One-dimensional input device of electric wheelchair for persons with severe Duchenne Muscular Dystrophy

Abstract

Persons with Duchenne Muscular Dystrophy (DMD) usually have difficult in operating electric wheelchairs (EWs) using standard input device due to the lack of muscular power and the deformation of their hands. To solve this problem, various kinds of input devices are developed considering their physical limits. However, as the disease progresses, persons with severe DMD will gradually lose the ability to operate the developed input devices. In this study, we first made an investigation of physical functions for persons with severe DMD and found that functions of upper limb, especially functions of the fingers, tended to remain better in at least one-dimensional direction. A novel one-dimensional input device (1DID) was developed for persons with severe DMD based on a quantitative evaluation of the hand functions. Thus, this device can be operated using slight force and one-dimensional movement of a finger. Therefore, persons with severe DMD can adjust the straight and turning motion of an EW using two 1DIDs with the cooperative operation by two fingers. The validity of this device was demonstrated by evaluation experiments of 10 persons with severe DMD including those who do not have a proper input device. The evaluation results also show that the developed 1DID has the possibility to be widely used as a generic input device with computers for persons with severe disabilities.

Keywords

Electric wheelchair Duchenne Muscular Dystrophy hand function one-dimensional input device cooperative operation

1. Introduction

Recently, the number of persons with severe disabilities is increasing in Japan [1]. Their severe limited mobility will have a negative effect on their life-range and Quality of Life (QOL). Electric wheelchair (EW) is one of the most widely used devices for persons with severe disabilities to regain some mobility.

Muscular Dystrophy is one of the diseases that leads to difficulty in operating an EW. It is a permanent disease with which the persons’ muscular power will decline gradually. There are two major types of muscular dystrophy: Duchenne Muscular Dystrophy (DMD) and Becker Muscular Dystrophy (BMD). This paper will focus more on DMD which progresses more rapidly than BMD [2]. For persons with DMD, EW is not only the tool to regain some mobility but also can improve their Abilities of Daily Living (ADL) [3] and the QOL [4].

The symptoms of DMD are mainly reflected in the following aspects. First, the symptoms of having difficulty in walking usually begins around the age of four in boys and worsens quickly. Most of the persons with DMD become unable to walk and start to use the EWs around the age of early tenth. At this age, their muscle atrophy joint contracture starts to stand out, but they can still use joystick controllers to operate the EWs. Persons with DMD become unable to use joystick controllers from the late teens because they have very little upper limb functions and no lower extremity functions, and their hands will be severely deformed [5]. Second, persons with DMD also face the inevitable consequence of diminishing pulmonary function at late teens [6, 7]. Progressive loss in pulmonary function leads to the decrease of lung compliance and hypercapnia, the latter one often appears when physical strength is less than 30% of normal. Fortunately, Noninvasive Positive Pressure Ventilation (NPPV) is developed to provide assistance for breathing. The appearance of on-electric-wheelchair type NPPV make it possible for persons with DMD expand their life-range [8]. Third, as the disease progresses, proper seating is a way to slow deformities, maintain mobility, and enhance QOL [4]. The seating system of the EW should be designed according to the disease progression. It also requires the active participation of the patients, the professional rehabilitation workers, and the paramedics [9].

This paper focuses on the first aspect that how to design the input device considering the physical functions of persons with severe DMD. In general, persons with disabilities use some kinds of input devices such as joysticks to control EWs. The parameters of these input devices such as reaction force, movement range of the remote, and holding positions can be adjusted to fit their residual physical functions. For persons with severe disabilities, input devices such as sound [10], EMG signals [11] and eye gaze [12] are used to operate the EWs. These methods usually have the limitations that require complicated pattern recognition, and are not capable of providing continuous signals. Moreover, EWs are equipped with more or less intelligence (Smart wheelchair) to assist those with disabilities to improve the operation [13, 14]. It should be noted here that an appropriate input device is necessary to transmit users’ intention even for the smart wheelchairs.

One of the features of myogenic diseases such as DMD is that distal muscle (ex. Muscles that move the ankle and the fingertips) tends to remain better than proximal muscle (ex. Muscles that move the trunk, upper arm and femoral muscle). Sim et al. proposed a method to quantitatively evaluate the fingertip force and range of motion of the fingers, and found that the hand function remains even if the upper limb dysfunction is severe [15]. In addition, considering users’ subjective feelings, persons with DMD are more inclined to operate input devices with hand functions instead of facial muscle functions [16]. Based on these findings, in this paper, functions of upper extremity, especially functions of hands, were focused as the residual functions when designing the novel input device.

Shino et al. developed two new joystick controllers for an EW based on a quantitative evaluation of the hand functions of persons with DMD [17]. However, joystick controllers are not available for persons with severe DMD who can only move their fingers in one-dimensional direction. The objective of this research is to develop a novel input device that can be operated with only one-dimensional movement of a finger. To achieve this objective, a novel one-dimensional input device (1DID) is developed after fully understanding and quantitatively evaluating the residual hand functions of persons with severe DMD. Evaluation experiments are then carried out to demonstrate the effectiveness of the novel 1DID that straight and turning motion of an EW can be adjusted using two 1DIDs. Specifically, investigations of the physical characteristics of persons with severe DMD is introduced in Section 2. The requirements and the development of the input device is introduced in Section 3. The evaluation of the input devices is discussed to prove the validity of the proposed 1DID in Section 4. In Section 5, the conclusion is introduced.

2. Investigation of persons with DMD

2.1 Physical characteristics of persons with DMD

The daily life style and the physical functions of nine persons with DMD were investigated to understand the characteristics of DMD. Participants were volunteers at Shimoshizu National Hospital in Japan. Table 1 lists the subject ID, age, whether the subject was using an EW, the input devices for the EW and the functional classification of the upper extremities. The functional classification of the upper extremities shows the different stages of upper limb dysfunction, the stage is higher, the function of the hands is worse [18]. The contents of the classification are shown in Table 2.

Table 1
Details about the subjects

ID	Age	Use of EW	Input device	The functional classification of EW
				of the upper extremities (1–13)
A	29	Using, everyday	Customized joystick	7
B	26	Using, everyday	Customized joystick	7
C	27	Using, 2 days/week	Customized joystick	9
D	19	Using, everyday	Customized joystick	10
E	21	Not using	–	10
F	23	Using, 2 days/week	Customized joystick	11
G	25	Not using	–	11
H	28	Not using	–	12
I	21	Not using	–	12

Table 2

The functional classification of the upper extremities (1–13) [18]

Stage	Ability of hands
1	Hold the 500 g weight or more with the dominant hand and move that hand directly forward and above.
2	Hold the 500 g weight or more with the dominant hand and raise the hand to the front 90 degrees.
3	Raise the dominant hand directly forward and above without weight.
4	Raise the dominant hand to the front 90 degrees without weight.
5	Flex the elbow joint for 90 degrees or more without weight.
6	Move the hand horizontally forward by extending the elbow on the desk.
7	Move the hand horizontally forward by extending the elbow on the desk using the recoil of the body.
8	Move the hand horizontally forward using the recoil of the body after extending the elbow on the desk.
9	Move the hand on the desk horizontally forward by the movement of the hand.
10	Turn over copy paper (postcard size: 10 $\times$ 14.8 cm) with the dominant hand.
11	Grasp the course cube (2.7 $\times$ 2.7 $\times$ 2.7 cm) with the thumb finger at the thumb frontal position.
12	Cannot grasp the course cube (2.7 $\times$ 2.7 $\times$ 2.7 cm) using the thumb finger at the thumb frontal position but the fingers can move.
13	Fingers cannot move.

Figure 1.

Deformation of hands for each subject (Subject ID: the stage of the upper extremities).

Figure 2.

Typical deformation [19].

Figure 3.

Customized joysticks for Subject C, D and F.

Figure 4.

Dynamic link model of hand and joint coordinate system [17].

After investigation, three characteristics were found among the volunteers. Firstly, muscle weakened, the loss of smoothness, the contracture of the joints were found as the DMD symptoms. Although they gradually lose their body functions, the functions of upper limb, especially the finger functions, tended to remain better. Secondly, the kinds and the stages of the symptoms were various among the persons with DMD. Figure 1 shows the hands of the subjects. As the degree of the classification of the upper extremities increase, the restriction and contracture of their hands become more severe. As shown in Fig. 2, the deformation of hands can be regarded as the combinations of three typical deformations: swan-neck deformity, hammer finger and boutonniere deformity [19]. For example, subject A, C, E and I were deformed as hammer fingers while Subject F and G were deformed as swan-neck deformity. Thirdly, the movement of the fingers tend to remain only in one-dimensional direction for persons with severe DMD that they will gradually lose the ability to use the joystick controllers.

2.2 Input devices for persons with DMD

Figure 3 shows customized joysticks for Subject C, D, and F. The length of the switches, the internal spring, and the appearance of the joysticks are adjusted to match the physical functions. However, for persons with severe DMD, whose fingers can move only in one-dimensional direction, the joystick controllers which need two-dimensional input can hardly be used. Therefore, it is necessary to develop a novel input device which can be used with only one-dimensional input.

3. The requirements and its development of the input device for persons with severe DMD

3.1 The requirements of input device

Various kinds of input devices have been developed for persons with severe disabilities [10, 11, 17]. The essence of designing the devices is understanding the user’s intentions from the input signal. Users’ intentions can be expressed in many kinds of forms, such as users’ sound [10], EMG signals [11] or simply a movement of the joystick. Their forms can be classified into two types according whether a pattern classifier is necessary. Methods using voice or EMG signals usually need a pattern classifier with the technology such as neural networks [20] and SVM [21]. More training is necessary if the numbers of motion commands extends. Besides, these methods are usually hard to adjust the velocity continuously by the user selves. On contrary, controllers like joysticks are more intuitive to use and easier to adjust the velocity continuously but require more physical functions. In this paper, the novel input device will be designed in an intuitive way which does not require a pattern classifier.

Based on the investigation from Section 2 that the finger function can be maintained better than other functions and considering the input device is used to operate an EW continuously. The requirements of the input device are determined as follows:

1.
The input devices can be held by the users.
2.
The input device can be controlled by slight force and movement even the hand is deformed.
3.
The straight and turning motion of an EW can be continuously adjusted by the input device.

3.2 The design concept of the input device

As discussed in Section 3.1, two-dimensional inputs are needed to control the straight and turning motion of an EW. The concept of the input devices can be classified into two types. One is a two-dimensional type controller which can adjust the straight and turning motion of an EW through one operation, and the other is a one-dimensional type controller which can control the straight and turning motion of an EW with the combination of two inputs such as the pedal and steering wheel in a car.

3.3 Evaluation method of hand function

To develop a novel input device for persons with severe DMD, the physical function should be quantitative evaluated. A novel evaluation method for hand functions was proposed in paper [17], the joint coordinate system of the fingers was defined, as shown in Fig. 4. The origin of the thumb was set at carpometacarpal joint (CM joint) and the origin of the other four fingers was set at metacarpophalangeal joint (MP joint). The fingertip force was measured by a 3-axis force sensor attached on the tip of a universal arm, as shown in Fig. 5. The subject was asked to press the sensor toward each axis for 10 s and the mean value of the last 7 s was used as the fingertip force. It should be noted that in the z direction we can only measure the force in the z $+$ direction. The active range of motion (ROM) was measured by motion capture cameras which was shown in Fig. 6. The coloured marks on the fingers were recorded by five camcorders and the video data was analyzed by the soft Kineanalyzer (KISSEI COMTEC Ltd). Four triplet markers, which were triangle with three different colour points, were attached to the center of the nail and three joints of one finger to create a tangential planes on the measured finger. Then the subject was asked to move the finger in each axis for 10 times. The mean value of the movable range of the center of the nail was regarded as ROM of the finger.

Figure 5.

Measurement of fingertip force [17].

Figure 6.

Measurement of range of motion [17].

3.4 Evaluation results of hand function

Figure 7 shows the evaluation results for thumb functions of Subject G and H. For Subject G, we focused on xz coordinates because the ROM in the y direction is narrow. In the case of Subject H, xy coordinates are focused because ROM in z $+$ direction is narrow. The micro-joysticks were designed to meet the evaluation results [17]. The shapes of the devices are designed considering their deformation of hands, and the devices were created with a three-dimensional printer. Figure 8 shows the input devices for Subject G and H.

3.5 The development of the one-dimensional input device (1DID)

Subject I is one of the persons with severe DMD at stage 12 who do not have a proper input device now. We first made an investigation of Subject I to understand his hand functions. The evaluation results of his hands are shown in Fig. 9, the force from the surface of the thumbs would only be able to continue in the z $+$ axis direction. Meanwhile, the motion range of thumbs were also best remained in z direction. Therefore, a 1DID is a proper solution here. The operating axis of the input device is determined as z $+$ axis direction because in this direction there exists strong reaction force and wide motion range relatively.

According to the evaluation results, the input device should be operated within around 0.2 N force and 5 millimetres movement in the z $+$ axis direction. Meanwhile, it is also important for people to sense their input with displacement feedback. Indeed, Sand et al. [22] showed that proprioception is important for fine tuning of movement when the force exerted is below 5 N.

Table 3
Details about the PAW sensors

Parameters	Value	Unit
Diameter	8	mm
Height	10	mm
Weight	1.5	g
Sensitivity	0.2	V/mm
Power supply voltage	3.3	V
Transient response time	250	$\mu$ s
Operating temperature	0 $\sim$ 50	${}^{\circ}$ C
Storage temperature	$-$ 10 $\sim$ 60	${}^{\circ}$ C

Figure 7.

Evaluation results of subjects’ hand function [17].

Figure 8.

Subjects using the designed input device [17].

Figure 9.

Hand functions of Subject I.

Figure 10.

PAW sensor for the 1DID.

Figure 11.

The design of operating method for the 1DID.

Figure 12.

The concept of deciding the parameters.

Figure 13.

Operating strategies of the 1DID.

After the investigation, we adapted the PAW sensor to meet the requirements. The PAW sensor is developed by RT COPORATION and its appearance is shown in Fig. 10a. The principle of PAW sensor is shown in Fig. 10b. LED and phototransistor are embedded under the urethane, the density change is detected by the amount of light transmission. The PAW sensor measures the height of urethane (movement of the finger) by the density change of the urethane. The entire structure is shown in Fig. 10c. There are two LEDs and two phototransistors in each PAW sensor, and by turning on the two LEDs alternately, it is possible to calculate the heights of four points (point ⟀, ⟁, ⟂ and ⟃). The parameters of the PAW sensor are shown in Table 3. The size of the PAW sensor just matches the size of the user’s thumb and other parameters such as sensitivity and height meet the requirements from evaluation results. One thing that need to be mentioned here is that although the appearance of the PAW sensor shown in Fig. 10a is similar to a button type controller, the PAW sensors can provide continuous signals by detecting how much it is pushed by users. Furthermore, people can sense their input since the urethane part can provide force and displacement feedback when they push the sensor.

3.6 Functions and operating methods of the device

As shown in Fig. 11a, the combination of the tilt angle ${\alpha}_{1}$ and the tilt direction ${\alpha}_{2}$ are used to control the straight and turning motion of an EW. The relationship between input ( $r\propto\alpha_{1},(\phi=\pi/2-\theta)\propto\alpha_{2}$ ) and the output ( $v$ and $\omega$ ) is shown in Eqs (1) and (2), where $r$ ( $\leqslant$ 1) and $\theta$ represent the magnitude and angle of the velocity vector while $v$ and $\omega$ are the speed and yaw rate of an EW, respectively. $\phi$ is the angle between $r$ and the normal. Referring to this concept, the operating method for the proposed device is shown in Fig. 11b. Two PAW sensors are used to control the $r$ and $\phi$ , respectively. It should be noted here that users can drive the EW going straight with only sensor A by giving the information of $r({\phi=0})$ . Sensor B is only necessary when the direction of the EW should be adjusted.

$\displaystyle v\propto r\cdot\sin\theta,\omega\propto r\cdot\cos\theta.$ (1) $\displaystyle\theta=\frac{{\pi}}{2}-\phi$ (2)

Because the physical functions of persons with severe disabilities is extremely weak and varies from person to person, the following situations may occur during actual operation:

The input range is different by different persons with DMD.

Changes in the gravity applied to the sensor due to the difference in posture.

Some persons with severe DMD cannot handle the device unless pushing the device because the contract of their hands is severe.

To deal with these situations, as shown in Fig. 12, subjects are asked to push the 1DID for several times to decide several parameters below. The parameters of initial value and the max value are decided by the operating range. The threshold is set here considering the initial and max values to deal with the noise at the beginning of the input.

After deciding these parameters, $r$ is calculated from the average height pushed by the user with regard to point ⟀, ⟁, ⟂ and ⟃ which are shown in Fig. 10c. To make the direction operating more intuitive and convenient, the PAW sensor which is used to control $\phi$ is first divided into the left and right parts. As shown in Fig. 11c, the heights of two diagonally related points in each part are compared to select the left or right side. The magnitude of $\phi$ is then decided by the average height of point ⟀, ⟁, ⟂ and ⟃. Equations (2) to (5) show how $r$ , $\phi$ and $\theta$ are calculated. Here ${d}_{1}$ , ${d}_{2}$ , ${d}_{3}$ and ${d}_{4}$ are the heights of point ⟀, ⟁, ⟂ and ⟃. ${d}_{\textit{ave}}$ is the average height pushed by the user with regard to points ⟀, ⟁, ⟂ and ⟃ compare to the threshold $d_{\textit{thre}}$ . $d_{\textit{limit}}$ is the max value for the input of $r$ and $\phi$ . Here, we also define $d_{\textit{range}}$ as the operating range which equals to $d_{\textit{limit}}-d_{\textit{thre}}$ .

$\displaystyle d_{\textit{ave}}=\frac{d_{1}+d_{2}+d_{3}+d_{4}}{4}-d_{\textit{% thre}}$ (3) $\displaystyle r=\left\{{{\begin{array}[]{ll}\frac{d_{\textit{ave}}}{d_{\textit% {range}}},&0<d_{\textit{ave}}\leqslant d_{\textit{range}}\\ 1,&d_{\textit{ave}}>d_{\textit{range}}\\ \end{array}}}\right.$ (4) $\displaystyle\phi=\left\{{{\begin{array}[]{ll}\frac{\pi}{2}\frac{d_{\textit{% ave}}}{d_{\textit{range}}}\text{sgn}({d_{1}-d_{4}}),&0<d_{\textit{ave}}% \leqslant d_{\textit{range}}\\ \frac{\pi}{2}\text{sgn}({d_{1}-d_{4}}),&d_{\textit{ave}}>d_{\textit{range}}\\ \end{array}}}\right.$ (5)

Except for forward mode, a backward mode and a reclining mode are set in the uses of the 1DID. The backward mode is necessary because EW is always used in narrow places. A reclining mode is also added to prevent seating problems [4, 9]. Figure 13 shows the operating strategies, if there is no input for 5 seconds, users are allowed to choose the modes. The mode is determined by the number of time that sensor A is pushed and the final decision is made by pushing sensor B. Different sound are designed to match each event so that users can understand whether they have a successful operation. The relationship between the events and the sounds are shown in Table 4.

Table 4

Relationship between events and sound for operating the EWs (“bi” and “pi” are low and high frequency sound, respectively)

Event	Sound
Select forward mode (mode 1)	“bi” rings for one time
Select backward mode (mode 2)	“bi” rings for two times
Select reclining mode (mode 3)	“bi” rings for three times
Decision	A long sound of “bi”
Allowed to select	“pi” rings for one time

Figure 14.

Description of experimental method.

Figure 15.

Evaluation results of Subject I for operating the 1DIDs.

3.7 Evaluation of the 1DID for a person with severe DMD

As mentioned before, Subject I is a person with severe DMD at stage 12 who do not have a proper input device now. The novel 1DID is developed based on his residual hand functions. His successful use of the device can partly prove that this device is suitable for persons with severe DMD. As shown in Fig. 14, Subject I was asked to operate the input signal first along the maximum arc and then along the middle arc using the 1DID with forward mode on the screen. The distance from the input signal and the origin spot represents $r$ and ${\theta}$ which are defined in Section 3.6. Only forward mode is discussed here because the hand functions required in the back mode is the same as in the forward mode. This evaluation experiment for Subject I had two purposes. The first was to evaluate whether Subject I can understand the operating method, and the other was to evaluate whether Subject I can adjust controlled marker continuously with the cooperative operation with two fingers using the 1DIDs. Figure 15 shows that the controlled marker can be adjusted for 180 degrees with both maximum radius and middle radius. Although there were several line across the screen, he can always successfully adjust the controlled marker to the left or right.

4. The evaluation of the 1DIDs for the other persons with DMD

To prove whether this device can be widely used by persons with DMD, nine subjects with different upper limb dysfunction degrees are investigated to evaluation experiments. The investigation is divided into three steps to specifically analyze whether these subjects can use the device, and to find out the possible problems during usage.

1.
Confirm whether the subjects can wear and hold the 1DID.
2.
Confirm whether the subjects can operate the 1DIDs with both hands.
3.
Confirm whether the subjects have the possibilities to change straight and turning motion of an EW continuously.

4.1 Step 1: Wearing the 1DID

Because the hands of the persons with DMD could be severely deformed, we should first investigate whether the 1DID can be properly worn and held by the subjects and what efforts are necessary to help these subjects wear and hold the 1DID.

4.2 Step 2: Giving continuous input signal with both hands

To evaluate whether the input device could be operated with each hand, subjects were asked to push the input device. As shown in Fig. 16, an integrator was used to accumulate the green bar from input signal. The green bar from the input signal grew faster when users push the device hardly. Each time the input exceeds the entire bar, the input accumulation will return to zero. The user is asked to give the input signal and stop the signal in the target line, in this paper, the target line is set in the middle. The subject would be regarded capable of operating the 1DID if he could stop the target bar near the target line.

Figure 16.

Evaluation experiment of Step 2 for each hand performance.

4.3 Step 3: Operating the 1DIDs to change the velocity vector (

r

and

\theta

)

Subjects were asked to finish the screen task which is introduced in Section 3.7. The aim of the evaluation experiment here is to show the possibility that the straight and turning motion of an EW can be continuously adjusted with the extremely limited physical functions of persons with severe DMD.

4.4 Results of the evaluation

For most of the subjects, it is possible to wear the 1DID by themselves or with the help of the device developer. Figure 17 shows one scenario when subjects are using the device. However, it is not easy for persons with severe DMD who can hardly maintain the posture and hold the device. Figure 18 shows one example that how occupational therapist helps this subject to wear the 1DID with their rich experience. One sponge was used to support the arm and another sponge was used to reduce the distance between the thumb and other fingers. Meanwhile, it is also found that some persons with severe DMD who are above stage 10 become unable to use the 1DID mainly due to their severe deformation of their hands. Because the fingertip force and the range of motion are two determining factors to affect the operation of this device, as shown in Fig. 19, a thin type of the 1DID is developed to reduce the required distance between the thumb and forefinger. Then, all the subjects became able to use the 1DID.

Figure 17.

Scenario when using the 1DID.

Figure 18.

Using the 1DID with support.

Figure 19.

Normal type and thin type device for persons with DMD.

Figure 20.

Evaluation results of Subject 1 and Subject 8 with experiments of Step 2.

Figure 21.

Evaluation results of Subject 1 and Subject 8 with experiments of Step 3.

Table 5

Results of evaluation experiment for 1DID device (able to use: $\surd$ , unable to use: $\times$ )

ID	Stage of upper	Right hand (r)	Right hand ( $\theta$ )
(ID in Table 1)	limb dysfunction	normal type (thin type)	normal type (thin type)
1	6	$\surd$	$\surd$
2	6	$\surd$	$\surd$
3	6	$\surd$	$\surd$
4 (A)	7	$\surd$	$\surd$
5 (C)	9	$\surd$	$\surd$
6 (D)	10	$\times\to(\surd)$	$\times\to(\surd)$
7	12	$\surd$	$\surd$
8	12	$\surd$	$\times\to(\surd)$
9	12	$\times\to(\surd)$	$\surd$

Figure 20 shows two results of Step 2 that the users are asked to give the signals and stop the signals at the target line. Subject 1 is a person with DMD at stage 6, it is found that subject 1 is able to use the 1DIDs to give signals with both hands, and this subject is able to stop the signal near the target line after several practice. Subject 8 is a person with DMD at stage 12, the function of his fingers are much worse than subject 1, the results show that although sometimes it is difficult to stop the signal at the target line accurately, it still reflects that Subject 8 wants to stop the signal near the target line.

The cooperation of two hands is necessary to complete the Step 3. One hand controls the magnitude of velocity vector ( $r$ ) at a target (middle or max) value by pushing one 1DID while the other hand changes the angle of the velocity vector ( ${\theta}$ ) by continuously changing the strength and direction of the push for 1DID. Figure 21 showed some results of step 3. The results show that both Subject 1 and Subject 8 can maintain the magnitude of velocity vector ( $r$ ) at the maximum value, however, the input signals from Subject 8 show some incorrect input signals when adjusting the angle of the velocity vector ( ${\theta}$ ). Meanwhile, there is larger deviation while maintaining middle magnitude of velocity vector ( $r$ ) for Subject 8. These might be because the hand functions of Subject 8 is much worse than Subject 1 that he had some difficulties in fine-tuning of the device. In fact, the results from the Step 2 also reflect this phenomenon that the stop timing of Subject 8 is not as accurate as Subject 1. Even though the operation of these subjects is not perfect, we still believe that the operating results can still intuitively represent the subjects’ intention even for whom with severe DMD. It should be noted here that driving an EW in real environments is a complicated behavior. More accurate and frequent input is necessary especially for the situation where fine steering capabilities are required. This is almost an impossible task for persons with severe DMD. Therefore, the EW should be equipped with an intelligent controller to help the user complete the driving process [13, 14]. Our future work is to develop a smart EW which can make full use of the users’ input and give assistance when necessary.

The conclusion for Steps 1, 2 and 3 are shown in Table 5, by adjusting the holding posture and thickness of the device, all the subjects became able to operate the 1DID.

4.5 Discussion about the evaluation results

Compared with joystick controllers, the 1DID only need one-dimensional movement of the finger and the subjects can control the magnitude and angle of the velocity vector. Subjects who participated in the experiments consider it necessary because they are experiencing continuous loss of physical functions. During the evaluations, it is found the softness, thickness of the urethane, and the sensitivity for the input device are three determined factors that affect the operation. The parameters can be determined through the quantitative evaluation of hand functions and inquiry from the users. Moreover, prolonged use of the device may cause the fatigue on the hand. Considering that the users need to provide input signals for the magnitude of velocity vector ( $r$ ) more frequently than for changing the angle of the velocity vector ( ${\theta}$ ) when driving the EWs, the functionally well-preserved hand is used to control the magnitude of velocity vector ( $r$ ). In addition, for persons with DMD who almost lost the abilities to move the thumb horizontally, the initial position between the device and the thumb becomes important because they are almost incapable to adjust the holding position once the position is incorrect. Furthermore, some subjects commented that the wires which connect the 1DID and EW are so heavy that affect their operation, it is necessary to use lighter wires or develop a wireless version in future. For persons with high stages, although the driving intention can be expressed to some extent with the 1DID, the accuracy is not enough. EWs need to equip with some intelligence so that the entire system can understand users’ real intention from the inaccurate input signals [13, 14].

5. Conclusion

In this paper, a novel 1DID for EW driving has been developed for persons with severe DMD who are not able to use joystick controllers. PAW sensor is adapted to meet the requirements of the fingertip force and motion range of finger for persons with severe DMD. The developed 1DID has the possibility to be widely used by persons with severe DMD because it requires only one-dimensional movement of a finger. The effectiveness of the proposed device is proven by the evaluation experiments of 10 persons with DMD that all of the subjects can use the 1DID with adjusting the thickness and holding posture. Although the subjects sometimes cannot adjust the input signal continuously, users can still use the 1DID to intuitively express their driving intention.

Future work is warranted, it can be concluded from the evaluation results that the 1DID has the potential to be widely used by persons with severe DMD. However, the ultimate goal of designing this 1DID is to help persons with severe DMD to regain their ability to drive an EW. Many factors such as fatigue, limited field of vision, and inaccurate input may affect their safe driving. Therefore, it is necessary to equip some appropriate assistant technology to ensure the safety of the EW driving.

Footnotes

Conflict of interest

None to report.

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