SYNOPSIS: HYPER REDUNDANT MANIPULATORS

Objective: 

The central idea of this project is to develop a redundant manipulator to work around obstacles and to reach inaccessible locations. Avoidance in its way towards the plants which are inhospitable to human being due to number of reasons like, high temperature, presence of toxic or radioactive substances demand such manipulators. Redundancy is required for obstacle avoidance (a manipulator is said to have redundant links if it has degrees of freedom more than required to reach a point. The present project is intended to meet demands of a complicated environment by harnessing the potential of redundant manipulator to move in a serpentine fashion.

View:  

The term hyper redundant is refers to redundant manipulators with very large degrees of freedom. These manipulators are analogous in morphology to snakes, elephant trunk and tentacles. For manipulators to be an effective option in soft automation, they require redundancy and veracity. Methods of differential geometry are used to formulate equations which guarantee that sections of the manipulator are confined to the tunnels, and therefore avoid obstacles. A hyper redundant manipulator is a redundant manipulator in which the number of redundant degrees of freedom is large or infinite. These manipulators are naturally suited to operation in highly constrained environments. Proposed tasks for future robotic systems, ranging from space exploration to medical devices will require robotic device and components that are simple, 

robust, lightweight, inexpensive, and easy to control. Hyper redundant binary systems have been proposed to meet this need. It has been shown that performance of a binary robotic system approaches that of a continuous system, as the no of DOF increases. However, high DOF systems are not feasible with conventional components. A major limitation is the actuator technology. In recent years important progress has been made in the area of dielectric polymer actuators.   

A “backbone curve” of constant length can be defined which exactly captures the continuous manipulator shape. In the case of many discrete links, the essential macroscopic features of the manipulator can be captured by a continuous backbone curve of the same length as the sum of manipulator can be captured by a continuous backbone curve of the same length as the sum of the link lengths. The obstacle avoidance computation can be performed using the continuous backbone curve, which is then used via a “fitting” procedure, to define the joint angles of a discrete-linked manipulator.  

fig. Joints of a manipulator

For increased redundancy, the modeling and design procedures become more complex. This results in more complex algorithms which increase computational delays, again complicating the systems controllability. To control redundant reconfigurable systems, it has been found that decentralized control architectures are desirable. Current research in multi-robot system has produced frameworks for team motion co-ordination as well as novel communication methods for self reconfigurable robots. 

 Steps Involved:

Path Planning and Obstacle Avoidance:

Intermediate path points for the end effectors are required for moving from start to goal point; also the manipulator should avoid obstacles. Initially we tried to test the traditional "Potential Field approach" graphically in OpenGL. It is very difficult to find a potential function applicable to all obstacles. We oncluded that potential field approach is not at all practical, as the manipulator tends to vibrate near the obstacles.

Next we have explored through another approach called: "Visibility Graph Search". This along with Inverse Kinematics has proved to be quite feasible. Though Inverse Kinematics for redundant manipulators is not easy to handle, one can simplify the InverseKinematics for 4 DOF parallel plane, serial manipulators. Finally, we will also demonstrate Path Planning and Obstacle Avoidance using Genetic Algorithm .

Manipulator/Work cell Design and Development:

In our three-link manipulator, links would be made of a light and sturdy composite material called "Perspex". The links would be driven by stepper motors. The following figure in the next page gives the overall look of our proposed design. Roller supports to links are given to avoid sagging. The design is portable and can be easily moved from one place to another.

Deriving articulate arm kinematic model (using forward kinematics):

A 3-DOF articulated arm is considered as the next example for obtaining the transformation matrix for the endpoint using forward kinematics technique.

 An articulated arm is a 3-DOF manipulator with three revolute joints, that is an RRR arm configuration as shown in fig . The axes of joint 2 and joint 3 are parallel and axis of joint 1 is perpendicular to these two. At the end of the arm, a faceplate is provided to attach the wrist. 

To determine the “ arm point” transformation matrix , the frames are assigned first as shown in fig. The resulting joint –link parameters are tabulated in table. For all the three joints, joint –offsets are assumed to be zero.

  Fig. Joint-link parameters for articulated arm

 Fig. Frame assignment for articulated arm

 Where  = length of the arm
             =perpendicular distance between two arms
The  link  transformation  matrices  are




Control:

Keeping the obstacles under consideration, redundancy resolution schemes will be developed to maximize the dexterous performance of the manipulator. We need to find the time behavior of the force and torques to 

be delivered by the joint actuators so as to ensure the execution of the desired trajectories. Control of end-effectors motion demands an accurate analysis of the characteristic of the mechanical structure, actuators etc. Therefore manipulator control is ensured to the closure of feedback loops, by 

computing the deviation between the reference inputs and the data provided by the proprioceptive sensors. A feedback control system is capable to satisfy accuracy requirements on the execution of the prescribed 

trajectories. Servo and model-based control strategies will be developed and experimentally evaluated with respect to their performance and cost in order to finalize the most suitable control scheme. In fact much of the challenge of the design and its efficient use focuses on this aspect. The data generated by the path-planning program is fed to control software called LABVIEW. This software converts the digital signal to analog using a control card called FLEX MOTION PC1-6c. The specifications of this control card are shown after few pages. The signal is fed to motor, which drives the manipulator using the gear head. The encoder senses the position of the joints at regular interval oftime. This provides data for feedback control in terms of velocity and position. It is converted to analog signal using the same control card. Thus the feedback loop is completed and the desired motion is obtained. 

I want to share this article with you all. The article is published in EE Times. Please read this--

Capacitive sensing expands to multi-touch all-point sensing in automotive apps

Aditya Kaul, Cypress Semiconductors

10/18/2011 12:30 PM EDT

The images created in Sci-Fi movies tend to push the limits of reality, such as when Tom Cruise uses a multi-touch screen to browse through information in the movie Minority Report. Capacitive sensing technology, however, has changed the way we interact with devices.  We no longer simple push buttons or throw switches.  Rather, we can touch, slide, and pinch the data itself on a touchscreen to interact with it.  The far-off interfaces of the movies are not such science fiction anymore.  In fact, they are already being adapted and designed into a variety of applications including our cars.

Multi-touch all-point sensing is an extension of capacitive sensing which has made it possible for touch technology to become much more intuitive by sensing the presence of multiple fingers simultaneously and being able to recognize gestures.  This article covers the basics of capacitive sensing and the evolution of touch sensing technology in automotive environments. After discussing the construction and internal operation of a multi-touch touchscreen/trackpad, it will also address the paradigm changes brought about by multi-touch all-point sensing in human machine interfaces (HMIs).

Multi-Touch Capacitive Sensing

At the heart any multi-touch all-point system is a capacitive sensor composed of a pair of adjacent electrodes. When a conductive object such as a finger comes in proximity to these electrodes, there is additional capacitance between the electrodes (see Figure 1) that can be measured with the help of a microcontroller. Alternately, capacitive sensing can also be used for proximity sensing where no contact is required between the sensor and the user's body. This can be achieved by increasing the sensitivity of the sensors.

Figure 1. Capacitive Sensing

Capacitive sensing is increasingly being used to replace mechanical buttons, knobs with touch sensitive buttons, and sliders (see Figure 2) for in-car systems like infotainment controls, trunk release, Heating Ventilation & Air Conditioning control (HVAC), and Passive Keyless Entry sensors (PKE). The consequent reduction in the number of mechanical components and grooves (which require more complex molds, trap dust, etc.) enhance reliability and reduce system costs.

Figure 2. Capacitive Sensing Interfaces

Touchscreens and Trackpads

Touchscreens enable users to directly “touch” the application in a device, thus reducing the dependence on external buttons. Similarly in a trackpad, users can interact with the system using instinctive actions and gestures like touching, tapping, pinching, and dragging. Touchscreens come in one of three main forms: Single-Touch, Multi-Touch Gesture, and Multi-Touch All-Point (see Figure 3).

Single-touch touchscreens were predominantly based on resistive touchscreen technology, locating both the screen and buttons within the same area. The limitations of resistive single-touch touchscreens are the ability to detect only one finger per screen at a time, limited gesture recognition capabilities, and poor performance due to wear and tear of the sensors.

These limitations led to the development of projected capacitance technology and multi-touch gesture touchscreens based on it. Multi-touch gesture touchscreens do not depend on pressure to detect user interaction.  They are also able to support  simultaneous multi-touch recognition and tracking along with gesture detection used to manipulate screen viewing size and orientation of web page views.

Multi-touch all-point refers to a touch sensing surface's (trackpad/touchscreen) ability to recognize the presence of two or more points of contact on the surface at the same time. Users have ten fingers across two hands and presence of multiple passengers in a car farther increases that number. Music browsing, map manipulation, and body electronic controls like seat position are a few examples of automotive applications that are prime candidates for this level of rich touchscreen functionality.

Trackpads in cars make it convenient for the driver to operate systems such as the navigation and audio subsystems without having to stretch out to reach the center console. Trackpads also enable character recognition, making alphanumeric keys redundant.

Figure 3. Types of Touchscreens

A Touchscreen typically has a glass/plastic covering overlay along with two layers of transparent conductors such as Indium Tin Oxide (ITO) that are separated by an insulating material (see Figure 4).  Patterns are etched on the ITO layer to form a grid of capacitors. The ITO layer has a high level of transparency which helps make touchscreens brighter and easier to read. Since there is no pressure required for detecting touch, the screen becomes more durable.

In a trackpad, the capacitive sensor construction is similar except that the system has an opaque covering layer and simple copper layers as sensors.

Figure 4. Touchscreen layers

The touchscreens sensors are scanned in order to detect any change in sensor capacitance to detect an finger touches. The data is analyzed to identify gestures, finger range, and finger direction movement.  The system may also drive output devices like LEDs, or control motors.

Capacitive touchscreens and trackpads with 10-finger support are now increasingly being adopted in cars, serving as the integrated interface for various car systems.  These multi-touch all-point sensing systems also allow multiple users within a car to simultaneously access the touchscreen. In addition, automotive networking protocols like CAN/LIN help integrate distributed electro-mechanical systems into a central console. This enables HMI designers to coordinate operation of all subsystems within the console from a single user interface to create an HMI with a unified style and increased flexibility while offering developers greater control over look and feel. 

Multi-touch all-point sensing is helping create displays with an intuitive and engaging user interface and offers a compelling value proposition. Touchscreens and trackpads will be increasingly more pervasive with larger sizes and more capable processors, until they eventually become the automotive interface of choice. 

Piezomotors are a Better Alternative in Many Applications

Background

The word piezo comes from the Greek word piezein, which means to squeeze or press. The piezoelectrical effect is best described as the ability of some materials (e.g. piezo ceramics) to generate an electrical charge in response to a mechanical force (e.g. being squeezed or pressed). The piezoelectric effect is reversible, in that materials exhibiting the effect also exhibit the reverse and/or inverse piezoelectric effect. Thus they change shape or size when excited by an electric charge.

Although, the inverse piezoelectric effect has been well known and studied for some years, it is only relatively recently that commercial devices incorporating piezo technology have begun to find practical applications in everyday devices (e.g. focusing mechanism of certain digital cameras, industrial valves, toys etc.).

This situation is now changing rapidly as an increasing number of companies search for alternatives to conventional electromagnetic motors, in order to solve modern day problems associated with the growing demand for; better performance, energy efficiency, miniaturization, and green technology.

In a growing number of instances companies are finding that piezomotor technology offers the only efficient and cost-effective answers to these problems.

Piezomotors offer a high performance, cost-effective, and reliable solution in many precision motion and flow control systems. Applications are numerous within diversified industries, including aerospace, industrial, medical device, optics, telecommunications, semiconductor, and nanotechnology.

Technology

While there are several types of piezomotor on the market, the design and technology employed by DTI in its standing wave-type piezomotors is quite unique and provides certain key advantages in both use and manufacturability. Available in a variety of sizes and configurations, DTI's full line of rotary and linear piezomotors and piezoelectric valves address many of the modern-day requirements for motion control systems.

DTI's piezomotors, whether rotary or linear, work on the same principle of electrically induced excitation of ultrasonic standing wave(s) within a piezoelectric resonator/ceramic. A schematic of one of DTI's rotary piezomotors with a ring-shaped piezoresonator (1) and stainless steel pushers (3) is shown in the figure. Pushers (3) are attached to the piezoresonator through a vibrational shell (2). An ultrasonic radial standing wave is electrically excited in the resonator causing the ring to expand and contract in radial direction, stimulating movement of the pushers along the radius. Because of their elasticity, the pushers vibrate with the same frequency, although phase shifted, in a direction orthogonal to the radius of the ring. The superposition of the two orthogonal movements results in elliptical movements (5) of the pushers. Because the pushers are held pressed (spring loaded) against the rotor (4), their movement, via friction at the pusher contact area, causes rotation of the rotor.

Key Benefits of Piezoelectric Motors vs. Electromagnetic Motors

Performance	Scalable Design	Low Cost
• 1000 X’s Better Resolution. • 100 X’s Faster Reaction Time. • 10 X’s Greater Torque/Force.	• 1 m O.D. to < 10 mm O.D. • Rotary and Linear Designs.	• Competitive pricing for most models.
Unique Properties	Low Voltage & Efficient	Environmental
• No gear-head required. • Non-magnetic (options available). • Wide temperature tolerance. For further information visit: http://www.discovtech.com	• 12 V DC, miniature PCB design accommodates many applications. • Low Energy Requirements.	• Ceramic Design Eliminates Ferrous or Copper Metals

WEG DEVELOPS ‘POST-STANDARDS’ APPROACH TO ENERGY SAVING, WITH HYBRID DESIGNS THAT SET NEW BENCHMARKS FOR EFFICIENCY

For signatories to the Kyoto Protocol, 2012 is a year of great importance. It’s when parties to the legally binding protocol report on their efforts, in respect of lowering the overall emissions from six greenhouse gases: carbon dioxide, methane, nitrous oxide, sulphur hexafluoride, HFCs, and PFCs - calculated as an average over the five-year period of 2008-12. The Kyoto Protocol is flawed of course – the USA is not a signatory, and Canada withdrew in 2011 – but it has proved to be a call to action across many energy-intensive market sectors. What all these sectors have in common is their use of electric motors, which are the single biggest consumer of electricity worldwide. They account for about two thirds of industrial power consumption and about 45% of global power consumption, according to a new analysis by the International Energy Agency. Unsurprisingly, In view of these figures, electricmotors have been one of the main target areas for improving energy efficiency. The resulting efforts in this area have generated new energy efficient standards, such as the latest IEC 60034-30:2009, a harmonised IE (International Efficiency) grading standard, which is central to the EU’s new eco-design directive 2005/32/EC. Many manufacturers have anticipated the new standard, and have produced energy efficient products to comply. But is this enough, bearing in mind that every standard is a compromise, in the final analysis? One company, WEG thinks not, and has exceeded the requirements of standards in its latest motor and drive designs – both LV and MV. The first evidence of this approach is WEG’s new WQuattro line of super premium efficiency motors. These employ a hybrid design to achieve the highest efficiency in the market, exceeding the requirements of the impending IE4 Super Premium Efficiency classification across their entire output range. The WQuattro line has been developed for users who consider energy saving a major priority. It is an environmentally- friendly range ofmotors that, due to its highly efficient performance - with no energy (joule) losses from its rotor - demands less energy from the grid. For the user, this translates into lower total cost of ownership, a reduction in CO2 emissions, and a faster return on investment. The WQuattro is a hybrid motor integrating a conventional three-phase distributed winding, and a rotor with an aluminium cage and internal high energy magnets. This combination makes the WQuattro ideal for direct- on- line starting and acceleration up to synchronous speed. With this type of operation the motor speed does not vary with load, despite overload variations, or cases of voltage drop, as long as the mains frequency is kept constant. Moreover, there is no requirement for positioning/speed sensors, or special protection relays, and the low bearing temperatures that result from synchronous operation also ensure longer life and reduced maintenance for the motors. In addition to developing highly energy efficient motors for general industrial and process applications, WEG has also focussed its design efforts on improving the efficiency of more specialist designs, such as permanent magnet (PM) motors. This technology has tended to be very much on the back burner, due to the design of standard squirrel cage motors, which are relatively inexpensive, robust and reliable, and well proven in operation. WEG’s new WMagnet series of PM motors, changes this situation by offering a range of user benefits that bring PM motors into mainstream usage. The WMagnet series delivers higher efficiencies - up to 97.5% - compared to equivalent size induction motors, and reduces size by up to 50% and weight by up to 36%. In addition, the motors are, generally, at least one frame size or core length smaller than the equivalent induction motor, and in some cases can be two frame sizes smaller. Massive Power Saving of 33% From PM Motors Alone… The energy efficiency of WEG’s PM design has been demonstrated in one of the prototype applications for the motors, at a textile mill. By replacing standard induction motors used on ring spinning machines with permanent WMagnet motors, the textile plant has reduced its annual power consumption by a massive 33% and increased its machine utilisation by 80%. Both the WQuattro and WMagnet are low voltage motors; however, a substantial section of the motor market is MV, and here, too, the potential for energy efficiency is considerable. WEG is exploiting this potential with its new MV drive, the MVW-01, which achieves 99% efficiency with a unique design that employs Multi-level Topology to minimise component levels, and high voltage (6.5kV) IBGT’s to reducemotor harmonic currents to extremely low levels. Unlike many MV drives on the market, which have 3 or 5- layer control, the WEG MVW-01 range has just two 2- layers. The benefit of this is a reduction in the number of components in the drive, and commensurate improvements in efficiency and reliability. With energy costs at record levels, the efficiency performance of the MVW-01 drives is all- important. It has been calculated that for every 1% of efficiency lost on 1MW drives, the user will pay an extra £5k per year on running costs – and that figure is just for the drive alone.For further information visit at:

 www.weg.net

New iBLDC Motors Empower Mechanical Engineers


Dunkermotor's new line of iBLDC™ motors empower Mechanical Engineers with integrated, intelligent, interfaced, infinitely configurable features. Dunkermotor's smart servo motors are available up to 550 W with built-in PLC functionality, matching planetary or worm gearheads, encoders, brakes, and fieldbus capabilities meeting M.E.'s application requirements without having to become a controls designer.

Please visit at: www.dunkermotoren.com

Pickering Interfaces Introduces New Range of 6GHz PXI Solutions

Clacton on Sea, UK – Pickering Interfaces is expanding its range of 3U PXI RF/Microwave solutions with the introduction of 4 new solutions with frequency coverage to 6GHz.

The 40-880 is a 10MHz to 6GHz solid state SPDT switch available as dual, quad, hex and octal configurations.

The 40-881 is a 10MHz to 6GHz solid state SP6T available as a single or dual version.

The 40-882 is a 10MHz to 6GHz solid state SP4T switch available in single, dual, triple or quad configurations.

The 6GHz switch solutions occupy one, two or three 3U PXI slots depending on the configuration.

The 41-182 is a 10MHz to 6GHz solid state programmable attenuator available in single, dual or triple configurations, each attenuator having an attenuation range of 0 to 31.75dB in 0.25dB steps.

All the new 6GHz solutions have been designed to have consistent RF performance with low VSWR and high switch isolation through the use of high levels of RF screening and SMA connection solutions. Each product uses solid state switches to ensure a very long service life when used within their rating. All switches include automatic termination of unused paths to reduce VSWR effects in connecting cables.

The 6GHz solutions are an excellent alternative to the use of electromechanical relay or microwave switch based designs. The designs provide a higher frequency alternative to electromechanical relay designs and a higher density, lower cost alternative to microwave switch designs, while offering faster operation and longer life.

All the new designs can be supported by any PXI compliant 3U PXI chassis and are supported by Pickering Interfaces Modular LXI chassis for applications requiring Ethernet based control. 

Pricing and availability information is supplied on web site: www.pickeringtest.com

Photransistors L14G1,L14G2 and, L14G3

Has Fairchild, General Electric, QT, and Telefunken left you in the lurch for Phototransistors? Still waiting for shipment? Wait no more! Same day shipping from American Microsemiconductor.

Finally , a dependable supplier of the Silicon Phototransistors. American Microsemiconductor Inc. is now supplying the L14G1, L14G2, and L14G3 narrow angle silicon phototransistor L14 family, in the TO-18 hermetic sealed package; featuring : 45 Volt breakdown, Current up to 2 mA, with 8 uSec switching.

A new design ? Use the reliable proven workhorse L14 series phototransistors and depend on us, we supply legacy semiconductors and then supply them for a long, long, long time. "We start where others stop."

Please visit at: store.americanmicrosemiconductor.com

Archiving Test Data — Digital or Hard Copy?

How long do you need to keep your test data? More importantly, will it be available and readable when you need it? In medical, security, and other industries, archiving test data is a legal requirement to chase problems that may arise in the field. These days, almost all such data is stored on some form of disk rather than the much bulkier paper. But disk formats change frequently and today's (or tomorrow's) computers may not be able to read your data from even a few years ago. Test & Measurement World columnist Martin Rowe looks at this increasingly sticky question.

For more information visit:  http://www.tmworld.com/blog/Rowe_s_and_Columns/41698-How_long_can_you_retrieve_test_data_.php

Constructing a Differential Drive Mobile Robot from

Simple Components

Introduction
One of the most difficult problems associated with construction mobile robots is starting. This document is designed to give you a quick introduction into the theory behind a differential drive mobile robot followed by a description of how such a robot can be built from commonly available components.
Differential Drive Theory

One meaning of "differential" is simply "proceeding at different rates".  Keeping this in mind, a differential drive is one where the drive--or movement--components of the vehicle move at different rates. For example, the diagram below illustrates a very simple differential drive vehicle.

Figure 1 Simple Differential Drive

Each wheel is connected to its own motor. A glide or unpowered castor wheel provides balance at one end of the vehicle. If both motors spin at the same rate and all components are identical then the vehicle will move in a straight line. If one wheel spins faster than the other does, the vehicle will have a tendency to turn in the direction opposite to the fast wheel. If each wheel spins in the opposite direction of the other, the vehicle will turn in place.

This form of steering is commonly found on tracked vehicles such as tractors and tanks. The drive has the advantage of simplicity and a very tight turning radius.

Making a Differential Drive Vehicle

A simple differential drive can be constructed in various ways. One cost-effective means is to use components that are readily available as junk or at a local retailer. To build sucha vehicle you will need several components as illustrated in the photo below.

Figure 2 Vehicle Components

These components are,
1.  An old radio or wire controlled car
2.  A carpet protector for a chair leg
3.  Several small screws
4.  Two 1" brackets
5.  Several narrow wire ties
6.  A hobby AA size batter holder
7.  A bamboo barbecue skewer
8.  Some Hook-and-loop tape (Velcro)
9.  A sample piece of counter-top arborite or Formica

The Drive

Remove the drives from the toy car. These cars tend to have very low voltage motors (3-9 volts DC) driving an arrangement of gears that supply power to the wheels. You can usually remove this arrangement by undoing appropriate screws. The goal is to remove the motor and gears intact. You will need two of these motor and gear arrangements. If a single car has only one, it will be necessary to use two similar cars. The best results are achieved when the drives are similar or identical on either side of your vehicle.

The Vehicle Body
Drilling holes in the Formica with a small drill in front of where the drives will be located will provide anchor points for the wire ties that will hold the motors in place. The diagram above shows a bottom view of the vehicle. Note how the wire ties hold the motors in place. The barbecue skewer is broken and jammed under the ties to firm them up and keep the motors from moving. Also shown in the picture is the glide made from
the carpet protector.

The photo above shows the top view of the vehicle. As on the bottom, a skewer is forced

under the wire ties. The black piece in the middle of the vehicle is one part of the hook

and loop tape. The other part is placed on the bottom of the battery holder. One bracket is

held in place with the bolt that holds the glide in place under the vehicle.

Providing Balance

A side view of the vehicle is provided below. Note how the glide balances the drive

wheels. For best performance, most of the vehicle's weight should ride over the drive

wheels. This can be accomplished by placing the battery holder over or near the rear

wheels.

Additional Vehicle Components

In the diagram below, note how the battery holder is placed on the hook and loop tape.

To allow for the mounting of additional components (possibly mounted on additional

Formica samples), a second bracket is attached to the first in the manner shown. The

remaining vehicle components will be fixed to this second bracket.

Final note

The vehicle should now be ready for final wiring to some form of controller. This is not

shown but can include something as simple as a joystick or something as complex as a

microcontroller or computer.  It is wise to determine how much current the motors draw

from the batteries before attempting to hook them to any electronic controller but, apart

from this caveat, the vehicle should be ready to go.