Pepper, the robot that has been trained to "perceive" human emotion, is opening up its platform to Android developers.

Maker SoftBank is hoping that it will spur new apps and new capabilities for the humanoid robot which has sold well but still has no clear defined purpose.

Ten thousand of the robots have been sold but developers have been slow to make apps for its closed Naoqi operating system.

Android will run on a tablet strapped to the robot's chest.

Neither Google nor SoftBank has disclosed what sort of business deal they have struck and it is unclear if the robot will take advantage of new features such as the recently announced artificial intelligence Google Assistant.

But it will almost certainly offer Google some degree of control over the robot as well as a cut of revenues.

Pepper has been in big demand in Japan with each batch of 1,000 units selling out in minutes. It will go on pre-sale in the US in July.

It costs 198,000 yen ($1,800) and each one is sold at a loss.

The 1.2m (4ft) humanoid bot features more than 20 motors and has articulated arms. It was designed to understand emotions and mimic human body language - so, for instance, its shoulders go up when it is in standby mode, imitating sleep.

So far, Pepper is being used as a waiter, salesman and customer service representative in around 500 companies in Japan, including Nestle, Mizuho Bank and Nissan.