- Email: [email protected]
Design of a robotic walking stick with mobility assistance control technology (MAVI) for visually impaired people
Materials Today: Proceedings xxx (xxxx) xxx
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
Design of a robotic walking stick with mobility assistance control technology (MAVI) for visually impaired people Oscar Arteaga ⇑, C. Samanta Hurtado, Héctor C. Terán, Miguel A. Carvajal, Jorge G. Ortíz, B. Daniel Tenezaca, V. Hernán Morales ⇑ Universidad de las Fuerzas Armadas ESPE, Sangolquí, Ecuador
a r t i c l e
i n f o
Article history: Received 14 July 2019 Accepted 16 November 2019 Available online xxxx Keywords: Robotic cane Biomechanics Lower extremities Walking stick MAVI
a b s t r a c t The investigation of the present research is a new mechatronic system for a robotic unicycle staff that thanks to a meticulous analysis of the new technologies applied to assistance of technological mobility of people with visual disability as an orthopedic walking stick or a walker. We proceed to contribute with the design of a stick-type mechatronic system coupled to a differential traction platform that facilitates the mobilization of people with motor deficiency by giving them an assistance system to support in the march. It was verified that the design supports the maximum weight established in the parameters of 14 [kg] It was shown that the walking stick can be used with people up to a weight of 93 [kg]. The performance of the load cells with an experimental work cycle by incorporating an application in Android so the user has a feeling of immersion and to provide the possibility of interacting with the device, being able to establish between the user and the robotic staff a bidirectional transfer in real time of information. The findings of the research, multi-axis load cells will be implemented in the future with a control was applying neural networks to minimize the displacement error. Ó 2019 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the scientific committee of the First International Conference on Recent Advances in Materials and Manufacturing 2019.
1. Introduction In recent times, new research that permits improving the quality of life of people with different physical disabilities, highlights aid for the mobility of blind and visually impaired people among which we can mention: exoskeletons, devices based on common devices such as walking sticks or walkers with the inclusion of new technologies using sensors and actuators that gives them much more autonomy and useful functions when they are used [1,2,3]. According to the last World Report on Disability published in 2017 by the World Health Organization. It is estimated that 15% of the world population lives with some type of disability which one of the most common has to do with problems in Mobility [4,5]. The smart walking stick incorporates an accelerometer and a gyroscope (to detect falls). A GPS module (to track the location)
⇑ Corresponding author. E-mail addresses: [email protected] (O. Arteaga), [email protected] (V.H. Morales).
and GSM connectivity (to alert other people in case of emergency) [6,7]. People who need more help walking can use the Keeogo leg exoskeleton a ‘‘walking assist device” that was developed by BTEMIA Inc. The Keeogo comes equipped with sensors placed at the level of the knee and hip joints that detect movement and offer additional motorized assistance to supplement muscle weakness [8,9]. The robotic walking stick unicycle is intended for various specific activities to help the patient; guiding him in his displacement, providing support in his rehabilitation and optimizing maneuverability, through a mobility system with walking stick and allows predicting the intention of movement of the user, as shown in Fig. 1 [10,11]. An essential parameter when using a walking stick is the amount of load exerted on it which is determined according to the type of injury and the evolution of the affected user [12]. Inadequate walking sticks can cause sequelae, such as muscle overload during daily activities and lack of support in the affected limb, lumbar area and upper trapezium, as shown in Fig. 2, as well as a deviation from the centre of gravity [13,14].
https://doi.org/10.1016/j.matpr.2019.11.222 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the scientific committee of the First International Conference on Recent Advances in Materials and Manufacturing 2019.
Please cite this article as: O. Arteaga, C. S. Hurtado, H. C. Terán et al., Design of a robotic walking stick with mobility assistance control technology (MAVI) for visually impaired people, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.222
2
O. Arteaga et al. / Materials Today: Proceedings xxx (xxxx) xxx
Fig. 1. Human Interaction Robot - Main applications: a) Guide, b) Rehabilitation, c) Maneuverability.
Fig. 3. Free-body diagram of the mobile platform.
normal force which represents the force necessary for the platform to move at a speed of 0.48 [m/s] its magnitude is directly proportional to the power and torque of the motor required, the calculation is obtained from the sum of static forces:
F ¼ Fr þ mt g sinh
ð1Þ
Where: Fr is frictional force, h is inclination angle of the plane Being the value obtained from (Eq. (1)) this allows to continue with the calculation of the torque in each wheel with the help of (Eq. (2)).
T wh ¼ ðF £whÞ=4 Fig. 2. Muscular sequelae in the lumbar area and upper trapezius.
2. Mechanic design 2.1. Design parameters. The design parameters chosen: maximum weight, travel speed, body weight, height, degrees of freedom, stability and mobility that allow the mobile platform to be structured with the baton so that everyone converges on the conception of the final product; The maximum weight of the platform must be 15 [kg]. It is formed so that the removable parts with three degrees of freedom, displacements x-axis, z-axis and rotation in y-axis, making it modular, see Fig. 4. It can support the maximum body weight of 15% of average people, the platform moves at a speed of 0.48 [m/s] while the height where the cane can be placed varies between the range of 744 to 806 [mm] all of the above must be configured with a gyroscope so as not to lose the stability and mobility required during human walking [15,16]. The analysis is divided into two parts: the mechanical design of the mobile platform and the mechanical design of the walking stick because the platform and the walking stick act independently which are subsequently complemented for the mobilization of people with motor deficiency. Mechanical design of the mobile platform helps to get the engine power, the extra weight exercised by the user, the weight of the walking stick, the weight of the sensors with a total of 17 kg. In this case, we worked with a load factor of 10% of the total weight; to ensure that any eventuality different to those that were assumed is covered, finally the total value of the weight is W t = 20,4 [kg], therefore the value of the magnitude of force is: W t = 20,4 [kg] 9,81 [m/s2] = 200 [N]. The calculations were made with a static coefficient of friction and dynamic coefficient friction for the static analysis of the platform on inclined surfaces having a maximum inclination angle of 15°. In the Fig. 3 the free body diagram of the platform is observed. It is identified in the Fig. 3 to like the radius of the wheel, N as the
ð2Þ
Where: Twh represents the torque required on each wheel and its value is for a diameter wheel, the power of the motor is found with the equation (Eq. (3))
P ¼ Twh xn
ð3Þ
The angular velocity of the wheels is obtained by the data of the required linear speed and the radius of the wheel. This is a preliminary step to obtain the magnitude of the power required in the engine, calculated by means of (Eq. (3)) the result is 56.42 [W]. 2.2. Mechanical design of the walking stick. The walking stick requires a mobile base that allows a certain degree of inclination, where the actuators can be placed with the help of articulations. The actuators are attached to a fixed base and a mobile base so that control of both its position in XYZ and its inclination is achieved, through ball joints with a simple joint type CS DIN 71,802 reaching a maximum operating angle of 45°. The force transmitted by the actuators that support the total loads is calculated with (Eq. (4)), considering a contingency percentage of 10% of the value of the total load.
Wus ¼ ð11:56kg þ 1kg þ 0:1kg Þ 1:1 9:8m=s2
ð4Þ
From the points P1, P2, P3, P4, P5, P6 with reference to the point in the Fig. 4, the position vectors of the different coordinates of interest is obtained, then calculate the force vectors according to their modules and with the equations of equilibrium of the system of forces the magnitudes of the forces are obtained:
! ! ! F1 ¼ 9:091 i þ 45:5 j ! ! ! ! F2 ¼ 4:545 i þ 45:5 j 7:885 k ! ! ! ! F3 ¼ 4:545 i þ 45:5 j 7:885 k The reaction moments are generated in the metal plate that supports the walking stick are:
Please cite this article as: O. Arteaga, C. S. Hurtado, H. C. Terán et al., Design of a robotic walking stick with mobility assistance control technology (MAVI) for visually impaired people, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.222
O. Arteaga et al. / Materials Today: Proceedings xxx (xxxx) xxx
3
3. Electronic design 3.1. Functional requirements. The implementation of the electronic system must be oriented to comply: position control in traction motors and linear motors, data acquisition of encoders and load cells [17]. 3.2. Module of conditioning and acquisition of signals. The module allows to measure the pressure data that the person makes to detect the direction which it wishes to move. The load cells have a capacity of 20–100 K lb with a recommended excitation of 10–12 V and a maximum excitation of 15 V, therefore, it requires the use of operational amplifiers and other devices to eliminate noise and in that way the signal condition is successful. For calculating the gain (Eq. (5)) is used
G ¼ 1 þ ð49:9kX=RGÞ
ð5Þ
Where: G represents the value of the gain and RG = represents the input impedance in the Fig. 6 is described by RV4. It is an adjustable value. The following equation allows to find the characterization of each cell is given by (Eqs. (6)–(8)) that are based on the values presented in the Fig. 6. This information is entered into the microcontroller, considering the characteristics of the analog to digital converter ADC 12bit. It is required (Eq. (9)) to know what is the relation between the voltage and the data of the converter, where the value of the gain calculated by means of (Eq. (5)) is 494. Fig. 4. Free body diagram of the tripod 3SPS.
y ¼ 0:268x2 þ 0:7303x 0:0018
ð6Þ
y ¼ 0:230x2 þ 0:764x 0:033
ð7Þ
! My ¼ 0Nm
y ¼ 0:2016x2 þ 0:7901x 0:0089
ð8Þ
! Mz ¼ 2:9575Nm
ADC ¼ V meqsure Resolution =V excitation
ð9Þ
! Mx ¼ 5:123Nm
The resulting moments are used for the static analysis of the structure; the model being submitted to an environment under the established design considerations Fig. 5; a safety factor greater than 2 is obtained by applying a distributed force of 15 [kgf].
Fig. 5. Static analysis of tripod 3SPS.
3.3. Power module. This module focuses on three stages: the position control of the DC motors, the digital encoder conditioning and the lineal position control in the motors. To control in close loop, the motors, position measurement is required by means of digital encoders conditioned by configurations with a timer in operation Encoder mode and the combination of two channels needed to obtain measurements in both directions through experimentation is determined that for each meter of displaced distance. There are 72 pulses of the encoder for its feedback, see Fig. 7. a). In the Fig. 7. b) a potentiometer is identified that
Fig. 6. Instrumentation amplifier for load cells.
Please cite this article as: O. Arteaga, C. S. Hurtado, H. C. Terán et al., Design of a robotic walking stick with mobility assistance control technology (MAVI) for visually impaired people, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.222
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O. Arteaga et al. / Materials Today: Proceedings xxx (xxxx) xxx
Fig. 7. Control diagrams a) Traction motor, b) linear motor.
allows knowing the position of the linear actuator and executing a closed loop control is used as a voltage divider where a 0 [V] represents the retracted stem and 5 V is fully extended. Finally, in the Fig. 8. a) The finished robotic walking stick unicycle is presented. The load cells are calibrated with the use of standard weights and a constant specific position, thus obtaining the output voltages to condition the signal by means of a ADC that converts an external analog voltage into a digital number thus maintaining its linearity of 2 to 8 kg between 50 and 175 [mV] respectively. It is finding a characteristic equation for each cell and a final equation linearized by extrapolation in the zones of 0 to 2 [kg] and from 8 to 10 [kg] to be entered into the microcontroller programming in order to obtain real results with the minimum error, Fig. 8. 4. Results In this section, an analysis of the parameters of human walking are important to understand the way of walking and moving of each individual is shown. Here are some more important parameters to know: Step length (LP) is the horizontal distance in the progression plane developed in one step. In other words, it is the distance measured in meters [m] from a certain point of one foot to the other.
Fig. 9. Scrolling-Device pulses.
Fig. 8. ADC converter Voltage - kilograms.
Fig. 10. Speed vs Weight (Flat floor).
Please cite this article as: O. Arteaga, C. S. Hurtado, H. C. Terán et al., Design of a robotic walking stick with mobility assistance control technology (MAVI) for visually impaired people, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.222
O. Arteaga et al. / Materials Today: Proceedings xxx (xxxx) xxx
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Fig. 11. Application robotic walking stick.
Stride length (LZ) is the distance in the forward direction in meters [m] between the initial contact of a foot and the subsequent initial contact of the same foot. This measurement should be the same for both feet even in the presence of gait asymmetries if the subject walks in a straight line. Cadence (CAD) is the measure of the number of steps per unit of time. Normally, it is expressed in steps per minute [steps/min] For the control of the traction motors the device is required to advance in a straight line where the encoders count the number of pulses, ON OFF Control is made with a variable power that can be set by the user. In the Fig. 9, shows the tests of linear speed and maneuverability with load to verify the behavior of the device. The behavior is analyzed with the experimental work cycle constant at 20% (2 [min]) where the control acts maintaining the balance between the difference of the real pulses and experimental pulses with a factor of 1.5, obtaining a greater number of pulses and displacement in meters. A decrease of the device error to 0.1%. The device was evaluated by increasing its load to a maximum of 12 [kg], obtaining its critical work point at 30% in a time of 15.37 s at an average speed of 0.195 [m/s], see Fig. 10. Once the tests were done, the application was developed for the use of the robotic baton in 4 states with independent screens and linking one device with another, that is bidirectional communication between the cell phone and the robotic baton with Android system as shown in the Fig. 11 a). In the Fig. 11 b) the patient’s parameters are entered as the weight of the user with a maximum of 15% of the total weight for an adequate human walk. The next screen, literal c) shows the options, ‘‘Start, Set and Record” starts the program. The option ‘‘Export” allows to capture the information in file in extension xlsx, which allows to observe a screen to enter the name of the patient to the rehabilitation and stores a file with the weight applied to each load cell at a distance of 24 [cm] each data, which allows obtaining a patient control file as shown in table 3 literal d)
5. Conclusions The maximum force of 15 [kg] was established for people up to a weight of 94 [kg] with a safety factor greater than two and a maximum of 15% of body weight when leaning on the unicycle pole with an adjustable height in the range of 744 to 806 [mm] at a speed of 0.48 [m/s]. In the behaviour of the device is analysed by increasing its working regime using pulse width modulation PWM keeping 20%
constant (2 [min]) where the control acts with a balance between the difference of real pulses and the experimental pulses of the encoders with a factor of 1.5, obtaining a greater number of pulses and displacement in meters. A decrease in the device error to 0.1 in a frequency range between 10 [kHz] and 20 [kHz]. This study was carried out to benefit the neediest and vulnerable people with the incorporation of a technology mobility device for people with visual disabilities (unicycle robotic walking stick), accomplished of improving the quality of life of people and helping in the rehabilitation area with data for the diagnosis and analysis of the user’s progress. In future research, it will be included tactile sensors which allows the distributed them of the human skin and the incorporation of a force-torque finger-tip sensor with a multi-axis load cell with a control applying neural networks. It will be incorporated into the unicycle walking stick. It is going to minimize the displacement error.
References [1] A.E. Challú, y.S. Silva-Castañeda, Towards an anthropometric history of latin America in the second half, Econ. Hum. Biol. 23 (2016). [2] P. Romtrairat, C. Virulsri, y.P. Tangpornprasert, An application of scissored-pair control moment gyroscopes in a design of wearable balance assistance device for the elderly, J. Biomech. (2019). [3] S. Galle, W. Derave, F. Bossuyt, P. Calders, P. Malcolm, D. De Clercq, Exoskeleton plantarflexion assistance for elderly, Gait Posture 52 (2017) 183–188, https:// doi.org/10.1016/j.gaitpost.2016.11.040, https://linkinghub.elsevier.com/ retrieve/pii/S0966636216306798. [4] Pedram Agand, Mohammad Motaharifar, Hamid D. Taghirad, Decentralized robust control for teleoperated needle insertion with uncertainty and communication delay, Mechatronics 46 (2017) 46–59, https://doi.org/ 10.1016/j.mechatronics.2017.06.004, https://linkinghub.elsevier.com/ retrieve/pii/S0957415817300806. [5] Michael Ronthal, Gait disorders and falls in the elderly, Med. Clin. North Am. 103 (2) (2019) 203–213, https://doi.org/10.1016/j.mcna.2018.10.010, https:// linkinghub.elsevier.com/retrieve/pii/S0025712518301329. [6] Jessica M. Baker, Gait disorders, Am. J. Med. 131 (6) (2018) 602–607, https:// doi.org/10.1016/j.amjmed.2017.11.051, https://linkinghub.elsevier.com/ retrieve/pii/S0002934317312950. [7] Taisuke Kobayashi, Kosuke Sekiyama, Tadayoshi Aoyama, Toshio Fukuda, Cane-supported walking by humanoid robot and falling-factor-based optimal cane usage selection, Rob. Auton. Syst. 68 (2015) 21–35, https://doi.org/ 10.1016/j.robot.2015.02.005, https://linkinghub.elsevier.com/retrieve/pii/ S0921889015000299. [8] Huageng Liu, Donghua Shi, Optimal control of a mobile robot on sphere, Theor. Appl. Mech. Lett. 9 (1) (2019) 27–31, https://doi.org/10.1016/ j.taml.2019.01.004, https://linkinghub.elsevier.com/retrieve/pii/ S2095034919300108. [9] V. Fedorenko, y.I. Fedorenko, Modeling of data acquisition systems using the queueing theory, AEU – Int. J. Electron. Commun. 74 (2017).
Please cite this article as: O. Arteaga, C. S. Hurtado, H. C. Terán et al., Design of a robotic walking stick with mobility assistance control technology (MAVI) for visually impaired people, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.222
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O. Arteaga et al. / Materials Today: Proceedings xxx (xxxx) xxx
[10] G. Palli y L. Moriello, Development of an optoelectronic 6-axis force/torque sensor for robotic applications, Sens. Actuators A Phys. 220 (2014). [11] A. Shashank y N. Schuurman, Unpacking walkability indices and their inherent assumptions, Health Place 55 (2019). [12] Chao. T., Ergonomic consideration of walking guidance design. In: International Conference on Service and Interactive Robots, Taiwan. [13] Borenstein, The GuideCane — A computerized travel aid for the active guidance of blind pedestrians. In: IEEE International Conference on Robotics and Automation, Albuquerque.
[14] M. H. & D. S. S, 2006. Mobility and monitoring for the elderly. IEEE Trans. Neural Syst. Rehab. Eng. [15] N. S, 2014. Intelligent walking stick control base on estimation of the human state. IEEE. [16] A. J. & C. R. A. Rentschler, 2016. J. Rehab. Res. Develop. [17] J. Huang, K. Sekiyama, y.T. Fukuda, Motion control of intelligent cane robot under normal and abnormal walking condition, IEEE Xplore (2011).
Please cite this article as: O. Arteaga, C. S. Hurtado, H. C. Terán et al., Design of a robotic walking stick with mobility assistance control technology (MAVI) for visually impaired people, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.222
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
Design of a robotic walking stick with mobility assistance control technology (MAVI) for visually impaired people Oscar Arteaga ⇑, C. Samanta Hurtado, Héctor C. Terán, Miguel A. Carvajal, Jorge G. Ortíz, B. Daniel Tenezaca, V. Hernán Morales ⇑ Universidad de las Fuerzas Armadas ESPE, Sangolquí, Ecuador
a r t i c l e
i n f o
Article history: Received 14 July 2019 Accepted 16 November 2019 Available online xxxx Keywords: Robotic cane Biomechanics Lower extremities Walking stick MAVI
a b s t r a c t The investigation of the present research is a new mechatronic system for a robotic unicycle staff that thanks to a meticulous analysis of the new technologies applied to assistance of technological mobility of people with visual disability as an orthopedic walking stick or a walker. We proceed to contribute with the design of a stick-type mechatronic system coupled to a differential traction platform that facilitates the mobilization of people with motor deficiency by giving them an assistance system to support in the march. It was verified that the design supports the maximum weight established in the parameters of 14 [kg] It was shown that the walking stick can be used with people up to a weight of 93 [kg]. The performance of the load cells with an experimental work cycle by incorporating an application in Android so the user has a feeling of immersion and to provide the possibility of interacting with the device, being able to establish between the user and the robotic staff a bidirectional transfer in real time of information. The findings of the research, multi-axis load cells will be implemented in the future with a control was applying neural networks to minimize the displacement error. Ó 2019 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the scientific committee of the First International Conference on Recent Advances in Materials and Manufacturing 2019.
1. Introduction In recent times, new research that permits improving the quality of life of people with different physical disabilities, highlights aid for the mobility of blind and visually impaired people among which we can mention: exoskeletons, devices based on common devices such as walking sticks or walkers with the inclusion of new technologies using sensors and actuators that gives them much more autonomy and useful functions when they are used [1,2,3]. According to the last World Report on Disability published in 2017 by the World Health Organization. It is estimated that 15% of the world population lives with some type of disability which one of the most common has to do with problems in Mobility [4,5]. The smart walking stick incorporates an accelerometer and a gyroscope (to detect falls). A GPS module (to track the location)
⇑ Corresponding author. E-mail addresses: [email protected] (O. Arteaga), [email protected] (V.H. Morales).
and GSM connectivity (to alert other people in case of emergency) [6,7]. People who need more help walking can use the Keeogo leg exoskeleton a ‘‘walking assist device” that was developed by BTEMIA Inc. The Keeogo comes equipped with sensors placed at the level of the knee and hip joints that detect movement and offer additional motorized assistance to supplement muscle weakness [8,9]. The robotic walking stick unicycle is intended for various specific activities to help the patient; guiding him in his displacement, providing support in his rehabilitation and optimizing maneuverability, through a mobility system with walking stick and allows predicting the intention of movement of the user, as shown in Fig. 1 [10,11]. An essential parameter when using a walking stick is the amount of load exerted on it which is determined according to the type of injury and the evolution of the affected user [12]. Inadequate walking sticks can cause sequelae, such as muscle overload during daily activities and lack of support in the affected limb, lumbar area and upper trapezium, as shown in Fig. 2, as well as a deviation from the centre of gravity [13,14].
https://doi.org/10.1016/j.matpr.2019.11.222 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the scientific committee of the First International Conference on Recent Advances in Materials and Manufacturing 2019.
Please cite this article as: O. Arteaga, C. S. Hurtado, H. C. Terán et al., Design of a robotic walking stick with mobility assistance control technology (MAVI) for visually impaired people, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.222
2
O. Arteaga et al. / Materials Today: Proceedings xxx (xxxx) xxx
Fig. 1. Human Interaction Robot - Main applications: a) Guide, b) Rehabilitation, c) Maneuverability.
Fig. 3. Free-body diagram of the mobile platform.
normal force which represents the force necessary for the platform to move at a speed of 0.48 [m/s] its magnitude is directly proportional to the power and torque of the motor required, the calculation is obtained from the sum of static forces:
F ¼ Fr þ mt g sinh
ð1Þ
Where: Fr is frictional force, h is inclination angle of the plane Being the value obtained from (Eq. (1)) this allows to continue with the calculation of the torque in each wheel with the help of (Eq. (2)).
T wh ¼ ðF £whÞ=4 Fig. 2. Muscular sequelae in the lumbar area and upper trapezius.
2. Mechanic design 2.1. Design parameters. The design parameters chosen: maximum weight, travel speed, body weight, height, degrees of freedom, stability and mobility that allow the mobile platform to be structured with the baton so that everyone converges on the conception of the final product; The maximum weight of the platform must be 15 [kg]. It is formed so that the removable parts with three degrees of freedom, displacements x-axis, z-axis and rotation in y-axis, making it modular, see Fig. 4. It can support the maximum body weight of 15% of average people, the platform moves at a speed of 0.48 [m/s] while the height where the cane can be placed varies between the range of 744 to 806 [mm] all of the above must be configured with a gyroscope so as not to lose the stability and mobility required during human walking [15,16]. The analysis is divided into two parts: the mechanical design of the mobile platform and the mechanical design of the walking stick because the platform and the walking stick act independently which are subsequently complemented for the mobilization of people with motor deficiency. Mechanical design of the mobile platform helps to get the engine power, the extra weight exercised by the user, the weight of the walking stick, the weight of the sensors with a total of 17 kg. In this case, we worked with a load factor of 10% of the total weight; to ensure that any eventuality different to those that were assumed is covered, finally the total value of the weight is W t = 20,4 [kg], therefore the value of the magnitude of force is: W t = 20,4 [kg] 9,81 [m/s2] = 200 [N]. The calculations were made with a static coefficient of friction and dynamic coefficient friction for the static analysis of the platform on inclined surfaces having a maximum inclination angle of 15°. In the Fig. 3 the free body diagram of the platform is observed. It is identified in the Fig. 3 to like the radius of the wheel, N as the
ð2Þ
Where: Twh represents the torque required on each wheel and its value is for a diameter wheel, the power of the motor is found with the equation (Eq. (3))
P ¼ Twh xn
ð3Þ
The angular velocity of the wheels is obtained by the data of the required linear speed and the radius of the wheel. This is a preliminary step to obtain the magnitude of the power required in the engine, calculated by means of (Eq. (3)) the result is 56.42 [W]. 2.2. Mechanical design of the walking stick. The walking stick requires a mobile base that allows a certain degree of inclination, where the actuators can be placed with the help of articulations. The actuators are attached to a fixed base and a mobile base so that control of both its position in XYZ and its inclination is achieved, through ball joints with a simple joint type CS DIN 71,802 reaching a maximum operating angle of 45°. The force transmitted by the actuators that support the total loads is calculated with (Eq. (4)), considering a contingency percentage of 10% of the value of the total load.
Wus ¼ ð11:56kg þ 1kg þ 0:1kg Þ 1:1 9:8m=s2
ð4Þ
From the points P1, P2, P3, P4, P5, P6 with reference to the point in the Fig. 4, the position vectors of the different coordinates of interest is obtained, then calculate the force vectors according to their modules and with the equations of equilibrium of the system of forces the magnitudes of the forces are obtained:
! ! ! F1 ¼ 9:091 i þ 45:5 j ! ! ! ! F2 ¼ 4:545 i þ 45:5 j 7:885 k ! ! ! ! F3 ¼ 4:545 i þ 45:5 j 7:885 k The reaction moments are generated in the metal plate that supports the walking stick are:
Please cite this article as: O. Arteaga, C. S. Hurtado, H. C. Terán et al., Design of a robotic walking stick with mobility assistance control technology (MAVI) for visually impaired people, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.222
O. Arteaga et al. / Materials Today: Proceedings xxx (xxxx) xxx
3
3. Electronic design 3.1. Functional requirements. The implementation of the electronic system must be oriented to comply: position control in traction motors and linear motors, data acquisition of encoders and load cells [17]. 3.2. Module of conditioning and acquisition of signals. The module allows to measure the pressure data that the person makes to detect the direction which it wishes to move. The load cells have a capacity of 20–100 K lb with a recommended excitation of 10–12 V and a maximum excitation of 15 V, therefore, it requires the use of operational amplifiers and other devices to eliminate noise and in that way the signal condition is successful. For calculating the gain (Eq. (5)) is used
G ¼ 1 þ ð49:9kX=RGÞ
ð5Þ
Where: G represents the value of the gain and RG = represents the input impedance in the Fig. 6 is described by RV4. It is an adjustable value. The following equation allows to find the characterization of each cell is given by (Eqs. (6)–(8)) that are based on the values presented in the Fig. 6. This information is entered into the microcontroller, considering the characteristics of the analog to digital converter ADC 12bit. It is required (Eq. (9)) to know what is the relation between the voltage and the data of the converter, where the value of the gain calculated by means of (Eq. (5)) is 494. Fig. 4. Free body diagram of the tripod 3SPS.
y ¼ 0:268x2 þ 0:7303x 0:0018
ð6Þ
y ¼ 0:230x2 þ 0:764x 0:033
ð7Þ
! My ¼ 0Nm
y ¼ 0:2016x2 þ 0:7901x 0:0089
ð8Þ
! Mz ¼ 2:9575Nm
ADC ¼ V meqsure Resolution =V excitation
ð9Þ
! Mx ¼ 5:123Nm
The resulting moments are used for the static analysis of the structure; the model being submitted to an environment under the established design considerations Fig. 5; a safety factor greater than 2 is obtained by applying a distributed force of 15 [kgf].
Fig. 5. Static analysis of tripod 3SPS.
3.3. Power module. This module focuses on three stages: the position control of the DC motors, the digital encoder conditioning and the lineal position control in the motors. To control in close loop, the motors, position measurement is required by means of digital encoders conditioned by configurations with a timer in operation Encoder mode and the combination of two channels needed to obtain measurements in both directions through experimentation is determined that for each meter of displaced distance. There are 72 pulses of the encoder for its feedback, see Fig. 7. a). In the Fig. 7. b) a potentiometer is identified that
Fig. 6. Instrumentation amplifier for load cells.
Please cite this article as: O. Arteaga, C. S. Hurtado, H. C. Terán et al., Design of a robotic walking stick with mobility assistance control technology (MAVI) for visually impaired people, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.222
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Fig. 7. Control diagrams a) Traction motor, b) linear motor.
allows knowing the position of the linear actuator and executing a closed loop control is used as a voltage divider where a 0 [V] represents the retracted stem and 5 V is fully extended. Finally, in the Fig. 8. a) The finished robotic walking stick unicycle is presented. The load cells are calibrated with the use of standard weights and a constant specific position, thus obtaining the output voltages to condition the signal by means of a ADC that converts an external analog voltage into a digital number thus maintaining its linearity of 2 to 8 kg between 50 and 175 [mV] respectively. It is finding a characteristic equation for each cell and a final equation linearized by extrapolation in the zones of 0 to 2 [kg] and from 8 to 10 [kg] to be entered into the microcontroller programming in order to obtain real results with the minimum error, Fig. 8. 4. Results In this section, an analysis of the parameters of human walking are important to understand the way of walking and moving of each individual is shown. Here are some more important parameters to know: Step length (LP) is the horizontal distance in the progression plane developed in one step. In other words, it is the distance measured in meters [m] from a certain point of one foot to the other.
Fig. 9. Scrolling-Device pulses.
Fig. 8. ADC converter Voltage - kilograms.
Fig. 10. Speed vs Weight (Flat floor).
Please cite this article as: O. Arteaga, C. S. Hurtado, H. C. Terán et al., Design of a robotic walking stick with mobility assistance control technology (MAVI) for visually impaired people, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.222
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Fig. 11. Application robotic walking stick.
Stride length (LZ) is the distance in the forward direction in meters [m] between the initial contact of a foot and the subsequent initial contact of the same foot. This measurement should be the same for both feet even in the presence of gait asymmetries if the subject walks in a straight line. Cadence (CAD) is the measure of the number of steps per unit of time. Normally, it is expressed in steps per minute [steps/min] For the control of the traction motors the device is required to advance in a straight line where the encoders count the number of pulses, ON OFF Control is made with a variable power that can be set by the user. In the Fig. 9, shows the tests of linear speed and maneuverability with load to verify the behavior of the device. The behavior is analyzed with the experimental work cycle constant at 20% (2 [min]) where the control acts maintaining the balance between the difference of the real pulses and experimental pulses with a factor of 1.5, obtaining a greater number of pulses and displacement in meters. A decrease of the device error to 0.1%. The device was evaluated by increasing its load to a maximum of 12 [kg], obtaining its critical work point at 30% in a time of 15.37 s at an average speed of 0.195 [m/s], see Fig. 10. Once the tests were done, the application was developed for the use of the robotic baton in 4 states with independent screens and linking one device with another, that is bidirectional communication between the cell phone and the robotic baton with Android system as shown in the Fig. 11 a). In the Fig. 11 b) the patient’s parameters are entered as the weight of the user with a maximum of 15% of the total weight for an adequate human walk. The next screen, literal c) shows the options, ‘‘Start, Set and Record” starts the program. The option ‘‘Export” allows to capture the information in file in extension xlsx, which allows to observe a screen to enter the name of the patient to the rehabilitation and stores a file with the weight applied to each load cell at a distance of 24 [cm] each data, which allows obtaining a patient control file as shown in table 3 literal d)
5. Conclusions The maximum force of 15 [kg] was established for people up to a weight of 94 [kg] with a safety factor greater than two and a maximum of 15% of body weight when leaning on the unicycle pole with an adjustable height in the range of 744 to 806 [mm] at a speed of 0.48 [m/s]. In the behaviour of the device is analysed by increasing its working regime using pulse width modulation PWM keeping 20%
constant (2 [min]) where the control acts with a balance between the difference of real pulses and the experimental pulses of the encoders with a factor of 1.5, obtaining a greater number of pulses and displacement in meters. A decrease in the device error to 0.1 in a frequency range between 10 [kHz] and 20 [kHz]. This study was carried out to benefit the neediest and vulnerable people with the incorporation of a technology mobility device for people with visual disabilities (unicycle robotic walking stick), accomplished of improving the quality of life of people and helping in the rehabilitation area with data for the diagnosis and analysis of the user’s progress. In future research, it will be included tactile sensors which allows the distributed them of the human skin and the incorporation of a force-torque finger-tip sensor with a multi-axis load cell with a control applying neural networks. It will be incorporated into the unicycle walking stick. It is going to minimize the displacement error.
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Please cite this article as: O. Arteaga, C. S. Hurtado, H. C. Terán et al., Design of a robotic walking stick with mobility assistance control technology (MAVI) for visually impaired people, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.222