Robotics and automation _ power sources and sensorsJAIGANESH SEKAR
Hydraulic, pneumatic and electric drives – determination of HP of motor and gearing ratio – variable speed arrangements – path determination – micro machines in robotics – machine vision – ranging – laser – acoustic – magnetic, fiber optic and tactile sensors.
Robotics deals with the design, construction, operation, and use of robots, as well as computer systems for their control, sensory feedback, and information processing. These technologies are used to develop machines that can substitute for humans and replicate human actions
Robotics and automation _ power sources and sensorsJAIGANESH SEKAR
Hydraulic, pneumatic and electric drives – determination of HP of motor and gearing ratio – variable speed arrangements – path determination – micro machines in robotics – machine vision – ranging – laser – acoustic – magnetic, fiber optic and tactile sensors.
Robotics deals with the design, construction, operation, and use of robots, as well as computer systems for their control, sensory feedback, and information processing. These technologies are used to develop machines that can substitute for humans and replicate human actions
Requirements of a sensor, Principles and Applications of the following types of sensors- Position sensors - Piezo Electric Sensor, LVDT, Resolvers, Optical Encoders, pneumatic Position Sensors, Range Sensors Triangulations Principles, Structured, Lighting Approach, Time of Flight, Range Finders, Laser Range Meters, Touch Sensors ,binary Sensors., Analog Sensors, Wrist Sensors, Compliance Sensors, Slip Sensors, Camera, Frame Grabber, Sensing and Digitizing Image Data- Signal Conversion, Image Storage, Lighting Techniques, Image Processing and Analysis-Data Reduction, Segmentation, Feature Extraction, Object Recognition, Other Algorithms, Applications- Inspection, Identification, Visual Serving and Navigation.
Content:
Introduction to Stepper Motors
Types of Stepper Motors
Main components of a stepper motor
How do these components work together
Control sequence to turn a stepper motor
Advantages and disadvantages of stepper motors
Practical Applications of stepper motor
Step Angle
Summary
For more information Email us:
Engineeringgaragevir@gmail.com
Regards;
xubair khan
Introduction
Types of end effectors
Mechanical gripper
Other types of grippers
Tools as end effectors
The Robot/End effectors interface
Considerations in gripper selection and design
Definition and origin of robotics – different types of robotics – various generations of robots – degrees of freedom – Asimov's laws of robotics – dynamic stabilization of robots.
Pneumatic Drives-Hydraulic Drives-Mechanical Drives-Electrical Drives-D.C. Servo Motors, Stepper Motors, A.C. Servo Motors-Salient Features, Applications and Comparison of all these Drives, End Effectors-Grippers-Mechanical Grippers, Pneumatic and Hydraulic- Grippers, Magnetic Grippers, Vacuum Grippers; Two Fingered and Three Fingered Grippers; Internal Grippers and External Grippers; Selection and Design Considerations.
Robotics and Autoamtion_ manipulators, actuators and end effectorsJAIGANESH SEKAR
Construction of manipulators – manipulator dynamics and force control – electronic and pneumatic manipulator control circuits – end effectors – U various types of grippers – design considerations.
Requirements of a sensor, Principles and Applications of the following types of sensors- Position sensors - Piezo Electric Sensor, LVDT, Resolvers, Optical Encoders, pneumatic Position Sensors, Range Sensors Triangulations Principles, Structured, Lighting Approach, Time of Flight, Range Finders, Laser Range Meters, Touch Sensors ,binary Sensors., Analog Sensors, Wrist Sensors, Compliance Sensors, Slip Sensors, Camera, Frame Grabber, Sensing and Digitizing Image Data- Signal Conversion, Image Storage, Lighting Techniques, Image Processing and Analysis-Data Reduction, Segmentation, Feature Extraction, Object Recognition, Other Algorithms, Applications- Inspection, Identification, Visual Serving and Navigation.
Content:
Introduction to Stepper Motors
Types of Stepper Motors
Main components of a stepper motor
How do these components work together
Control sequence to turn a stepper motor
Advantages and disadvantages of stepper motors
Practical Applications of stepper motor
Step Angle
Summary
For more information Email us:
Engineeringgaragevir@gmail.com
Regards;
xubair khan
Introduction
Types of end effectors
Mechanical gripper
Other types of grippers
Tools as end effectors
The Robot/End effectors interface
Considerations in gripper selection and design
Definition and origin of robotics – different types of robotics – various generations of robots – degrees of freedom – Asimov's laws of robotics – dynamic stabilization of robots.
Pneumatic Drives-Hydraulic Drives-Mechanical Drives-Electrical Drives-D.C. Servo Motors, Stepper Motors, A.C. Servo Motors-Salient Features, Applications and Comparison of all these Drives, End Effectors-Grippers-Mechanical Grippers, Pneumatic and Hydraulic- Grippers, Magnetic Grippers, Vacuum Grippers; Two Fingered and Three Fingered Grippers; Internal Grippers and External Grippers; Selection and Design Considerations.
Robotics and Autoamtion_ manipulators, actuators and end effectorsJAIGANESH SEKAR
Construction of manipulators – manipulator dynamics and force control – electronic and pneumatic manipulator control circuits – end effectors – U various types of grippers – design considerations.
An introduction to Energy Saving Opportunities in Pumping Systems Leonardo ENERGY
The objective of this webinar is to give an introduction to energy saving in pumping systems, with an emphasis on the control strategies available for optimising the different types of systems commonly found in industry and commercial buildings. It will also give an overview of the cost effective selection of energy efficient pumps and motors.
Pumping systems use more energy than any other type of motor driven system, and so should always be a primary candidate when looking to make energy savings at a site.
Introduction to hydraulics and pneumatic by Varun Pratap SinghVarun Pratap Singh
Download Link (Copy URL):
https://sites.google.com/view/varunpratapsingh/teaching-engagements
This file contains basic information about hydraulics and pneumatic systems.
This presentation describes the complete working of flywheel based Kinetic Energy recovery system. It is used in racing cars like F1 and other racing cars.
Robot Drives And End Effectors
Robot drive systems: Hydraulic, Pneumatic and Electric drive
systems, classification of end effectors, mechanical grippers, vacuum grippers, magnetic grippers,
adhesive gripper, gripper force analysis and gripper design
Hydraulic liquids, are the medium by which power is transferred in hydraulic machinery. Common hydraulic fluids are based on mineral oil or water.Examples of equipment that use hydraulic fluids include excavators and backhoes, hydraulic brakes, power steering systems, transmissions, garbage trucks, aircraft flight control systems, lifts, and industrial machinery.Work is taken from fluids due to mechanical advantage ,i.e, applying low input in form of force and getting a higher output in form of a large force .
This presentation gives the information about introduction to control systems
Subject: Control Engineering as per VTU Syllabus of Aeronautical Engineering.
Notes Compiled By: Hareesha N Gowda, Assistant Professor, DSCE, Bengaluru-78.
Disclaimer:
The contents used in this presentation are taken from the text books mentioned in the references. I do not hold any copyrights for the contents. It has been prepared to use in the class lectures, not for commercial purpose.
This template was created for DSCE, Aeronautical students. You have to replace the institution details.
Create a separate document for each chapter, so that under numbering, you can change the sequence of chapter main heading according to chapter wise. i.e., 2.1, 2.2 etc.
Same procedure is applicable to Figure caption and Table caption.
This template can be used to generate, BE seminar report, M.Tech and Ph.D thesis also.
This template is created to assist UG students in generating their thesis without much hassle.
Contents are taken from VTU website. I don’t hold any copyright for this document.
Hareesha N G
Assistant Professor
DSCE, Bengaluru
This document is an Instruction manual for Computer aided machine drawing
Subject: Computer aided machine drawing (CAMD)
Syllabus contest is as per VTU, Belagavi, India.
Notes Compiled By: Hareesha N Gowda, Assistant Professor, DSCE, Bengaluru-78.
This document gives the class notes of Unit-8: Torsion of circular shafts and elastic stability of columns. Subject: Mechanics of materials.
Syllabus contest is as per VTU, Belagavi, India.
Notes Compiled By: Hareesha N Gowda, Assistant Professor, DSCE, Bengaluru-78.
This document gives the class notes of Unit-8: Torsion of circular shafts and elastic stability of columns. Subject: Mechanics of materials.
Syllabus contest is as per VTU, Belagavi, India.
Notes Compiled By: Hareesha N Gowda, Assistant Professor, DSCE, Bengaluru-78.
This document gives the class notes of Unit 6: Bending and shear Stresses in beams. Subject: Mechanics of materials.
Syllabus contest is as per VTU, Belagavi, India.
Notes Compiled By: Hareesha N Gowda, Assistant Professor, DSCE, Bengaluru-78.
This document gives the class notes of Unit 5 shear force and bending moment in beams. Subject: Mechanics of materials.
Syllabus contest is as per VTU, Belagavi, India.
Notes Compiled By: Hareesha N Gowda, Assistant Professor, DSCE, Bengaluru-78.
This document gives the class notes of Unit 3 Compound stresses. Subject: Mechanics of materials.
Syllabus contest is as per VTU, Belagavi, India.
Notes Compiled By: Hareesha N Gowda, Assistant Professor, DSCE, Bengaluru-78.
This document gives the class notes of Unit 2 stresses in composite sections. Subject: Mechanics of materials.
Syllabus contest is as per VTU, Belagavi, India.
Notes Compiled By: Hareesha N Gowda, Assistant Professor, DSCE, Bengaluru-78.
This document contains: Mechanics of Materials: Question bank from old VTU Question papers ; Pprepared by Hareesha N G, DSCE, Bengaluru. These questions are picked from last 06 years of old VTU question papers.
This presentation was prepared for a seminar. I have shared this with you. This is not related to curriculam. Please writre your criticisms to: hareeshang@gmail.com.
This presentation gives the information about Screw thread measurements and Gear measurement of the subject: Mechanical measurement and Metrology (10ME32/42) of VTU Syllabus covering unit-4.
This presentation gives the information about Force, Pressure and Torque measurements of the subject: Mechanical measurement and Metrology (10ME32/42) of VTU Syllabus covering unit-6.
This presentation gives the information about mechanical measurements and measurement systems of the subject: Mechanical measurement and Metrology (10ME32/42) of VTU Syllabus covering unit-5.
This CIM and automation laboratory manual covers the G-Codes and M-codes for CNC Turning and Milling operations. Some concepts of Robot programming are also introduced.
Overview of the fundamental roles in Hydropower generation and the components involved in wider Electrical Engineering.
This paper presents the design and construction of hydroelectric dams from the hydrologist’s survey of the valley before construction, all aspects and involved disciplines, fluid dynamics, structural engineering, generation and mains frequency regulation to the very transmission of power through the network in the United Kingdom.
Author: Robbie Edward Sayers
Collaborators and co editors: Charlie Sims and Connor Healey.
(C) 2024 Robbie E. Sayers
Industrial Training at Shahjalal Fertilizer Company Limited (SFCL)MdTanvirMahtab2
This presentation is about the working procedure of Shahjalal Fertilizer Company Limited (SFCL). A Govt. owned Company of Bangladesh Chemical Industries Corporation under Ministry of Industries.
Student information management system project report ii.pdfKamal Acharya
Our project explains about the student management. This project mainly explains the various actions related to student details. This project shows some ease in adding, editing and deleting the student details. It also provides a less time consuming process for viewing, adding, editing and deleting the marks of the students.
NO1 Uk best vashikaran specialist in delhi vashikaran baba near me online vas...Amil Baba Dawood bangali
Contact with Dawood Bhai Just call on +92322-6382012 and we'll help you. We'll solve all your problems within 12 to 24 hours and with 101% guarantee and with astrology systematic. If you want to take any personal or professional advice then also you can call us on +92322-6382012 , ONLINE LOVE PROBLEM & Other all types of Daily Life Problem's.Then CALL or WHATSAPP us on +92322-6382012 and Get all these problems solutions here by Amil Baba DAWOOD BANGALI
#vashikaranspecialist #astrologer #palmistry #amliyaat #taweez #manpasandshadi #horoscope #spiritual #lovelife #lovespell #marriagespell#aamilbabainpakistan #amilbabainkarachi #powerfullblackmagicspell #kalajadumantarspecialist #realamilbaba #AmilbabainPakistan #astrologerincanada #astrologerindubai #lovespellsmaster #kalajaduspecialist #lovespellsthatwork #aamilbabainlahore#blackmagicformarriage #aamilbaba #kalajadu #kalailam #taweez #wazifaexpert #jadumantar #vashikaranspecialist #astrologer #palmistry #amliyaat #taweez #manpasandshadi #horoscope #spiritual #lovelife #lovespell #marriagespell#aamilbabainpakistan #amilbabainkarachi #powerfullblackmagicspell #kalajadumantarspecialist #realamilbaba #AmilbabainPakistan #astrologerincanada #astrologerindubai #lovespellsmaster #kalajaduspecialist #lovespellsthatwork #aamilbabainlahore #blackmagicforlove #blackmagicformarriage #aamilbaba #kalajadu #kalailam #taweez #wazifaexpert #jadumantar #vashikaranspecialist #astrologer #palmistry #amliyaat #taweez #manpasandshadi #horoscope #spiritual #lovelife #lovespell #marriagespell#aamilbabainpakistan #amilbabainkarachi #powerfullblackmagicspell #kalajadumantarspecialist #realamilbaba #AmilbabainPakistan #astrologerincanada #astrologerindubai #lovespellsmaster #kalajaduspecialist #lovespellsthatwork #aamilbabainlahore #Amilbabainuk #amilbabainspain #amilbabaindubai #Amilbabainnorway #amilbabainkrachi #amilbabainlahore #amilbabaingujranwalan #amilbabainislamabad
Water scarcity is the lack of fresh water resources to meet the standard water demand. There are two type of water scarcity. One is physical. The other is economic water scarcity.
Hybrid optimization of pumped hydro system and solar- Engr. Abdul-Azeez.pdffxintegritypublishin
Advancements in technology unveil a myriad of electrical and electronic breakthroughs geared towards efficiently harnessing limited resources to meet human energy demands. The optimization of hybrid solar PV panels and pumped hydro energy supply systems plays a pivotal role in utilizing natural resources effectively. This initiative not only benefits humanity but also fosters environmental sustainability. The study investigated the design optimization of these hybrid systems, focusing on understanding solar radiation patterns, identifying geographical influences on solar radiation, formulating a mathematical model for system optimization, and determining the optimal configuration of PV panels and pumped hydro storage. Through a comparative analysis approach and eight weeks of data collection, the study addressed key research questions related to solar radiation patterns and optimal system design. The findings highlighted regions with heightened solar radiation levels, showcasing substantial potential for power generation and emphasizing the system's efficiency. Optimizing system design significantly boosted power generation, promoted renewable energy utilization, and enhanced energy storage capacity. The study underscored the benefits of optimizing hybrid solar PV panels and pumped hydro energy supply systems for sustainable energy usage. Optimizing the design of solar PV panels and pumped hydro energy supply systems as examined across diverse climatic conditions in a developing country, not only enhances power generation but also improves the integration of renewable energy sources and boosts energy storage capacities, particularly beneficial for less economically prosperous regions. Additionally, the study provides valuable insights for advancing energy research in economically viable areas. Recommendations included conducting site-specific assessments, utilizing advanced modeling tools, implementing regular maintenance protocols, and enhancing communication among system components.
2. UNIT-7: ACTUATORS:
Syllabus
• Types
• Characteristics of actuating system: weight, power-
to-weight ratio, operating pressure, stiffness vs.
compliance, Use of reduction gears
• comparison of hydraulic, electric, pneumatic
actuators
• Hydraulic actuators-proportional feedback control
• Electric motors: DC motors, Reversible AC motors,
Brushless DC motors
• Stepper motors- structure and principle of
operation, speed-torque characteristics
3. Introduction-Types
• Actuators are the muscles of robots.
• If you imagine that the links and the joints are the skeleton of
the robot, the actuators act as muscles, which move or rotate
the links to change the configuration of robots.
• The actuator must have enough power to accelerate and
decelerate the links and to carry the loads, be light, economical,
accurate, responsive, reliable, and easy to maintain.
• There are many types of actuators available.
– Electric motors
– Servomotors
– Stepper motors
– Direct-drive electric motors
– Hydraulic actuators
– Pneumatic actuators
– Shape memory metal actuators
– Magneto-strictive actuators
4. Introduction
• Electric motors — especially servomotors — are the most commonly
used robotic actuators.
• Hydraulic systems were very popular for large robots in the past and
are still around in many places, but are not used in new robots as
often any more.
• Direct drive electric motors, the shape memory metal type-actuators,
and others like them are mostly in research and development stage
and may become more useful in the near future.
5. CHARACTERISTICS OF ACTUATING SYSTEMS
Weight, Power-to-Weight Ratio, Operating Pressure
• It is important to consider the weight of the actuating system, as well
as its power-to-weight ratio.
• For example, the power-to-weight ratio of electric systems is
average.
• Stepper motors are generally heavier than servomotors for the same
power and thus have a lower power-to-weight ratio.
• The higher the voltage of an electric motor, the better power-to-
weight ratio it has.
• Pneumatic cylinders deliver the lowest power-to-weight ratio.
• Hydraulic systems have the highest power-to-weight ratio.
• However, it is important to realize that in these systems, the weight
is actually composed of two portions. One is the hydraulic actuator,
and the other is the hydraulic power unit.
• The system's power unit consists of a pump, which generates the
high pressure needed to operate the cylinders and rams, a reservoir,
filters, electric drive motors to drive the pump, cooling units, valves,
6. CHARACTERISTICS OF ACTUATING SYSTEMS
Weight, Power-to-Weight Ratio, Operating Pressure
• The actuators' role is only to move the joints.
• However, the power unit is normally stationary and located
somewhere away from the robot itself.
• The power is brought to the robot via an umbilical tether hose.
• Thus, the actual power-to-weight ratio of the cylinders is very high
for the moving parts.
• However, the power unit, which is very heavy, does not move and is
not counted in this ratio.
• If the power unit must also move with the robot, the total power-to-
weight ratio will be much less.
• The power that the hydraulic system delivers is also very high, due to
high operating pressures.
• This may range from 55 psi to 5,000 psi pressures. Pneumatic
cylinders normally operate around 100 to 120 psi.
• The higher pressures in hydraulic systems mean higher powers, but
they also require higher maintenance, and if a leak occurs, they can
become more dangerous.
7. Stiffness vs. Compliance
• Stiffness is the resistance of a material against deformation.
• It may be the stiffness of a beam against bending under the load, the
resistance of a gas against compression in a cylinder under load and
so on.
• The stiffer the system, the larger the load that is needed to deform it.
Conversely, the more compliant the system, the easier it deforms
under the load.
• Stiffness is directly related to the modulus of elasticity of the
material.
• The modulus of elasticity of fluids can be around 1 x 106
psi, which is
very high.
• As a result, hydraulic systems are very stiff and noncompliant.
Conversely, pneumatic systems are easily compressed, and, thus, are
compliant.
• Stiff systems have a more rapid response to changing loads and
pressures and are more accurate.
• Obviously, if a system is compliant, it can easily deform (or compress)
under changing load or changing driving force, and, thus, will be
inaccurate.
8. Stiffness vs. Compliance
• Similarly, if a small driving force is applied to a hydraulic ram, due to
its stiffness, it will respond more rapidly and more accurately than a
pneumatic system, which can deform under the same load.
• Additionally, the stiffer the system, the less it gives or deforms under
load, and thus the more accurately it holds its position.
• Now consider a robot that is used to insert an integrated circuit chip
into a circuit board.
• If the system is not stiff enough, the robot will not be able to push
the chip into the board, since the actuator may deform under the
resistive force.
• On the other hand, if the part and the holes are not perfectly aligned,
a stiff system cannot give enough to prevent damage to the robot or
the part, whereas a compliant system will give to prevent damage.
• So, although stiffness causes a more responsive and more accurate
system, it also creates a danger if all things are not always perfect.
• Thus, a working balance is needed between these two competing
characteristics.
9. Use of Reduction Gears
• Some systems, such as hydraulic devices, produce very large forces
with short strokes.
• This means that the hydraulic ram may be moved very slightly while
delivering its full force.
• As a result, there is no need to use reduction gear trains to increase
the torque it produces and to slow it down to manageable speeds.
• For this reason, hydraulic actuators can be directly attached to the
links, which simplifies the design, reduces the weight and cost and
rotating inertia of joints, reduces backlash, increases the reliability of
the system, due to simpler design and fewer parts, and also reduces
noise.
• On the other hand, electric motors rotate at high speeds (up to many
thousands of revolutions per minute) and must be used in
conjunction with reduction gears to increase their torque and to
decrease their speed, as no one would want a robot arm to be
rotating at such speeds.
• This, of course, increases the cost, number of parts, backlash, inertia
of the rotating body, etc., as was mentioned earlier, but also
increases the resolution of the system, as it is possible to rotate the
link a very small angle.
10.
11. • So, the motor will only "feel" a fraction of the actual inertia of the
load (which in the case of a robot, constitutes both the manipulator
and the load it carries with it)
12.
13.
14.
15.
16.
17. Hydraulic Actuators
• Hydraulic systems and actuators offer a high power-to-weight ratio, large
forces at low speeds (both linear and rotary actuation) compatibility with
microprocessor and electronic controls, and tolerance of extreme
hazardous environments.
• However, due to leakage problems, which is almost inevitable in hydraulic
systems, and due to their power unit weight and cost, they are not used
any more.
• Nowadays, most robots are electric. However, there are still many robots in
industry that have hydraulic actuators.
• Additionally, for special applications such as very large robots and civil
service robots, hydraulic actuators may be the appropriate choice.
• The total force that a linear cylinder can deliver can be tremendously large
for its size.
• A hydraulic cylinder can deliver a force of F = p x A lb, where A is the
effective area of the piston or ram and p is the working pressure.
• For example, for a pressure of 1.000 psi, every square inch of the cylinder
develops 1.000-lb of force.
18. • In rotary cylinders, the same principle is true, except that the output
is a torque where:
19. • where dx is the desired displacement and dx/dt is the desired velocity
of the piston.
• As you can see, by controlling the volume of the fluid going into the
cylinder the total displacement can be controlled.
• By controlling the rate in which the fluid is sent to the cylinder, the
velocity can be controlled.
• This is done through a 'servo-valve’ that controls the volume of the
fluid, as well its rate.
20. A hydraulic system generally consists of the following parts:
1. Hydraulic linear or rotary cylinders and rams. These provide the force
or torque needed to move the joints and are controlled by the servo
valves or manual valves.
2. A hydraulic pump which is a high-pressure pump that provides high-
pressure fluid to the system.
3. Electric (or others such as diesel engine) motor, which operates the
hydraulic pump.
4. Cooling system, which rids the system of the heat generated. In some
systems, in addition to cooling fans, radiators and cooled air are
used.
5. Reservoir, which keeps the fluid supply available to the system. Since
the pump is constantly supplying pressure to the system, whether or
not the system is using it, all the extra pressurized fluid, as well as all
the returned fluid from the cylinders, flow back into the reservoir.
21. A hydraulic system generally consists of the following parts:
6. Servo-valve is a very sensitive valve that controls the amount and the
rate of fluid to the cylinders. The servo-valve is generally driven by a
hydraulic servomotor.
7. Safety check valves, holding valves, and other safety valves
throughout the system.
8. Connecting hoses, which are used to transport the pressurized fluid
to the cylinders and back to the reservoir.
9. Sensors, which are used to control the motion of the cylinders. They
include position, velocity, magnetic, touch, and other sensors.
26. THE LIMITED ANGLE ROTARY ACTUATOR:
• The limited angle rotary actuator is applied when the shaft has to rotate over a
limited angle.
• The animation shows how this simple actuator works: in this case the shaft can
rotate over an angle of about 270 degrees.
• This type of actuator is, among others, used as a rotator actuator on (small) cranes
and excavators.
27. • Figure is a schematic drawing of a typical hydraulic
system.
28. • Figure is a schematic drawing of a position control pilot valve for a
hydraulic cylinder, also called a spool valve.
• This is a balanced valve, which means that the pressures on the two
sides of the spool are equal. Thus, it takes very little force to move
the spool even though it may be under very high pressures.
• When a servomotor is attached to the spool valve to operate it, a
servo-valve is created. The servo valve and the cylinder together
form a hydraulic servomotor.
As the spool moves up or
down, it opens the supply
and return ports through
which the fluid travels to
the cylinder or is returned
to the reservoir.
29. • Depending on the size of the opening of the port, the supply fluid
flow rate is controlled, and so is the velocity of the cylinder.
• Depending on the length of time that the port is kept open, the total
amount of the fluid to the cylinder, and thus its total travel, is
controlled.
• The command to the servomotor controlling the spool valve comes
from the controller.
• The controller sets the current to the servomotor, as well as the
duration the current is applied, which, in turn, controls the position
of the spool.
• Thus, for a robot, when the controller has calculated how much and
how fast a joint must move, it sets the current and its duration to the
servomotor, which, in turn, controls the position and rate of
movement of the spool valve, which, in turn, controls the flow of the
fluid and its rate to the cylinder, which moves the joint.
30. • Thesensors provide feedback to the controller for accurate and
continued control.
• Figure shows the flow of the fluid as the spool valve moves up or
down.
• As you can see, a simple motion of the spool controls the motion of
the cylinder.
31. • To provide feedback to the servo-valve, either electronic or
mechanical feedback can be added to the valve. (Otherwise, it will
not be a servo-valve, but a manual spool valve).
• Figure shows a simple mechanical feedback loop.
• A similar design is used in a two-stage spool valve to provide
feedback to the valve.
32. • Figure shows the schematic of the, block diagram
for the feedback loop.
33. ELECTRIC MOTORS
• When a wire carrying a current is placed within a magnetic field, it experiences a
force normal to the plane formed by the magnetic field.
• If the wire is attached to a center of rotation, the resulting torque will cause it to
rotate about the center of rotation.
• Changing the direction of the magnetic field or the current causes the wire to
continuously rotate about the center of rotation, as shown in Figure .
• In practice, to accomplish this change in the current, either a set of commutators
and brushes are used for DC motors, the current is electronically switched for DC
brushless motors, or AC current is used for AC motors.
This is the basic principle behind all
electric motors.
Similarly, if a conductor is moved within a
magnetic field crossing the flux, a current
develops through the conductor. This is
called a generator.
Figure: When a wire carrying a current is
placed within a magnetic field it will
experience a force in a direction normal to a
plane formed by the current and the field.
34.
35. • There are many types of electric motors that are used
in robotics. They include the following:
– DC motors
– reversible AC motors
– brushless DC motors
– stepper motors
• Except for stepper motors, all other types of motors
can be used as a servomotor.
• In each case, the torque or power output of the motor
is a function of the strength of the magnetic fields and
the current in the windings.
• Some motors have permanent magnets (PMs). These
motors generate less heat, since the field is always
present and no current is needed to build them.
36. • Others have a soft iron core and windings, where an
electric current creates the magnetic field.
• In this case, more heat is generated, but when needed, the
magnetic field can be varied by changing the current,
whereas in permanent magnet motors, the field is
constant.
• Additionally, under certain conditions, it is possible that the
permanent magnet may get damaged and lose its field
strength, in which case the motor becomes useless.
• For example, you should never take a motor apart, as the
permanent magnet will become significantly weaker.
• This is because the iron mass around the magnet holds the
field intact until they are separated.
37. • To increase the strength of the permanent magnets in
motors, most manufacturers magnetize the magnets
after assembling the motor. Motors without
permanent magnets do not have this problem.
• One important issue in the design and operation of all
motors is the dissipation of heat.
• As with the heat generated in many other devices, the
generated heat in motors eventually becomes the
deciding factor about its size and power.
• The heat is generated primarily from the resistance of
the wiring to electric current (load related), but
includes heat due to iron losses, including eddy current
losses and hysteresis losses, friction losses, brush
losses, and short-out circuit losses (speed related) as
well.
38. • The higher the current, the more heat is generated, as W = RI2
.
• Thicker wires generate less heat, but are more expensive, are heavier
(more inertia), and require more space.
• All motors generate some heat. However, what is important is the
path that the heat must take to leave the motor since if the heat is
dissipated faster, more generated heat can be dissipated before
damage occurs.
• Figure shows the heat leakage path to the environment for an AC-
type motor and a DC-type motor.
39. • In DC-type motors, the rotor contains the winding and
carries the current, and thus, heat is generated in the rotor.
• This heat must go from the rotor, through the air gap,
through the permanent magnets, through the motor's
body, and be dissipated into the environment.
• As you know, air is a very good isolator. Thus, the total heat
transfer coefficient for the DC motor is relatively low.
• On the other hand, in an AC-type motor, the rotor is a
permanent magnet, and the winding is in the stator.
• The generated heat in the stator is dissipated to the air by
conduction through the motor's body.
• As a result, the total heat transfer coefficient is relatively
high, especially because no air gap exists.
40. • As a result, AC-type motors can be exposed to relatively
higher currents without damage, and thus they are
generally more powerful for the same size.
• Stepper motors, although not AC motors, have a similar
construction; the rotor is a permanent magnet, and the
stator contains the windings. Thus, stepper motors have
good heat dissipation capability.
• Of course, another major factor in the difference between
brushed and brush-less motors is the life of the brushes
and commutators, as well as the physical limitation of
mechanical switching by brushes.
• Brushless DC motors, AC motors, and stepper motors are
all brushless, and thus they and are sturdy and generally
have long life (only limited by the life of rotor bearings).
41. DC Motors
• DC motors are very common in industry and have been used for a
long time. As a result, they are reliable, sturdy, and relatively
powerful.
• In DC motors, the stator is a set of fixed permanent magnets,
creating a fixed magnetic field, while the rotor carries a current.
• Through brushes and commutators, the direction of current is
changed continuously, causing the rotor to rotate continuously.
• Conversely, if the rotor is rotated within the magnetic field, a DC
current will develop, and the motor will act as a generator.
• If permanent magnets are used to generate the magnetic field, the
output torque TM is proportional to the magnetic flux φ and the
current in the rotor windings Irotor , Then,
42. • where kt is a constant. Since in permanent magnets, the flux is constant, the
output torque becomes a function of /rolor, and to control the output toque, /
(or corresponding voltage) must be changed. If instead of permanent
magnets, soft iron cores with windings are used for the stator as well, then
the output torque is a function of currents in both the rotor and the stator
windings:
• Here both k, and kfarz constants.
• Through the use of powerful magnets made of rare earth materials
and.alloys, the performance of motors has been improved significantly. As a
result, the power-to-weight ratio of motors is much better than before, and
they have replaced almost all other types of actuators.
• To overcome the problem of high inertia and large size of many electric
motors, a disk or shell motor can be used. In disk and shell motors, the iron
core of the rotor winding is removed to reduce its weight and inertia, and
as a result, these motors are capable of producing very large accelerations
(zero to 2,000 rpm in one ms [3]); they respond very favorably to changing
currents for control purposes. A shell motor's rotor looks similar to a
regular DC rotor without the massive iron core. However, in a disk motor,
the rotor is a flat, thin, plate, with windings pressed (etched) into it, as if
one would flatten a rotor into a disk. The wires are generally cut out of a
copper plate and embedded into a disk. The permanent magnets are
43. • generally small, short cylindrical magnets that are
placed on the two sides of the disk. As a result, disk
motors are very thin and are used in many
applications where both space and acceleration
requirements are important. Figure 6.15 is a
schematic of a disk motor.
Figure 6.15 Schematic of a disk motor. The
rotor has no iron core and thus has very little
inertia. As a result, it can accelerate and
decelerate very quickly.