Study of Charged Frame ESD Immunity Testing Specified in ISO 7176-21

The EMC product standard for electrically powered wheelchairs is ISO 7176-21, which requires charged frame electrostatic discharge (ESD) immunity testing. When a moving wheelchair carrying a buildup of electrostatic charge due to triboelectrification of the wheels and floor comes into contact with a grounded metal object, the resulting air-gap discharge may cause the wheelchair to malfunction. Since the IEC 61000-4 series does not cover immunity testing that simulates such ESD events, ISO 7176-21 independently provides the test method. Currently, many companies are developing personal care robots to assist human in daily activities. Considering the risk presented by such robots that involve physical contact with humans, the charged frame ESD test will be a test item for the safety validation of personal care robots that are mobile and battery powered. In practice, however, when charged frame ESD tests are conducted according to the test procedure specified in ISO 7176-21, some issues and questions arise in regard to such matters as the means of charging the robot under test, the material of the insulating support on which to place the robot, and simulation of discharge from a robot rider or wearer. This paper investigates the test procedure of ISO 7176-21 and proposes modifications for enabling charged frame ESD testing to be properly carried out for personal care robots.