The exact position in space of the end effector or tool head, for those machines, is not directly observed, but is calculated by software monitoring sensors on actuator axes. Mike Smith and the rest of the staff of the Mechanical Engineering Workshop for their expert skill and assistance in the construction of the mechanical apparatus.
Mechatronics
Motivation for the Study
However, this depends on the resolution of the sensor system involved and the positioning ability of the robot. The design of the robot and sensor system was specific to the agricultural and food processing/packaging industries.
Scientific Contribution of the Dissertation
The exact position of the end effector or tool head in space is not detected directly. Knowing the initial position of the robot, the control system uses differential measurements from sensors on the axes that track the linear movement and rotation of the shaft/gears to track the position of the end effector.
Project Specifications
Mechanical Specifications
Research, design and implement a sensor system that will align a machine's end effector with its base and be able to detect its location in space. Sensor repeatability: The repeatability of the sensor system should be higher than 97% with the robot positioned at its absolute maximum distance from the screen.
Research Publications
Chapter 8, Calibration, Simulation Results, and Prototyping: discusses mechanical and software calibration of the system. Simulation results of forward and inverse kinematics, vibrations, planned trajectory and control system are presented.
Chapter Summary
Chapter 2, Parallel Mechanisms: Presents a history of the most influential parallel robots ever conceptualized or built. Chapter 4, Mechanical Design: Discusses the design of parallel robots and then presents the design of the modified delta mechanism.
A History of the most Influential Parallel Robots
Many uses have been proposed for the hexapod, many of which have been accurate predictions of the future. The corporate office of the Sikorsky Aircraft Division of United Technologies then sent a request to the Franklin Institute to design and build a 6 DOF helicopter flight simulator.
Comparison between Parallel and Serial Technology
The problem of parallel mechanisms with 2 and 3 DOF can be described by exact equations of motion and exact mathematical solutions that relate the position of the end effector to the actuated variable magnitudes, i.e. moreover, not all the peculiarities of the 6 DOF parallel mechanism can be found easily. , but they are easy to identify for parallel mechanisms with 2 and 3 DOF.
The Flex-Picker Robot
Chapter Summary
An Overview of Current Location Sensing Technologies
- Global Positioning System (GPS)
- Differential GPS (DGPS)
- Assisted GPS (AGPS) / Indoor GPS
- Triangulation
- Lateration
- Interferometers
- Grid Encoders
- Scene Analysis
- Simultaneous Location and Mapping (SLAM)
- Other
- Sensor System Concept
- Sensor System Resolution
With the addition of a second transmitter with known location and orientation, the receiver's position can be calculated in the base coordinate system. SLAM in the mobile robotics community generally refers to the process of creating geometrically accurate maps of the environment.
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Advantages and Disadvantages of Sensor Concept Advantages
Resolution is independent of screen size, and detector screens can be scaled up to the exact resolution designed.
Chapter Summary
Design of Parallel Kinematic Machines
- Structural Design a. Machine Topology
- Dimensional Synthesis a. Dimensioning
- Design Considerations
Structural design - includes the general arrangement of the mechanical structure, such as the type and number of joints and the way they are connected. Dynamic modeling is discussed in Section 4.3.2 k, but is not used in the robot control system.
Dimensional Synthesis .1 Dimensioning
- System Modelling
The lack of general explicit solutions occurs even in the simpler case of pure translational motion of the end effector. The correct configuration or solution for the end-effector coordinates has z0 more negative than the z-coordinates of the knee joints.
The vector a can be written as PEB''EE • it is the vector from the origin of {ee} to the connection of the i leg on the end effector platform,. The vector c is the vector from the origin of {bs} to the connection point of the i'h leg on the base platform; it is denoted by the notation P ''BS. Construct circles with radii equal to the length of the upper arm centered on the "thigh" joint.
Leg positions
In this configuration, the manipulator cannot resist forces perpendicular to the plane of the base or end effector. Near a single configuration, large movements of joint variables can result in a small movement of the end effector. It then works inward to the limit of the working range (increasing Z min and decreasing Z max, finding the first Z min and the first Z max that give actual solutions to the inverse kinematics, for each XY pair).
Chapter Summary
This chapter also provides a combined geometric and algebraic method for solving both the forward and inverse kinematics and provides an illustration of the workspace envelope. The solutions for FK and IK are closed and these can be solved quickly by the control software. Singularities of PKMs are mentioned and those of the machine designed are given, as well as how they are determined in IK and avoided.
Processor
The controller is used to transfer the reference numbers of those sensors being stimulated to the PC through its ART US transmitter and the PCs RS-232 serial port. A protocol for serial communication is the RS-232C standard, which stands for Recommend Standard Number 232, C is the latest revision of the standard. Null modem cables pass transmit and receive, DTR & DSR & CD and RTS.
Servo Motors
When a pulse is sent to a servo that is less than 1.5ms, the servo rotates to one position and holds its output shaft a few degrees counterclockwise from the neutral point. The minimum and maximum pulse width that will command the servo to return to a valid position are functions of each servo. This is the time it takes for the servo to change from one position to another.
Analogue To Digital Converters
The torque of the servo was sufficient to carry and keep all masses attached to its shaft, which was the main requirement. The voltages at each of these maximum and minimum positions were different for each servo. The positive reference voltage on the ADC for each servo was set to the voltage displayed at the maximum position.
Laser Stimulant
Even though each servo may have a different voltage at say 120°, the digital value of each output of each ADC will read the same.
Light Detectors
- Available Light Sensing Options
These sensors can be designed to measure microwatts to milliwatts of optical power and are inexpensive at high volume. Additional functions such as current-to-voltage conversion and reference level detection (e.g. a Schmitt trigger) can be integrated. Wavelength - An effective choice of detector can be made based on the range of wavelengths involved.
Buffers/Amplifiers
At least 90% of detector applications should be met by using phototransistors, photodarlingtons, photodiodes or photoconductive cells. When the light level is extremely low, the ambient electronic noise level is high, or there are limited space requirements, alternatives such as optical ICs, hybrids, or photomultipliers should be explored. Errors no longer accumulate from one extremity to the next, but are limited to the resolution of the combined laser and sensor arrangement.
Serialization
Power Supply
Schematics and PCBs
Chapter Summary
In the macro phase it consists of tracking and checking the coordinates in 3D space in software. This is done by solving the inverse kinematics for each position of the robot's trajectory and obtaining angular values for the rotation of the upper legs. The robot's trajectory is the path in 3D space that the reference coordinates of the end effector must follow.
Macro Stage Control
The microstep consists of an embedded system that controls the position of each leg and the manner in which it drives the legs to the desired angular position at maximum speed with a control algorithm that inherently takes system dynamics into account.
Micro Stage Control
- Characterising the system
- Control System in S-Domain
- Control System in the Z-Domain (Discrete time)
- Controller Implementation
A comparison of the best-fit approximation and the acceptable approximation of the Laplace transform is shown in Figure 49 b. To get the inverse transfer function, divide the Z transform of the output function by the Z transform of the input function. It is the transfer function Z of the product of the zero-order retention and the plant transfer function.
Chapter Summary
MATLAB Software
- Forward and Inverse Kinematics
- Workspace Envelope
- Vibration
- Trajectory Simulation for Solid Edge (SE)
At time tt the new angles are calculated (with added offset) and fed as input to the forward kinematics that calculates the position in space of the end effector. The spatial displacements of the end effector in X, Y and Z are then calculated compared to the original position without vibration. To create a graphical simulation in SE of the mechanical system moving on a trajectory, an M file was written to solve the inverse kinematics for points along that trajectory.
Visual Basic (VB) Software
- Graphical Control of End Effector
- Graphical Display of Data
- Transfer of Control Signals / Receiving Data
- Software Calibration
For a linear change in position, the change in angle values of the upper legs differs in some way that the spline interpolation in SE cannot fit exactly. This routine calibrates the coordinate system, that is, it aligns the software coordinate system with the real world system of the sensor displays. The text box in the lower left corner displays the results of the inverse kinematics solution.
CAVR Embedded Software
- Command Interpretation / Data Reception
- Shift Register control
- Data processing
- Data Transfer
- ADC control
- PWM Generation
- Control Algorithm
The photo box at the bottom right displays video captured by a web camera. converter is fed into the serial input of the following register). Once this is done, the values are stored in the output feedback values used in the control algorithm. There are 3 compare interrupts and when there is a match between the value stored in one of the compare interrupt registers and the value currently in the timer interrupt register, the corresponding compare interrupt is executed.
Chapter Summary
Calibration
- Mechanical Calibration
- Software Calibration
Errors may occur in the alignment of the screens and should be taken into account. The y-coordinate of the vertical detector screen should be the same if the detector screens are properly aligned. It does not affect, restrict or reduce the movement of the end effector in any way.
Simulation Results
- Forward and Inverse Kinematics Solver
- Vibration
- Trajectory calculation for Solid Edge (SE)
Any effect on the frame of the motors and during movement of the end effector cannot be detected visually. Vibration on the end effector is the result of oscillation of the upper arms of the machine. The video simulation confirmed that the end effector did not rotate or tilt on any of the X, Y or Z axes.
Control System Simulation
The output of the continuous-time closed loop system (S-domain) is a first-order response, this can be seen in Figure 69a. The difference between the outputs of the systems with each controller at any time is shown in Figure 69 c. The difference between the outputs of the systems with controllers Z2 and S is shown in Figure 69 e.
Prototype
Performance Tests and Results
- Mechanical (Positioning)
- Electronic (Sensing) Repeatability
Due to the unavailability of a 3D metrology system, a method was designed to estimate the accuracy of the PKM. The axial accuracy of the positioning is 2 mm, 3 mm and 3 mm for the X, Y and Z axes. The spatial accuracy is about 4 mm, which is the magnitude of the vector from the intended position to the actual position (occurs at data set 14, for coordinate set 3).
Chapter Summary
These features were then used to create a vibration model and visualization of the workspace boundary. II] "Design of the 'Granit' Parallel Kinematic Manipulator" by Alessandro Tasora1, Paolo Righettini2, Steven Chatterton2. Proceedings of the IEEE International Workshop on Intelligent Robots and Systems, pl442-1447, Osaka, Japan, November.
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Coordinates for the center of the end effector.. fprintfC\nSolving the knee coordinates for each leg ..\n').
