Piston position measuring device

• US 20030084719A1
• Filed: 12/12/2002
• Published: 05/08/2003
• Est. Priority Date: 03/08/2000
• Status: Active Grant

• Current Assignee: Rosemount Incorporated (Emerson Electric Company)
• Original Assignee: Rosemount Incorporated (Emerson Electric Company)
• Inventors: Wiklund, David E., Krouth, Terrance F., Habegger, Richard J., Hineman, Richard R.
• Granted Patent: US 6,817,252 B2
• Time in Patent Office: Days
• US Class Current: 73/239
• CPC Class Codes: F15B 15/2838 with out using position sensors, e.g. by volume flow measurement or pump speed
• CPC Class Codes: G01F 1/36 the pressure or differential pressure being created by the use of flow constriction

Abstract

A measuring device is provided for determining a position of a piston contained within a hydraulic actuator as a function of a hydraulic fluid flow. The measuring device includes a bi-directional flow sensor positioned inline with the hydraulic fluid flow and a piston position module. The flow sensor is configured to produce a flow rate signal that is indicative flow rate of the hydraulic fluid flow into and out of a first cavity. The piston position module is configured to receive the flow rate signal from the flow sensor and produce a piston position signal that is indicative of the position of the piston within the hydraulic actuator as a function of the flow rate signal.

Claims

1. A device for measuring a position of a piston slidably contained within a hydraulic cylinder of a hydraulic actuator, the piston and the hydraulic cylinder define a first cavity, the device comprising:

a bi-directional flow sensor positioned inline with the hydraulic fluid flow and having a flow rate signal output that is indicative the flow rate of the hydraulic fluid into and out of the first cavity; and

a piston position module adapted to receive the flow rate signal output and responsively provide a piston position signal output related to the piston position within the hydraulic cylinder as a function of the flow rate signal output.

2. The device of claim 1, wherein the bi-directional flow sensor includes:

a bi-directional flow restriction member adapted to produce a pressure drop;

a differential pressure sensor embedded in the flow restriction member and adapted to produce a differential pressure signal that is indicative of the pressure drop; and

processing electronics adapted receive the differential pressure signal and to produce the flow rate signal output as a function of the differential pressure signal.

3. The device of claim 1, wherein the flow rate signal output is in accordance with one of an analog communication protocol and a digital communication protocol.

4. The device of claim 1, wherein the piston position module includes:

an analog to digital converter electrically coupled to the flow sensor and adapted to receive the flow rate signal and convert the flow rate signal into a digitized flow rate signal; and

a microprocessor electrically coupled to the analog to digital converter and adapted to receive the digitized flow rate signal output, calculate a volume of hydraulic fluid in the first cavity as a function of the digitized flow rate signal, and produce the piston position signal output as a function of the volume of hydraulic fluid in the first cavity.

5. The device of claim 4, wherein:

the device includes an input/output port electrically coupled to the microprocessor; and

the microprocessor is further configured to provide the piston position signal output through the input/output port.

6. The device of claim 1, including a limit switch coupled to one of the hydraulic cylinder and the piston, wherein the piston position signal output is further a function of the limit switch.

7. The device of claim 1, wherein the bi-directional differential pressure flow sensor is insensitive to position.

8. The device of claim 1, wherein the bi-directional differential pressure flow sensor includes a differential pressure sensor embedded in a flow restriction member.

9. The device of claim 1 includes a temperature sensor and wherein the piston position signal output is further a function of temperature.

10. The device of claim 1 wherein the piston position signal is a function of an integral of the flow rate signal.

11. The device of claim 1 wherein the differential pressure sensor comprises first and second pressure sensors having first and second pressure outputs and wherein differential pressure is related to a difference between the first and second pressure sensor outputs.

12. A hydraulic actuator, comprising:

a hydraulic cylinder having first and second ports formed therein for receiving first and second hydraulic fluid flows therethrough, respectively;

a piston slidably received in the hydraulic cylinder, wherein the piston and the hydraulic cylinder define first and second cavities fluidically coupled to the first and second hydraulic fluid flows through the first and second ports, respectively;

a first flow sensor positioned inline with the first hydraulic fluid flow and having a first flow rate signal output that is indicative of a flow rate of the first hydraulic fluid flow into and out of the first cavity; and

a piston position module adapted to receive the first flow rate signal and having a first piston position signal output, produced as function of the first flow rate signal, that is related to a first position of the piston within the hydraulic cylinder.

13. The hydraulic actuator of claim 12, wherein:

the apparatus includes a second flow sensor positioned inline with the second hydraulic fluid flow and having a second flow rate signal output that is indicative of a flow rate of the second hydraulic fluid flow into and out of the second cavity;

the piston position module is further configured to receive the second flow rate signal and having a second piston position signal output, produced as a function of the second flow rate signal, that is related to a second piston position within the hydraulic cylinder.

14. The hydraulic actuator of claim 13, wherein the piston position module is further configured to perform diagnostics using the first and second flow rate signal outputs.

15. The hydraulic actuator of claim 12 wherein the differential pressure sensor comprises first and second pressure sensors having respective first and second pressure outputs and wherein the differential pressure is a function of a difference between the first and second pressure outputs.

16. The device of claim 12 including a temperature sensor and wherein the flow rate signal is a function of a temperature.

17. The device of claim 12 wherein the first flow sensor includes a restriction member inline with the first hydraulic fluid flow and wherein the differential pressure is developed across the restriction member.

18. A method of measuring a position of a piston slidably contained within a hydraulic cylinder of a hydraulic actuator, the piston and the hydraulic cylinder define a first cavity, the method comprising:

measuring a differential pressure in a flow of hydraulic fluid into and out of the cavity;

determining a flow rate of hydraulic fluid into the cavity as a function of the differential pressure; and

calculating the position of the piston within the hydraulic cylinder as a function of the fluid flow rate.

19. The method of claim 18, further comprising:

producing a piston position signal that is indicative of the position of the piston within the hydraulic cylinder.

20. The method of claim 18, including measuring temperature of the hydraulic fluid and wherein piston position is a function of temperature.

21. The method of claim 18, wherein measuring differential pressure comprises subtracting a first measured static pressure from a second measured static pressure.