Force and tactile feedback in preloaded cantilever snap-fits under manual assembly

The purpose of this study was to investigate the tactile feedback of snap-fit fasteners when used in manual assembly. An important aspect of this assembly process is the assembler’s ability to perceive the snap-fit’s engagement. This sensing of engagement yields a high level of confidence that assembly is both complete and secure. Force and tactile feedback are critical elements in this process. Many snap-fits are used in conjunction with sealing elements that produce a constant force that remains in effect after snap-fit assembly is completed. The effect of sealing element preload magnitude and stiffness was studied using a test station, force deflection measurements, and jury pool data. A low value of preload with low stiffness was determined to be most favorable in terms of force and tactile feedback, with no preload only slightly less favorable. In order to sense the engagement signal of the catch, some resistance to assembly was found to be beneficial. A dimensionless term called “engagement signal-to-hold-force ratio” is proposed as an additional way of rating the effect of assembly forces for snap-fits. It was found that higher signal-to-hold-force ratio, as well as higher values of engagement signal, corresponded to higher confidence of assembly among experimental subjects.

Relevance to Industry

In the automotive industry, force and tactile feedback are essential for sensing the full engagement of snap-fit parts during the assembly of critical components, such as electrical and fuel system interconnects. Both the design of the snap-fit and the presence or absence of preload will affect force and tactile feedback. Many of these applications require the compression of an elastic gasket with a preload needed for air, fuel, or electrical isolation. Preload and preload stiffness factors are examined in this paper with the aim of achieving a better understanding of these effects so that snap-fit confidence of assembly and assembly robustness can be enhanced in industrial settings.     

一种三维力反馈手控器

结合力触觉感知的需要,设计了一种具有三维力反馈的手控器.介绍了三维力反馈手控器的工作原理及其控制电路的设计,该手控器通过电机驱动器控制手控器的三维输出,通过电机编码器获取人手运动所产生的运动三维编码信息,采用C8051F340的USB接口以方便上下行控制数据的通信,采用上、下行FIFO输入输出缓冲器以降低对控制器的实时性要求.最后设计了虚拟环境有限空间弹性球运动实验进行功能验证,并对所设计的手控器样机进行了性能测试.结果表明,所设计的手控器控制电路满足了手控器力反馈控制的需要,性能良好.     

Maintaining and modifying pace through tactile and multimodal feedback

Older adults are recommended to remain physically active to reduce the risk of chronic diseases and to maintain psychological well-being. At the same time, research also suggests that levels of fitness can be raised among this group. This paper describes the development and evaluation of a mobile technology, which enables older adults to monitor and modify their walking habits, with the long-term aim of sustaining appropriate levels of physical activity. An empirical study was conducted with twenty older adults to determine the feasibility of the proposed solution, with results indicating that tactile signals could be perceived while in motion and could support participants in walking at a range of paces. However, the effects were difficult to discern due to limitations of the hardware. In response, a novel low-cost prototype was developed to amplify vibrations, and effectiveness of redundant auditory information was investigated with the goal of enhancing the perception of the cues. A second study was conducted to determine the impact of multimodal feedback on walking behavior. Findings revealed that participants were able to maintain a desired level of pace more consistently when redundant auditory information was presented alongside the tactile feedback. When the visual channel is not available, these results suggest that tactile cues presented via a mobile device should be augmented with auditory feedback. Our research also suggests that mobile devices could be made more effective for alternative applications if they are designed to allow for stronger tactile feedback.     

Analysis and design of a new piezoresistive tactile sensor system for robotic applications

The development of an experimental tactile sensor system fitted on a robot work-table is analyzed in this paper. In the first stage of this research a 16 × 16 piezoresistive sensor was used, attached on the work-table of an ASEA IRB-2000 robot. The keypoint of the above design is that the sensor is not used just to obtain texture information, as it is happens when it is fitted on the gripper, but also to obtain tactile data from the object nonvisible base-surface and finally the object weight. The experimental system is designed so as to allow variation in the design parameters to determine the best set of parameter values for optimal performance of the sensor. Experiments carried out show the operability of the above system and, furthermore, the advantages using this sensor topology.     

A study of tile design for tactile guide pathways

Tactile guide paths can assist blind people to follow a particular route by using their shod feet to detect and distinguish raised patterns. Two kinds of tile are used to form a tactile guide path, pathway tiles with raised strip patterns are used to indicate the direction of travel to be taken and dome tiles with raised dot patterns are used to indicate a potential hazard or a junction. However, the contrast between these two tiles is not very great, so the users may not detect a junction or hazard. The experiment reported here compared existing guide paths with a possible new design, in which, the stimulation from pathway tiles was altered to provide a higher contrast with dome tiles. Twenty-three blind subjects participated in this study. They negotiated an existing guide path and a new design guide path. Each path was 30.3 m long and containing 10 junctions. Performance and responses of the subjects were used to evaluate the paths. The results showed that junction discrimination accuracy and time for the new design were significantly better than for the old design. The subjects also said that that new design was better.

Relevance to industry

Improving the discriminability of the patterns on tactile guide paths may result in enhancing the mobility of blind people. They can then perhaps become more independent and employable.     

Friction model of fingertip sliding over wavy surface for friction-variable tactile feedback panel

A friction-variable touch panel is capable of presenting virtual bumps and holes on its flat surface through the control of the surface friction when a fingertip slides over it. To improve the presentation, we developed a friction model of a fingertip sliding over a sinusoidal surface with an amplitude of 0.5–2.5 mm and a spatial wavelength of 20–50 mm. When a metal ball rolls over a wavy surface with a low friction and contact area, the ratio of the horizontal force to the normal force is equal to the gradient of the surface (this is referred to as the ball bearing model) and is hardly affected by the normal load and rolling speed. In contrast, the profile of the force ratio of a sliding finger is substantially skewed and affected by the sliding direction and normal force exerted by the finger. To model this skewed force ratio, we formulated the asymmetric pressure distribution in the finger-surface contact area and used the effects of the adhesion friction to model the dependency of the force ratio on the normal force and sliding direction. The developed model of a bare finger with these features was found to sufficiently simulate the experimentally observed force ratios. The model can be easily applied to friction-variable touch panels and enables the achievement of a wide variety of haptic contents with macroscopically concave or convex surfaces.     

A pattern classification by dynamic tactile sense information processing

This paper describes pattern classification with an artificial tactile sense. In this method, an object's shape is determined by touching, groping and grasping it with an artificial hand with tactile sense.

A simplified experiment classifying cylinders and square pillars was performed by an artificial hand with on-off switches instead of pressure sensitive elements. Highly reliable results were obtained. In addition, results of a surface groping experiment are given.     

A comparison of tactile,auditory, and visual feedback in a pointing task using a mouse-type device

A mouse was modified to add tactile feedback via a solenoid-driven pin projecting through a hole in the left mouse button. An experiment is described using a target selection task under five different sensory feedback conditions (‘normal’, auditory, colour, tactile, and combined). No differences were found in overall response times, error rates, or bandwidths; however, significant differences were found in the final positioning times (from the cursor entering the target to selecting the target). For the latter, tactile feedback was the quickest, normal feedback was the slowest. An examination of the spatial distributions in responses showed a peaked, narrow distribution for the normal condition, and a flat, wide distribution for the tactile (and combined) conditions. It is argued that tactile feedback allows subjects to use a wider area of the target and to select targets more quickly once the cursor is inside the target. Design considerations for human-computer interfaces are discussed.     

A vibrotactile approach to tactile rendering

While moving our fingertip over a fine surface we experience a sensation that gives us an idea of its properties. A satisfactory simulation of this feeling is still an unsolved problem. In this paper, we describe a rendering strategy based on vibrations that play an important role in the tactile exploration of fine surfaces. To produce appropriate excitation patterns we use an array of vibrating contactor pins. Similar to the colour model in computer graphics, we simulate arbitrary vibrations as a superposition of only two sinewaves. Each sinewave is intended for the excitation of a specific population of mechanoreceptors. We carried out first tests of our rendering strategy on Brownian surfaces of different fractal dimensions.     

Direction coding using a tactile chair

This laboratory study examined the possibility of using a car seat instrumented with a tactile display to communicate directional information to a driver. A car seat fitted with an 8 × 8 matrix of vibrators embedded in the seat pan was used to code eight different directions. Localization response time and angular accuracy were examined as a function of stimulus direction, presence of a tactile attention cue, temporal pattern, stimulus layout, age, and gender. The mean absolute angular error was 23°, and both localization accuracy and response times were superior for the back left, backward, and back right directions. Of the various temporal pattern/attention cue combinations examined, results favored the relatively fast patterns consisting of vibration bursts of 125 or 250 ms without a centrally located attention cue over 500 ms bursts that were preceded by an attention cue. Observed age and gender effects were relatively modest, suggesting that using tactile cueing to communicate direction is effective across a wide range of users. In addition, the tactile stimulus was detected by more than 90% of the participants under surprise trial conditions. Overall, these results indicate that the tactile chair provides a promising and robust method of providing directional information.     

A user study on tactile graphic generation methods

Methods to automatically convert graphics into tactile representations have been recently investigated, creating either raised-line or relief images. In particular, we briefly review one raised-line method where important features are emphasized. This paper focuses primarily on the effects of such emphasis and on comparing both raised-line and relief methods (produced by a Tiger Braille printer) through psychophysical experiments including discrimination, identification, and comprehension (involving 14 sighted and 6 blind subjects). Results show that raised-line pictures outperform relief images in all three tasks. Also, emphasizing important features significantly increases comprehension of tactile graphics. Raised-line images, however, disregard intensity/colour information unlike relief pictures. A technique incorporating intensity into raised-line graphics is also presented. Further experiments show the validity of this technique.     

Cost-efficient drilling using industrial robots with high-bandwidth force feedback

Here we present a method for high-precision drilling using an industrial robot with high-bandwidth force feedback, which is used for building up pressure to clamp-up an end-effector to the work-piece surface prior to drilling. The focus is to eliminate the sliding movement (skating) of the end-effector during the clamp-up of the end-effector to the work-piece surface, an undesired effect that is due to the comparatively low mechanical stiffness of typical serial industrial robots. This compliance also makes the robot deflect due to the cutting forces, resulting in poor hole position accuracy and to some extent in poor hole quality. Recently, functionality for high-bandwidth force control has found its way into industrial robot control systems. This could potentially open up the possibility for robotic drilling systems with improved performance, using only standard systems without excessive extra hardware and calibration techniques. Instead of automation with expensive fixtures and precise machinery, our approach was to make use of standard low-cost robot equipment in combination with sensor feedback. The resulting sliding suppression control results in greatly improved hole positioning and quality. The conceptual idea behind the force control is useful also in many other robotic applications requiring external sensor feedback control.     

The use of force feedback and auditory cues for performance of an assembly task in an immersive virtual environment

Using an immersive virtual environment, this study investigated whether the inclusion of force feedback or auditory cues improved manipulation performance and subjective reports of usability for an assembly task. Twenty-four volunteers (12 males and 12 females) were required to assemble and then disassemble five interconnecting virtual parts with either auditory, force, or no feedback cues provided. Performance for the assembly task was measured using completion time and number of collisions between parts, while the users preferences across conditions were evaluated using subjective reports of usability. The results indicated that the addition of force feedback slowed completion time and led to more collisions between parts for males. In contrast, females exhibited no change in the mean completion time for the assembly task but did show an increase in collision counts. Despite these negative performance findings when adding force feedback, users did report perceived increases in realism, helpfulness and utility towards the assembly task when force feedback was provided. Unlike force feedback, the results showed that auditory feedback, indicating that parts had collided during the assembly task, had no negative performance effects on the objective measures while still increasing perceived realism and overall user satisfaction. When auditory cues and force feedback were presented together, performance times, number of collisions, and usability were not improved compared to conditions containing just auditory cues or force feedback alone. Based on these results, and given the task and display devices used in the present study, the less costly option of excluding auditory and force feedback cues would produce the best performance when measured by the number of collisions and completion time. However, if increased ratings of usability for an assembly task are desired while maintaining objective performance levels and reduced cost, then the inclusion of auditory feedback cues is best.     

A Novel Seven Degree of Freedom Haptic Device for Engineering Design

In this paper, the authors intend to demonstrate a new intuitive force-feedback device that is ideally suited for engineering design. Force feedback for the device is tension-based and is characterised by 7 degrees of freedom (3DOF for translation, 3DOF for rotation, and 1DOF for grasp). The SPIDAR-G (SPace Interface Device for Artificial Reality with Grip) allows users to interact with virtual objects naturally by manipulating two hemispherical grips located in the centre of a device frame. Force feedback is achieved by controlling tension in cables that are connected between a grip and motors located at the corners of a frame. Methodologies will be discussed for displaying force and calculating translation, orientation and grasp using the length of 8 connecting cables. The SPIDAR-G is characterised by smooth force feedback, minimised inertia, no backlash, scalability and safety. Such features are attributed to strategic cable arrangement and control that results in stable haptic rendering. Experimental results validate the feasibility of the proposed device and example applications are described.     

Development of Tactile Mapping system for the stiffness characterization of tissue slice using novel tactile sensing technology

In this study, we modified our previously developed Micro-Tactile Sensor (MTS) not only to measure elasticity with high sensitivity but also to detect the instant of contact. First, modal analysis of the MTS was undertaken using finite element analysis to find a frequency where longitudinal and rotational vibration modes exist. Second, the MTS oscillated using these two types of vibration, and its basic performance was assessed. While the resonance mode of major longitudinal vibration shifted in an indentation and elasticity dependent manner, a disappearance of the rotational vibration upon contact resulted in abrupt change in resonance frequency which was used to signal touch detection. Last, using the modified MTS, we developed Tactile Mapping technology and used it to obtain a contour image and topographical Young's modulus information for a slice of porcine heart with coronary artery.     

A Faà di Bruno Hopf algebra for a group of Fliess operators with applications to feedback

A Faà di Bruno type Hopf algebra is developed for a group of integral operators known as Fliess operators, where operator composition is the group product. Such operators are normally written in terms of generating series over a noncommutative alphabet. Using a general series expansion for the antipode, an explicit formula for the generating series of the compositional inverse operator is derived. The result is applied to analytic nonlinear feedback systems to produce an explicit formula for the feedback product, that is, the generating series for the Fliess operator representation of the closed-loop system written in terms of the generating series of the Fliess operator component systems. This formula is employed to provide a proof that local convergence is preserved under feedback.     

A systematic approach to the Kansei factors of tactile sense regarding the surface roughness

Designing products to satisfy customers' emotion requires the information gathered through the human senses, which are visual, auditory, olfactory, gustatory, or tactile senses. By controlling certain design factors, customers' emotion can be evaluated, designed, and satisfied. In this study, a systematic approach is proposed to study the tactile sense regarding the surface roughness. Numerous pairs of antonymous tactile adjectives are collected and clustered. The optimal number of adjective clusters is estimated based on the several criterion functions. The representative average preferences of the final clusters are obtained as the estimates of engineering parameters to control the surface roughness of the commercial polymer-based products.     

A generalization of the small-gain theorem for nonlinear feedback systems

A generalization is given of the usual small-gain theorem which allows greater flexibility in use of gain bounds for stability analysis of nonlinear feedback systems.     

System of personal identification by using tactile stimuli

This paper proposes a personal identification system that uses tactile stimuli. Recently, scientists have been conducting research in biometrics using biomedical information. However, there is the problem that biomedical information is unchangeable. For example, if a thief steals another user’s biomedical information, that person has no information to register. Due to the problems of sight information and unchangeable biomedical information, we propose a solution that uses the sense of tactile stimuli. Tactile information is difficult to steal and relies on human memory, which is unchangeable. This paper proposes a system that uses a pattern formed by a tactile stimuli time series instead of a password number as the identification key. We also discuss the results of an identification experiment and a memory property experiment. This work was presented in part at the 13th International Symposium on Artificial Life and Robotics, Oita, Japan, January 31–February 2, 2008     

Aspects of Haptic Feedback in a Multi-modal Interface for Object Modelling

In our everyday life, interaction with the world consists of a complex mixture of audio (speech and sounds), vision and touch. Hence, we may conclude that the most natural means of human communication is multi-modal. Our overall research goal is to develop a natural 3D human-computer interaction framework for modelling purposes without mouse or keyboard and where many different sensing modalities will be used simultaneously and cooperatively. This article will focus on the various interface issues on the way to an intuitive environment in which one or more users can model their prototypes in a natural manner. Some technical framework decisions, such as messaging and network systems, will also be investigated.