Capacitive sensing probe motion control system
Various methods and systems are provided to control a probe moving towards fluid held in a container. The probe is moved towards the fluid to take a sample of the fluid in the container. To take a sample, probe is actuated to hit the fluid surface and to pass the fluid surface by a predetermined distance. Capacitive sensing which incorporates the probe itself is used to support an approach engine for controlling the motion of the probe. The approach engine determines the speed of the probe based on capacitance measurements, and in some cases based on position information of the probe. The approach engine ensures the probe hits the surface of the fluid in the container in order to take a sample while ensuring the probe does not hit the bottom of the container.
1. A method for controlling movement of a probe towards a container having fluid therein, the method comprising:
receiving a first capacitance measurement from a capacitive sensor, wherein the first capacitance measurement is indicative of capacitance between the probe and a conductive plate underneath the container; and
transmitting a first signal to the motion control engine for moving the probe towards the container at a first speed, wherein the first speed is determined based on the first capacitance measurement.
2. The method according to claim 1 , further comprising:
receiving a first position information from a motion control engine, wherein the first position information is indicative of the position of the probe relative to the conductive plate; and
wherein the first speed is determined based further on the first position information.
3. The method according to claim 1 , wherein the first speed is zero to stop the movement of the probe towards the container if the first capacitance measurement exceeds a predetermined capacitance threshold.
4. The method according to claim 1 , wherein the predetermined capacitance threshold indicates that the probe is likely to have hit the surface of the fluid in the container.
5. The method of claim 1 , further comprising:
receiving a second capacitance measurement and a third capacitance measurement from the capacitive sensor, wherein the second capacitance measurement and the third capacitance measurement are each indicative of the capacitance formed between the probe and a conductive plate underneath the container;
determining a change in capacitance between the second capacitance measurement and the third capacitance measurement to estimate a slope indicative of change in capacitance with respect to change in position information; and
transmitting a second signal to the motion control engine for moving the probe towards the container at a second speed, wherein the second speed is determined based on the change in capacitance.
6. The method of claim 1 , wherein the capacitive sensor is configured to take the first capacitance measurement by providing an excitation source to the conductive plate and reading the first capacitance measurement from the conductive plate.
7. The method of claim 1 , wherein the capacitive sensor is configured to take the first capacitance measurement by grounding the conductive plate, providing an excitation source to the probe and reading the first capacitance measurement from the probe.
8. The method of claim 5 , wherein the second capacitance measurement and the third capacitance measurement are normalized based on a power series function representative of measurement data comprising position information versus capacitance measurements obtained from moving the probe towards the empty container.
9. The method of claim 5 , wherein the second speed is less than the first speed if the change in capacitance exceeds a predetermined slope threshold to slow the movement of the probe.
10. The method of claim 1 , wherein the capacitive sensor is configured to take the first capacitance measurement by providing an excitation source to the probe and reading the first capacitance measurement from the conductive plate.
11. The method of claim 9 , wherein the predetermined slope threshold indicates that the probe is reaching close to the surface of the fluid in the container.
12. The method of claim 1 , wherein the capacitive sensor is configured to measure the capacitance between the probe and the conductive plate having a dielectric mix comprising air, the fluid in the container, and the container.
13. The method of claim 1 , wherein the first capacitance measurement is normalized based on a power series function representative of measurement data comprising position information versus capacitance measurements obtained from moving the probe towards the empty container.
14. A system for controlling movement of a probe towards a container having fluid therein, the system comprising:
a capacitive to digital converter for converting measurements from a capacitive sensor into a digital signal;
a motion control engine for moving the probe towards the container;
an approach engine coupled to the output of the capacitive to digital converter configured to:
receive a first capacitance measurement from the capacitive sensor, wherein the first capacitance measurement is indicative of capacitance between the probe and a conductive plate underneath the container; and
transmit a first signal to the motion control engine for moving the probe towards the container at a first speed, wherein the first speed is determined based on the first capacitance measurement.
15. The system according to claim 14 , wherein the first speed is zero to stop the movement of the probe towards the container if the first capacitance measurement exceeds a predetermined capacitance threshold.
16. The system of claim 14 , wherein the approach engine is further configured to:
receive a second capacitance measurement and a third capacitance measurement from the capacitive sensor, wherein the second capacitance measurement and the third capacitance measurement are each indicative of the capacitance formed between the probe and a conductive plate underneath the container;
determine a change in capacitance between the second capacitance measurement and the third capacitance measurement to estimate a slope indicative of change in capacitance with respect to change in position information; and
transmit a second signal to the motion control engine for moving the probe towards the container at a second speed, wherein the second speed is determined based on the change in capacitance.
17. The system of claim 14 , wherein the first capacitance measurement is normalized based on a power series function representative of measurement data comprising position information versus capacitance measurements obtained from moving the probe towards the empty container.
18. A non-transitory computer readable storage medium having instructions stored thereon for controlling movement of a probe towards a container having fluid therein, wherein the instructions when executed by at least one processor cause the at least one processor to perform the following operations:
receiving a first capacitance measurement from a capacitive sensor, wherein the first capacitance measurement is indicative of capacitance between the probe and a conductive plate underneath the container; and
transmitting a first signal to the motion control engine for moving the probe towards the container at a first speed, wherein the first speed is determined based on the first capacitance measurement.
19. The medium according to claim 18 , wherein the first speed is zero to stop the movement of the probe towards the container if the first capacitance measurement exceeds a predetermined capacitance threshold.
20. The medium of claim 18 , wherein the at least one processor is further configured to perform the following operations:
receive a second capacitance measurement and a third capacitance measurement from the capacitive sensor, wherein the second capacitance measurement and the third capacitance measurement are each indicative of the capacitance formed between the probe and a conductive plate underneath the container;
determine a change in capacitance between the second capacitance measurement and the third capacitance measurement to estimate a slope indicative of change in capacitance with respect to change in position information; and
transmit a second signal to the motion control engine for moving the probe towards the container at a second speed, wherein the second speed is determined based on the change in capacitance.