DEPARTMENT OF MECHANICAL ENGINEERING, PAPUA NEW
GUINEA UNIVERSITY OF TECHNOLOGY
Hydraulic
Power
Robotic Arm
With Dr R. Fono -Tamo
Mechanics of Machines and Machine Element Design
AUTHORS
GAM Getake Jnr – 18301258
GAUDI Nehemiah - 19301212
GIPIS Max - 19301229
GUNA Pelpel - 18301289
HARO Anthony Xavier - 19301236
HAWEK Martin Jnr - 19301243
HENGE Fiona - 19301250
HONDONE Barford - 13301816
JOHNSON Josek – 19302255
KADIKO Melanie – 19301267
ABSTRACT
Imagine you lifting a truck by yourself. Have you seen a machine that picks up huge amount of loads with
little effort? Hydraulics is the answer. Hydraulics is a mechanical function that operates through the force
of liquid pressure. Hydraulics systems works on a similar principle as any other mechanical systems and
uses a force over an area or distance. Hydraulics are used for mass manufacturing operations, such as
auto assemblies and in construction sites too. This helps people to carry out heavy duty jobs with less
amount of energy and effort producing more and costing less. The system is easy and accurate by which
can be controlled, and can generate a large amount of power. Hydraulic Robotic Arm is a system which is
coupled by machines and hydraulics that basically does everything mentioned above.
This project model is built with simple recyclable materials to illustrate the approach and demonstrating
the principle behind the hydraulic power systems coupled with robotics.
Table of Contents
Chapter 1 – Introduction ………………………………………………………………………………………………………………1
Introduction about the mechanism ……………………………………………………………………………………………….2
Chapter 2 – Literature Background …………………………………………………………………………………………...4
2.1 - Principle of hydraulic robotic arm ………………………………………………………………………………………….5
2.11 Pascal’s Law – Introduction ……………………………………………………………………………………………………5
2.12 Pascal’s Principle ……………………………………………………………………………………………………………………5
2.13 Hydraulics – Pascal’s Principle ……………………………………………………………………………………………….5
2.14 How does the hydraulic work? ……………………………………………………………………………………………...6
2.15 Pascal’s law and mechanical advantage ………………………………………………………………………………...7
2.2 – Robotic Arm ………………………………………………………………………………………………………………………….8
2.21 Brief History of robots …………………………………………………………………………………………………………...8
2.22 Kinematics of robots ……………………………………………………………………………………………………………...8
2.23 Classification of robots …………………………………………………………………………………………….…………….9
2.24 Robotic Arm specifications ……………………………………………………………………………………………………10
Chapter 3 – A review on the hydraulic system of the model ……………………………………………………..12
3.1 – Pressure with a syringe ………………………………………………………………………………………………………..13
3.2 – Hydraulic System Model ………………………………………………………………………………………………………14
3.3 – Force Analysis ………………………………………………………………………………………………………………………15
Chapter 4 – Construction of the Hydraulic Robotic Arm …………………………………………………………..…17
Chapter 5 – Results and findings ………………………………………………………………………………………………….21
5.1 – Mechanics ……………………………………………………………………………………………………………………………22
5.2 – The properties of the tubes ………………………………………………………………………………………………….22
5.3 – Air pockets inside the tubes …………………………………………………………………………………………………23
5.4 – The ability of the claw ………………………………………………………………………………………………………….23
Conclusion ……………………………………………………………………………………………………….………………………24
Recommendations ……………………………………………………………………………………………………………..…….24
Reference …………………………………………………………………………………………………………………………….…..25
CHAPTER
1
Introduction to the
Hydraulic Powered
Robotic Arm
1
Hydraulic Robotic Arm is a system which is coupled by machines and hydraulic. It was developed by
engineers for a variety of reasons, the most important of which was that it could be used in conditions
that were too difficult or unsafe for humans to handle directly or in automated systems.
It is widely applicable in all kinds of large engineering equipment’s such as the arm frame of a crane. The
arm system has redundant freedom, is strong and nonlinear, and has rigid and flexible properties. The
hydraulic robotic arm's dynamic differential equation is built with the hydraulic cylinder's driving force
as the main force.
A hydraulic drive system is a drive or power transmission system that drives hydraulic machinery with
pressurized hydraulic fluid. The term "hydrostatic" refers to the energy transfer between flow and
pressure, not the kinetic energy of flow.
A hydraulic drive system consists of three parts: The generator (e.g. a hydraulic pump), driven by an
electric motor, a combustion engine or a windmill; valves, filters, piping etc. to guide the control system;
and the actuator (e.g. a hydraulic motor or hydraulic cylinder) to drive the machinery.
The robotic arm, which is based on the Proportional-Derivative (PD) Control theory, operates on both
current and predicted process conditions. There is no decoupling of the parts, and rank is only reduced
as a result of feedback from the arm's position, pose, and movement control. The resulting
simultaneous movement demonstrates that the mathematical equation used to control the mechanical
arm's behavior accurately describes each dynamic character.
1.1 Introduction about the mechanism
This present work involves constructing and operating a mechanical arm that is controlled by syringes
filled with some fluid which lifts and moves small objects such as a soft drink can, matchbox etc. using
hydraulics for power. It is a simple demonstration device for engineering education that consists of
various parts connected to each other in a pre-designed manner which are guided in a constrained way
to obtain required output.
APPLICATION
These arms are used in assembly lines of mega factories to assemble various parts of a product and
also to paint vehicles. They are also used in earth movers to pick up heavy weight and keep them
where required.
PARTS
The work includes the construction of:
I.
II.
III.
IV.
Single axis for use in the completed mechanical arm
Grasping hand
Lifting arm
Rotation base
2
In the mechanism, each part has been provided with certain degree of freedom to move in a
constrained way to guide other parts and also pick up small weight items and to place them
wherever required. The complete mechanism consists of a vertical link and to its free end is hinged
another horizontal link which is free to oscillate about that hinge in an up-down way of motion. To
this link is connected another horizontal link in which two cut out cardboard is connected to act as
grasping arm to pick up the items.
3
CHAPTER
Principal of
Hydraulic
Robotic
Arm
2
4
2.1 Principal of Hydraulic Robotic Arm
2.11 Pascal’s Law - Introduction
In the early days, loads and weights were lifted by ropes as
pulleys, levers, blocks and tackles. Movements for ship’s
rudder, or a steering a vehicle where made possible by
mechanical linkages like cams, levers, couplings, and gears
which is a quite complicated system. These methodologies
had some limitations that are not possible to carry out. This
system also involved a lot of man labor and effort with long
working hours but even with that less mass was produced.
With the increasing population growth, and the advancement
in technology, the hydraulic system was introduced. It was
then made possible for the invention of hydraulic machinery
Figure 2.11 Man lifting a stone
that satisfied the lack in market production.
2.12 Pascal’s Principle
Pascal’s principle, also called Pascal’s law, in fluid (gas or liquid) mechanics, statement that, in a fluid at
rest in a closed container, a pressure change in one part is transmitted without loss to every portion of
the fluid and to the walls of the container. Thus the shape of the container clearly has no effect on the
pressure transmitted in the fluid and the principles applies only in enclosed fluids. This was observed
and the principle was first enunciated by the French scientist Blaise Pascal.
2.13 Pascal’s Principle and Hydraulics
Hydraulic systems use incompressible fluid, such as oil or water to transmit force from one point to
another within the fluid. Pascal’s Law states that when there is a pressure increase at any point in an
enclosed fluid, the same increase occurs in all other points in the fluid. This principle is used mostly in
the braking systems.
Thus, now it is known that if there is a change of pressure in one point the same change will occur in any
other point within the enclosed fluid. This is how the Pascal’s Law can be interpreted.
5
2.2 How does Hydraulic Work
According to Pascal’s principle, in a hydraulic system a pressure exerted on a piston produces an equal
increase in pressure on another piston in the system. If the second piston has an area 10 times that of
the first, the force on the second piston is 10 times greater, though the pressure is the same as that on
the first piston. For instance, if a U tube is filled up with water and two pistons are placed at each ends
of the u tube, pressure exerted on the left piston will be transmitted throughout the fluid and towards
the bottom of the right piston. The two pressure for the left and right piston is always equal in
magnitude. Assume if the tube on the left side is made wider and big in area than the right-hand side
piston;
For example, if a 1N load is placed on the right piston, an increase in pressure due to the weight of the
load is exerted in the fluid and up against the bottom of the larger piston. The additional pressure will be
exerted on the area of the larger piston. While the pressure exerted is the same, and since the area is 10
times more, 10 times as much as the force will act on the larger piston. Hence the larger piston will
support 10N load- ten times the load on the smaller piston. A good example for this effect is the
hydraulic press, based on Pascal’s principle, which is used in such applications as hydraulic brakes.
6
2.21 Pascal’s Law and Mechanical Advantage
Pascal’s Law allows forces to be multiplied. The mechanical advantage (MA) is calculated as:
𝑀𝐴 =
𝑡ℎ𝑒 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑜𝑓 𝑤ℎ𝑒𝑟𝑒 𝑡ℎ𝑒 𝑓𝑜𝑟𝑐𝑒 𝑖𝑠 𝑎𝑝𝑝𝑙𝑖𝑒𝑑⁄
𝑡ℎ𝑒 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑜𝑣𝑒𝑟 𝑤ℎ𝑒𝑟𝑒 𝑡ℎ𝑒 𝑙𝑜𝑎𝑑 𝑖𝑠 𝑚𝑜𝑣𝑒𝑑
Shown below is the illustration of the application of a hydraulic lift. If the area on the left is 𝐴1 = 1 m²
and the area on the right is 𝐴2 = 10 m², external input force acting on the left piston is 𝐹1 = 1N. The
weight force of 1 Newton lowers the fluid on the left 10 meter downward, as a result of this effect the
piston on the right lifts a 10 Newton load 1 meter up.
Figure 2.21 Application of a hydraulic lift
The 100 newton load on the 1 square meter area causes an increase in the pressure on the fluid in the
system. In every meter of the 10 square meter, the pressure is equally distributed throughout and acts
on each meter. Thus the larger piston is able to lift a 1000 newton load. The more the area of the
second piston the more the mechanical advantage and so results in more force in lifting heavier loads.
Formulas representing this illustration is;
𝐴1
𝐴2
=
𝐷2
𝐷1
Where: 𝐴1 = Area 1, 𝐴2 = Area 2, 𝐷2 = Distance moved 2, 𝐷1= Distance moved 1
A simple machine (lever) system can be interpreted using the equation above since force is multiplied.
The mechanical advantage can be found by rearranging the terms in the above equation to:
𝑀𝐴 =
𝐷1
𝐴1
=
𝐷2
𝐴2
For the example above, the MA would be 1:10 (one square meter is to 10 square meter or vice versa).
7
1.4 Robotic Arm
1.41 Brief History of Robots
The idea of a moving mechanical device made in an imitation of a human being termed automata
originates in the mythologies of many cultures around the world. Engineers and inventors from ancient
civilizations, including Ancient China, Ancient Greece and Ptolemaic Egypt attempted to build selfoperating machines, some resembling animals and humans. The term ‘robot’ was first applied as a term
for artificial automata in the 1920’s play R.U.R by Czech writer Karel Capek. The word ‘robot’ itself was
not new, having been in the Slavic language as robota (forced labor), a term which describes the
majority of robots fairly well. Most robots in the world are designed for heavy, repetitive manufacturing
work. They handle tasks that are difficult, dangerous or boring to human beings.
The most widely accepted definition of an industrial robot is one developed by the Robotic Industrial
association:
‘An industrial robot is a reprogrammable multifunctional manipulator designed to move materials, parts,
tools or specified devices through variable programmed motions for the performance of a variety of
tasks.’
2.22 Kinematics of robots
The technology of robotics is concerned with the design of the mechanical manipulator, the computer
systems used to control it and the industrial application of robots. The mechanical manipulator of an
industrial robot is made up of a sequence of link and joint combinations. The links are the rigid members
connecting the joints. The joints (also called axes) are the moveable components of the robot that cause
relative motion between adjacent links. There are five principle types of mechanical joints used to
construct the manipulator and they are outlined in the table below;
Joint
Description
Linear Joint
Type L joint; the relative
movement between the input
link and the output link is a
translational sliding motion,
with the axes of the two links
parallel.
Orthogonal
Joint
Type O joint; the relative
movement between the input
link and the output link is a
translational sliding motion,
but the output link is
perpendicular to the input
link.
Schematic
8
Rotational
joint
Type R joint; this provides
rotational relative motion,
with the axes of rotation
perpendicular to the axes of
the input and output links.
Twisting joint
Type T joint; this provides
rotary motion, but the axis of
rotation is parallel to the axes
of the two links.
Revolving joint
Type V joint; the axis of the
input link is parallel to the axis
of rotation of the joint, and
the axis of the output link is
perpendicular to the axis of
rotation.
Table 1: Collinear and orthogonal are translational joints; rotational, twisting, and revolving are rotary
joints.
2.23 Classification of robots
Robots are principally classified into two groups as:
a) Serial robots which are the most common industrial robots and they are designed as a series of
links connected by motor-actuated joints that extend from a base to an end-effector. Often
they have anthropomorphic arm structure described as having a “shoulder”, an “elbow” and a
“wrist”. Serial robots usually have six joints, because it requires a least six degrees of freedom
to place a manipulated object in an arbitrary position and orientation in the workspace of the
robot.
b) Parallel robots are mechanical system that uses several computer-controlled serial chains to
support a single platform, or end effector. Their ‘parallel’ distinction, as opposed to a serial
manipulator, is that the end effector of this linkage is directly connected to its base by a number
of (three or six) separate and independent linkages working simultaneously.
9
2.24 Robotic Arm specifications
Robots can be further grouped into several categories according to their movement, lack of restriction
rate, source of power used for revolving joints, control methods, sharpness degree and two letter code.
The main focus of this report is the robotic arm which a type of mechanical arm with multiple segments
that is usually programmable, with similar functions to a human arm. Its control systems can be
programmed several times to do more complex processes. The computer controls the robot arm by
rotating individual step motors connected to each joint. Unlike ordinary motors, step motors move in
exact increments. This allows the computer to move the arm very precisely, repeating exactly the same
movement over and over again. The robot uses motion sensors to make sure it moves just the right
amount.
A robotic arm, when classified according to its movement, is a stationary robot. This type of robot
performs its task without changing position. The term ‘stationary’ is more associated with the base of
the robot and not the whole robot. The robot moves above the base to perform the desired operation.
According to its lack of restriction rate, a robotic arm is classified as a cylindrical robot by studying the
functions of the first three organs. The robotic arm has its first joint as revolving, the second and third
are a prismatic kind. Although their mechanical constitution is well made, their wrist location line
changes according to horizontal action. Hydraulic action is usually used as movement at the joints.
In accordance with its control methods, this hydraulic power robotic arm is controlled from a point, that
is, there is no determined working area for these kind of robots and is controlled by an operator.
Robotic arms feature rotary joints that can range from a simple two-joint structure to a complicated
structure with 10 or more joints. This robotic arm is composed of an assembly of six links and six joints.
Its links, which are considered to form a kinematic chain, are connected by joints allowing either
rotational motion or translational (linear) displacement. This type of robot has six degrees of freedom,
meaning it can pivot in six different ways to perform assigned tasks. The shoulder of the robot is
mounted to a stationary base than to a moveable body. The device attached to the manipulator which
interacts with its environment to perform tasks is called the end-effector and is found on the sixth joint.
The arm is connected to a base that has a twisting joint. Rotary joints connect the links in the arm; each
joint is a different axis and provides an additional degree of freedom.
10
A robotic arm performs tasks by interacting with its environment and are extensively used in the
industrial manufacturing sector, especially in assembly operations, die-casting, fettling machines, gas
and arc welding and applying paint.
Figure 2.24 Links and Joints
11
3
CHAPTER
A Review on
Hydraulic System
Model of the
Hydraulic Robotic
Arm.
12
A Review on Hydraulic System Model of the Hydraulic Robotic Arm.
In the early stages of any engineering
project, models are essential for visualizing
and developing sophisticated engineering
systems in a virtual environment and more
importantly identifying the possible issues
that may emerge during and after its
development. By employing engineering
models, product development cost and
time can be significantly reduced.
Hydraulics are a ubiquitous and an
extremely important element of machines
and they work on the basis of
incompressible fluids introduced by Blaise
Pascal in the mid-1600s. The subject of this
report, the hydraulic robotic arm, also utilizes
Figure 3.1. Components of the hydraulic robotic arm model
Pascal’s law in operation. Hydraulics are
typically engaged in pumping incompressible
fluids. From our subject’s point of view, we are concerned with the pressure that is induced by pumping
that triggers relative motion which requires coordinated manipulation of the boom, arm and syringes on
the hydraulic robotic arm model.
A practical example of the hydraulic robotic arm is the hydraulic excavator. Apart from having the same
components involved in their arms’ maneuver, i.e. the boom, arm and hydraulics, the hydraulic robotic
arm and hydraulic excavator also operate the on the same pressure principle. Deriving a system model is
a critical component in the development of the subject. Therefore, this chapter is aimed at providing an
overview of the hydraulic system of the robotic arm model.
3.1 Pressure within a syringe.
The model of the robotic arm operates on syringes that substitute hydraulics on this miniature scale;
water substitutes hydraulic oil. As hydraulics, syringes utilizes the pressure induced by incompressible
fluids (water) to either halt or permit relative motion in a hydraulic system. Although gravity and fluid
viscosity may affect the motion of the hydraulics, their influence is arguably subtle. Thus promoting the
force associated with the induced pressure to be the incentive for motion of the hydraulics or in our
case, the reciprocating motion of the syringe’s piston within its barrel.
Interesting thought, if a syringe is full of liquid, why doesn’t it pour out? Or what is stopping it from
pouring out? This phenomenon is due to atmospheric pressure and surface tension.
Consider placing a syringe with its piston raised in a cup of water, air encapsulated in the syringe will
increase in volume, and thus the pressure of the air will decrease far below atmospheric pressure. Since
atmospheric pressure is pushing on the water surface, water will be forced into the syringe due the
force of the air pushing against it from within the syringe being significantly less than that of the
atmosphere. The water will enter the syringe until the additional weight of the water causes an
equilibrium with the atmospheric force pushing the water in. Thus, liquid cannot exit without decreasing
13
the pressure from within the syringe. In addition, typically the diameter of a syringe is relatively small
and the capillary (surface tension) forces at the liquid and air interface are sufficiently strong so as to
prevent shearing of the interface and intrusion of air bubbles. Hence, the push of atmospheric pressure
and surface tension keeps the water in.
3.2 Hydraulic System Model
In the previous article, we have established that water contained in a full syringe cannot spontaneous
leak due to the effects of atmospheric pressure and surface tension. Furthermore, a syringe in a body of
water cannot be filled if its internal pressure is equal to sum of the atmospheric pressure and pressure
exerted on the syringe at its depth. While being submerged the intrusion of air bubbles increases the
volume of air hence decreasing the internal pressure. The reduction in internal pressure allows water to
flow into the syringe; if atmospheric pressure and surface tension forces are at equilibrium with the
syringe’s internal forces, flow of water is halted. In spite of what preceded, what if atmospheric pressure
was eliminated?
Surface tension alone cannot cater for the force required to maintain equilibrium. Eliminating the
atmospheric pressure results in the effect of gravity being conspicuous. Separating the pair, allows the
weight of the piston and its rod in the syringe to pushes out water. Water being removed, gives a bare
syringe that is no use to the subject. Although, if water removed from one syringe enters another, this
creates a steady-flow system governed by the theorem of continuity which incents the reciprocating
motion of respective pistons. This system is the basis of the hydraulic system model.
Figure 3.2 Shown are syringes that are each to be connected to another (not shown) thus creating
a steady flow system.
14
3.21 Force Analysis
The force exerted by water on any piston in the hydraulic system model is presumably some function of
the velocity of its corresponding piston and the viscosity of water. Consider depressing a syringe at a
constant velocity of around 0.005m/s. The diameter of the drip tube and syringe barrel are measured to
be 0.004m and 0.014m respectively.
Since the steady flow system is governed by continuity,
𝑄 = 𝐴1 𝑣1 = 𝐴2 𝑣2 then, A1=1.54x10-3m2 and A2= 1.26x10-5m2.
NB: Subscripts 1 and 2 denote syringe and drip tube respectively.
Since water travels a distance of L in the drip tube before entering a syringe, the drop in
pressure will be accounted for by the Hagen-Poiseulle equation that describes pressure drop
due to fluid viscosity (hagen-poiseuille equation, 2021). Pressure drop due to gravitational pull
may still occur. Here Bernoulli’s equation will be needed but for simplicity lets observe the drip
tube that is completely horizontal.
From Hagen-Poiseulle equation, ∆𝑝 =
8𝜇𝐿𝑄
𝜋𝑅4
Where L and R are pipe length and radius and µ is dynamic viscosity of water and Q is volume
flow rate. So,
𝑄 = 𝐴1 𝑣1 = (1.54x10−3 )(0.005) = 7.7x10−6 𝑚3 /𝑠
Thus,
∆𝑝 =
∆𝑝 =
8𝜇𝐿𝑄
𝜋𝑅4
3.85𝐿
𝜋
=
8(1)𝐿(0.0000077)
𝜋(0.002)4
Assuming µ of water is 1mPa.s
MPa
Calculated is the change in pressure between the syringe and drip tube. The force exerted on
the piston,𝐹𝑝 , pushing it to a raised position can be obtained by,
𝐹𝑝 = (∆𝑝 − 𝑝1 )(𝐴2 ) 𝑤ℎ𝑒𝑟𝑒 𝑝1 𝑖𝑠 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 𝑖𝑛 𝑡ℎ𝑒 𝑠𝑦𝑟𝑖𝑛𝑔𝑒
𝐹𝑝 = (
3.85(106 )𝐿
− 𝑝1 ) (1.26(10−5 )) 𝑁
𝜋
15
The model’s torque is the product of the weight of each syringe and component by the component’s
length perpendicular to the direction of the weight from its center of gravity. Although the actual boom,
arm and claw of the hydraulic robotic arm are irregularly shaped, for the sake of simplicity of their
analysis, they are assumed to be straight joint links whose lengths are defined by the distance between
two joints as shown in figure 3.3.
Figure 3.21. Configuration for components torque
The force responsible for the reciprocating motion in the hydraulic system model, i.e.
3.85(106)𝐿
𝐹𝑝 = (
𝜋
− 𝑝1 ) (1.26(10−5 )) 𝑁, manipulates the movement of each component by opposing
their spontaneous torque. Therefore, the boom, arm and claw of the hydraulic robotic arm reciprocates.
16
CHAPTER
4
Construction of the
Hydraulic powered
robotic arm model.
17
Construction of the Hydraulic Powered Robotic Arm
First Stage: Each piece of the robotic arm were cut (all dimensions are in cm).
1. Cut 2 rectangular shape from the cardboard (A1)
2. Another 2 rectangular shapes were cut (B2)
3. A trapezium shape was cut then it was divided in half (C3)
4. Two rectangular shapes were cut there was a hole created (D4)
5. Two claws were cut with tie wires joined (E5)
18
6. Each syringe was drilled using a small bit
7. The bigger base, a hole was made for the battery to be placed inside (F6)
Second Stage (standing the arm): After each step, skewers were fixed with square cut off pieces.
1. At equal sides of the end of the rectangular
shape cardboard(A1), holes were created for the
skewer to go through to hold it in place. The
syringe was used to space the both rectangular
cardboards(A1).
2. The shorter rectangular shape (B2) was joined
onto A1 with the aid of the skewer.
3. The base was created with D4 and C3 was glued
on either side (standing vertically up).
4. Now the arm was standing up
5. The claw(E5) was then added onto the top arm(A1)
Third Stage (Placing the syringe): Each syringe was tied with a cable tire and looped again with
another cable tire
1. From the base (D4 +C3) up onto the bottom arm a
syringe was placed in between, it was held in place
with a skewer. This enabled movement for the bottom
arm
2. From the top arm(A1) down to the bottom arm (B2)
there was a syringe placed to enable movement for
the top arm.
3. Another syringe was placed along the top arm to
control motion of the claw. The tie wire was pushed
into the hole of the syringe
4. One of the paddle sticks was glued at the side of the
base and was then packed (glued) with cardboard to
make it high. Another paddle stick was then glued on top of the packed cardboard. At the end
19
the syringe was connected using the skewer firmly attaching it to the board to hold it in place.
The syringe enables the body to rotate around.
Fourth Stage: Building the controls
1. A rectangle cardboard with the dimension
of 30cm by 9cm was cut to be used as the
base.
2. Cardboard was stacked(glued) at the edge
of the length of the base with a thickness
of 2.5cm.
3. The paddle sticks were all drilled. At either
ends the paddle sticks were halved and
glued onto the sides. 13 cm in from both
sides two more paddle sticks were glued onto the stacked cardboard. Skewers were then put
inside the hole to allow to cater for the syringes
4. The tie wire was evenly spaced on the cardboard for the syringe to be resting downwards and
tied onto the tie wires. The four syringes were drilled and attached onto the skewers
5. Once the syringe was in place cable tire was used to hold the syringes in place. They were tied
onto the tie wire.
6. For each syringe each color liquid was injected with the aid of tubes into the syringe. Each
syringe from the control board was connected to one of the syringes on the hydraulic robotic
arm frame.
20
CHAPTER
5
Results and
Findings
21
5.1 Mechanism (how the different parts operate)
Test and operation
Pushing on the handle of the control levers applies pressure to the water in the syringe at the control
panel. Since water is confined and incompressible, Pascal’s principle comes into action, stating that “the
pressure is transmitted undiminished to all parts of the water and to the walls of its container.” Since
the plunger of the fixed syringes at the other end of the tube forms part of the “container” for the
water, and they are the only parts of the container that can expand, the pressure causes the plunger in
the fixed syringes to move, causing the appropriate component of the arm to move.
Four tests were successfully applied to the model as follows:
1. When pressing on the green syringe, another syringe located inside the lower arm (boom, refer
to fig. 3.1) produces a force to move the lower arm an upward and downward direction initially
from the vertical position. The syringe within the lower arm has the function to carry both the
weight of the lower arm and the load of the upper arm, moving the upper arm vertically up and
down and transmitting the sum of load to the main vertical boom(C3).
2. When pressing on the yellow syringe it moves the upper syringe in the boom. The syringe then
causes the upper arm to move in a upward and downward direction initially from the horizontal
position.
3. When pressing the red syringe, it moves the relative syringe that is responsible for activating the
claw and is located in the upper arm. When the control syringe is pressed, it moves the two tie
wires connected in the direction of the movement; forward and backward. The wires are
connected to the claw which performs the grabbing function. As the syringe moves forward, the
claw open an and closes when it is withdrawn.
4. When pressing the purple syringe, which is connected to the syringe responsible for the rotation
of the whole arm, it then produces a force which rotates the whole arm around.
5.2 The Properties of the tubes
One of the most important component of the hydraulics robotic arm is the connecting tubes. The tubes
connect pairs of syringes relative to each other and acts as medium to transfer the fluid (colored water).
The connecting tubes are High Flexibility and Elastic Plastic Tubes, therefore having the properties of
flexibility, elasticity and plasticity.
Further elaboration of these three properties will be made in this subsection, especially on how they
were applicable to the building and operation of the hydraulic robotic arm.
Firstly, for the flexibility of the tubes, this property enables the tube to have the ability to ease with
which the system can respond to uncertainty in a manner to sustain or increase its value delivery. Which
means that it can deform elastically and return to its original shape when the applied stress is removed.
Thus, it was possible for the tubes to be connected, be bended very easily through and between the
cardboard and sticks of the arms, and stretched to the required position.
Secondly, for the elasticity of the tubes (similar to flexibility) the tube regains its original shape and size
after the removal of deforming forces. This fact was applicable when the end of the tubes were heated
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with hot water to expand it so can easily fit the nozzle of the 10mL syringe. The hot water having slightly
high temperature expanded the end of the tube has it was fitted in and then when it cooled, it shrunk to
its original size fastening tightly to the syringe’s nozzle. Notice that we did not go over the elastic limit.
The elastic limit of a substance is defined as the maximum stress (hot water) that can be applied to the
substance (tube) before it becomes permanently deformed and does not return to its initial size.
Finally, for the plasticity of the tubes, it is the ability of a solid material to undergo permanent
deformation, a non-reversibility change of shape in response to applied forces. In the building of the
arm the plasticity property was avoided as much as possible so that the tubes are not deformed and
become ineffective.
5.3 Air pockets inside the Tubes
The term “formation of air pockets’’ describes the
accumulation of air bubbles in certain areas inside
pipes or tubes. They occur due to gas (mostly air)
contained in the fluid handled in dissolved or
undissolved (bubble) state.
In this case, air pockets were found inside the
tubes during the first trial with water alone. This
made it harder for the pressure be transmitted
smoothly from the push and pull of the syringes at
the control panel to the other relative fixed
syringes to cause movement.
Fig. 4.3a Connected tubes with air pockets in them
For improvement and prevention of air pockets
forming, the pressure inside the fluid path was increased causing the detachment of the air bubbles
from the tubing. As pressure is applied to the air, its’ spaced-out particles in gaseous state come
together and are converted into the liquid state. It this way when adding the water into the tubes, they
are all uniform particles because they are all in liquid state.
5.4 The claw’s ability
The main function of the claw is to perform a grabbing movement on the intended object and releases it
after it has been moved. The materiel must be in the functional range of the arm for it to be effectively
moved. During the testing of the claw upon the completion of the arm, it was found that the claw could
not effectively grab the materiel it was intended to grab. This was caused due to the low friction
coefficient of the claw’s contact points (grip) which are located at the end of the claw. The grip was
smooth because of the cartridge that was used to construct the claw. In order to improve the ability of
the claw to grip properly, a material with high friction coefficient must be place at the contact point of
the claw.
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Conclusion
After several attempts of construction, we were finally able to finish the project. This design of the
hydraulic power robotic arm uses extremely simple ideas and mechanisms to achieve a complex set of
actions and is intended to imitate the actions of the actual operators. Testing of the model post
completion has led us to identify a few minor setbacks in terms of its behavior such as the difficulty in
getting the precise value for all the dimensions of the lengths and angles and so the geometry of the
elements/links of the model weren’t perfect hence affecting the parameters of the model like freedom
of movement. Also small amounts of gases were trapped within the tubes making it a little difficult for
the transmission of pressure from one point to another and some of the parts were slightly heavy
causing more stresses to be developed in the hydraulic links and tubes.
However, the results from the model still served its overall purpose, that was to help us understand the
basic principle of simple mechanism using hydraulic principles, its kinematic and dynamic analysis and to
get a feel of how the forces acting can affect the integrity of structural elements. By evaluating the
model and its response to the certain actions we have seen that it has demonstrated concepts which are
in context with the subjects concerned for this project. That is, the different types of joints, particularly
binary joints, the overall degree of freedom of the model, the different types of kinematic pairs,
particularly turning pairs and rolling pairs, and the type of link , particularly fluid links and rigid links are
associated with the subject Mechanics of Machines. Moreover, understanding of where exactly and
what kind of machine elements to be used, for this case, where the hydraulic piston and cylinder to be
used and where the different bearing to be applied. As well as understanding the kind of geometry is
perfect for rigid links (its arms and base) and how well it can withstand certain load and moments and
the required properties of the hydraulic fluid used are related to the subject Machine Element Design.
Therefore, it is safe to say that this model captures and demonstrates the important parameters that
needs to be taken into account when designing and manufacturing a real hydraulic robotic arm that can
be used for various manufacturing and or construction purposes and the students involved are now well
versed in explaining the simple concept behind the workings of hydraulic powered machinery, especially
a robotic arm and can be able to execute operations using a hydraulic power robotic arm.
Recommendation
It is now known to us that with the hydraulics principle incorporated into
robotics or machinery, work that includes heavy duty labor in the past
has been improved by doing it with less effort. The design can be
improved by considering going into more complexities that is unlimited
in human nature. The robotic arm can be made more reliable in the
future with providing a coded program that can be used by just pressing
a central switch that controls all of the components of the hydraulic
robotic arm both in the model design and in future scopes. This way it
saves energy and effort as we know the levers on the control panel are moved manually. The source of
energy that helps with the movement of the hydraulics of robotic arm can also be considered improving.
The depletion of natural non-renewable resources today can limit advancements in the design of the
robotic arm. Thus, the other sources of energy should also be used such as; Solar energy, Biomass, etc.
Moreover, other machinery that has low capacities of energy storage resulting in wasted surplus energy
can work along-side with the robotic arm, sharing its energy with the robotic arm.
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