System for determining the position of a piston along its path of travel for a fluid-dynamic actuator

• US 8,776,667 B2
• Filed: 10/21/2008
• Issued: 07/15/2014
• Est. Priority Date: 10/22/2007
• Status: Active Grant

• Current Assignee: AMA S.p.A
• Original Assignee: AMA S.p.A
• Inventors: Cani, Paolo, Reggiani, Wainer
• Primary Examiner(s): LETTMAN, BRYAN MATTHEW
• Application Number:
  US12/734,296
• Publication Number:
  US 20100282068A1
• Time in Patent Office: 2,093 Days
• Field of Search: 731/142.8, 92/5.R, 250/206.1, 250/231.7, 250/231.8, 417/63
• US Class Current: 92/5.R
• CPC Class Codes: F15B 15/2846 using detection of markings, e.g. markings on the piston rod
• CPC Class Codes: F15B 15/2876 using optical means, e.g. laser
• CPC Class Codes: G01B 11/024 by means of diode-array scanning
• CPC Class Codes: G01B 11/14 for measuring distance or clearance between spaced objects or spaced apertures G01B11/26 takes precedence; rangefinders G01C3/00

Abstract

A fluid-dynamic actuator having a detection system for determining the position of a piston along its path of travel within a cylinder. The piston includes a head and rod extending therefrom. First grooves are machined on respective sections of the rod. Projections of the first grooves onto a first plane parallel to the longitudinal axis of the rod define segments arranged obliquely with respect to the axis. Second grooves extend along the axis for predetermined lengths such that a respective number of second grooves run across each section. Optical sensors detect the presence of second grooves through a second plane transverse to the axis and a displacement of segments along a line coplanar with the second plane due to movement of the piston. A processor counts detected second grooves to determine the position of the piston as a function of the count of second grooves and the displacement of segments.

Claims

1. A fluid-dynamic actuator comprising:

a cylinder (2) and a piston (3), which includes a rod (5) having a longitudinal axis (6);

the piston (3) being movable inside the cylinder (2) along a path of travel (9) parallel to said axis (6);

the actuator (1) further including a detection system (13) for determining a position of the piston (3) along a path of travel (9), and wherein said detection system (13) comprises;

a plurality of first grooves (14), which are machined on an outer surface of respective sections (15) of the rod (5) so that respective projections of the first grooves (14) onto a first plane parallel to the axis (6) define respective first segments (14a) parallel to one another and arranged obliquely with respect to a projection of the axis (6) onto the first plane;

a plurality of second grooves (17), which are machined on an outer surface of the rod (5) and extend parallel to the axis (6) for respective lengths such that a respective number of second grooves (17) run across the outer surface of each of the sections (15);

optical sensing means (19, 21) to detect the presence of second grooves (17) in correspondence with a second plane (20) transversal to the axis (6) and fixed with respect to the cylinder (2) and a first displacement (32) of the first segments (14a) along a reading line (31) defined by an intersection of the second plane (20) with the first plane, said first displacement (32) being due to a movement of the piston (3) along the path of travel (9); and

processing means (22) to identify the section (15) of rod (5) present in correspondence with the second plane (20) by counting the detected second grooves (17) and to measure the position of the piston (3) along the path of travel (9) as a function of the identified section (15) and of said first displacement (32).

2. The actuator according to claim 1, wherein said first segments (14a) form, with said projection of the axis (6), an acute angle (30) having a defined value;

said processing means (22) being suitable to determine said position of the piston (3) along the path of travel (9) as a function of the acute angle (30).

3. The actuator according to claim 2, wherein said acute angle (30) has a value in the range of between and 45 degrees and 60 degrees.

4. The actuator according to claim 1, wherein said second plane (20) is perpendicular to said longitudinal axis (6).

5. The actuator according to claim 1, wherein said sections (15) of the rod (5) are of a same length (L);

said processing means (22) being suitable to determine said position of the piston (3) along the path of travel (9) as a function of said length (L).

6. The actuator according to claim 1, wherein a second number (N2) of said plurality of second grooves is equal to a first number (N1) of said plurality of first grooves minus one so that a zero number of said second grooves (17) run across the outer surface of at least one of said sections (15).

7. The actuator according to claim 1, comprising a third groove (29) which is machined on said outer surface of the rod (5) so that a projection of the third groove (29) onto said first plane defines a second segment (29a) parallel to said axis (6);

said optical sensing means (19, 21) being suitable to detect a second displacement (34) of the second segment (29a) along said reading line (31), said second displacement (34) being due to a rotation of said piston (3) with respect to said cylinder (2) about said axis (6);

said processing means (22) being suitable to determine said position of the piston (3) along the path of travel (9) as a function of the second displacement (34).

8. The actuator according to claim 7, wherein said processing means (22) is are configured to calculate a compensation factor of said rotation of the piston (3) as a function of said second displacement (34) and to process said first displacement (32) with the compensation factor in order to determine said position of the piston (3) along the path of travel (9).

9. The actuator according to claim 7, wherein said plurality of first grooves (14) are arranged along a first portion of outer surface (16) of the rod (5);

said optical sensing means (19, 21) comprising a first illuminator (23), which is arranged alongside the rod (5) so as to illuminate a first sub-portion of surface (24) of said first portion of outer surface (16) so that a projection of the first sub-portion of surface (24) onto said first plane defines a reading zone (24a) extending along said reading line (31), and a first optical sensor (25) to acquire an image of the reading zone (24a) such that said first displacement (32) and said second displacement (34) are detectable on said image.

10. The actuator according to claim 1, comprising a third groove (29) which is machined on said outer surface of the rod (5) so that a projection of the third groove (29) onto said first plane defines a second segment (29a) parallel to said axis (6);

said processing means (22) being configured to measure said first displacement (32) as the distance between the first segment (14a) of said identified section (15) of rod (5) and said second segment (29a) along said reading line (31).

11. The actuator according to claim 1, wherein said plurality of first grooves (14) are arranged along a first portion of an outer surface (16) of the rod (5);

said optical sensing means (19, 21) comprising a first illuminator (23), which is arranged alongside the rod (5) so as to illuminate a first sub-portion (24) of the first portion of outer surface (16) so that a projection of the first sub-portion (24) onto said first plane defines a reading zone (31) extending along said reading line (31), and a first optical sensor (25) to acquire an image of the reading zone (24a) such that said first displacement (32) is detectable on said image.

12. The actuator according to claim 11, wherein said first optical sensor (25) comprises a CCD sensor.

13. The actuator according to claim 1, wherein said plurality of second grooves (17) are arranged along a second portion of outer surface (18) of the rod (5);

said optical sensing means (19, 21) comprising at least a second illuminator arranged alongside the rod (5) so as to illuminate a second sub-portion of surface (27) of said second portion of outer surface (18) having an elongated form and being arranged so as to be crossed longitudinally by said second plane (20), and a plurality of second sensors (28), each of which to detect the presence of a respective one of said second grooves (17) in the second sub-portion of surface (27).

14. The actuator according to claim 13, wherein said plurality of first grooves (14) are arranged along a first portion of outer surface (16) of the rod (5);

said second portion of outer surface (18) of the rod (5) being diametrically opposite said first portion of outer surface (16).

15. The actuator according to claim 13, wherein each of said second optical sensors (28) consists of a photodiode.

16. The actuator according to claim 13, wherein said second illuminator (26) comprises a plurality of illuminating units, each of which is associated with a respective one of said optical sensors (28).

17. The actuator according to claim 1 comprising a chamber (10) separate from said cylinder (2) and through which said rod (5) passes slidingly;

said optical sensing means (19, 21) being housed inside the chamber (10).

18. The actuator according to claim 17, wherein said piston (3) is movable inside said cylinder (2) under the action of a pressurized fluid;

the cylinder (2) and said chamber (10) being connected via an aperture (11) through which said rod (5) passes and which is provided with compression rings (12) to prevent the pressurized fluid from entering the chamber (10).