Moving robot grounding problem 1

[timtsa]

Hi All,
We are now building a two-wheel moving robot. It is driven by two 25Amp-hr, 12V sealed lead-acid battery. Single phase AC is generator by using DC/AC inverter. The locomotion part is constructed by using two Panasonic 3-phase AC servo motors. Could anyone tell me the servo motors and its drivers should be grounded to the chassis or be completely insulated from the chassis, viewed from the point of electrocution? Your answer could be a great help to us.
Thanks.

 

[jbartos]

Suggestion: The servo motors should be grounded to avoid the potential difference between the servo motor and surrounding conductive metal surfaces. In case that some potential difference exists and some conductive metal, e.g. tools, inadvertently causes a connection, some sparking or arcing with associated will develop and could cause damages.

 

[timtsa]

Hi jbartos,
Thank you very much for your suggestion. However, if I grounded the AC servo drivers and motors (and also the DC/AC inverter) to the metal chassis, would I violated the code of pactice for Electrical Saftey? As from the principle of electrical safety, AC operated equimpment should be grounded, or else should have double insulation design. Our moving Robot can not be grounded because of its mobile characteristic. Thanks.

 

[IRstuff]

Your chassis should only be grounded at your system's single-point ground. Everything else must be isolated from the shield that is the chassis. All external shields and chassis components must have sufficiently low resistance across mechanical interfaces to ensure proper shielding. Although MIL-B-5087 is no longer enforced, it still a good guide to proper bonding, which required no more than 2.5 milliohm resistance across mechanical bonds.

Aside from the electrical hazard, there is also the issue of electromagnetic interference, both external and internal.

TTFN

 

[Ares]

Your system does not have to be grounded.
Isolate both power terminals from the chassis and monitor if the isolation is maintained.
If that isolation is breached shut down the battery.
Isolated power cct’s provide the highest level of safety.
Power you employ may be dangerous only if a circuit can be completed through a person body. That cannot happen if you isolate all wires.
Movement of your robot can create static electricity on the chassis, you schould think about discharging that to prevent unplesant shocks that may lead to more serious accidents.