The days of a guaranteed pain-free visit to the dentist may not be far off thanks to a petite Japanese woman in a pink sweater who goes by the name of Simroid. She has a limited vocabulary and a strange complexion, but the 160cm-tall humanoid robot is happy to feel your pain.

Simroid, who will be used at medical colleges, releases a clearly audible "ouch!" whenever a trainee dentist touches a nerve and a reassuring "that's better" when the drill hits the right spot.

"We want to use the robots to train students in medical techniques that don't cause unnecessary pain," said Naotake Shubui, a professor at Nippon Dental University who helped develop Simroid.

The robot is one of hundreds of cutting-edge devices and contraptions on display this week at the world's biggest robot exhibition. The Big Sight complex in Tokyo has been turned into a shrine to Japan's fascination with machines, shaping their purpose in an age of falling birthrates and shrinking workforces.

Decades after they revolutionised production lines, robots could soon be serving tea to office workers or directing shoppers. In a reassuringly benign variation on the scenarios beloved of sci-fi filmmakers, today's robots look, and act, like the well-intentioned humans who invented them.

In Japan, robots can already be found working as home helps, office receptionists and security guards, as well as on the factory floor. There were more than 370,000 industrial robots in use in Japan in 2005, according to a report by Macquarie bank, 40% of the world total, with 32 robots for every 1,000 manufacturing workers. The economy ministry calculates that the Japanese robot market will be worth more than £26bn by 2025.

There are compelling economic reasons for Japan's obsession with robots. The population recently went into long-term decline and a reduced workforce is expected to struggle to fill jobs in the health and welfare sectors. As long as Japanese leaders remain cautious about relaxing immigration laws, robots will be seen as at least part of the solution.

Even the job of the nightwatchman, once the preserve of semi-retired salarymen, is being turned over to robots such as Alsok's Reborg-Q, a Dalek-like invention whose sensors and 360-degree vision enable it to detect intruders or fires.

"The potential for service robots is huge," said Alsok spokesman Koji Shigeta. "They not only fill a gap, but perform functions that humans are simply unable to do, like keep watch over the same spot for hours on end."

Alsok's clients, who pay 380,000 yen (£1,680) a month to rent a security robot, credit their robocops with a fall in petty crime on their premises, Shigeta said.

Human endeavour is being supplemented - and even replaced - by mechanical efficiency in almost every area, from hands-free vacuum cleaners and golf-bag carriers to a robotic baby who teaches childcare skills to expectant couples, right down to freeing trapped wind and changing nappies.

Few aspects of daily life are unaffected, even those considered most private. In the next couple of years, a robot called Lady Bird will be put to use cleaning public lavatories; she is equipped with sensors and speech-recognition technology to avoid any embarrassing encounters.

But many believe the age of the service robot will truly have arrived once machines are capable of connecting with humans on an emotional level. Judging by the Tokyo exhibition, that process has already begun.

Tocco-chan, for example, serves the sole purpose of making people laugh. The panda-like toy, developed by students at Waseda University, scans its companion's face for the traces of a smile and attempts to provoke a proper laugh with a fit of giggles of its own.

Instead of talking to themselves, people who live alone can have an uncomplaining housemate in the form of Chapit, a mouse-shaped device that chats in several languages and uses a speech-triggered remote control function to turn on kettles, TVs and other appliances.

Inevitably, service robots do not always do as they are told, although their makers blame malfunctions on nothing more sinister than technical glitches.

Hitachi's long-awaited EMIEW 2, which is designed to carry out office work, crashed into a desk during a recent demonstration after wireless internet traffic interfered with his signals.

And although Mr Cube, a robot with dextrous hands developed by Kawasaki, can complete the Rubik's cube, his time of about five minutes is some way off the world record of 9.77 seconds - held by a human.