Sunday, February 8, 2009

teknologi robot

Robotic Technology
Basic Robot Topology

Design Requirements
• Performance requirements are critical to all successful designs
– What is the robot expected to do?
• How long? How precisely? With how much guidance?...
• How big/heavy/strong/fast?
– What are the environmental conditions?
– What is the time frame in which it will operate?
– How expensive should it be?

Mathematical Modeling
• Modeling the robot to some degree is important to understand its performance and limitations
• Models can be of varying complexity
• Best technical approach for modeling is to develop a series of models, from simple to complex, as required to satisfy questions
• Always know underlying assumptions on which each model is based
– Respect the limitations of models
– Balance use of simplified models to minimize design cycle time
• Be a critical observer of all model results

Feedback Sensor Selection
• High fidelity sensoring can be a critical element in a successful design
– Balance use of direct sensing versus estimation to meet your performance specifications
• Understand sensor requirements:
– Type and system interface
– Accuracy/Precision/Limits/redundancy management issues
• Always co-locate sensor unless absolutely unavoidable
• Understand sensor signal processing

Actuator Selection
• Response characteristics are critical:
– Speed/strength/motion
– Delay in response?
• Power supply requirements
• Physical attributes
– Size
– Weight
– Cost
• Types:
– Electrical: motors/solenoids etc.
– Mechanical: springs/dampers
– Hydraulic or Pneumatic: pistons
Processing Consideration
• Computer or microprocessor control is inherent
• How fast (sampling rate)
– Delay?
• How precise (how are numbers represented)
– Number of bits
• Fixed or floating point numbers?

Control Design Concepts
• Keep it simple
– Strive to maintain linearity
– Avoid extraneous logic and switchable modes
• Design for transient free mode switching
– Understand failure modes and effects
• Design for robustness to failures where appropriate
• Balance performance with stability concerns
– Always adhere to stability guidelines Sensors Sensors

System Integration
• Ensure input devices do not degrade the system
– Control input interface devices
– Sensors must be mounted in environmentally friendly locations
• Ensure constraints imposed by other subsystems do not compromise system
– Structural load considerations
• Use high fidelity simulation of entire system for validation (hardware in the loop to extent possible)
– Functional tests for system features
– End-to-end tests for system integration
– Stress test system as extensively as possible
– Develop regression tests if upgrades are planned

Robotics Functions

Transducer: Sensors and Actuators
• Transducer
– A device that converts a signal from one physical form to a corresponding signal having a different physical form
• Physical form: mechanical, thermal, magnetic, electric, optical,chemical...
• Sensor
– A device that receives and responds to a signal or stimulus
• This is a broader concept that includes the extension of our perception capabilities to acquire information about physical quantities
• Transducers: sensors and actuators
– Sensor: an input transducer (i.e., a microphone)
– Actuator: an output transducer (i.e., a loudspeaker)

Design Consideration
• Range
– Sensors have a limit on upper and lower bounds of the states they measure
• Precision/Accuracy/Resolution/Tolerances
– Precision is how repeatable are measurements when sensing the same state (not always the same as accuracy due to drift etc.)
– Accuracy is how close is the sensed value to the actual value of the sensed state
– Resolution is how finely can the sensor distinguish changes in state
– Tolerances are bounds identified with respect to the above rating a sensorís performance
• Type
– Analog/Digital
• Analog sensors may have a digital interface but still exhibit idiosyncrasies of analog equipment (i.e. airspeed sensor may still be subject to temperature drift)
• Direct digital sensors do not drift (i.e. digital encoders for rotation or translation)
• Noise
– Noise cannot be distinguished from real data so signal to noise ratio for sensor is important

Sensor Types
• Position
– Relative vs. absolute
• GPS provides globally referenced position
• Rangefinders provide local position information with respect to the environment
– Characteristics (where do the sensors work well and where do they not, what important features must be taken into account
• GPS works well in open spaces; may not work at all in most urban areas
• Rangefinders may work well until environment becomes cluttered or uneven
• Velocity
– Groundspeed
– Air or water speed for aerial or marine robots
• Typically a local measurement relative to the robot itself
• Acceleration
– Almost always an absolute measure unless calibrated
• Orientation (pitch/roll/compass heading)
• Rotational rate

Sensor Classification
Sampled data system constraints
• Aliasing occurs if data with a waveform higher than 1/2 the frequency is sampled
– High frequencies are “aliased” to lower frequencies
– Prefiltering is required to eliminate aliasing if input cannot be guaranteed to adhere to max frequency constraint

Sensor Placement
• Co-location
– Always best to place sensor closest to location of importance
• Flexible structures typically require understanding of mode shapes
• Environment
– Heat
– Electromagnetic interference
• Cameras should not be next to motors etc…
• Several types exist (mechanical and optical).
• Mechanical example: flywheel gyroscope
– Conservation of angular momentum
– Torque on axes depends on T = I.ω.Ω

Light Sensor: Photoelectric
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Thursday, February 5, 2009

struktur Robot

Robot Structure

Robot Design Consideration
1. Bottom-Up Approach
2. Top-Down Approach
3. Bottom-Up and Top-Down
4. Budget
Bottom-Up Approach
A simple method
Detail design is unnecessary
Start from robot body construction
The use of power and weight is not balance
Final implementation does not fit robot contest requirements
Top-Down Approach
A relative complex scientific method
Detail design is necessary
Overall robot functions has been defined
Possible to construct in modular
Difficult to rebuild and redesign
Robot Materials Consideration
Light in weight
Easy to manufacture

Robot Structure
1. Plastic Robot Platform
2. Basic Wooden Platform
3. Building a Metal Platform
Acrylic can be used to build the foundation and frame of the Mini Robot

The best overall wood for robotics use, especially for foundation platforms, is plywood

The best overall wood for robotics use, especially for foundation platforms, is plywood.

Attaching the motor
The wooden platform you have constructed so far is perfect for a fairly sturdy robot, so the motor you choose should be too. Use heavy-duty motors, geared down to a top speed of no more than about 75 rpm; 30 to 40 rpm is even better.

If you have the right tools, working with metal is only slightly harder than working with wood or plastic.

Robot Materials
Types of Batteries

When you think “rechargeable battery,” you undoubtedly think nickel-cadmium—or “Ni-Cad” for short. Ni-Cads aren’t the only battery specifically engineered to be recharged, but they are among the least expensive and easiest to get. Ni-Cads are ideal for most all robotics applications.
Note that Ni-Cads can suffer from “memory effect” whereby the useful capacity of the battery is reduced if the cell is not fully discharged before it is recharged.

Nickel metal hydride (NiMH) batteries represent one of the best of the affordable rechargeable battery technologies. NiMH batteries can be recharged 400 or more times and have a low internal resistance, so they can deliver high amounts of current.

Nickel metal hydride batteries are about the same size and weight as Ni-Cads, but they deliver about 50 percent more operating juice than Ni-Cads. In fact, NiMH batteries work best when they are used in very high current situations.

Unlike Ni-Cads, NiMH batteries do not exhibit any memory effect, nor do they contain cadmium, a highly toxic material.

The battery in your car is a lead-acid battery. It is made up of not much more than lead plates crammed in a container that’s filled with an acid-based electrolyte. When the battery goes dead, recharge it, just like a Ni-Cad. Although lead-acid batteries are powerful, they are heavy.

Representative discharge curves for several common battery types.

The charge/discharge curves of a typical rechargeable
battery. Note that the charge time is longer than the discharge time.

You can obtain higher voltages and current by connecting several cells together. There are two basic approaches:
1. To increase voltage, connect the batteries in series. The resultant voltage is the sum of the voltage outputs of all the cells combined.
2. To increase current, connect the batteries in parallel. The resultant current is the sum of the current capacities of all the cells combined.

Memory effect in Ni-Cad battery can be altered in two ways:
The dangerous way. Short the battery until it’s dead. Recharge it as usual. Some batteries may be permanently damaged by this technique.

The safe way. Use the battery in a low-current circuit, like a flashlight, until it is dead.
Recharge the battery as usual. You must repeat this process a few times until the memory
effect is gone.

Battery Monitor
Quick! What’s the condition of the battery in your robot? With a battery monitor, you’d know in a flash. A battery monitor continually samples the output voltage of the battery during operation of the robot (the best time to test the battery) and provides a visual or logic output.

Gears and Gear Reduction
The normal running speed of motors is far too fast for most robotics applications. Locomotion systems need motors with running speeds of 75 to 150 rpm. Any faster than this, and the robot will skim across the floor and bash into walls and people.

Arms, gripper mechanisms, and most other mechanical subsystems need even slower motors.

The motor for positioning the shoulder joint of an arm needs to have a speed of less than 20 rpm; 5 to 8 rpm is even better.

There are two general ways to decrease motor speed significantly: build a bigger motor (impractical) or add gear reduction.

Pulleys, Belts, Sprockets, and Roller Chain
Akin to the gear are pulleys, belts, sprockets, and roller chains. Pulleys are used with belts, and sprockets are used with roller chain. The pulley and sprocket are functionally identical to the gear. The only difference is that pulleys and sprockets use belts and roller chain, respectively, to transfer power. With gears, power is transferred directly.


Pulleys come in a variety of shapes and sizes. You’re probably familiar with the pulleys and belts used in automotive applications. These are likely to be too bulky and heavy to be used with a robot. Instead, look for smaller and lighter pulleys and belts used for copiers, fax machines, VCRs, and other electronic equipment. These are available for salvage from whole units or in bits and pieces from surplus outlets.

Pulleys can be either the V type (the pulley wheel has a V-shaped groove in it) or the cog type. Cog pulleys require matching belts. You need to ensure that the belt is not only the proper width for the pulley you are using but also has the same cog pitch.


Sprockets and roller chain are preferred when you want to ensure synchronism. For large robots you can use 3/8-inch bicycle chain. Most smaller robots will do fine with 1/4-inch roller chain, which can frequently be found in surplus stores. Metal roller chain is commonly available in preset lengths, though you can sometimes shorten or lengthen the chain by adding or removing links. Plastic roller chain, while not as strong, can be adjusted more easily by using snap-on links.

The Clapper
The “clapper” gripper is a popular design, favored because of its easy construction and simple mechanics. You can build the clapper using metal, plastic, or wood, or a combination of all three.

Two-Pincher Gripper
The two-pincher gripper consists of two movable fingers, somewhat like the claw of a lobster.

Build A Robot
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