A compact touch probe for a coordinate measuring machine (CMM), including internal digital signal processing,
- the compact touch probe comprising:
- a displacement sensor configured to output at least one sensor signal that is responsive to displacement of a stylus attached to the compact touch probe,
- an interface connector including first and second electrical connections that electrically connect the compact touch probe to the CMM;
- touch probe electronic circuitry, included entirely within a housing of the compact touch probe, comprising:
- a regulated power supply circuit;
- probe operating circuits and memory;
- a trigger signal generating circuit that inputs the at least one sensor signal and generates a touch trigger signal corresponding to a displacement of the stylus;
- and
- a digital communication circuit including a differential signal configuration that inputs and outputs differential digital signals through the first and second electrical connections,
- wherein:
- the touch probe electronic circuitry further comprises a supply isolation circuit configuration that is coupled to the first and second electrical connections to receive a connected supply voltage from the CMM through the first and second electrical connections and that is configured to isolate the regulated power supply circuit from loading the differential digital signals that pass through the first and second electrical connections, the supply isolation circuit configuration comprising:
- a first end of a first winding of a differential mode choke coupled to the first electrical connection, with a second end of the first winding of the differential mode choke connected to a positive input of the regulated power supply circuit,
- a first end of a second winding of the differential mode choke coupled to the second electrical connection, with a second end of the second winding of the differential mode choke connected to a negative input of the regulated power supply circuit, and
- at least a first supply isolation capacitor coupled between the positive and negative inputs of the regulated power supply circuit,
- the digital communication circuit comprises the differential signal configuration that is AC coupled to the first and second electrical connections through a communication isolation configuration comprising a first communication isolation capacitor coupled in series to the first electrical connection and a second communication isolation capacitor coupled in series to the second electrical connection, and the differential signal configuration is configured to input and output the differential digital signals through the first and second electrical connections, the differential digital signals comprising:
- control and data signals that are input and output superimposed on the connected supply voltage during control and data time periods, and
- touch trigger signals generated by the trigger signal generating circuit that are output superimposed on the connected supply voltage during trigger signal time periods that are different than the control and data time periods;
- and
- at least a majority of the differential digital signals are formatted based on a serial communication code scheme that is nominally DC-balanced.