In this project, the team proposes to build a mobile Extra-Vehicular Activity Robotic Assistant equipped with a manipulator arm. The two main characteristics of the proposed robot are its ability to interpret and execute high level commands given by a human operator, and its ability to detect, isolate and recover from the different types of failures that might affect its hardware. The types of hardware failures that the team will consider to illustrate the fail-safe operation are: (i) failure to one of the electric motors actuating the manipulator arm, and (ii) failure to one of the navigation sensors of the robot.

The high level commands will be used to initiate a multitude of tasks that the robot has to carry out autonomously. The fail-safe operations will allow the robot to continue its mission even in the event of a hardware failure. This proposal describes the proposed design and the method of approach to implement and test the high-level command (HLC) and the fail-safe operations (FSP) of the robot.

2. Mentor / Research Group

The JSC mentor for this project is Mr. David Cheuvront. He is the Technology Integration Division Manager at the Lyndon B. Johnson Space Center. The Technology Integration Division oversees current designs and technologies involved in space exploration and makes decisions whether or not there is a need for technological advancements that need to be made to increase productivity in space exploration. Mr. Cheuvront worked for the Canadian Space Agency in Ottawa, Japan’s Space Agency, and the European Space Agency.

3. Collaboration

In addition to collaborating with Mr. Dave Chevront, the team will be advised by Dr. Mounir Ben Ghalia and Dr. Hamid Zarnani. The team will consult with other engineering students who have worked on previous robotics projects, and with past UTPA graduate students.

4. Team ID / Member Profiles

The team members are currently enrolled in ELEE 4461, Senior Design Project I. The name chosen for the team is Space Autonomia. Originally, the team came up with the name Autonomy in Space. The name was chosen due to the autonomous function of the robot. Then, after some discussions among the team, a consensus was reached to select the name Space Autonomia. Autonomia is the Spanish word for autonomy. The team has named the robot to be designed and built: Autonomo.

The faculty advisor is Dr. Mounir Ben Ghalia. He is an Assistant Professor of Electrical Engineering Department who specializes in robotics and control systems theory. Dr. Ben Ghalia can be contacted via email at benghalia@panam.edu .

The team is lead by Ana Castillo, a Sr. Electrical Engineering student. The team also consists of Nelson Carrasquero, a Sr. Electrical Engineering student, Mario Contreras Jr., a Sr. Electrical Engineering student, and Gabriel Rodriguez, a Sr. Electrical Engineering student. Anna and Nelson will be working on the Fail-Safe operations of the robot. Mario and Gabriel will be working on the High Level Command system. All team members will contribute to the design and construction of the robot structure and the manipulator arm.

5. Background

The area of robotics plays an important role in space exploration. Different types of robotic Technologies have been developed. One of the technologies used in space exploration is tele-robotics. In this technology, a robot is controlled from a remote and safe location by a human operator.

Fail-Safe operations are increasingly important in autonomous or industrial robots which are subject to failures. In this project, a fail-safe system will be designed and built allowing the robot to detect, isolate, and recover from a hardware failure. The High-Level Command allows the robot to carryout a series of complex tasks upon receipt of a speech-command by a human operator. This operative feature removes the need for giving detailed instructions to the robot. Once a high level command is received, the robot starts carrying out its tasks in an autonomous fashion.

6. Design Objective

Team Space Autonomia will demonstrate the effectiveness of a HLC and fail-safe system. The design objects are:

Design a 3-link manipulator
Design a chassis for the robot
Design a control system for the drive module
Design a collision detection and avoidance system
Design a hardware failure detection module
Design a recovery module
Design a voice-recognition system

The HLC will allow the operator to command the robot. The robot will then process the HLC into a series of low level instructions to carry out its main task. The high level command consists of a word phrase that the robot will then process in order to identify the task it must perform. For instance, the operator will give the command “Task 1” and the robot will respond accordingly.

The fail-safe system will detect, isolate, and recover from any faults that may occur during the robot’s mission.

7. Design Plan

7.1 High Level Command

The HLC will consist of a voice command that a human agent will issue to the robot.

The main reasons for adopting a speech-command as the form of HLC operation are :

1. Security purposes

2. High level command implementation

3. Voice command is suitable technique for communication

The first reason ensures that the robot will respond to only authorized operators. This feature guarantees system operation security. Although circumvention is possible, the effort needed to do so acts as a deterrent. Sending other types of data (text) across is just as well; however, it has its caveat (fourth reason). Single verbal HLC allows for complicated tasks to be carried out. A caveat for using data (text) for HLC arises in the particular use of the system (robot). Consider, for instance, the case where the robot has to carry out military tasks under heavy fire. The Commanding Officer (CO) would only speak (at the very least) to the robot to perform its task.

Using other types of HLCs requires for the CO to spend more time on sending data, either by keyboard, or using a stylus to select task from a PDA-like device. Another example is that of an astronaut commanding a robot to assist him/her carrying out a mission.

7.1.2 Speech Recognition System

Figure 1 shows the block diagram of the HLC module.

Figure 1: Block design approach of HLC

The team proposes the use of a wireless microphone headset to transmit the voice signal to the robot. The receiver will be a walkie-talkie in the same frequency as the headset. The speech recognition system will process the signal and store the command in a static RAM IC. Figure 2 shows the schematic of the speech recognition board.

Figure 2: Schematic of speech recognition board [2]

This circuit allows the operator to speak a word in less than 0.92 seconds. Using a speaker dependent and word isolation method, the speech recognition system has a maximum of 40 words, stored in an 8Kx8 static RAM. In order to store these words in memory, the keypad is used [1]. For instance, pressing “0” then “1” programs the word as 01. This works similarly up until word 40.

From Figure 2, the LED acts as status indicators for the operator. If the circuit accepts the word, the LED flashes. However, if the LED does not flash, the word was not correctly programmed, and so must be programmed again. The 7-segment display shows the word programmed or word number currently being programmed.

For security purposes, the robot will acknowledge a high level command only if it is issued from one of the team members. Hence, each command word has to be recorded by each team member in his or her own voice. In addition, if the robot encounters problems interpreting high level commands, a back up system will be used to send individual low level commands to the robot (e.g. move forward, lift arm, etc). Once the command is given and correctly processed, the robot will perform its task.

7.2 Description of the Manipulator Arm

The objective of the manipulator arm is to collect samples of soil and store them in containers located in the back of the robot. The mechanical arm will consist of three links, an end effector, and four revolute joints. Each joint is actuated by a servo motor. The longitude of the arm totally extended will be approximately five feet. The arm will be made of aluminum. Bumper-switch sensors will be placed on the end effector of the arm to detect the surface from which the sample will be taken. Figure 3 illustrates the configuration of the arm. This configuration is composed of a base platform that acts as the base of the arm and connects the arm to the mobile platform. The base platform will have a servo motor that performs a yaw motion. This motion will allow the arm to reach an adequate position to store the sample in the containers placed in the back of the robot. Joint 1, 2, 3, and 4 will move in a pitch form to provide the desired degree of freedom needed to perform the task of sample collection. There will be a mechanism between joints 3 and 4. This mechanism is actuated by a servo motor and will perform a roll motion of the end effector. The actuator of joint 3 will illustrate the redundancy concept for the implementation of the fail – safe system. The actuator of joint 3 will act as a back up system in case the actuator of joint 2 fails. Therefore, the actuator of joint 3 will remain inactive if the actuator of joint 2 works properly.

Figure 3: Mechanical Arm Configuration

7.3 Fail – Safe System Applied to Actuator

One of the main objectives of this project is to apply the fail – safe concept to actuators. A fail safe operation feature allows the robot to go into a safe mode in the event when the system happens to fail. The actuators of joints 2 and 3, shown in Figure 3, will be used to illustrate and simulate an example of fail – safe system. The fail - safe system that will be implemented in this project follows three processes: fault detection, isolation, and recovery.

7.3.1 Failure Scenario and Failure Detection System

The possible actuator failures that may occur during its function are illustrated in the diagram shown in Figure 4. All the possible failures can be detected by the fail – safe system that will be designed for this project. However, just two of them will be simulated and practically illustrated. The following scenario will be used to simulate and illustrate a fault due to external factors.

Figure 4: Causes of Actuator Failures

An object will be placed manually between the segments of joint 2. This will hinder the joint motion. In the scenario previously mentioned, when an object is placed between the two segments of joint 2, the motor will require more power to produce a greater torque; therefore, the magnitude of the current drawn by the motor will increase. When the current drawn by the motor increases abnormally, this situation, will be flagged as an effector failure. In order to detect the failure, a system will be designed to measure and monitor the current drawn by the electrical motor of joint 2. This system will consist of a circuit (built using op-amp) that will measure the current drawn by the motor, and it will be interfaced with the microcontroller to monitor the current behavior of the motor. The microcontroller will compare the actual behavior with the ideal behavior of the motor. If the actual output magnitude differs from the ideal output magnitude by a large percentage, then the microcontroller will determine that the actuator is not working properly.

7.3.2 Defective Actuator Isolation

If the process of failure detection encounters that the actuator is not working properly, then the isolation process will be initiated. This process will disable the defective actuator by shutting the power off. This process will be implemented by the microprocessor which will disable the port to which the motor is connected.

7.3.3 Recovery

Once the defective actuator is isolated from the system, the recovery process will be initiated. The recovery process consists of tow tasks. The first task will be to determine the angle at which the joint 2 is locked. This task is needed to determine the new kinematics of the arm. The second task will be to activate the actuator of joint 3 to restore the degree of freedom of the manipulator.

7.4 Collision Avoidance System

As soon as Autonomo starts moving, it runs the risk of colliding with obstacles. This problem will be evaded by implementing a collision avoidance system. Five ultrasonic sensors from the Polaroid 6500 series will be used for the implementation of the collision avoidance system [3]. These sensors will be located on the front of the robot, pointing at different angles to avoid signal interference within each other. The Polaroid 6500 ranging module can detect objects in a range from 6 inches to 35 feet, and along with the transducer generate an acoustic pulse wave at 49.4 kHz.

The collision avoidance system will consist in interfacing the microcontroller with the Polaroid 6500 ranging module to find the distance between the sensor and the object. The Polaroid 6500 ranging module has a timer which has the function of taking the time of flight of the sonar transmitted. The time of flight of the wave is sent from the Polaroid 6500 ranging module to the microcontroller. The microcontroller will compute the distance, by multiplying one half the speed of sound times the elapsed time. This will provide the result of the distance between the sensor and the object. Once the microcontroller has determined the distance, it will execute a function to command the robot to take another path free of obstacles.

7.5 Fail Safe System Applied to Sensors

Another implementation of a fail - safe system will be applied to one of the ultrasonic sensors used in the collision avoidance system. The processes of failure detection, isolation, and recovery will be used to implement the fail – safe system.

7.5.1 Fault Detection

The possible failures that the Polaroid 6500 sensor may encounter during its function are illustrated in the diagram shown in Figure 5. All the possible failures, shown in Figure 5, will be detected by the fail safe system that will be designed for this project.

Figure 5: Causes of Sensor Failure

The diagram shown in Figure 6, illustrates the algorithm of how failures will be detected. The Polaroid 6500 ranging module sends a fixed electrical signal continuously to the electrostatic transducer to generate the sound wave at 49.4 kHz. Circuit 1 will measure the electrical signal, and along with the microcontroller will monitor the electrical signal to find any irregularity of the ranging module. Once the electrostatic transducer receives the sound bouncing signal, it will be converted it to an electrical signal, then amplifies it. Circuit 2 will measure the electrical signal, and send the output obtained to the microcontroller. The electrical signals measured by Circuit 1 and 2 will be examined and compared by the microcontroller. If the microcontroller determines, that the measured output of the electrical signal is not equal to the values that the transducer should have under normal operation, then the Polaroid 6500 sensor will be flagged as failing.

Figure 6: Algorithm of Failure Detection Process

7.5.2 Defective Sensor Isolation

The faulty ultrasonic sensor will be isolated by shutting of its supplied power. This way, the faulty Polaroid 6500 sensor will not interfere with the operation of the other sensors.

7.5.3 Recovery

Once the microcontroller has isolated a faulty sensor, it will activate a back up sensor already mounted in front of the chassis.

8. Illustrations of Robot Structure

Figures 7 and 8 show the front view of the robot and the back view of the robot respectively.

Figure 7: Front View of Robot Figure 8: Back View of Robot

9. Conclusion

Today, autonomously operated machines play a very important role in space exploration missions. With these systems in place, tasks can be carried out by efficiently by astronauts or by other people. The proposed design will isolate a conceptual robotic system. The proposed design will illustrate a conceptual autonomous robotic system. The integrated HLC and fail - safe operation will make future space robotics more robust.

References

[1] Iovine, John. (1998). Robots, Androids, and Animatrons: 12 Incredible Projects You

Can Build. New York. McGraw-Hill.

[2] Image (Figure 2) source:

http://www.imagesco.com/articles/hm2007/SpeechRecognitionTutorial02.html

[3] Acroname URL: http://www.acroname.com/robotics/parts/R11-6500.html

Appendix A: Timeline

Appendix B: Budget

ITEM NAME				COST
Sensors				$200.00
Heavy Torque Electric Motors				$500.00
PC 104 Board				$700.00
Chassis and Wheels				$400.00
PIC (microcontrollers)				$20.00
PIC Pro Starter Kit				$200.00
Supplies				$100.00
Total				$2,120.00