1. A controller configured to determine a measurable capacitance, the controller configured to:
apply a pre-determined voltage to a first sensing electrode of a plurality of sensing electrodes using a first switch;
apply a first guard voltage to a guarding electrode using a second switch;
share charge between the first sensing electrode and a passive network, such that shared charge is accumulated on a filter capacitance of the passive network;
apply a second guard voltage different from the first guard voltage to the guarding electrode;
measure a voltage on the filter capacitance for a number of measurements equal to at least one to produce at least one result; and
determine the measurable capacitance using the at least one result.
2. The controller of claim 1 wherein the first guard voltage comprises a voltage selected to approximate the pre-determined voltage.
3. The controller of claim 1 wherein the second guard voltage comprises a voltage selected to be in a range between and including a threshold voltage and a reset voltage.
4. The controller of claim 1 wherein the second guard voltage comprises part of a variable voltage waveform, the variable voltage waveform changing with a time constant selected to approximate the voltage on the filter capacitance.
5. The controller of claim 1 wherein the wherein the second guard voltage comprises a pulse modulated signal.
6. The controller of claim 1 wherein the second guard voltage comprises a voltage approximating an average voltage on the filter capacitance.
7. The controller of claim 1 wherein the controller is further configured to share charge between the first sensing electrode and the passive network using a third switch.
8. A controller adapted to determine a capacitance value associated with a sensor electrode, the controller configured to:
apply a guard signal to a guarding electrode, the guard signal comprising a waveform having at least two different voltages;
determine the capacitance value by
repeatedly applying a voltage to the sensor electrode,
accumulating charge on an integrating capacitance by repeatedly sharing charge between the sensor electrode and the integrating capacitance,
generating quantized values by repeatedly measuring a voltage on the integrating capacitance using a quantizer of the controller,
repeatedly changing charge on the integrating capacitance based on the quantized values, and
determining the capacitance value associated with the sensor electrode using the quantized values.
9. The controller of claim 8 wherein a first voltage of the at least two different voltages of the guard signal approximates the voltage applied to the sensor electrode.
10. The controller of claim 8 wherein the waveform of the guard signal has a time constant such that the waveform of the guard signal approximates a waveform of the voltage on the integrating capacitance.
11. The controller of claim 8 wherein a second voltage of the at least two different voltages of the guard signal approximates an average of the waveform of the voltage on the integrating capacitance.
12. The controller of claim 8 wherein the at least two different voltages of the guard signal span a range substantially similar to a range defined by the voltage applied to the sensor electrode and a reset voltage of the integrating capacitance.
13. The controller of claim 8 wherein the at least two different voltages of the guard signal span a range substantially less than a range defined by the voltage applied to the sensor electrode and a reset voltage of the integrating capacitance.
14. The controller of claim 8 wherein the at least two different voltages of the guard signal comprise voltages that extend beyond the voltage applied to the sensor electrode and a reset voltage of the integrating capacitance.
15. A controller including a memory, the memory including executable instructions for determining a measurable capacitance associated with a sensing electrode by:
applying a guard signal to a guarding electrode, the guard signal comprising a waveform having at least two different voltages;
applying a voltage to the sensing electrode;
sharing charge between the sensing electrode and a passive network such that shared charge is accumulated on an integrating capacitance of the passive network;
measuring a voltage on the integrating capacitance for a number of measurements equal to at least one to produce at least one result; and
determining the measurable capacitance using the at least one result.
16. The controller of claim 15 wherein the at least two different voltages of the guard signal span a range substantially similar to a range defined by the voltage applied to the sensing electrode and a reset voltage of the integrating capacitance.
17. The controller of claim 15 wherein the at least two different voltages of the guard signal span a range substantially less than a range defined by the voltage applied to the sensing electrode and a reset voltage of the integrating capacitance.
18. The controller of claim 15 wherein the at least two different voltages of the guard signal comprise voltages that extend beyond the voltage applied to the sensing electrode and a reset voltage of the integrating capacitance.
19. The controller of claim 15, wherein the at least two different voltages of the guard signal comprises a voltage approximating the voltage applied to the sensing electrode.
20. The controller of claim 15, wherein the guard signal averages to a voltage approximating an average voltage on the integrating capacitance.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A printhead assembly comprising:
a plurality of printhead modules each having a plurality of modular printhead tiles each having a plurality of micro-electromechanical nozzle assemblies for operatively printing on a printing medium;
a ducting assembly having a laminated stack of layers, each layer of the stack having a number of apertures which, when the layers are stacked, provide ducts whereby ink is able to flow from an ink reservoir to the nozzle assemblies;
a number of electrical connector assemblies for operatively connecting the respective printhead tiles together; and
a casing in which the printhead modules are arranged so as to be removably mounted in linearly aligned relationship through removable engagement of each printhead module with the casing.
2. A printhead assembly as claimed in claim 1, in which each printhead module has a support member and the casing has a support frame, the support member having a first tab received in a recess of the support frame and a second tab clamped between the support frame and a mounting element mounted to the support frame so as to allow constrained movement of the relevant printhead module relative to the casing.
3. The printhead assembly of claim 2, wherein the support member defines a raised portion and a recessed portion at an end thereof, each printhead tile having electrical connecting strips which overlie the respective recessed portions, the assembly including a connecting member having a series of parallel spaced conducting strips, said connecting member being shaped and configured for fitment into a cavity defined by the raised and recessed portions of two abutting support members to connect the connecting strips of two tiles via said conducting strips.
4. The printhead assembly of claim 3, having a sealing adhesive provided at an interface of the support members.
5. The printhead assembly of claim 4, wherein the sealing adhesive is an epoxy.
6. The printhead assembly of claim 3, which includes a printhead controller integrated circuit for controlling operation of the printhead tiles via the connecting strips.
7. The printhead assembly of claim 3, wherein the connecting member is a rectangular block having the series of conducting strips on each surface thereof.
8. The printhead assembly of claim 3, wherein the connecting member is formed of a strip of silicone rubber printed to provide sequentially spaced conductive and non-conductive material strips.
9. The printhead assembly of claim 3, wherein the conducting strips of the connecting member are provided in a 2:1 relationship with the connecting strips of the tiles.