Planning the Emergency Collision Avoidance Strategy Based on Personal Zones for Safe Human-Machine Interaction in Smart Cyber-Physical System

Human contact is a key issue in social interactions for autonomous systems since robots are increasingly appearing everywhere, which has led to a higher risk of conﬂict. Particularly in the real world, collisions between humans and machines may result in catastrophic accidents or damaged goods. In this paper, a novel stop strategy related to autonomous systems is proposed. This control method can eliminate the vibrations produced by a system’s movement by analysing the poles and zeros in the model of autonomous vehicles and goods. Using the pole placement technique, the motion of a system is guaranteed to be more stable, more ﬂexible and smoother. Moreover, several control proﬁles are employed in the switching mechanism to choose the proper vibration-free eﬀect. The main contributions of this paper are (i) the recommendation of an active stopping planner using diﬀerent smooth generators from a modelling study, (ii) the validation of their physical characteristics and (iii) the launching of a switching algorithm based on the socially aware navigation framework of a robot. This theoretical work is based on the virtual environment of MATLAB, and the experiment is implemented in the practical platform of an automated guided vehicle. From these results, it can be seen that the proposed approach is robust, eﬀective and feasible for applications in storehouse management, public transportation or factory manufacturing.


Introduction
Together with the growth of science and technology, autonomous systems have increased considerably in the context of the industrial revolution 4.0. As a result, machines have appeared in the surrounding space of humans. In the manufacturing environment, shared space is necessary for cooperation, as it enhances industrial productivity. Typically, an autonomous robot executes its tasks in the real world. Even in the absence of men, robots should attempt to avoid conflict with other objects. As a matter of fact, the autonomous machine is able to behave more intelligently in real life.
Since social consciousness has become a popular topic, human-oriented studies have attracted not only researchers but also practitioners. All kinds of transportation models are required to complete the steering function among humans. Not all of them know how to respond in the event of a crash. One of the means of public transportations in our society is the bus, which serves many passengers. An extended optimal velocity traffic flow model on two lanes that includes a bus stop and a bus deceleration area was suggested in [1]. Two new traffic states were found such that lane-changing occurred frequently, whether ahead of or behind the bus, and the stop-and-go wave would occur on both lanes instantaneously. With the growing density of vehicles, the lanechanging region around a bus varies. Considering impact due to abnormal deceleration of the current vehicle, the traditional criticality of the working conditions is hardly able to ensure safety [2]. A new calculation method was established in the event of a sudden reaction to maintain the criticality safety distance. It matches the demands for no injuries on an expressway as well as prevents rear-end collisions. Regarding personal characteristics, the health of a driver has an effect on driving protection. e cognitive dysfunction of a patient [3] on public roads is a subject to study.
ey are occasionally unable to drive owing to symptoms of executive dysfunction. Each tester was equipped with wearable sensors to analyse his/her driving behaviour. It was found that there exists a difference in deceleration posture between patients and healthy adults at an intersection. is indication can guide medical treatment for individual healthcare. Normally, most transportation on a road is carried out by private cars. As the density of traffic has increased, the risk of harm to people has also increased. To indicate regions of deceleration, the individual road markers notifying drivers of the need for deceleration have been input into a PC-based simulator [4]. e interface between the computer and participants generates a threedimensional scene presenting visual, auditory and tactile effects. A car user's psychological feelings and visual illusions are fed back to confirm the authenticity of the situation. Regarding a person's hostility, an automatic braking system has been derived with consideration of a pleasant car owner [5]. From graphical inputs, a driver's perceived risk of collision was defined to formulate the braking support system. e findings show the need to output smooth deceleration profiles uniformly with very simple calculations. e action of braking initializes at the time of judgment to reduce speed. More generally, a driver risk evaluation method leans on the analysis of recorded driving data [6]. An estimation covering the acceleration, deceleration and steering actions is observed and scored by a risk consultant. Other types of carriers have also drawn attention from investigators. e common aero vehicle slows down its speed by performing a coning motion without a velocity profile [7]. A one-order approximate model of the velocity and long range is extracted; then, the features of the coning motion target velocity and position precision are obtained by orthogonally allocating the trajectory acceleration and velocity over the load. On the prototype of a train, the construction of an air brake and its nonlinear performance are examined [8].
e deceleration control of the pneumatic brake system is compared with different PID schemes to display its feasibility and accuracy.

Background Works
Safety is a constant topic of interest in numerous fields. e problem of collision avoidance mainly involves two modes of transportation: two objects moving in either opposite directions or in the same direction. Currently, the methods of ensuring safety could be categorized into passive plans and active plans. In the passive schedule, one object selects a stopping stratagem with respect to the behaviours of another. is rule offers the advantages of a dynamic braking motion, conserves kinetic energy and can afford movement in a short time. However, when faced with several objects, a time delay in communication or braking could result in serious harm. e time restriction becomes stricter because the response may not occur in time. Particularly, when an object is moving in the direction opposite to that of the driver, the human body may be wounded. Active deceleration results in a higher level of protection since one decides to halt independently. If an objector person is shown to prevail in the moving space, the driving speed of the will vehicle robustly slow down. e core of the strategy is how to break the whole system to maintain the current status.
ere have been several studies concentrated on the investigation and implementation of human-machine interaction safety system which are summarized in Table 1. Some reports researched the vision-based approach that issued from tracking human's direction and computing the time or distance between operator and machine [9,30]. e sharing fenceless space where there is no physical barrier is monitored by optical sensors. e major point is that the mentioned cyber-physical system architecture could assess the collision risk on the scale of millisecond. Based on realtime evaluation of safety distance, this leads to fast response time, trigger the safety policies and ensure the coexistence of human-machine. However, the loading status must be known and the relation between response time and image processing should be tested. In some technical investigations, the actively invisible distance from operator to robot is measured by vision-based method [31], laser scanner [10], or both [32]. Most of these studies fuse data from different sources to define the relative position, configuration of upper body or pose. Similar to the distance-based or timebased method, the space separation approach relies on the classification of working space. In the manufacturing environment, the surrounding zones of any object are categorized as three levels, such green zone, yellow zone and red zone [9]. e farthest one, named as green, is quite safe and there is no need of actions. Closing to the centre, it must deliver the alerting message or warning signal to human and robot controller must reduce speed in yellow zone. In emergency area or red zone, the notifications to inform the potential collision and, stop command or moving away command would force robot in order to prevent the collision. In the same idea but in different work, authors [33] presented a real-time safety system by allowing safe humanrobot interaction at very low distances. It required to leverage known robot joint angle values and precise estimation of human's position in the working area. ere is not much modification in robot platform, for instance, computer vision tool is additionally attached in body of robot and implementation in robot software consents to manipulate.
Following the concept of robot's awareness, developers in [11] represented a collision-free interaction model which is not only control the robot in collision-avoidance path, but also perceive information from human's activities. To support the mentioned requirements, a context-aware collision avoidance interaction system design that consists of sensing module, path planning module and context-aware human pose recognition module was mainly described. In the similar manner, some researchers [12] suggested the 2 Complexity  [11] e context-aware collision-free system with sensing module for path planning based on human pose recognition is introduced (i) Detecting potential collision and planning a path to reach target simultaneously (ii) Be able to distinguish human pose and assembly context (i) Burden computation, an exact human pose recognition algorithm and various assembly sequence are challenges Yingzhong T. et al. [12] A universal control system which allows an operator to communicate his motions to the robot manipulator, is proposed on the self-adaption workspace mapping method (i) No need to find parameters by trial-and-error (ii) It adapts to different operators and robots in workspace (i) e recognition and classification of human movements were not focused (ii) e effective distance between operator and system was not discussed.
Zong C. et al. [13] A study for the adaptability of the tracked robot in complex working environment is explored. It includes the mechanical structure, static stability in three terrains for human-robot interaction (i) Appropriate dimension, good mass distribution and limited velocity is advantageous to maintain the system stability on terrains (i) Load capacity and financial effectiveness are crucial to investigate Wang H. et al. [14] e investigation on improving the performance of RFID robot system by anticollision scheme is exemplified. e tag collisions in the current slot are detected by proposed method, then further resolve each small tag collision to enhance system (i) is approach is beneficial to boost the moving speed and identification reliability of the RFID robots in complex environments (i) e solution did not fully consider in the context of collaboration, stability or dynamical control (ii) e phenomenon of weak signal, tags on multi-RFID robots and identification efficiency might occur in practice Zong C. et al. [15] e dynamic process of climbing stairs for the tracked mobile robot is analysed by reason of on the novelty of mechanical structure and working principle (i) e feasibility of design and flexible motion could be gained in unknown environment (i) e advanced algorithms should be considered to deal with different sizes of stairs Complexity 3 Due to the fundamental emotion modulation theory and the neural mechanisms of generating complex motor patterns, a model of emotion generation and modulation to train a recurrent neural network for robot control to perform goal-directed tasks (i) e emotion-modulating method is able to control manipulator with higher accuracy and faster learning rate (i) Various faces with many emotions involve the excellent training process Guo S. et al. [20] A novel idea for nonlinear multiview Laplacian least squares (MvLL) which construct a global Laplacian weighted graph in order to introduce category discriminant information as well as protect the local neighbourhood information, is proposed.
(i) e effectiveness and robustness of MvLL approach is approved although the tasks of multipose and multifeature are taken (i) e largest disadvantage of this method is the high time complexity Zheng E. et al. [21] e new musculoskeletalbased-method manipulated by the electrical Impedance Tomography (EIT) signals for continuously estimating wrist flexion/extension angles is mentioned in the field of wearable robot (i) e model-based method performed better with small training data sizes (i) It is limited in extracting motion information on large data and multi-degree-offreedom 4 Complexity A novel methodology by integrating the cognitive learning techniques and the developed control techniques, which allow the robot to be highly intelligent to learn senior surgeons' skills and to perform the learned surgical operations in semiautonomous surgery, was discussed e control algorithm does not only provide the learning ability of the human operation skill from multiple demonstrations on a specific task, but also can transfer the learned motion from open surgery by guaranteeing the robot constraints More complicated motions entail advanced sensors and burden computation Su H. et al. [23] An improved human-robot collaborative control scheme was proposed in teleoperated minimally Invasive surgery scenario e contributions are not only the improvement of surgical task accuracy and robot constraint, but also the computation efficiency without trajectory planning Adding one more force sensor for external forces sensing should be conceived and performed with the physical interaction between the surgical tip and the organs Su H. et al. [24] e swivel motion reconstruction approach was applied to imitate human-like behaviour using the kinematic mapping in robot redundancy in this research e algorithm gains the highly online regression prediction for accuracy enhancement and fast computation

It is important to integrate both human upper limb kinematic models and joint limits
Collision-free approach based on data fusion for navigation method in CPS Yang Q. et al. [25] A novel approach of outdoor localization with 3D-laser scanner is proposed to solve the problem of poor localization accuracy in GPS-denied environments. A path planning strategy based on geometric feature analysis and priority evaluation algorithm is also adopted to ensure the safety and reliability of mobile robot's autonomous navigation and control e robot has high accuracy of localization without GPS so that the mean error of position is 0.1 m and the mean error of path angle is 6°in the experiment. e function of obstacle avoidance includes static obstacle avoidance, dynamic vehicle avoidance and going through narrow regions e mechanical structure of mobile platform does not guarantee to overcome any outdoor environment Sanders D. et al. [26] e purpose of this investigation is to study the effect on time to complete a task depending on how a human operator interacts with a mobile robot. is kind of interaction utilizes two teleoperated mobile-robot systems, three different ways of interacting with robots and several different environments It may perform better without a sensor system to assist in more complicated environments. Sometimes, it performs better with a camera mounted on the robot compared with premounted cameras observing the environment It relies heavily on visual feedback and experienced operators Chen D. et al. [27] A control framework was used and consisted of two levels: one was a decision level to give the possible positions of all nodes in sensor networks, while the other was a control level to move along the edge of obstacles such that the problem of obstacle avoidance can be transformed into a coordination problem of multiple robots e proposed control approach can guide the mobile robot to avoid obstacles and deal with the corresponding dynamical events so as to locate all sensor nodes for an unknown wireless network If the number of obstacles increases, the average localization errors between the actual locations and the estimated locations significantly increase Complexity universal control system that naturally releases an object manipulation mission from combining the human's gesture to robot manipulator. e advanced functions, for example recognition and classification of shoulder, elbow, wrist or tip of fingers are utilized to control the robot end point. By providing the learning abilities for robot after some iteration processes, a cooperative robot for pick-and-place tasks becomes more intelligent in its workplace. Toward an optimal solution, the research on collaborative robot [16] investigated an avoidance strategy that generated the alternative trajectory to possibly traversed. e superior outcomes are both to prevent collision and to minimize travelling time. Exploiting information receiving from these sensors properly, the robot controller lonely decides motion planning which is the best option in the presence of operator.
Another research topic of safety human-machine interaction is the analysis of dynamic characteristics so as to give a final decision by itself in an emergency case. For these circumstances, a hierarchical model predictive control method was depicted in [17] for four-wheel independentdriving vehicle. An integrated framework that comprises the artificial potential field module for path replanner and feedback compensation control module for path follower, is still capable to track the collision-free trajectories in the illconditioned states and supervise the other driving behaviours on the neighbour lane. To deal with uncertain factors in driving actuators and unexpected problems in emergency steering situation, a decision-making layer is implemented into the hierarchical control architecture [18]. e risk indexes associated with collision and destabilisation, are continuously estimated in threat assessment model. An alternative approach has explicitly incorporated vehicle stabilization into path tracking and collision avoidance framework [17]. Sometimes, it permits that the stable motion of vehicle could be violated temporarily if needed to keep away from potential collisions. As a result, this method differs from any others since prioritizing collision avoidance is higher than.
ough, most of studies does not focus on interaction between autonomous grounded vehicle and human while there is a considerable increasing number of automated solutions in e-commerce, logistics and supply chain. In general, when mobile robot or autonomous vehicle leaves research laboratory and join in manufacturing environment, it must be able to deal with emergency circumstances which occur suddenly. Some of them might necessitate manoeuvrings, i.e., emergency collision-free that requires short time response and maintain vehicle stability. e techniques of emergency collision avoidance for autonomous vehicle are demonstrated in [34]. e situation discussed in this paper is that in which a human interacts with a machine, where the robot is equipped with intelligent awareness to evade concurrences. e engine must determine which stop policies are proper while still preserving the balance and keeping the freight undamaged. By investigating the theory of a mass and spring system, the constraints needed to stabilize the whole structure are achieved robustly. Using the actual context of a distribution centre, where workers are obliged to share their workspace, the automated guided vehicle is employed as the platform to prove the proposed approach. Some smooth motion profiles are used in this hardware test to verify the effectiveness and success of our policy.

Problem Statement
e target hardware in our research [35] is based on the automated vehicle shown in Figure 1, which could track a reference trajectory or move freely. Its mission is to lift up the shelf, bring cargo to its destination and set the shelf down. Depending on the applications, navigation tools (radio frequency identification, laser sensor or magnetic guide sensor) are additionally attached to the platform. It can work autonomously in a warehouse while the operator stays along distance away. Nevertheless, in developing countries or in some scenarios where a man needs, without a stop policy, the availability of a machine presents nearby, which may cause an unexpected accident as in Figure 2.
We assume that m 1 and m 2 are the mass of the machine hardware and freight, respectively. Once the robot elevates An innovative method of human motion prediction according to an autoregressive model for teleoperation was motivated. e robot's motion trajectory could be updated in real time through updating the parameters of the proposed model is approach combines both the prediction of human movement as a feedforward component and a virtual force as feedback e actively interactive performance of robot as well as the existing trouble in time delay should be considered Jing L. et al. [29] A hybrid shared control approach based on EMG signals sensor and artificial potential field is invented to avoid obstacles owing to the repulsive force and attractive force from human perception It provides an alternative force feedback solution along with muscle activation and human's control of intention and prediction e robustness and long distance control of the proposed work could be noticed 6 Complexity the shelf, the two become a rigid body. Without loss of generality, the freight m 2 is connected to the frame via two springs with stiffnesses of k 1 and k 2 . e whole modelling procedure is described in Figure 3. tTo govern the dynamics characteristic, the interacting forces on the system are examined in Figure 4. If the other forces, such as friction forces, exist, they can be ignored. v → is the velocity of the vehicle for the same direction of movement. F → qt is the inertial force from the vehicle to the cargo. e state variable x of the system denotes displacements of each element in vector form: x � x 1 x 2 T . Applying Newton's law, the relationship among them can be realized as.
(1) is rewritten in the positive direction, e above equations are related to the time domain. To convert them into the frequency domain, by taking the Laplace transformation, we obtain the following where X 1 , X 2 mean the Laplace transformations of. x 1 , x 2 By using mathematical manipulation, the related constraints in the proposed model are expressed as or ω n is the natural frequency of the damped system. If the base X 1 is utilized precisely, the performance of mass X 2 can be measured via (4). In the initial issue, the  velocity of X 1 is governed by the trapezoidal scheme shown in Figure 5. ree phases occur for this shape: acceleration, constant speed and deceleration. We are focused on the relationship between the deceleration period and stop status. v max , A max : maximum value of the velocity v and acceleration At a , t c , t d : time period of acceleration, constant speed and deceleration, respectively t 0 , t 1 , t 2 , t 3 : time slice at the beginning of acceleration, constant speed, deceleration and end of motion, respectively.
Analysing the above equations, the natural characteristic of the overall system is revealed through poles and zeros which are depicted in the real-imagine coordinate as Figure 6. Since these points locate at the vertical axis, they are usually symmetrical about the horizontal axis.
Poles: k � 1, 2, 3, . . . Zeros: eoretically speaking, the autonomous system tends to oscillate if the system states are at the poles. In detail, when the conditions in (5) are satisfied, the unexpected vibration might occur and ascend inside this system. As a result, the incident event could cause harm to workers quickly.

Proposed Stop Strategy
To overcome these challenges, a pole placement for cancelling the unstable points is introduced. e advantages of this approach are that it suppresses the residual vibration, carries out the tuning rule regarding physical factors and the actuator specification, and does not require the exact information of the model. erefore, free-vibration motion can be achieved in a robust manner.

Robust Pole Placement Technique.
Our motivation is to present the novel approach for stable control according to the analysis of system state. Deriving from the idea of pole placement technique, the pole-zero cancelation method is applicable if the zero points are duplications of the locations of the poles. In Figure 7, the outcome of this work is to identify the condition for relocating zero points to positions of poles. By substituting into (5)-(6), the vibration-less conditions are as follows. ������ In the physical view, when duration T 3 , from t 2 to t 3 , is the integer multiples of the period of oscillation, the vibration suppression is entirely effective after the vehicle completes its motion. is key constraint guarantees that there is no sudden vibration during the deceleration stage and that the vehicle actively breaks at the specified position. From this idea, various stop profiles are researched to determine which is proper for different cases.

Stop Profiles.
e criteria to rate the proper profile are able to suppress the vibration of both the vehicle and cargo; the policy of the generating mechanism depends on the system constraints and ensures the real-time performance. First, the trapezoidal profile is chosen due to its simplicity but effectiveness, and it does not cost much in terms of the timing generation. Later, without loss of generality, the strategy is exerted on numerous profiles for comparison. If the initial velocity V 0 is given, then the expression of the asymmetric S-curve speed profile [36] can be manifested as follows: With In Figure 8, the asymmetric S-curve motion profile of the mobile base is written with the unit step function u(t). Totally, there are seven segments with [t i , t i+1 ], i ∈ 0, 1, 2, 3, 4, 5, 6, 7 { }. V max , A max , J max are maximum values of velocity, acceleration and jerk correspondingly. V i is the final value of velocity in the time slice [t i−1 , t i ]. τ m is ratio between velocity and acceleration while t j and t a are the acceleration/ deceleration time and constant acceleration respectively. us, equation (12) depicts the time-varying velocity of system. From equations (13) to (19), the components of velocities in each period are identified. e relationship between maximum acceleration and maximum velocity as well as tuning parameters is illustrated from equations (20) to (23).
10 Complexity Substituting the above into (4), the information of mass m 2 can be measured as In the time domain, (10) is expressed in time-varying form.
(26) It has been indicated that the performance of a vehicle in lifting cargo m 2 is discoursed via four sine functions. eir mutual characteristics equalize the frequency but shift the phase. To acquire the desired output, these terms of (11) are forced to dismantle each other. In the case where the control algorithm is valuable, the oscillating performance of m 2 approaches zero. e concern in this paper is to develop a policy for stabilizing the movement of a system with different deceleration phases. Again, using the asymmetric S-curve profile, the general conditions needed to eliminate the vibration of cargo are demonstrated. 2πm ⇔cτ m � mT n .
From the above results, it is clear that the fluctuation can be destroyed when the motion planning period equals an integer multiplied by the period of natural oscillation. It is desired that at the end of mobile platform movement, the vibration of m 2 is completely cancelled as soon as possible. Some simulations with a trapezoid, an S-curve, and an asymmetric S-curve or without a strategy are shown in Figures 9-12, respectively.
Generally, it is critical to find the minimum distance for vehicle to generate the smooth stop profile. If ΔP i symbolizes the moving distance during a period, later the number of displacements in deceleration duration are expressed as follows: MDB (minimum distance barrier): the cyber limitation (δ min ) in awareness of autonomous system to decelerate safely and smoothly minimizes to be required.
In dissimilar profiles, the restrictions of minimum distances are different. Each type exists a predetermined range from vehicle to human which avoid to interrupt.

Active Policies with Respect to Safety.
In the paper [37], a unified framework that enables a robot to safely and socially reach both a dynamic human and a human group was developed. Basically, the real-world environment around a human is personal space, where people interact only with close objects such as relatives, and a machine is obligated to inviolate this barrier. In further space, named social space, humans will communicate with others, for example, shaking hands and engaging in oral discussion. A machine should not stay in the social space so that humans feel comfortable and safe. Representing the furthest distance, public space is a cyber interval in which humans come across each other. is is a commonly acceptable gap to preserve a complete stop strategy.
To adapt to the virtual spaces around humans, it is indispensable to launch a switching mechanism among the stop strategies. Given a target distance δ, the mechanism initially ranges from autonomous machines to men.
Here, H � h 1 , h 2 , . . . , h n , where h i is the ith person. e human states of person h i are regulated as and v h i is the linear velocity. For the vehicle, its states are denoted as Figure 13, Algorithm 1 is utilized whenever an autonomous vehicle carries out a decision before one is made by a human. In this study, the direction a person faces and the location of the right hand or left hand are not our concern. It is noted that the estimation of the relative distance is not the key discussion. We use Kinect digital camera to gain the depth map from the environment, with far distances, and a skeleton option in tracking mode to calculate the current travelling distance. We input the parameters; the values of δ APB , δ SPB , δ TPB are computed in advance. Because of these data, it can be known which stop policy is best to activate.

Experimental Validation
In this paper, we suggest two classifications of the experiments. In the first laboratory test, the performance of the separated deceleration scheme needs to be measured. e machine is installed with a consciousness regarding the stop behaviour. e vibration results of different strategies are compared to discover the proper profiles for each situation. e second one tests whether to switch among the strategies in real life.
An experimental platform was setup as in Figure 15 to validate our approach. We developed one practical automated guided vehicle to serve in manufacturing factories or distribution centres. To imitate the reaction of cargo, a mass m 2 connected to a vehicle by means of a linear aluminium ruler is replaced above the lifting component of the vehicle.
A sensing board boostXL Texas Instrument, is placed together with the mass to weigh some physical parameters along the x, y, z axes. To process data in real-time mode, the development kit LaunchPad MSP432P401 R is utilized to record vibrating outputs. is device supports a powerful 32 bit ARM Cortex-M4F microcontroller up to a 48 MHz system clock, 256 KB of flash memory, and 64 KB of SRAM. e data are then transmitted to the embedded computer to acknowledge the system status. To control two servo motors, the TM4C evaluation board and DCS3T-27 driver are used to close the feedback loop. Tiva C series TM4C123 G LaunchPad including the TM4C123GH6PMI microcontroller with two motion control PWM modules capable of generating 16 PWM outputs, two quadrature encoder interfaces, and several driving platforms.  Figure 13: Description of the proposed switching mechanism for stop profile generation.

Complexity
In the first validation test, our target is to categorize the performance of these three policies and that without a policy. e separated results in each case should be shown in Figure 16. In the initial stage, because of a sudden break while travelling, the largest swinging wave appears indicating unbalanced movement. Without any policy, the amplitude of the vibration reaches its maximum height after a moment. It takes more time to decline the output variation. Applying the TPB scheme, the result becomes better in terms of a small swing and fast response to suppress vibration. For the effect of the SPB algorithm, the achieved performance is of smaller magnitude for oscillation and suppresses it more quickly. Lastly, the most superior performance of the smallest level of vacillation and the fastest response are achieved by APB scheme while the powerful computation of micro-processor is required. To visualize the differences of their impact, a combined result representing a comparison of the proposed strategies is displayed as in Figure 17. e deep impression on the diminishing vibration of the APB method has been observed. However, its constraints require a machine far enough away to decelerate. On the other hand, the schemes of SPB and TPB satisfy the conditions of vibration suppression while not need more spaces to execute.   Table 2 reveals the comparative performance for all laboratories. is research regards how fast the oscillation is terminated and how many times the largeness of the oscillation decreases. When the proposed control techniques are not considered, the acceleration of mass m 2 tends to decrease the vibrating magnitude by 1.26 times after 1.47 s. In the primary scheme, TPB helps to lessen the number of times to 1.78 after 1.46 s from the moment of the unexpected stop. In other tests, under the power of the SPB and APB schemes, the vibration declines by 3.07 times and 5.56 times after 1.41 s and 1.27 s, correspondingly. It is concluded that the APB technique can offer the best performance in terms of antioscillation even though it is expected that more space will be required to complete the stop strategy. e others show that a smaller oscillating range and faster response of the system can be attained, and the travelling distance desired by a mobile vehicle can be increased.
Equations (28) and (30)    operate under the E28 and E30 conditions. After several experiments, it is known that the tolerance of the vibrating frequency in TPB is smaller than that in APB or SPB. e sensitive curve in Figure 18 denotes the variation in amplitude when the estimated natural frequency differs from the practical natural frequency. In this study, it is assumed that the natural frequency error is ±20% of the real value. e motion that satisfies both E28 and E30 is defined as a crater. If it satisfies only one of the above vibration-less conditions, the movement is categorized as a chasm. Notably, the impacts needed to reduce the residual vibration of a crater are larger than those of a chasm.
In general, if the tuning parameters satisfy both E28 and E30, then the residual vibration amplitude will decline in comparison with only E28 or E30 whenever the error modelling is small enough.

Conclusions
An active stop strategy with vibration cancelation control and collision avoidance between humans and machines (i.e., material transportation) was proposed in this paper. e antivibration control constraint is analytically well-defined based on a dynamic modelling of a vehicle and cargo. Various profiles for activating the stop policy were inspected, and the specific characteristics of each profile were analysed. In particular, the physical characteristics of TPB, SPB and APB were analytically compared to the case without an active stop planner. From the points of view of smoothness and robustness, both investigated strategies drive the whole platform to halt under flexible motion while the system is constantly stabilized. Owing to the socially aware navigation framework of a mobile platform in dynamic surroundings, we developed a switching mechanism to select the proper profile for different social situations. We certified the effectiveness of the proposed approach through both simulation work and a real-world laboratory test. Clearly, the newly investigated stop method could be incorporated into any path planning technique to enhance the performance of human-awareness of an autonomous system. It is clear that our approach has undergone successful integration such that the robot behaviour is improved to a socially acceptable response, achieving safe restrictions while conserving system parameter constraints.
Compared to the works invented by authors [23], although the interaction force is not mentioned and the natural frequency seems to be difficult to estimate, our study focusses on stable control for the autonomous vehicle. Compared to our previous topic [35], not only the potential human-machine interaction is examined, but also the internal system state is mainly concerned. Future work is required. We will investigate the proposed approach in different scenarios of social interaction (i.e., in front of group discussion) and dynamic environments. Additionally, various types of intelligent control should be considered to enhance the decision making for autonomous system.  Figure 18: Sensitivity curves of variation in the vibration magnitude against the natural frequency error with f n τ m � 1.2229.

Complexity
Furthermore, it is raised a promising research issue that the constrained parameter set could be optimized by using machine learning techniques. Note to practitioners. In general, the robot trajectory is scheduled and planned in host computer and human could wear the tracking device to avoid collision. However, in some emergent cases, robot must be clearly aware the human appearance and actively prevent collision.
us, the proposed method achieves the purpose of collision avoidance and socially interactive action. Additionally, the switching mechanism to decide proper strategy based on the distancing communication between human and robot is suggested in this work. It is potentially utilized in logistic warehouse, service restaurant, and so on.

Data Availability
No data were used to support this study.

Conflicts of Interest
e authors declare that they have no conflicts of interest.