Portable articulated arm coordinate measuring machine with optical communications bus

A portable articulated arm coordinate measurement machine (AACMM), comprising:

• a manually positionable articulated arm portion having opposed first end and second end, the arm portion including a plurality of connected arm segments, each of the arm segments including at least one position transducer for producing a position signal, wherein the plurality of connected arm segments includes a first arm segment and a second arm segment;
• a measurement device coupled to the first end;
• a base coupled to the second end;
• an electronic circuit configured to receive the position signals from each of the at least one position transducers and to determine three dimensional coordinates of the measurement device with respect to the base;
• a probe end disposed between the measurement device and the first end;
• a first bus for communication with the electronic circuit, wherein at least a portion of the first bus is an optical communication bus configured to transmit light;
• and
• a rotary coupler having a first portion and a second portion, the second portion configured to rotate relative to the first portion about a first axis, a first bearing having first part and a second part, the first part affixed to the first portion and the second part affixed to the second portion, a second bearing having a third part and a fourth part, the third part affixed to the first portion and the fourth part affixed to the second portion, the first portion affixed to the first arm segment, the second portion coupled to the second arm segment, the rotary coupler configured to transfer the transmitted light through the optical communication bus between the first portion and the second portion;
• wherein the rotary coupler includes the at least one position transducer of the first arm segment that measures the rotation of the second portion about the first axis and includes a first element and a second element, the first element affixed to the first portion and the second element affixed to the second portion, the first element being one of the group consisting of a periodic pattern of a measurable quantity and a first read head spaced from and in communication with the periodic pattern of a measurable quantity, and the second element being the other of the group consisting of the periodic pattern of a measurable quantity and the first read head spaced from and in communication with the periodic pattern of a measurable quantity.