Capacitance-type measuring device for absolute measurement of positions

Capacitive-type measuring apparatus comprising:

• first and second support members, said support members being relatively displaceable with respect to each other, and at least one of said support members being displaceable relative to a measurement axis;
• an array of first transmitter electrodes disposed on said first support member in alignment with said measurement axis;
• an array of first receiver electrodes disposed on said second support member in alignment with said measurement axis and such that differing portions of said first receiver electrode array are capacitively coupled with said first transmitter electrode array in dependence on the relative positions of said supporting members;
• an array of second transmitter electrodes disposed on said second support member in relative alignment with said first receiver electrode array, at least one group of first receiver electrodes being respectively electrically connected to a corresponding at least one group of second transmitter electrodes, each of said second transmitter electrodes in said at least one second transmitter electrode group being electrically connected to a corresponding one of said first receiver electrodes so as to be offset from the corresponding first receiver electrode by an amount which is a predetermined function of the position of the second transmitter electrode relative to the center of said at least one second transmitter electrode group.

Capacitive-type measuring apparatus comprising:

• first and second support members, said support members being relatively displaceable with respect to each other, and at least one of said support members being displaceable relative to a measurement axis;
• an array of first transmitter electrodes disposed on said first support member in alignment with said measurement axis;
• at least one array of first receiver electrodes disposed on said second support member in alignment with said measurement axis and such that differing portions of said at least one first receiver electrode array are capacitively coupled with said first transmitter electrode array in dependence on the relative positions of said supporting members;
• an array of second transmitter electrodes disposed on said second support member in relative alignment with said at least one first array of first receiver electrode, each of said second transmitter electrodes being electrically connected to a corresponding one of said first receiver electrodes so as to be offset from the corresponding first receiver electrode by an amount which is a predetermined function of the position of the second transmitter electrode relative to a reference position on said measurement axis;
• the spatial range occupied by the second transmitter electrodes, over which the degree of electrode offset between the second transmitter electrodes and the first receiver electrodes changes by a predetermined amount, defining a first measurement range;
• an array of third transmitter electrodes disposed on said second support member in relative alignment with said at least one array of first receiver electrodes,
• at least one group of first receiver electrodes being respectively electrically connected to a corresponding at least one group of third transmitter electrodes, each of said third transmitter electrodes in said at least one third transmitter electrode group being electrically connected to a corresponding one of said first receiver electrodes so as to be offset from the corresponding first receiver electrode by an amount which is a predetermined function of the position of the third transmitter electrode relative to the center of said at least one third transmitter electrode group, and such that the degree of electrode offset changes over said third transmitter electrode group by said predetermined amount, and the spatial range occupied by said at least one third transmitter electrode group defining a second measurement range smaller than said first measurement range.

Capacitive-type measuring apparatus comprising:

• first and second support members, said support members being relatively displaceable with respect to each other, and at least one of said support members being displaceable relative to a measurement axis;
• electrode array means disposed on said first and second support members in relative alignment with said measurement axis for providing a plurality of discrete signal transmission paths each having a capacitive transfer function which varies in dependence on the relative positions of said first and second support members with respect to each other, said electrode array means comprising a transmitter electrode array having at least one group of N transmitter electrodes spaced from each other relative to the measurement axis, wherein N has a value which is an integer multiple of four, said electrode array means producing an output signal in response to excitation signals applied to said transmitter electrode array;
• means for generating N groups of N excitation signals for application to the respective N electrodes of said at least one group of transmitter electrodes in a predetermined spatial order, each of said groups of excitation signals comprising two sets of excitation signals which are phase inverted with respect to each other and in spatial phase quadrature when applied to said transmitter electrodes, and the relative spatial phase positions occupied by the respective sets of excitation signals in each group of excitation signals successively incrementally changing from one group to the next;
• means for selectively applying a first pair of first and second ones of said groups of excitation signals to said at least one group of transmitter electrodes to produce successive first and second electrode array means output signals;
• means for demodulating said first and second output signals to produce first and second demodulation signals, and for performing a dual ramp integration of said first and second demodulation signals wherein said first demodulated signal is integrated for a predetermined time interval by integrator means, and said second demodulated signal is integrated by said integrator means until the integrator output returns to a reference level, said first and second ones of said groups of excitation signals being selected such that said integration of said second demodulation signal causes integration of the integrator output in the reverse direction from said integration of said first demodulation signal output;
• means for measuring the integration time of said second demodulated signal integration and for producing an output when the integration time exceeds a predetermined limit value;
• means responsive to said output of said integration time measuring means for resetting said demodulation and dual ramp integration means, for repetitively selectively applying a different further pair of first and second ones of said groups of excitation signals to said at least one group of transmitter electrodes, and for causing said demodulation and dual ramp integration means to integrate the resultant first and second demodulation signals until there is no output from said integration time measuring means.