaft when there is no power to the engine. This design
does not provide for the transmission of torque cables through a flexible
connection on corrugated tubes, as can be seen from the design.
Winding force up to 170 kg and s. depending on the engine torque.
The thickness of the coiled cable 3mm.
Weight without engine: 1.2 kg
Brakes for unit 1:
After carrying out information and analytical studies of the existing
couplings/brakes to perform the task, it was decided to develop their own
clutch/brake, as found options had several of the following shortcomings
or all together: large size, large mass, too high price of the product, high
energy consumption.
In the process of development, considerable attention was paid to the
development of a brake system to hold the engine shaft. The ideology of
this module, brake application would save energy in the moments when
the engine would work only on the content, but also had to consider the
fact that when there is no power in the system, the mechanism should
freeze statically in order to not overload the user's weight.
Preliminary sketch work:
Therefore, design work was carried out in the direction of creating its
own design of the brake/restraint system, which would satisfy us on all the
previously mentioned parameters. The result was accepted in to the
development of the brakes following the sketch layout.
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The following scheme was used to calculate such a system. Although
given that the system is still lever, and therefore to the extent of operating
conditions and wear pads, the values of the required labor forces may vary,
so we get some approximate average values of the forces necessary for
the work, which will not be constant. This design, despite its obvious
shortcomings, is a compromise solution that allows to perform the task.
Description:
Holding torque (averaged): 13 Nm
Magnet strength: 25 kg∙s (Annex 9)
Spring summary force: 22 kg∙s
Weight: 0.28 kg
Estimated response time: 0.1 s
Brake system, which provides for the creation of a holding moment on
the shaft of the system in the absence of power to the drive. Brake pads
are tightened by springs. Dilute the pads installed opposite each other
magnets.
Box 2:
Winding force up to 185 kg and C. depending on the engine model.
The thickness of the coiled cable 3mm.
Weight (without engine): 1.4 kg
Composed of equipped motor Nema 34 for transmitting torque to the
shaft of the winder rope and braking system for fixing the position of the
shaft when there is no power to the engine. The main difference from block
1 is that this Assembly already implies a further transfer of force through
the cables for flexible communication.
Box 3:
Winding power up to 65kg is. depending on the engine model.
The thickness of the wound cable 2 mm.
Weight (without engine): 1.4 kg
Description: Composed by equipped motor Nema 23 for transmitting
torque to the shaft of the winder rope and braking system for fixing the
position of the shaft when there is no power to the engine. The main
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difference from blocks 1 and 2 is that this Assembly provides work with
smaller loads.
Brake system for unit 3:
Description: brake system that provides for the creation of a holding
torque on the shaft of the system in the absence of power to the drive.
Brake pads are tightened by springs. Bred pads are installed opposite each
other of the electromagnets.
The average calculation is similar to that given in the brakes for block
1.
Holding torque (averaged): 8 Nm
Magnet strength: 25 kg∙s (App)
Combined force of springs: 16kg s
Weight: 0.23 kg
Estimated response time: 0.1 s.
6.2. Designed hinges
6.2.1. Pelvis:
Hinge 1.0
For this hinge in the process of development was adopted a different
concept of placement of adjacent parts/nodes compared to other
subsequent hinges, as in the case of this it was possible to minimize
mechanical losses (to make actually a direct connection, without passing
the cable on the corrugations), namely by placing the hinge.
It is worth considering that the weight of this hinge will not affect the
torque generated on the hinge. Therefore, in the future, all elements of the
design of the feet will be possible to place it as close to the axis of the hinge.
Description: pelvic joint having one degree of freedom. The torque is
due to the tension forces of the cables module 2. What is obvious already
from the structure itself, a rigid connection formed only between the pulley
and the thigh link, which are placed on the shaft without rigid fastening.
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Axle load (static): up to 4,000 N.
Approximate torque: 170 Nm.
Hinge 1.1
Description: the Main difference is that this design has already been
obtained after numerous tests of various variants of the key links, so this
design completely repeats the description of the Hinge 1.0, but has already
been performed and tested clearly for a given TS. At the same time as you
can immediately see, the range of parts was significantly reduced
compared with the first sample.
Axle load (static): up to 4000 N. Approximate torque: 170 Nm.
6.2.2. Knee
Hinge 1.0
Description: a hinge that has one degree of freedom and is functional
in a given anthropomorphic design, plays the role of a knee.
Load (static): 2400 H
Torque: 110 Nm
Designed from widely available standard parts and profiles, which
makes the design relatively cheap, but testing of individual parts showed
that with this approach, the delivered TK is unattainable.
Hinge 1.1
Description: hinge, which has one degree of freedom and functionally
in this anthropomorphic design plays the role of the knee.
Load (static): 3350 H
Torque: 180 Nm
The design of course increased in weight compared to the previous
one, but it also has a number of advantages. As you can see, this
arrangement has a better power circuit, needs a much smaller range of
parts, is able to work with much higher power loads.
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6.2.3. Foot
Hinge 1.0
Description: the joint, which has one degree of freedom and is
functional in a given anthropomorphic design, plays the role of the foot
joint. Designed in such a way as to have a minimum weight, however, can
be used for a construction whose user has a purpose lower limbs, which,
despite the loss of the ability to move, under certain conditions of fastening
could serve as the main support. Provided that the user does not have legs,
the use of such a structure is impossible at least due to insufficient rigidity
of the structure and its individual parts, as well as in General due to
excessive friction.
Load (static):550 N
Hinge 1.1
Description: the design is similar to the purpose of the previous one,
but is made taking into account the final TK and has a more advanced and
technological structure. The joint, which has one degree of freedom and is
functional in this anthropomorphic design, plays the role of the foot joint.
In conjunction with other dependent parts, is able to perform the role of
the foot, even for those users who have no legs at all, which itself means
that absolutely all the load at the support will be perceived by the foot and
all the dependent nodes and parts.
The torques, as can be further seen from the solid construction, on
this hinge arise due to the action of the foot support and as a consequence
of the tension/tie of the springs. Such a structure is often called a brace.
This performance allows you to unload when walking feet for people
with normally functioning legs, and in another case – is able to partially or
completely return this ability.
Load (static): 2800 N.
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6.2.4. Joint rotation of the foot relative to the axis of the tibia
Description: this hinge tentatively serves to change the angle of
rotation between the coaxial series connected by the presented hinge. It is
specially designed in this work to perform a turn of the hip link relative to
the axis of the link passing along. Rotation in the hinge is carried out due
to the force created by the rope in one direction or another.
Loads: Axial load :up to 240 kg in static position and up to 150 kg in
dynamics.
Weight: 0.37 kg
Generated torque: 10-30 Nm (with this configuration depending on
the engine from the Nema23 model range )
6.2.5. Frame
Description: the Bearing element of the structure is designed for the
installation of parts and assemblies of the developed design. The welded
frame will be tentatively placed behind the user's back and remind in the
context of the finished design, carrying the backpack system behind.
Material: Steel 30
Dimensions : (HxW) mm 570х440
Weight: 4.6 kg
The design in the future will require additional work on the weight.
First of all, a possible option to achieve the desired result – drilling metal.
Study of the manufacturing option of this element from the sheet
material showed that such an analogue would not cost commensurate
expensive compared to the design made of standard rolling profiles.
6.2.6. Parts testing
Since one of the requirements that has been put into the concept of
development is a significant reduction in weight, the designed parts that
take a significant load must be checked with strength and deformability.
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