Depends on what you mean by a “robot” but you might look at the ZenXY machine from V1Engineering. It’s an open source project meant to be used for drawing in sand but could be swapped and flipped over to use as a drawing machine. You could also Google “pen plotter projects” or something similar as I’ve seen a few out there that do exactly what you’re asking.

As others have said, a 3D printer can do this too if you replace the extruder with a pen and configure it correctly. You’re just looking for any sort of CNC controlled device for the hardware. For the software you’ll need something that can generate gcode to draw what you want. Sandify is a tool that was created to work with the above mentioned ZenXY in order to create drawings and export them as gcode, but you’d need to do these ahead of time and have them stored on the device.

KITT*

From a mother dog and father dog who loved each other very much.