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Visual-motoric control


For humans, the most important sensorial system is their vision systemgif. Nearly all actions which are performed are fed back and supervised by observation. Therefore, the combination of the two modalities vision and motoric control is a very natural and intuitive one, leading to a bimodal visual-motoric control. In this section, we do not deal with low-level visual-motoric coupling, like the muscular control of the eye which is necessary to fix an object over time (see 1.2.1 ), but with the interaction of visual and tactile feedback in motoric control tasks.

With today's standard computer equipment, every human-computer interaction includes some kind of visual-motoric coupling, no matter whether the user types in some text with a keyboard, performs click or drag-and-drop actions with a mouse or trackball, draws a model in a CAD system with a graphic tablet or a 6D input device, or controls a manipulator or mobile robot with a master-slave manipulator or a 6D input device.

In any case, the effects of the actions are --- at least --- observed on a monitor. But, as far as we know, the influence of visual and tactile feedback to these standard control tasks has not been sufficiently investigated yet. Although several people have performed experiments, usually only small numbers of subjectsgif have been used and only few aspects of device/task combinations have been analyzed and evaluated. Even worse, most researchers did not take into account any tactile feedback, e.g. [102,58,12,13,68,235,198,197,100,152], with the exception of, e.g. [48,111,6].

Therefore, we designed several experiments which will be directed towards the

  1. Analysis and evaluation of the effect of different input devices for several interaction/manipulation tasks and the
  2. Analysis and evaluation of input devices with tactile feedback.
In order to get sufficient sample data, comprehensive tests with a large number of subjects have to be carried out. Otherwise, statistical errors will be introduced and the results obtained might not be transferable. Unfortunately, the number of experiments grows which each additional free variable because of combinatorial explosion. A simple example might illustrate the situation:
If we limit one of our experiments (a positioning task, see below) to 2D space (#Dimensions Dim = 1), take three different angles (#Angles = 3), three distances (#Distances D = 3), and use objects with five different sizes (#Sizes S = 5), we will need

i.e. 45 different scenes (graphical setups). When each of our five devices will be used (see below), and each one is tested with all combinations of feedback modes, we will get a number of 18 different device/feedback mode combinations here (#Modes = 18). Because every test has to be carried out by at least 15 subjects (#Subjects = 15) (see above), the total number of tests will be

which is a rather large number, even under the limitations given above. And it is the number of tests for only one experiment!

The hypothesis which we want to test are, among others, that Various experiments have been designed and implemented to cover basic operations --- in which the variable test parameters can be measured exactly --- as well as interaction and manipulation tasks which are more oriented towards common applications, like selection from a menu or dragging an icon. They will be carried out in 2D and 3D space, respectively. Some experiments will be described below:
A pointer shall be placed as fast and accurate as possible at a rectangular region (with width W and height H) in an angle , thereby covering distance D. This will be investigated in 2D as well as in 3D space. The influence of visual and tactile feedback will be determined. The applicability of the well-known Fitts' law [102] will be analyzed under the conditions described above. The results will be relevant for all kinds of graphical interaction tasks.
Positioning and selection:
Positioning of an object at a specified target region in a fixed plane which is presented in 2D or 3D space. This is a basic experiment for any drag-and-drop operation.
Selection, positioning, grasping, and displacement:
One of several objects shall be grasped, retracted, and put at another position. This includes the features of the experiments described above and extends them with respect to robotic applications like assembly and disassembly.
Positioning and rotation with two-handed input:
The first (predominant) hand controls the movement of a mobile robot, whereas the second hand controls the direction of view of a stereo camera system which is mounted on the mobile robot. The task is to find specific objects in the robot's environment. This is a very specialized experiment in which repelling forces of obstacles can be used and in which the possibility to move the camera might be directly related to the velocity of the robot and the potential danger of the situation.gif

Because most input devices with tactile feedback which are available on the market are either very simple, not available on the market, or really expensive (see 2.2.4 ), two input devices with tactile and force feedback, respectively, have been designed and built:
Mouse with tactile feedback:
Following the idea of Akamatsu and Sato [6], a standard 2-button mouse for an IBM PS/2 personal computer has been equipped with two electromagnets in its base and a pin in the left button. For input, the standard mouse driver is used; for output, the magnets and the pin can be controlled by a bit combination over the parallel printer port by our own software, so that the magnets will attract the iron mouse pad and the pin will move up and down. Both magnets and the pin can be controlled independently. In order to make the mouse usable with our SGI workstation, a communication between the PC and the workstation is established over the serial communication line. In principle, any standard mouse can be easily equipped with this kind of tactile feedback.
Joystick with force feedback:
A standard analog joystick has been equipped with two servo motors and a micro controller board. Communication between the joystick controller and a computer is realized over a serial communication line. The joystick's motors can be controlled in order to impose a force on the stick itself, thus making force reflection possible.

Another device, Logitech's CYBERMAN, has been bought. It is the cheapest device on the market (< 200,- DM) with tactile feedback, although in this case there is only a vibration of the device itself. For the experiments, five devices are available at the moment: the mouse with tactile feedback, the joystick with force feedback, the CYBERMAN, and two 6D input devices, the SPACEMASTER and the SPACEMOUSE. An interesting question is how the tactile feedback will be used --- considering the hardware as well as the software --- in different applications. Some suggestions and comments will be given in the following paragraphs.

Obviously, the devices which are equipped with tactile feedback capabilities realize this feedback in completely different ways. The mouse with tactile feedback uses two electromagnets as a kind of ``brake'', i.e. if a current is applied to them, the movement of the mouse will be more difficult for the user, depending on the current. In addition, a pin in the left mouse button can be raised and lowered frequently, causing a kind of vibration. This will motivate the user to press the button. Although in principle the current of the magnets and the frequency of the pin vibration can be controlled continuously, this will usually not be used, therefore we call this kind of feedback binary. Logitech's CYBERMAN can also only generate binary feedback: If a special command is sent to the device, it starts to vibrate. Again, the frequency and duration of the vibration can be controlled with parameters, but a continuous feedback is not possible.

The situation changes completely when the joystick with force feedback is considered. Here, two servo motors control the position of the joystick, thus allowing a continuous control in the x/y-plane. When the user pushes the stick, but the servo motor tries to move it in the opposite direction, the user gets the impression of force feedback, because the movement becomes more difficult or even impossible.

Figure 3.3 : Schematic description of the Meta Device Driver (MDD)

In order to make the usage of the different devices as easy as possible, a common ``meta device driver'' (MDD) has been developed for all tools (see figure 3.3 ). The parameters which are sent to the devices follow the same structure as well as the values received from them. This concept has been developed in order to hide the specific characteristic of a device behind a common interface (cf. figures 3.1 and 3.2 ). It has been realized as a C++--library and can be linked to any application. If more devices will be available, the MDD can easily be extended.

With respect to the software, several different possibilities exist to give the user a visual and/or tactile feedback. Visual feedback is used by every window manager, e.g. the border of a window is highlighted when it is entered by the mouse cursor. In order to study the effect of tactile feedback, various feedback schemes have been developed. Two of them will be described in more detail below:

Figure 3.4 : A typical scene which is used for simple 2D positioning tasks with visual and tactile feedback. The circle marks the start position, the black object is the target, and all grey objects are used as obstacles.

  1. The first scheme is used for simple objects in 2D that are divided in targets and obstacles for the experiments. Figure 3.4 shows a typical scene with five obstacles and one target. Whenever the cursor enters an obstacle or the target region, the tactile feedback is launched.

    For the mouse, the magnets and the pin (or a combination of both) may be used. For the CYBERMAN, the vibration is switched on. For the joystick, things get more complicated. A force function, like the one shown in figure 3.5 needs to be implemented. In this case, the user ``feels'' some resistance when entering the object, but if the center is approached, the cursor will be dragged into it.

    Figure 3.5 : A force function which may be applied to objects in 2D space in order to control the joystick

  2. The second scheme is applied to objects in 3D space which are treated as obstacles, e.g. walls in a mobile robot collision avoidance task. The magnets of the mouse can be used to stop further movement against an obstacle, and the CYBERMAN's vibration can be switched on for the same purpose. Again, the joystick has explicitly to be programmed with a predefined, parametrized function in order to prevent the ``mobile robot'' from being damaged. Figure 3.6 shows the principle implementation of this function.

    Figure 3.6 : A force function which may be applied to objects in 3D space in order to control the joystick. The x-axis denotes the distance between the cursor and the object, and the y-axis the applied force.


next up previous contents
Next: Interaction Up: Bi- and Multimodal Previous: Recording and replay

Esprit Project 8579/MIAMI (Schomaker et al., '95)
Thu May 18 16:00:17 MET DST 1995