# A Pneumatically-Actuated Mouse for Delivering Multimodal Haptic Feedback
## 4 Multimodal Haptic Effects
### Impact Response  
The main idea behind impact is to deliver a high amount of force in a relatively short interval of time. This imparts the illusion of a strike rather than sustained pressure, as was the case in static pressure rendering. Impact rendering can be achieved by opening the positive valve for a short amount of time and allowing the air to fill up the haptic mouse. Afterwards, the positive valve is closed and negative valve is opened to drain all the air immediately. A user or receiver would perceive a sudden spike of high pressure for a limited amount of time. The solenoid valves used in the haptic mouse have a response time of 2 ms, which makes it possible to deliver a sudden impact force. It was empirically established that opening the positive valve for 100 ms at 10 psi air pressure renders rigid, brisk, and precise impact feedback. However, the type of impact feedback can be changed depending on the application or rendering requirement. An example of 150 ms impact rendering is shown in Figure 5(a).  
Figure 5: Quantitative analysis of high frequency vibration rendering by the haptic mouse.  
Experiment: Actuation Delay in Impact Rendering  
The main idea behind impact rendering is to deliver a large enough force in a rapid fashion at a precise point in time. The first key point in this statement is that the magnitude of force should be large enough to deliver an impact. The second point is the ability to generate a force swiftly, or in other words, a high gradient of acceleration. It has already been established that the haptic mouse can generate acceleration magnitude of up to 0.6 Gs, as shown in Figure 4(b). An experiment was conducted to test the practical swiftness of the impact capabilities of the haptic mouse. The main aim of this experiment was to test if any delay between the time an impact command is instructed and the time it is actually executed by the hardware occurs.  
Setup and Procedure: The delay in question here is the time it took for actual execution of impact from the time a command was generated at the Arduino output pin (electrical high). This was done by attaching an accelerometer to the haptic mouse and recording its readings with a time stamp of occurrence. The Arduino board was programmed to fire commands at exact points in time and this time was also recorded. When the Arduino outputs an electrical high at the corresponding output port, the valves begin to fill up the mouse chambers with air. This causes an increase in volume of the mouse, which triggers accelerometer readings. The accelerometer records these readings along with a timestamp.  
Results: An inspection of both sets of data showed a slight discrepancy between the output command time and the actual actuation time. The time it took to send the output command was 264 ms, while the accelerometer recorded its first significant change at 287 ms. The difference in times shows that there was a delay of 23 ms between command and actual execution. This 23 ms is the actuation delay of the haptic mouse. The impact response and timings are shown in Figure 5(b).  
The delay in a pneumatic system can depend on a number of factors, the primary candidate being the response time of the valves, which in this case is 2 ms. Apart from the valves, delays can occur due to the source of air supply and its efficiency. The length of the hose also plays an important role. According to previous research ion haptics and multimodal feedback, a delay between 27 ms and 71 ms can be deemed as perceptually insignificant [33; 34; 35].