Ergonomics Considerations of Usability Test of UAV Handheld Control Unit

Abstract

Consumer UAV (Unmanned Aerial Vehicle) has changed our daily life in many ways of aerial entertainment and photography. User experience and usability design were considered as priority factors which determined consumer’s purchase selection. Therefore, manufactures of consumer UAV focused on human factors and ergonomics considerations that help to guide UAV deign finalization and verification. Specifically, UAV handheld control unit should be drawn more attention to achieve efficient interaction and user satisfaction. This research firstly reviewed on technical literatures and standard specifications to distinguish key factors of ergonomics design requirements of UAV handheld control unit. And Delphi method was adopted to establish an index system of ergonomics evaluation of UAV handheld control unit involved with control-display interface, warning, and special usage. Finally, usability test method was developed to realize user experience evaluation and expert technical measurement of UAV handheld control unit. Both ergonomics considerations and usability test methods were designed to provide guidance support for relevant consumer UAV designers and testers.

1 Introduction

Nowadays, with prosper of consumer UAV industry, its marketing scale has blown out with updating product and expert solutions. The battlefield of consumer UAV market was concentrated on the competition of user experience rather than production technology. For instance, the traditional product test of UAV mainly focused on flight performance and requirement-function realization. However, user experience and usability design became more popular as key points to achieve consumer satisfaction.

As primary interface between user and UAV, the handheld control unit played a significant role of providing effective and efficient interaction, which was ensured to perform remote-control task and realize multi-function task including aerial photography. The common control device was widely applied in both industry and daily life, therefore, the ergonomics design had direct and significant influence on task performance, user experience even health care and personnel safety. To improve human machine interaction, the control device was required to design in accordance with user physical and psychological characteristics as well as behavior custom.

As shown in Fig. 1, a typical UAV handheld control unit contained various hardware of controls and displays [1]. The controls should be designed including with button, finger wheel, joystick, and switch while the displays were included with display screen and indicating light [2].

Fig. 1.

Example of UAV handheld control unit

1.1 Research Reviews

The recent study of ergonomics issues on UAV handheld control unit was hardly found, however, the designers tended to rely on scheme evolution and their experience due to the lack of specifications or standards. In contrast of ergonomics or usability test, realization of functional capabilities drew more attention during test and evaluation phase.

Ergonomics research of controller mainly focused on type selection and design requirement or criteria using physical measurement, subjective evaluation as well as visual simulation. Yao recruited 70 professional truck drivers to carry out ergonomics evaluation for control device of truck cockpit based on subjective feelings and driving experience [3]. Liu developed manipulation classification of control device and analyzed characteristics parameter of ergonomics design for selection [4]. In addition, recent study of ergonomics test and evaluation research concentrated on household electric applications including air conditioner manual [7], household appliances interface [6], TV screen and control unit [5,6,7].

1.2 Current Standards

With prosper development of UAV industry, relevant standard organization realized the importance of UAV standard and became expert standardize team to promote systematic work. Such as ISO/TC20/SC16, JARUSJ, SAE AS-4 were most active worldwide standard organization. And SAC/TC435/SC1 in China was just established and became the first sub-committee of UAV system in 2018. However, ergonomics requirement of UAV handheld control unit was merely found in the current standards, which still focused on design requirement and overall layout of control device of typical product, especially in automobile or working machine.

For instance, ISO 9241-400 provided ergonomics guidelines of principles and requirements for physical input devices which contained keyboard, mouse, joystick, trackball, touchscreen, and other devices. Generic ergonomic principles were specified and valid for the design and use of input devices [8]. ISO 9241-410 provided ergonomics design criteria for physical input devices which should be coincided with product characteristics under target user task situation [9]. ISO 9241-411 provided ergonomics evaluation methods for the design of physical input devices mentioned in ISO 9241-400 and specified evaluation methods of design attribute and determined criteria based on task situation [10]. Besides, HF-STD-001B specified technical requirements (diameter, length, manipulation power) for thumb tip and fingertip-operated displacement joysticks [11].

In China, there were certain published standards involved with ergonomics design and evaluation of the controls such as GB/T 14775-1997 “General ergonomics requirements for controller” and GB/T 32261.2-2015 “Usability of consumer products and products for public use-part 2: summative test method” [12, 13]. In consideration of specific household electric product, newly-released standards provided technical requirement and ergonomics evaluation for refrigerator (GB/T 36608.1-2018) and air conditioner (GB/T 36608.2-2018) [14, 15].

To sum up, foreign researches of ergonomics consideration of consumer product have realized further achievement and concentrated on problem-solving of daily life issues, which was conformed to the idea of human-centered design. Yet domestic researches in such field were required more promotion and innovation, therefore, study on ergonomics design and evaluation of UAV handheld control unit could be imperative.

2 Ergonomics Considerations of Design Requirements

2.1 Overall Design

The shape and size of UAV handheld control unit should be considered in overall design whereas its geometric size was designed to fit the primary requirement of use and convenience of handheld posture. The shape of contact area with hands should be designed as sphere, cylinder, or ring while that with fingers should have ripples suitable for touch. In addition, the aesthetics of appearance and comfort of operation should also be taken into account.

Moreover, the overweight of UAV handheld control unit should be noticed to avoid the unavailability of special users with uniform distribution of mass and balanced mass center. And the layout of overall design of controls and displays should be considered and coincided with requirements of function allocation, priority grouping, operation order and frequency. Besides, healthy material and comfort color as well as pleasant texture should also be involved with overall design.

2.2 Controls

Selection of the controls should be designed in accordance with actual operation needs which determined the choice of button, finger wheel, joystick, and switch. Therefore, layout of the controls became the next consideration that the spacing and grouping design should be satisfied the requirements of convenience and operability. However, the consistency requirement of control coding was obvious to follow yet this principle was difficult to achieve perfect designed due to the ignorable details with trifles and the counter-balance with other considerations such as usage pattern and update alternatives. Besides, the control coding of color, size, and shape should be also considered.

2.3 Displays

The ergonomics requirement of display screen should be followed with relevant standards or specifications which recommended appropriate design parameters of screen luminance, resolution, and contrast ratio. And the display interface should be well-designed to support friendly and easy user experience. In addition, display information should be shown including flight status, parameters, residual electricity and other auxiliary information that satisfied user’s visual acquisition of UAV’s current status.

2.4 Interactions

Interaction with UAV through handheld control unit should be designed to ensure usability that realized effective and efficient interaction in multiple interaction modals including hand-control, finger-control, touch screen control or even speech recognition control in order to achieve satisfied user experience. The specific requirements of interaction were contained simplicity requirement, consistency requirement, compatibility requirement, movement relationship requirement, and diversity requirement.

2.5 Warnings

The ergonomics considerations of warnings design contained visual and auditory requirements which should be provided with instant and salient cuing warned if any fault or failure happened. The visual requirement of warnings was mainly involved with blink, salient color or luminance while warning sound loudness and frequency should be taken into account of auditory requirement.

Nonetheless, limitations of night light or poor ambient illuminance should be considered to meet the minimum requirement of visibility. Besides, the workload and fatigue of handheld posture should be improved especially for long-term usage.

3 Ergonomics Evaluation Index System

3.1 Establishment

Based on ergonomics factors analysis of UAV handheld control unit, a primary index system of ergonomics evaluation was put forward in three-layer structure of thirty-two bottom indices.

The top layer of index system was coincided with Chapter 2 that was involved with I₁ overall design, I₂ controls, I₃ displays, I₄ interactions and I₅ special usage (including warnings and alarms).

The middle layer indices were extracted and specified from the upper layer:

• 1. I_1.1 appearance, I_1.2 weight, and I_1.3 material were belonged to overall design.

• 2. I_2.1 selection, I_2.2 layout, and I_2.3 coding were belonged to controls.

• 3. I_3.1 screen, I_3.2 information, and I_3.3 content were belonged to displays.

• 4. I_4.1 modal and I_4.2 usability were belonged to interactions.

• 5. I_5.1 warning, I_5.2 environment adpatation, and I_5.3 long-term use were belonged to special usage.

And thirty-two bottom indices were dissolved from the middle layer as shown in Fig. 2.

Fig. 2.

Three-layer structure of ergonomics evaluation index system

3.2 Optimization

Delphi method was used to select single index and optimize the proposed index system. Six participants including ergonomics experts and UAV designers were recruited in Delphi’s survey and required to complete a questionnaire to determine the significance of each index. According to the classic data process of Delphi method, the Mean, Mode and P33 were calculated as statistics results of index system and significant value threshold was set up as 3.0 which suggested an inappropriate index with significance below it.

Top Layer.

As shown in Fig. 3, the results of the top layer indicated suggestion of a retained index of I₅ Special Usage (P33 < 3).

Fig. 3.

Delphi results of the top layer

Middle Layer.

As shown in Fig. 4, the results of the middle layer indicated suggestion of retained indices of I_1.3 Material, I_3.2 Information, and I_3.3 Content (P33 < 3) and an abandoned index of I_5.2 Environment (Mode & P33 < 3).

Fig. 4.

Delphi results of the middle layer

In addition, certain participants advised to add human error protection into the middle layer followed by I₂ controls and interface design into I₃ displays. And also, transmission delay should be taken into consideration.

Bottom Layer.

As shown in Fig. 5, the results of the bottom layer indicated suggestion of retained indices of I_1.3.1 Material, I_2.3.4 Color Coding, I_2.3.5 Character Coding, I_3.2.1 Timely, I_3.3.3 Completeness, I_4.1.2 Flexibility, and I_5.2.1 Dark Adpatation (P33 < 3).

Fig. 5.

Delphi results of the bottom layer

In addition, foreign languages should be considered in I3.3 information and battery endurance as well as operation and storage environment should be added into I5.3 long-term usage.

3.3 Verification

Focus team method was used to examine the results of Delphi’s questionnaire and verify the determination of index system. Five experts were recruited as focus team which contained two ergonomics experts and three UAV designers. After the demonstration of Delphi’s results, the focus team was required to discuss revision of the former index system and recommendation of the final one. To sum up, their conclusion came to an agreement that certain indices should be deleted such as I_2.3 coding and I_5.2 environment, while others should be adjusted that layout requirement (I_2.2) should be moved under I₁ overall design and the middle layer under I₂ controls should be updated into rationality, convenience, and human error protection.

Therefore, the ergonomics evaluation index system of UAV handheld control unit remained three-layer structure with forty-four bottom indices:

• Five indices of the top layer were involved with I₁ Overall Design, I₂ Controls, I₃ Displays, I₄ Interactions, and I₅ Special Usage.

• Fifteen indices of the middle layer were contained with (1) I_1.1 appearance, I_1.2 weight, I_1.3 layout, and I_1.4 delay, (2) I_2.1 rationality, I_2.2 convenience, and I_2.3 human error protection, (3) I_3.1 screen, I_3.2 interface, I_3.3 information, and I_3.4 content, (4) I_4.1 modal and I_4.2 usability, (5) I_5.1 warning, and I_5.2 long-term use.

• Forty-four indices of the bottom layer were contained with:

  • (1.1) I_1.1.1 shape and I_1.1.2 size, (1.2) I₁₂₁ quantity and I_1.2.2 balance, (1.3) I_1.3.1 position, I_1.3.2 grouping, I_1.3.3 spacing, and I_1.3.4 socket, (1.4) I_1.4.1 data-link delay and I_1.4.2 transmission fluency,

  • (2.1) I_2.1.1 input controls, I_2.1.2 touch control, and I_2.1.3 gesture control, (2.2) I_2.2.1 force, I_2.2.2 feedback, and I_2.2.3 custom, (2.3) I_2.3.1 operation error, I_2.3.2 false touch, and I_2.3.3 fool proof,

  • (3.1) I_3.1.1 luminance, I_3.1.2 contrast ratio, I_3.1.3 color rending, and I_3.1.4 clarity, (3.2) I_3.2.1 friendliness, I_3.2.2 aesthetics, and I_3.2.3 learnability, (3.3) I_3.3.1 timely, I_3.3.2 readability, and I_3.3.3 foreign language, (3.4) I_3.4.1 accuracy, I_3.4.2 comprehension, and I_3.4.3 completeness,

  • (4.1) I_4.1.1 rationality, I_4.1.2 flexibility, and I_4.1.3 diversity, (4.2) I_4.21 effectiveness, I_4.2.2 efficiency, and I₄₂₃ satisfaction,

  • (5.1) I_5.1.1 visual, I_5.1.2 auditory, and I_5.1.3 tactile, (5.2) I_5.2.1 fatigue, I_5.2.2 endurance, and I_5.2.3 environment.

4 Usability Test Method

According to the ergonomics factors and index system, the usability test methods to evaluate UAV handheld control unit were developed and involved with both quantitative requirement of technical measurement and subjective assessment of user experience.

4.1 Technical Measurement

Technical measurement of usability test method was used to adopt professional measuring instrument to evaluate the appearance, weight and transmission delay of UAV handheld control unit. The specific requirement of technical measurement contained:

• Appearance evaluation was required to measure geometrics characteristics of overall design parameters which were involved with length, breadth, and thickness. In addition, the size and spacing of the typical controls were also included in appearance evaluation.

• Weight evaluation was required to measure quantitative characteristics of overall weight, center of gravity, and weight distribution.

• Force evaluation was required to measure operation power of button-pressing, switch-turning, and screen/pad-touching.

• Transmission delay evaluation was required to measure delay time, packet loss, and spread spectrum ratio. To be noticed, transmission delay was not strictly considered as ergonomics evaluation index, however, it surely affected accuracy and efficiency of UAV remote-control which might lead to bad user experience due to graphic disfluency or operation latency. Therefore, it was recommended to include in technical measurement and an acceptable threshold was suggested as “<200 ms” of transmission delay that could be merely perceived during ordinary usage.

4.2 User Experience

User experience of usability test method was used to adopt traditional subjective questionnaire to evaluate preference perception during scenario-based use-case test. The test scenario of user experience was designed as typical usage of UAV which contained with initialization and preparation, basic operation of handheld control unit, and ordinary operation of flight and videography. As shown in Fig. 6, the specific task of use-case was designed in accordance with UAV manual. The whole test procedure of user experience should be included with participant recruitment, training and practice, scenario-based test, and questionnaire research.

Fig. 6.

Use-case of user experience

• Participant recruitment was designed to focus on requirements of participant selection, sample size, and informed consent constraint. Besides, both ergonomics scholars and UAV designers should be invited as technical experts and recruited in this test. And sample size was suggested as twelve participants at least which should be included with four experts and eight UAV users.

• Training and practice were designed to help the participants master the basic UAV operations and become qualified users. It was recommended that the training and practice phase might be skipped when the participants were of rich experience of UAV usage, however, the formal test should not start until they were all familiar with test product and normal operation.

• Scenario-based test was designed as formal test of user experience with specific use-case shown in Fig. 6. During the case of initialization and preparation, the participants were required to initiate UAV system by installation of control unit and battery charging. And the cases of basic and ordinary operations required the participants to experience function and performance of UAV which should be evaluated in the next questionnaire research.

• Questionnaire was used to measure user experience of UAV in five-star grading evaluation using weighted quantization calculation. According to the index system mentioned in 3.3, the questionnaire was designed as satisfaction rating of both static and interactive evaluation. The former one concentrated on physics characteristics evaluation of appearance and layout design, while the latter one contained usability and user experience of UAV interactions of control and display interface.

5 Conclusion

In conclusion, this research firstly analyzed five main considerations of ergonomics design of UAV handheld control unit which were concerned with overall design, controls, displays, interactions, and warnings. And a three-layer index system of forty-four bottom indices was established and verified for ergonomics evaluation using Delphi questionnaire method. Moreover, usability test method was developed in consideration of technical measurement and user experience of UAV handheld control unit.