The case of the Haptic Effects

The Adventures of COFIE Club

The case of the Haptic Effects

C.P. Ravikumar, Texas Instruments

Art by Ananya Ravikumar

“It was such a touching experience,” said Simran.  The members of the COFIE club had decided to visit an orphanage meant for women with disabilities.  The orphanage provided not only shelter for its inmates, but also offered them vocational training that could earn them a living someday.  Little artefacts made by the women were on display for passers-by who may want to purchase them.  Several inmates were also enrolled in part-time educational programs.  Lakshmi aspires to get a degree from a women’s polytechnic college. But the subject on Computer Architecture is proving to be her bête noire.

Sitting on her wheelchair, Lakshmi listens intently to Rahul’s explanation of instruction sets and assembly language programming.  He tries his best to teach her bubble sorting.  The other members of COFIE club are busy teaching mathematics, physics, and history to some of the young girls who are appearing in the tenth grade exam.  An elderly couple is visiting the inmates with a large box of sweets.  The members of the COFIE club are also rewarded. Timmy  is especially happy about this part of the visit. He also does not mind all the affection the inmates shower on him.

“Woof! Woof!”  he expresses his sense of satisfaction.

“It was such a touching experience,” said Simran, when they came out of the gate of the orphanage. “We take so many things for granted, like being able to pick up a pencil that you accidentally drop. Or being able to go and get a glass of water when you feel thirsty.”

The others were silent. Indeed, it was a touching experience for all of them, especially when the inmates thanked them with great sincerity.

“A touching experience,” Milind repeated. “I was reading an article about Haptics just yesterday. In fact, haptics provides the users of electronic gadgets a touching experience in a literal sense of the word.”

“Would you care to elaborate?” said Sahil, dramatically. 

Haptics

“Take the cell phone, for example,” continued Milind.  “In the vibration mode, it can alert a user about an incoming call or a message by taking recourse to the sense of touch. I was just thinking how useful haptics can be in the orphanage. Did you notice that they had one attendant for all of them to take care of their needs? What if this attendant could carry a little device – something that she could carry in her pocket or even wear as a ring or a bracelet – that would alert her when an inmate needed help?”

“Such a thing can be useful for nurses on duty at a hospital as well,” agreed Sahil. “A cell phone can be a distraction, but an application-specific device such as this one can improve the quality of service. It would also be less expensive.”

“I remember reading about a project from IIT Madras about an assistive system for the blind!” said Simran. “This project won a prize in TI India Analog Design Contest. Their system warned the blind user about a sudden change in altitude in their walking path. What if the user is approaching a gaping hole or a flight of stairs? There was also a project from Sri Vishnu College of Engineering to assist the blind user about obstacles in the indoor environment. Imagine if the blind person’s cane has a Haptics actuator. It can catch the attention of the user more effectively.”

“Who needs the Wikipedia when you are around?” said Rahul. “You are right. I can think of another application. How about a wakeup alarm for students?  The haptics device can be worn as a wristband.  I know I could use one!”

“According to an article that I read, there are three types of haptics actuators,” continued Milind. “What we are familiar with, the vibration of the cell phone, is the first one to become popular. It is known as eccentric rotating mass, or ERM technology.”

“You just described yourself,” teased Rahul. “You are eccentric and a rotund mass.”

“Ha Ha,” scoffed Milind. “The linear resonant accelerator, or the LRA, is a more power-efficient device. It takes half the power to produce twice the force.  As its name indicates, an LRA operates on the principle of resonance. If the frequency of the input waveform matches that of the rotatable mass, a resonance phenomenon occurs and the mass will vibrate.  ”

“I remember resonance!” said Simran. “The reactance of the inductor becomes equal in magnitude to the reactance of the capacitor in a series RLC circuit at the frequency of resonance! And that frequency is one over two pi root LC.”

“You pass!” said Sahil. “Now, let us continue with the lecture.”

Piezo Actuators

“Well, there is a new kind of actuator called piezo actuator,”  continued Milind. “A piezo actuator vibrates when you apply a voltage.  Piezo actuators are used in high-definition haptics. There are  lots of haptic effects  available today for gadgets such as cell phones.  To create a haptic effect, you need an actuator and a driver to provide the input voltage waveform for the actuator. Haptics technology adds a new dimension to infotainment.  There are software development kits and Haptics libraries available for application developers.  Haptics technology is also being used in applications such as simulation of surgery.  One can also think of new applications, like we were discussing earlier.”

“Imagine a cooking program on TV where you can feel the texture of the cake or the crunchiness of the potato chips,” drooled Sahil.

“Cake and chips! I am hungry now!” said Milind.

“Woof! Woof!” agreed Timmy. At last, the humans had spoken two words that he really liked to hear.

Before I conclude

I encourage you to follow the links that I have provided and read the online literature which I have cited.  And for those of you who are keen to pursue a project using Haptics technology, TI provides Haptics drivers for all the three types of actuators – ERM, LRA, and Piezo.  Evaluation modules are also available to demonstrate the capabilities of these drivers.  If you are an educator who teaches mobile computing, biomedical instruments, or human-machine interfaces, these products will trigger your imagination. I believe excellent student projects can be carried out using these tools.  Students who wish to take part in the Texas Instruments Innovation Challenge – India Analog Design Contest 2014 – I hope I have “touched” your imagination!

As usual, I will end the blog with a quiz. Read the online literature before answering these questions!

Quiz!

1. The following table shows the acceleration a of vibration of an LRA when the frequency f of the input voltage is varied, keeping the amplitude of the voltage constant.

 The bandwidth of the LRA is given by

a) 160 Hz

b) 20 Hz

c) 40 Hz

d) 60 Hz

 2. The DRV8601 driver is used to drive the above LRA. This driver is known to support the auto-resonance feature.  The benefit of auto-resonance is

a) The driver automatically adjusts the resonance frequency of the LRA through tuning, if the resonance frequency were to change due to aging or environmental factors

b) The driver automatically adjusts the frequency of the AC voltage input to the LRA if the resonance frequency were to change due to aging or environmental factors

c) The driver automatically adjusts the amplitude of the AC voltage input to the LRA if the resonance frequency were to change due to aging or environmental factors

d) All of the above

3. Which of the following is NOT included in the evaluation kit DRV2605EVM-CT from Texas Instruments?

a) ERM and LRA actuators

b) MSP430 Launchpad

c) Capacitive touch buttons

d) On-board MSP430 Microcontroller

4. Haptic effects are used in smart phones for

a) Improve typing speed and reducing entry errors

b) Entertainment e.g. haptic emoticons in messages

c) Add another dimension to games

d) All of the above

5. “Crunch” is an example of a haptic effect. To create this effect,

a) From the audio signal for “crunch,” a waveform is generated by a driver such as DRV2605 so that it can be applied to the actuator for the simulation of the crunch effect

b) A waveform for the haptic effect “crunch” can be stored in the ROM of the driver such as DRV2605, and played out for creating the haptic effect

c) A microcontroller generates the necessary PWM waveform to be applied to a driver such as DRV2605, which in turn generates the inputs to be applied to the actuators

d) Either (a), (b), or (c)