Robot joints have resolvers which are essentially transformers. Does that mean each resolver needs AC power supplied to it for it to work?
How resolver works
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unsaint43 -
August 25, 2016 at 12:50 AM -
Thread is marked as Resolved.
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Multiple options exist. Absolute encoders, relative encoders, resolvers... all variations on the same theme. Yes, resolvers usually need some sort of AC voltage at the coils, but often from a "external" viewpoint, a resolver only needs a reliable power supply and handles the precise low-level coil AC internally.
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SkyeFire, thanks for your answer. I knew ABB robots have resolvers at the base. Recently I learned Fanuc robots have encoders (pulse coders, I believe) rather than resolvers. So here is what I concluded.... , the batteries in a ABB robot power the SMB which in turn provides the small AC voltages for the resolvers. And the batteries in a Fanuc robot base power the encoders directly. I hope I am correct.
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I do not believe that the batteries are used to power the encoders or resolvers. Rather, the batteries are used to retain memory.
For example... well, it's been a while since I worked on an ABB, but if I recall how the IRC5 works correctly, each servo motor has an absolute encoder mounted directly to the drive shaft. But even a few degrees of arc motion on an axis requires multiple motor rotations, due to the gear ratios. So, there is a memory chip (SRAM or something similar) in the robot base that retains a count of how many times the encoder has made a full rotation, and in which direction, since a zero-reference was performed. Normally, this memory (and the battery charge) is maintained by the power from the controller. However, when the controller is powered down, or the cables are disconnected, the batteries prevent the memory from being erased. This way, the robot does not lose its zero reference. However, if the batteries are faulty (usually from old age), the robot will lose its zero reference every time main power is lost. This is also why it is necessary to replace these batteries with main power active. Removing these batteries without the main power will cause the zero reference to be lost.
KUKA robots use a slightly different method. The memory chip in the base of the robot arm is non-volatile EEPROM, so no batteries are required in the robot base. However, batteries are required inside the control cabinet to guarantee that, when main power is lost for any reason, the central computer and communications can run from the battery power long enough to perform a controlled shutdown of the operating system, and complete a memory update of the EEPROM chip.
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SkyFire, thanks again for your description. The memory card at the base of ABB robots is called SMB (Serial Measurement Board). Yes, the battery is to keep the SMB powered up when normal power is gone. Fanuc robots also have batteries on the base of the robot and at the controller. So, I thought both ABB and Fanuc robots the same battery application design. But I was recently told by someone that the batteries at the base of a Fanuc robot are to keep the robot encoders. I disagreed of course because I assumed Fanuc robots would have something like SMB on their bases. But I just could not find any information about any card at the base of Fanuc robots. That is why I contacted Fanuc directly. In reply, a Fanuc rep emailed me and told me that Fanuc robots have Serial Pulse coders.
Now, I am not sure if the rep was referring to encoders or some kind of a memory card by "Serial Pulse coder."
Here is the problem that bugs the hell out of me. For example... http://pico-systems.com/osc2.5/catalog…?products_id=34
On this web page, they call this device Fanuc Serial Encoder converter and in parenthesis "pulse coder." And in description, "Converts signals from Fanuc Serial pulse coders." So what gives? This device is a pulse coder that converts signals from pulse coders? WHAT?!!!!? No wonder everybody is confused!!
Sorry about the rant. I will post more as I find more about this mysterious "pulse coder." Thanks.
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Well, there's lots of different types of encoders. The simplest encoder is the "quadrature" encoder, which produces 2 sine waves at 90deg relative phase angles. Each full wave indicates a specific fraction of a rotation, and the phase angles indicate direction.
I would guess that a "pulse encoder" is something similar, but perhaps putting out square waves instead of sines. Or, it could be something different, like a pulse-train signal that triggers every 1/X degrees, and a separate signal that indicates direction.
There are, of course, many variations on the theme. So brand-specific decoders or translators may be necessary to convert from one standard to another.