Systems and methods for control of pumps employing gravimetric sensing

• US 6,296,450 B1
• Filed: 09/03/1999
• Issued: 10/02/2001
• Est. Priority Date: 09/03/1999
• Status: Expired due to Term

• Current Assignee: Fenwal Incorporated (Fresenius SE & Co. KGaA)
• Original Assignee: Baxter International Inc.
• Inventors: Yu, Clement Lim, Mullen, Richard E, Westberg, Tom, Brown, Richard I
• Primary Examiner(s): FREAY, CHARLES GRANT
• Application Number:
  US09/390,269
• Time in Patent Office: 760 Days
• Field of Search: 417/18, 417/36, 210/745, 609/67
• US Class Current: 417/18
• CPC Class Codes: F04B 2205/09 Flow through the pump
• CPC Class Codes: F04B 49/06 Control using electricity regulating by means of floats actuating electric switches F04B49/04
• CPC Class Codes: F04B 49/12 by varying the length of stroke of the working members

Abstract

Systems and related methods pump fluid through a pump having a stroke volume. The systems and methods employ gravimetric control measures to monitor fluid flow through the pump. An actuator interacts with the pump during a stroke interval (T_Stroke) to pump fluid through the pump. The systems and methods couple a receptacle to the pump, to either dispense fluid into the pump or to receive fluid from the pump. The systems and methods detect changes in weight of the receptacle over a sample time period. The systems and methods achieve a desired flow rate (Q_Desired) by deriving an actual flow rate (Q_Actual) by sensing changes in weight of the receptacle over the sample time period, taking into account the density of the fluid, and adjusting the stroke interval based upon Q_Actual so that Q_Desired is achieved.

Claims

1. A system for pumping a fluid having a density comprising

a pump having a known stroke volume (SV), which is essentially constant,

an actuator interacting with the pump during a stroke interval (T_Stroke) to pump fluid through the pump,

a receptacle to dispense fluid into the pump or to receive fluid pumped from the pump,

a weigh sensor to detect changes in weight of the receptacle over a sample time period, and

a controller coupled to the actuator and the weigh sensor and including a control function to achieve a desired flow rate (Q_Desired) by deriving an actual flow rate (Q_Actual) by sensing with the weigh sensor changes in weight of the receptacle over the sample time period, taking into account the density of the fluid, and adjusting the stroke interval based upon Q_Actual so that Q_Desired is achieved.

2. A system according to claim 1

wherein the actuator achieves a stroke interval T_Stroke comprising a time interval component to draw fluid into the pump (T₁), a time interval component to expel the fluid from the pump (T₂), and an idle time interval component (T₃),

and wherein the controller adjusts one or more of the time interval components T₁, or T₂, or T₃ to achieve Q_Desired, according to the following relationship:

$T_{n<br><br>\left(\mathrm{Adjusted}\right)}=k<br><br>\left(\frac{\mathrm{SV}}{Q_{\mathrm{Desired}}}\right)-T_{n<br><br>\left(\mathrm{NotAdjusted}\right)}$

where;

T_n(Adjusted) is the magnitude of the time interval component or components after adjustment to achieve the desired flow rate Q_Desired;

T_{n(NotAdjusted)} is the magnitude of the value of the other time interval component or components of T_Stroke that are not adjusted, wherein the adjusted stroke interval after adjustment to achieve the desired flow rate Q_Desired is the sum of T_n(Adjusted) and T_{n(NotAdjusted)};

k is a correction factor that accounts for interactions between the pump and the upstream and downstream pressures, expressed as follows;

$k=T_{\mathrm{Stroke}}\times <br><br>\left(\frac{Q_{\mathrm{Actual}}}{\mathrm{SV}}\right).$

3. A system according to claim 1

wherein the controller derives a pump correction factor k that accounts for interactions between the pump and the upstream and downstream pressures, as follows:

$k=T_{\mathrm{Stroke}}\times <br><br>\left(\frac{Q_{\mathrm{Actual}}}{\mathrm{SV}}\right).$

4. A system according to claim 3

wherein the controller includes a diagnostic function to detect abnormal operating conditions based upon k and generate an alarm output.

5. A system according to claim 4

wherein the diagnostic function generates the alarm output based upon deviance between magnitude of k and an expected value.

6. A system according to claim 4

wherein the diagnostic function generates the alarm output based upon deviance between polarity of k and an expected polarity.

7. A system according to claim 1

wherein the controller includes a diagnostic function to detect changes in weight of the receptacle when the actuator is not operating and generate an alarm output.

8. A system according to claim 1

wherein the control function derives an actual flow rate (Q_Actual) by sensing multiple measurements of the changes in weight of the receptacle over the sample time period.

9. A system according to claim 8

wherein the multiple measurements are processed by an averaging technique.

10. A system according to claim 8

wherein the multiple measurements are processed by a recursive technique.

11. A system according to claim 1

wherein the control function derives an actual flow rate (Q_Actual) by sensing changes in weight of the receptacle over multiple sample time intervals.

12. A system according to claim 11

wherein the multiple measurements are processed by an averaging technique.

13. A system according to claim 11

wherein the multiple measurements are processed by a recursive technique.

14. A system according to claim 1

wherein the pump includes a pump chamber having the essentially constant volume.

15. A system according to claim 1

wherein the pump includes a peristaltic pump.

16. A system according to claim 1

further including tubing communicating with the pump to couple the pump in-line between a source of blood and a blood separation device.

17. A system for pumping a fluid comprising

a pump having a known stroke volume (SV), which is essentially constant,

an actuator interacting with the pump during a stroke interval (T_Stroke) to pump fluid through the pump at a flow rate (Q_Actual),

a receptacle to dispense fluid into the pump or to receive fluid pumped from the pump,

a weigh sensor to detect changes in weight of the receptacle over a sample time period, and

a controller coupled to the actuator and the weigh sensor and including a diagnostic function to detect abnormal operating conditions based upon a pump correction factor k, which accounts for interactions between the pump and the upstream and downstream pressures, and to generate an alarm output, the pump correction factor k being derived as follows:

$k=T_{\mathrm{Stroke}}\times <br><br>\left(\frac{Q_{\mathrm{Actual}}}{\mathrm{SV}}\right).$

18. A system according to claim 17

wherein the diagnostic function generates the alarm output based upon deviance between magnitude of k and an expected value.

19. A system according to claim 17

wherein the diagnostic function generates the alarm output based upon deviance between polarity of k and an expected polarity.

20. A system according to claim 17

wherein the controller includes a diagnostic function to detect changes in weight of the receptacle when the actuator is not operating and generate an alarm output.

21. A system according to claim 17

wherein the pump includes a pump chamber having the essentially constant volume.

22. A system according to claim 17

wherein the pump includes a peristaltic pump.

23. A system according to claim 17

further including a blood separation device coupled to the pump.

24. A system according to claim 17

further including tubing communicating with the pump to couple the pump in-line between a source of blood and a blood separation device.

25. A blood processing system coupled to a blood separation device comprising

a cassette containing at least one pneumatically actuated pump station comprising a pump chamber having a known stroke volume (SV), which is essentially constant,

a pneumatic actuator to hold the cassette and selectively apply pneumatic force to the pump station during a stroke interval (T_Stroke) to pump fluid having a density through the pump chamber,

a receptacle to dispense fluid into the pump chamber or to receive fluid pumped from the pump chamber,

a weigh sensor to detect changes in weight of the receptacle over a sample time period, and

a controller coupled to the actuator and the weigh sensor and including a control function to achieve a desired flow rate (Q_Desired) by deriving an actual flow rate (Q_Actual) by sensing with the weigh sensor changes in weight of the receptacle over the sample time period, taking into account the density of the fluid and adjusting the stroke interval based upon Q_Actual so that Q_Desired is achieved.

26. A system according to claim 25

wherein the pneumatic actuator achieves a stroke interval T_Stroke comprising a time interval component to draw fluid into the pump (T₁), a time interval component to expel the fluid from the pump (T₂), and an idle time interval component (T₃), and

wherein the controller adjusts one or more of the time interval components T₁, or T₂, or T₃ to achieve Q_Desired, according to the following relationship:

$T_{n<br><br>\left(\mathrm{Adjusted}\right)}=k<br><br>\left(\frac{\mathrm{SV}}{Q_{\mathrm{Desired}}}\right)-T_{n<br><br>\left(\mathrm{NotAdjusted}\right)}$

where;

T_n(Adjusted) is the magnitude of the time interval component or components after adjustment to achieve the desired flow rate Q_Desired.

T_{n(NotAdjusted)} is the magnitude of the value of the other time interval component or components of T_Stroke that are not adjusted, wherein the adjusted stroke interval after adjustment to achieve the desired flow rate Q_Desired is the sum of T_n(Adjusted) and T_{n(NotAdjusted)};

k is a correction factor that accounts for interactions between the pump and the upstream and downstream pressures, expressed as follows;

$k=T_{\mathrm{Stroke}}\times <br><br>\left(\frac{Q_{\mathrm{Actual}}}{\mathrm{SV}}\right).$

27. A system according to claim 26

wherein the controller derives a pump correction factor k that accounts for interactions between the pump and the upstream and downstream pressures, as follows:

$k=T_{\mathrm{Stroke}}\times <br><br>\left(\frac{Q_{\mathrm{Actual}}}{\mathrm{SV}}\right).$

28. A system according to claim 27

wherein the controller includes a diagnostic function to detect abnormal operating conditions affecting the pump station based upon k and generate an alarm output.

29. A system according to claim 28

wherein the diagnostic function generates the alarm output based upon deviance between magnitude of k and an expected value.

30. A system according to claim 28

wherein the diagnostic function generates the alarm output based upon deviance between polarity of k and an expected polarity.

31. A system according to claim 28

wherein the controller includes a diagnostic function to detect changes in weight of the receptacle when the actuator is not operating and generate an alarm output.

32. A system according to claim 26

wherein the control function derives an actual flow rate (Q_Actual) by sensing multiple measurements of the changes in weight of the receptacle over the sample time period.

33. A system according to claim 32

wherein the multiple measurements are processed by an averaging technique.

34. A system according to claim 32

wherein the multiple measurements are processed by a recursive technique.

35. A system according to claim 26

wherein the control function derives an actual flow rate (Q_Actual) by sensing changes in weight of the receptacle over multiple sample time intervals.

36. A system according to claim 35

wherein the multiple measurements are processed by an averaging technique.

37. A system according to claim 35

wherein the multiple measurements are processed by a recursive technique.

38. A method for pumping a fluid having a density comprising the steps of

providing a pump having a known stroke volume (SV), which is essentially constant,

operating an actuator to interact with the pump during a stroke interval (T_Stroke) to pump fluid through the pump,

coupling a receptacle to the pump to dispense fluid into the pump or to receive fluid pumped from the pump,

detecting changes in weight of the receptacle over a sample time period, and controlling the pump to achieve a desired flow rate (Q_Desired) by deriving an actual flow rate (Q_Actual) by sensing changes in weight of the receptacle over the sample time period, taking into account the density of the fluid, and adjusting the stroke interval based upon Q_Actual so that Q_Desired is achieved.

39. A method according to claim 38

wherein, in operating the actuator, the stroke interval T_Stroke comprises a time interval component to draw fluid into the pump (T₁), a time interval component to expel the fluid from the pump (T₂), and an idle time interval component (T₃), and

wherein, in controlling the pump, one or more of the time interval components T₁, or T₂, or T₃ is adjusted to a new magnitude to achieve Q_Desired, according to the following relationship:

40. A method according to claim 38

further including the step of deriving a pump correction factor k that accounts for interactions between the pump and the upstream and downstream pressures, as follows:

41. A method according to claim 40

further including a diagnostic step of detecting abnormal operating conditions based upon k and generate an alarm output.

42. A method according to claim 41

wherein the diagnostic step generates the alarm output based upon deviance between magnitude of k and an expected value.

43. A method according to claim 41

wherein the diagnostic step generates the alarm output based upon deviance between polarity of k and an expected polarity.

44. A method according to claim 38

further including a diagnostic step of detecting changes in weight of the receptacle when the actuator is not operating and generate an alarm output.

45. A method according to claim 38

wherein, in controlling the pump, an actual flow rate (Q_Actual) is derived by sensing multiple measurements of the changes in weight of the receptacle over the sample time period.

46. A method according to claim 45

wherein the multiple measurements are processed by an averaging technique.

47. A method according to claim 45

wherein the multiple measurements are processed by a recursive technique.

48. A method according to claim 38

wherein, in controlling the pump, an actual flow rate (Q_Actual) is derived by sensing changes in weight of the receptacle over multiple sample time intervals.

49. A method according to claim 48

wherein the multiple measurements are processed by an averaging technique.

50. A method according to claim 48

wherein the multiple measurements are processed by a recursive technique.

51. A method according to claim 38

wherein, in providing the pump, the pump includes a pump chamber having the essentially constant volume.

52. A method according to claim 38

wherein, in providing the pump, the pump includes a peristaltic pump.

53. A method according to claim 38

further including the step of coupling the pump to a blood separation device.

54. A method for pumping a fluid comprising the steps of

providing a pump having a known stroke volume (SV), which is essentially constant,

operating an actuator to interact with the pump during a stroke interval (T_Stroke) to pump fluid through the pump at a flow rate (Q_Actual),

coupling a receptacle to the pump to dispense fluid into the pump or to receive fluid pumped from the pump,

detecting changes in weight of the receptacle over a sample time period, and

detecting abnormal operating conditions based upon a pump correction factor k, which accounts for interactions between the pump and the upstream and downstream pressures, and generating an alarm output, the pump correction factor k being derived as follows:

$k=T_{\mathrm{Stroke}}\times <br><br>\left(\frac{Q_{\mathrm{Actual}}}{\mathrm{SV}}\right).$

55. A method according to claim 54

wherein the alarm output is generated based upon deviance between magnitude of k and an expected value.

56. A method according to claim 54

wherein the alarm output is generated based upon deviance between polarity of k and an expected polarity.

57. A method according to claim 54

further including the step of detecting changes in weight of the receptacle when the actuator is not operating and generate an alarm output.

58. A method according to claim 54

wherein, in providing the pump, the pump includes a pump chamber having the essentially constant volume.

59. A method according to claim 54

wherein, in providing the pump, the pump includes a peristaltic pump.

60. A method according to claim 54

further including the step of coupling the pump to a blood separation device.