Trang 1 MINISTRY OF EDUCATION AND TRAINING HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY AND EDUCATION FACULTY FOR HIGH QUALITY TRAINING GRADUATION THESIS ELECTRONICS AND TELECOMMUNICATION E
INTRODUCTION
Abstract
With today's engineers, the robots sector has advanced to a very impressive level The correctness of each processing stage and the server's lightning-fast response time both contribute to increased working efficiency and a little decrease in the likelihood of worker injuries Although the degree of robotics in major firms has advanced significantly, many small businesses may not have the resources to purchase all the newest and most advanced robots They frequently make use of numerous, outdated serial robots that lack agility, adaptability, precision, and user feedback A parallel robot is a sort of robot that was created and refined to at least substantially lessen and restrict the aforementioned drawbacks
A parallel robot is a closed-loop mechanism that has at least two chains, as opposed to a serial robot, which operates continuously, has an open structure connected to kinematic connections, and is controlled sequentially or simultaneously Distinct kinematics connected to the sole at the end effector The advantages of parallel robots are their strong rigidity, high mechanical strength, high load capacity, high acceleration, low dynamic mass, and simple structure Parallel robots have been and are still being utilized in a variety of industries, such as medical, astronomy, 3D printing simulation, machine tools, etc., because of the advantages mentioned above
In a production setting, industrial robots occasionally adopt the shape of a "mechanical arm" that is based on the fundamental structural components of a human arm It is structured to employ mechanical systems to do human-like activities, which is unnatural, necessitates open-loop serial kinematics, and is a goal of mechanical systems development A serial controller is a prime illustration of this architecture This structure has the benefit of providing an expansive and flexible workspace that can be used with the same dexterity as a human hand, but because of its heavy weight and numerous joints on the operator, it has poor lifting capability, poor durability, and poor moving accuracy at high speeds
Therefore, a machine to replace the traditional serial robot that has good dynamics and precise positioning is urgently needed for situations where load lifting capacity is the key goal And in the process of coming up with answers for that, researchers have discovered that some species, like elephants or buffaloes, have the capacity for both support and transportation Due to its construction of four parallel legs and standing on a strong surface, heavy objects are excellent for manipulation In conclusion, it can be said that manipulators with end-action control, actuators positioned in parallel, and connections to the ground by some sort of kinematic chain will be stiffer and more accurate.
Problems
Parallel robots were also found and investigated in Vietnam in the 2000s, but often this merely involves making models and coming up with ways to handle kinetic problems; no specific robot needs to be designed and produced The Vietnam Institute of Mechanics' Mechatronics Department conducted research and constructed one of the first parallel robots, a 6-legged parallel hexapod, in the years 2009–2010 In order to develop and train researchers for this field, numerous research institutes of significant universities, including Hanoi Polytechnic, Ho Chi Minh City Polytechnic,
Figure 1 1 Robot in industrial mechanical arm form
Ho Chi Minh City Technical Pedagogy, etc., have opened more industries like robotics and artificial intelligence
While researching and researching robots in parallel, our team chose the topic
"DESIGN, CONSTRUCTION AND MODEL CONTROL OF FIVE BAR - PARALLEL ROBOT MODEL" And with the topic of my group, I hope that it will partly help with the study of parallel robots like this in the future.
Purpose of design
+ Optimize the robot’s workspace + The movement speed of the link bars is fast + High rigidity
+ Good load capacity + Can perform many difficult operations + High operating accuracy
+ Parallel mechanism robots can carry out a wide range of tasks, including the assembly of minute components and the movement of delicate processes requiring extreme precision, such as milling, drilling, turning, welding, and assembly
+ Limited operating space and design
+ Complex and hard-to-solve kinematics problems
+ The workspace will have many singularities if the length of the connecting rods is not designed well.
Limited of the project
Fabrication, construction and operation of a five-bar parallel robot model due to time and space limitations, as well as the level and experience of the group
Due to the fact that there are many limitations, my group will conduct research focusing on some of the following contents:
− Calculation of kinematics, dynamics, positioning and simulation of the robot working area
− Modeling a robot with five parallel bars
− Create a five-bar parallel robot model
− Set up the robot to operating.
Presentation content, overview of chapters
− Robot’s kinematics and workspace of the robot
❖ Chapter 4: Construction, experiment, synthesis and analysis
❖ Chapter 5: Results, comments and Conclusion
MECHANICAL DESIGN
Overview Of Parallel Manipulator Constructs
After reviewing and studying the basic configurations of the robot arm to determine the configuration that best suits the given goal, the team members agreed to choose a parallel robot There are the options suggested:
A Cartesian robot (also known as a linear robot) is an industrial robot with three major control axes that are perpendicular to each other and linear (travel in a straight line rather than turning) Moving hands up and down, back and forth corresponds to three sliding joints This mechanical layout, among other benefits, simplifies the robot arm solution When referred to as a crane base, Cartesian robots with horizontal five walls are supported at both ends of the platform; they are mechanically similar to cranes but not conventional robots Crane robots are often huge
+ Allows for precise positioning throughout the work area
+ It has a large tonnage and range
+ Simple to program and inexpensive
+ The addition of cranes or other types of material handling equipment other data in the robot workspace is not appropriate very For the above type, there are many difficulties in maintaining the position of the actuators and electric actuators Low degree of freedom
+ Can not move in all orbits
+ Not the fastest robot yet
SCARA robot works by rotating on the same plane along vertical axes (Z axis)
In particular, they are faster and more flexible than the Cartesian robot Configuration allows the creation of simple structures Used for simple assembly that does not require complete part orientation
+ The SCARA robot's ability to repeat tasks will be more accurate and less expensive than an articulated robot
+ More complex quests can be completed through matching
+ Limited Z axis so the operating space is not large
+ Can only take a fixed workpiece and work on a fixed route
2.1.3 Define the Five Bar – Parallel Robot
From the advantages and disadvantages of the above robots, my team discussed selecting the research and development planar parallel robot Any space and orbit problems are easily solved
+ Different Type 2 singularities often exist for each of the various working modes of parallel robots (solutions to the inverse kinematics) + Therefore, by simply changing working modes, it is feasible to reach any point from the entire workspace (or from a significant portion of it) without sacrificing accuracy and inherent stiffness Active-joint control makes it simple to pass through Type 1 singularities only while switching between working modes
+ Easy to make, research and develop
+ Designing and manufacturing to achieve maximum operating space and high working speed is a big challenge
+ Singularities are a big hindrance to smooth operation
+ Ensure the stability and accuracy of the machine when working at high speed
Analysis And Design Five-Bar Parallel Robot Configuration Selection
2.2.1 Analysis and Design of the Link Bar
The goal of this project is to optimize the robot's workspace We will proceed to evaluate how the length of the link bars affects the active space
Figure 2 3 Overview about the Robot’s links
Figure 2 4 Case I of simulating workspace
Figure 2 5 Case II of simulating workspace
Figure 2 6 Case III of simulating workspace
Based on the above simulation results, in order for the robot to have the largest workspace, it must be l1= l2= l3= l4= l 0 mm
The rest we need to determine the length of d relative to the length l It is easy to see that the smaller the deviation, the larger the operating space However, if d < l then the close links between the 2 motors will not be traversed due to mechanical noise Therefore, the optimal design is d > l, a small interval that will avoid mechanical noise as much as possible
The length d will be determined by the sum of the radius of the motor shaft, the radius of the active link head attached to the motor, the length l, the factor of safety and the length of the locating pin fastening between the active link with motor shaft drive
From that, we can calculate that d > 220 mm, so the group chooses d$0 mm
2.2.2 Five-Bar Parallel Robot Design
From the above analysis, we choose the link bar length to be 200mm The material is aluminum which is lightweight and high strength a Five-Bar Parallel Robot Base Frame
The base frame consists of 2 main components:
− The base is plasma-cut from an aluminum sheet with a thickness of 5mm to ensure stability and keep the 2 motors in place
− The base is shaped by aluminum bars which is lightweight, solidity and high aesthetics
Figure 2 7 Five-Bar Parallel Base Frame
Figure 2.8 is Active link - a link bar directly connected to the 2 motors, designed with a length of 200mm, machined with 2 cylindrical holes at 2 ends, 1 connector is connected to the motor shaft, the other end connects to the passive link
At the connector with the engine, 2 extra threaded holes are added on the outside to fix the rod and the motor shaft is more firmly, the other end is drilled to connect to the next rod
In the bottom of the link is hollowed out a part to reduce the weight of the bar and is a place to fix the air pipes or wires to the end effector, increasing the aesthetics of the robot.
The passive link 1 is designed similar to the active bar mentioned above with a length of 200mm, this bar is designed to be thinner and lighter to reduce vibrations at the end effector d Passive Link 2
The passive link 1 is designed similar to the passive link 2
The part connected to the active link of the passive link 2 is made lower than that of the passive link 1 This design helps the 2 passive links move more flexibly and reduce the angle needed by the mechanical part, increasing the angle rotary for engine
Durability Calculation And Material Selection
We choose A6061 Aluminum material to test and choose for all of the links
The allowable normal stress of A6061 aluminum is 137.29 N/mm2
Active link has a cross-sectional area D = 30 mm and height h = 15 mm:
⇔ 𝑁 ≤ 137.29 × 450 = 61780.5 𝑁 (2.2) Compared to the stated goal of transporting objects weighing less than 1kg at high speeds Aluminum A6061 can fulfill the required standards
Passive link 1 has a cross-sectional area with a width of D = 30 mm and a heigh of h = 10 mm:
Figure 2 11 Stress simulation of Active Link
Similar to the above, we get the following result
41187 N is the maximum force the Passive Link 1 can withstand Aluminum A6061 can fulfill the required standards
Passive link 2 has a cross-sectional area with a width of D = 30 mm and a height of h = 10 mm:
Similar to the above, we get the following result
41187 N is the maximum force the Passive Link 2 can withstand Aluminum A6061 can fulfill the required standards
Figure 2 12 Stress simulation of Passive Link 1
Figure 2 13 Stress simulation of Passive Link 2
Iron pin with cylindrical cross-sectional area of radius 4mm
The maximum shear force that the iron pin can withstand is 19100.8824 N
Calculation And Motor Selection
Let M1 be the torque of Motor 1 ( N.m)
M2 be the torque of Motor 2 (N.m)
We have the mass of Link1_a, Link2_a and (1/2) EP points are:
Total length of Link1_a, Link2_a is:
Torque of Link1_a + Link2_a, from the origin point Link1_a:
We have the mass of Link1_b, Link2_b and (1/2) point EP are:
Total length of Link1_b, Link2_b is:
Torque of Link1_b + Link2_b, from the origin point to Link1_b:
⇒ Choosing the motor has torque that can reach 2.5 (N.m)
Choose a motor with a torque greater than 5 (N.m)
With the requirement that the end effector move the positions with a small error, the machine operates smoothly to increase acceleration and moment of inertia, so the proposed group plan is to use a reduction gearbox, specifically a reduction gearbox 1 /10 with the following parameters
Table 1 Parameter Table Gearbox 57PX10
With the requirement for torque is at least 5 (Nm), when using this reduction gearbox, we achieve large acceleration and high torque, smoother movement
From there, through the 1/10 gear ratio, it is easy to calculate the engine torque greater than 0.5 Nm will be enough to meet the requirements set forth
Recommended use Step motor Nema 23 57*57*56 (mm) with the datasheet table below
Holding Torque at continuous current
Holding Torque at peak current
Under – Voltage Trip VDC Logic
Over – Voltage Trip VDC Logic
Complete Design
From all the above evaluations and tests, we get the complete design model as below:
Figure 2 15 Five-Bar Parallel Robot In Design
The purpose of this design is to create a flexible robot with the largest workspace with requirements, such as easy disassembly and light overall weight with high strength, so the team prioritized components made from aluminum
Equal lengths of connecting rods will create the largest working space to maximize labor productivity
L0 : Length from origin point to engine A1 và A2
L1 : Length from origin engine A1 to rotary joint P1
L2 : Length form rotary joint P1 to end-point E
a1 : Angle created by link A1 P1 and x axis
a2 : Angle created by link A2 P2 and x axis
p1 : Angle created by link P1 E and x axis
p2 : Angle created by link P2 E and x axis
From the above diagram we have:
Y p2 = (L 1 ( sin( a2 )) (2.19) From (2.16), (2.17), (2.18) và (2.19) we have:
1 : Angle created by A1Eand x axis
2 : Angle created by A2E and x axis
2 : Angle created by P1P2 and x axis
Applying the trigonometric system in a right triangle A1EH we have:
Applying the trigonometric system in a right triangle A2EH we have:
On the other hand, applying Cos's Theorem in triangle A1P1E we have:
Similarly, apply Cos's Theorem in triangle A2P2E we have:
Applying Pythagorean Theorem in a right triangle A1EH we have:
Applying Pythagorean Theorem in a right triangle A2EH we have:
Replace (2.13) and (2.14) into (2.11), (2.12) we have:
In triangle EP1P2 we have:
Different modes can be used to configure the robot workspace The DexTAR Robot has been used to study and put this into practice The following is a summary of these modes:
Workspace of the robot
The operating space of parallel robots is usually smaller than that of serial robots of similar size and is often classified by singularities And where singularities, broadly defined, are those where the natural stiffness of the parallel robot changes dramatically
Most parallel robots have two different types of singularities
Configurations at the point where the end effector finally reaches one or more degrees of freedom are called singularities of type 1 They can be understood as corresponding to the boundary of the workspace, i.e where one in the arms reachs its inner or outer limit
Type 2 singularities (also referred to as parallel singularities) are more complex configurations located within the active space in which the actuators cannot resist the applied force and/or torque Applied to the end-actuator
And the most typical approach is to leave the Type 2 singularities inside the workspace and navigate the robot in a region without a single singularity However, even if this area is maximized, it is still smaller than the complete workspace Although smaller, that is also compensated by the robot's working modes Working and navigating the robot in an area without a single singularity However, even if this area is maximized, it is still smaller than the complete workspace Although it is smaller, that is also compensated by the robot's working modes
The A1C and A2C are stacked on the left side The set A1CA2 in this case is unrestricted and can freely rotate around the point A1
On the right side, the A1C and A2C links are aligned The robot could not withstand the force applied to the A1A2 series and the mechanism was completely stuck The robot also cannot escape the type 2 singularities Therefore, an external force must be applied to remove the device
2.6.3 Cases belonging to 2 types of singularity:
Belongs to type 1 singularity and occurs when O1, A1, C lie on the same line and A1, A2 overlap:
Figure 2 20 Case where 3 points are collinear
Here the locations of the Type 1 singularity are arcs of circles of radius 2L and centered at points O1 and O2, as well as the point themselves O1 and O2
Belongs to a type 2 singularity and is a circle of radius L represented by point C when A1 and A2 overlap:
Figure 2 21 Case where A 1 and A 2 overlap
The set of coordinates of points corresponding to a type 2 singularity is [𝑥 1𝑛 𝑦 1𝑛 ] and [𝑥 2𝑛 𝑦 2𝑛 ] with 𝛼 𝑛 is dependent on the operating mode of the machine will be calculated as follows: x 1n = l 2 cos α1n + x OP1 (2.40) y 1n = l 2 sin α1n + y OP1 (2.41) x 2n = l 2 cos α2n + x OP2 (2.42) y 2n = l 2 sin α2n + y OP2 (2.43)
Parametric equations for two circle Type 2 singularities (C và C’) is:
When 0 ≤