GB2567160A

GB2567160A - Measurement apparatus

Info

Publication number: GB2567160A
Application number: GB1716127.4A
Authority: GB
Inventors: D Giudice Sebastiano
Original assignee: Rolls Royce Power Engineering PLC
Current assignee: Rolls Royce Power Engineering PLC
Priority date: 2017-10-03
Filing date: 2017-10-03
Publication date: 2019-04-10
Also published as: GB201716127D0

Abstract

An apparatus for measuring the internal surface 105 of a hollow cylinder 101, comprising: a carrier frame 102 having extendable arms 103a-d, each arm having a radially outward end 104 for contacting the internal surface; a sensor support 106 mounted to the carrier frame for rotation about a rotation axis; a linear position sensor 107 slidably mounted to a radially outward end 108 of the sensor support; and a control unit to control movement of the carrier frame, the sensor support and the position sensor. The position sensor may comprise a retroreflective element and a laser. A method of measuring an internal surface comprises the steps of: i) placing the apparatus in a hollow cylinder; ii) moving the position sensor radially outward until contact is made with the internal surface; iii) taking a position measurement; iv) retracting the position sensor; v) rotating the sensor support relative to the carrier frame; vi) repeating steps iii) to v) until a plurality of measurements are taken around the internal surface; moving the carrier frame along the rotation axis; and repeating steps iii) to vii) until a plurality of measurements have been taken within the cylinder.

Description

(57) An apparatus for measuring the internal surface 105 of a hollow cylinder 101, comprising: a carrier frame 102 having extendable arms 103a-d, each arm having a radially outward end 104 for contacting the internal surface; a sensor support 106 mounted to the carrier frame for rotation about a rotation axis; a linear position sensor 107 slidably mounted to a radially outward end 108 of the sensor support; and a control unit to control movement of the carrier frame, the sensor support and the position sensor. The position sensor may comprise a retroreflective element and a laser. A method of measuring an internal surface comprises the steps of: i) placing the apparatus in a hollow cylinder; ii) moving the position sensor radially outward until contact is made with the internal surface; iii) taking a position measurement; iv) retracting the position sensor; v) rotating the sensor support relative to the carrier frame; vi) repeating steps iii) to v) until a plurality of measurements are taken around the internal surface; moving the carrier frame along the rotation axis; and repeating steps iii) to vii) until a plurality of measurements have been taken within the cylinder.

At least one drawing originally filed was informal and the print reproduced here is taken from a later filed formal copy.

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MEASUREMENT APPARATUS

The present disclosure concerns an apparatus for taking measurements of the internal surface of a hollow cylinder.

Accurate measurements of the internal dimensions of hollow cylinders are important for many applications, for example to ensure other components fit correctly within an internal bore. A three point bore gauge may commonly be used to take accurate measurements of the internal diameter of a hollow cylinder. Taking accurate measurements of any variation in diameter or circularity of a hollow cylinder requires multiple measurements to be taken. Doing so can be laborious and time-consuming, and requires user interaction with the measurement tool to take each measurement. This becomes more difficult as the size of the cylinder increases. For larger size cylinders, for example those used in large scale industrial plants, specialised measurement tools may be required to take accurate measurements. In environments where human interaction may be limited or not possible, such as in chemical or nuclear reactors, automated or semi-automated methods of measurement may be necessary.

According to a first aspect there is provided an apparatus for measuring the internal surface of a hollow cylinder, the apparatus comprising:

a carrier frame having a plurality of extendable arms, each arm having a radially outward end for contacting the internal surface;

a sensor support mounted to the carrier frame for rotation about a rotation axis parallel to a central axis of the hollow cylinder;

a linear position sensor slidably mounted to a radially outward end of the sensor support; and a controller unit connected and arranged to control movement of the carrier frame within the hollow cylinder, movement of the sensor support about the rotation axis and linear movement of the linear position sensor to acquire measurements from the linear position sensor at a plurality of points around the internal bore surface of the hollow cylinder.

The apparatus provides for a way of accurately measuring the internal dimensions of a hollow cylinder with a minimum of input from a human operator, thereby allowing measurements to be taken in environments where human interaction may be difficult or impossible.

The linear position sensor may comprise:

a retroreflective element mounted to the radially outward end of the sensor support; and a laser measurement unit mounted to the sensor support and arranged to direct a laser beam towards the retroreflective element to measure a distance therebetween.

Using a retroreflective element in combination with a laser measurement unit allows for high accuracy of relative distance measurements, theoretically to within the order of the wavelength of light used for the laser beam.

The sensor support may comprise an actuator configured to move the linear position sensor in a radial direction to and from the internal surface. Moving the linear position to and from the internal surface prevents the part of the sensor contacting the internal surface from becoming worn or damaged, and also prevents any damage to the internal surface from any sliding contact The actuator may for example comprise a servo motor and a cam, although other arrangements such as a linear actuator based on rotation of a screw thread may be possible.

The sensor support may comprise a resilient compressible element, such as a compression spring, between the actuator and the linear position sensor. The compressible element prevents the linear position sensor from making a hard contact with the internal surface, thereby preventing any damage and controlling the contact pressure with the internal surface to ensure more repeatable measurements are made.

The sensor support may comprise a linear displacement sensor arranged to provide a signal indicating displacement of the linear position sensor to the controller unit. The linear displacement sensor only needs to provide a signal indicating whether the linear position sensor is moving, and not its actual location. A benefit of the displacement sensor is that the controller unit can, upon detection of movement stopping indicating contact between the linear position sensor and the internal surface, stop the actuator moving the linear displacement sensor to prevent a hard contact between the sensor and the internal surface.

The controller unit may be configured to trigger acquisition of a position measurement from the linear position sensor when the signal from the linear displacement sensor indicates the linear position sensor has stopped moving. This allows each measurement to be taken as soon as the sensor is in position, thereby speeding up acquisition of a series of measurements.

The controller unit may be configured to control operation of motors configured to rotate the sensor support relative to the carrier frame and displacement of the carrier frame relative to the cylinder. The controller unit can thereby carry out an entire sequence of measurements on the cylinder, rotating the sensor support between measurements with one motor and causing linear displacement of the carrier frame with another motor.

Two or more of the extendable arms may be located at positions offset relative to each other along the axis of the cylinder. This arrangement improves the stability of the carrier frame relative to the cylinder, preventing unwanted movement of the frame during and between measurements.

Each extendable arm may have a wheel assembly at the radially outward end to contact the internal surface. This allows the apparatus to be readily moved along the internal surface of the cylinder.

The wheel assembly may allow for movement of the extendable arm relative to the internal surface in a direction parallel with the rotation axis and in a direction around the axis. Movement in both directions, for example using omni wheels, allows for more flexibility in how the apparatus is positioned within the cylinder.

According to a second aspect there is provided a method of acquiring measurements of an internal surface of a hollow cylinder using the apparatus according to the first aspect, the method comprising the steps of:

i) locating the apparatus within the hollow cylinder such that the radially outward ends of each of the plurality of extendable arms of the carrier frame contact the internal surface;

ii) moving the linear position sensor radially outward from the sensor support until contact is made with the internal surface;

iii) taking a position measurement using the linear position sensor;

iv) retracting the linear position sensor from the internal surface;

v) rotating the sensor support relative to the carrier frame about the rotation axis;

vi) repeating steps iii) to v) until a plurality of position measurements have been taken around the internal surface;

vii) moving the carrier frame in a direction parallel with the rotation axis; and viii) repeating steps iii) to vii) until a plurality of position measurements have been taken around the internal surface and along the axis of the hollow bore of the cylinder.

Various features indicated above in relation to the first aspect may also be applied to the second aspect.

According to a third aspect there is provided a computer program comprising instructions for causing a computer to perform the method according to the second aspect. The computer program may be provided on a non-transitory medium such as a read only memory (ROM), non-volatile memory or computer readable disc.

The skilled person will appreciate that, except where mutually exclusive, a feature described in relation to any one of the above aspects may be applied mutatis mutandis to any other aspect. Furthermore except where mutually exclusive any feature described herein may be applied to any aspect and/or combined with any other feature described herein.

Embodiments will now be described by way of example only, with reference to the Figures, in which:

Figure 1 is a schematic plan view of an apparatus for measuring the internal surface of a hollow cylinder in position within the cylinder;

Figure 2 is a sectional side view of the apparatus of Figure 1;

Figure 3 is a schematic diagram of a linear position sensor for taking measurements within a hollow cylinder and its connection with a controller unit; and

Figure 4 is a schematic flow diagram of an example method for measuring the internal surface of a hollow cylinder.

Figure 1 illustrates an example apparatus 100 for measuring the internal surface 105 of a hollow cylinder 100. The apparatus 100 principally comprises a carrier frame 102 and a linear position sensor 107 rotatably mounted to the carrier frame 102. The apparatus 100 is configured to be positioned within the hollow cylinder 101 and take a series of measurements at points around the internal surface 105 and along the length of the cylinder 101. The measurements can be taken under the control of a controller unit 301, shown in Figure 3 and described in more detail below, allowing a series of measurements to be taken automatically and under remote control, allowing direct user interaction with the cylinder to be minimised.

The carrier frame 102 comprises a plurality of extendable arms 103a-d, four of which are shown in the example illustrated in Figure 1. The number of arms may be greater or fewer than the four shown in Figure 1. A typical realistic minimum number is three arms, so that the apparatus can be held in a stable position within a nominally circular bore. In some arrangements, however, two arms may be sufficient, for example if the end of each arm has a sufficiently wide footprint to secure the apparatus in position.

Each of the arms 103a-d in the example of Figure 1 is shown as being spring loaded with a compression spring 109 so that the apparatus 100 is held in position against the internal surface 105. Other ways of resiliently holding each arm in position against the internal surface may be possible, for example using compressible mounts in combination with linear actuators, which may be motor driven.

Each of the plurality of extendable arms 103a-d contacts the inner surface 105 of the cylinder 101 at its radially outward end 104. Each arm 103a-d may comprise one more wheels 111 at its radially outward end 104. In the example shown in Figure 1, each arm comprises a wheel assembly 111 at its radially outward end 104. The wheel assemblies 111 may be configured to allow the apparatus 100 to rotate within the cylinder 101 and may also allow the apparatus 100 to move linearly along the axis of the cylinder 101. Suitable wheel assemblies for the purpose of allowing movement in both directions are generally known as omni wheels, as they allow for omnidirectional movement.

A sensor support 106 is mounted to the carrier frame 102 for rotation about a rotation axis 201 (Figure 2). In the example shown in Figure 1, the sensor support 106 is in the form of an arm extending from a central hub 110 rotatably mounted to the carrier frame 102. In alternative embodiments the sensor support may for example be in the form of a ring rotatably mounted to the carrier frame 102, so does not necessarily need to take the form of an arm.

A linear position sensor 107 is slidably mounted to a radially outward end 108 of the sensor support 106. In the example of figure 1, the linear position sensor comprises a spherically mounted retroreflector (SMR) 303 (shown in more detail in Figure 3), the position of which can be determined using a laser beam mounted on the sensor support 106. The SMR 303 is linearly moveable in a radial direction relative to the sensor support 106 to allow the SMR 303 to be moved into position on the inner surface 105 at different points and retracted from the surface between measurements. Referring to Figure 3, the position of the SMR 303 may be adjusted using a cam 304 driven by a servo motor 305. As the servo motor 305 is driven, the cam 304 is driven radially outwards against a spring 306 until the SMR 303 reaches the internal surface 105 of the cylinder 101. Any further movement of the cam 304 can be absorbed by compression of the spring 306 to avoid damage to the SMR 303. A linear displacement sensor 307, such as a linear variable displacement transducer (LVDT), connected to the SMR 303 provides a displacement signal 308 to a controller unit 301, indicating that the SMR 303 has stopped moving. This may be used to send a signal to the servo motor 305 to stop rotation, and may also be used to provide a trigger signal 309 to initiate a measurement of the position of the SMR 303 by a laser 310.

In the example shown in Figure 3, the SMR 303 is mounted on a holder 311, which is attached to the end of a piston 312 slidably mounted within a piston body 313. The cam 304 contacts the other end of the piston 312 and causes the piston 312 to slide within the piston body 313 as the cam 304 rotates under the action of the servo motor 305.

The use of an SMR to measure points on the internal surface of the cylinder allows for a high degree of accuracy, typically considerably less than 1 micrometre. For less stringent applications, a more simple mechanism for taking a measurement may be possible, for example by using a linear displacement sensor such as an LVDT alone. Other mechanisms for actuating the displacement sensor may also be possible than that illustrated, such as a motor driving a screwthread to cause the linear position sensor to move radially outwards and inwards. An advantage of the cam arrangement shown in the illustrated examples is that the movement of the linear sensor can be quick, allowing measurements to be taken at higher speed and frequency.

As illustrated in Figure 3, a controller unit 301 is connected and arranged to control movement of the carrier frame 102 within the hollow cylinder 101, as well as control movement of the sensor support 106 about the rotation axis 201 and linear movement of the linear position sensor 107 to acquire measurements from the linear position sensor 107 at a plurality of points around the internal bore surface 105 of the hollow cylinder 101. Further motors 314 are provided to allow for rotational movement of the sensor support 106 and for movement of the extendable arms 103a-d both about and along the axis 201 of the cylinder 101, under the control of the controller unit 301.

Figure 2 illustrates an example of the apparatus 100 in a side sectional view, showing a particular arrangement for the extendable arms 103a-c, three of which are shown. Two of the arms 103b, 103c are positioned at different points along the rotational axis 201 of the cylinder 101. This allows for additional stability of the apparatus when in position within the cylinder, preventing the apparatus 100 from rotating about an axis orthogonal to the rotational axis 201, which would result in distorted measurements of the internal surface 105. In the example shown, the rotational axis 201 of the cylinder is coincident with the rotational axis of the sensor support 106. This does not, however, always have to be the case, since rotation of the sensor support will result in a series of relative measurements that, when taken together, will result in an overall measurement of the internal surface 105 regardless of whether the rotational axes coincide. The axes are, however, preferably at least approximately parallel with each other.

Figure 4 is a schematic flow diagram illustrating an example series of operations for taking measurements on a hollow cylinder using the apparatus described herein. The method starts at step 401 with locating the apparatus 100 within the cylinder 101 to be measured, such that the radially outward ends 104 of the extendable arms 103a-d contact the inner surface 105 of the cylinder 101. At step 402, the linear position sensor 107 is moved radially outward from the sensor support 106 until contact is made with the internal surface 105. As described above, contact may be detected by detecting when a linear displacement sensor shows no further movement, which can trigger the subsequent step 403 of taking a position measurement using the linear position sensor 107. Once the measurement is taken, the next step 404 is to retract the linear position sensor 107 from the internal surface and then, at step 405, to rotate the sensor support 106 relative to the carrier frame 102. If any further measurements are to be taken (decision step 406), the preceding steps 403-405 are repeated. If all measurements for that axial position along the cylinder have been completed, the next step 407 is to move the apparatus in the axial direction along the cylinder 101. Steps 403 to 407 are then repeated until (at decision step 408) there are no more axial positions to measure along the cylinder. The process then ends at step 409.

The process described above may be carried out entirely automatically and computer controlled, for example under the control of the controller unit 301 suitably programmed or remotely using a general purpose computer.

The method as described above can be performed automatically, at least once the apparatus is positioned in place at a starting point within the cylinder 101. The method is therefore suitable for environments where is may be difficult or impossible for human interaction with the cylinder to be measured.

It will be understood that the invention is not limited to the embodiments abovedescribed and various modifications and improvements can be made without departing from the concepts herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.

Claims

1. An apparatus (100) for measuring the internal surface (105) of a hollow cylinder (101), the apparatus (100) comprising:

a carrier frame (102) having a plurality of extendable arms (103a-d), each arm having a radially outward end (104) for contacting the internal surface (105);

a sensor support (106) mounted to the carrier frame (102) for rotation about a rotation axis (201) parallel to a central axis of the hollow cylinder (101);

a linear position sensor (107) slidably mounted to a radially outward end (108) of the sensor support (106); and a controller unit (301) connected and arranged to control movement of the carrier frame (102) within the hollow cylinder (101), movement of the sensor support (106) about the rotation axis (201) and linear movement of the linear position sensor (107) to acquire measurements from the linear position sensor (107) at a plurality of points around the internal bore surface (105) of the hollow cylinder (101).

2. The apparatus (100) of Claim 1, wherein the linear position sensor comprises a retroreflective element (303) mounted to the radially outward end (108) of the sensor support (106) and a laser measurement unit (310) mounted to the sensor support (106) and arranged to direct a laser beam towards the retroreflective element (303) to measure a distance therebetween.

3. The apparatus (100) of Claim 1 or Claim 2, wherein the sensor support (106) comprises an actuator (304, 305) configured to move the linear position sensor (107) in a radial direction to and from the internal surface (105).

4. The apparatus (100) of Claim 3, wherein the actuator (304, 305) comprises a servo motor (305) and a cam (304).

5. The apparatus (100) of Claim 3 or Claim 4, wherein the sensor support (106) comprises a resilient compressible element (306) between the actuator (304, 305) and the linear position sensor (107).

6. The apparatus (100) of any one of Claims 3 to 5, wherein the sensor support (106) comprises a linear displacement sensor (307) arranged to provide a signal (308) indicating displacement of the linear position sensor (107) to the controller unit (301).

7. The apparatus (100) of Claim 6, wherein the controller unit (301) is configured to trigger acquisition of a position measurement from the linear position sensor (107) when the signal (308) from the linear displacement sensor (307) indicates the linear position sensor (107) has stopped moving.

8. The apparatus (100) of any preceding claim, wherein the controller unit (301) is configured to control operation of motors (314) configured to rotate the sensor support (106) relative to the carrier frame (102) and displacement of the carrier frame (102) relative to the cylinder (101).

9. The apparatus (100) of any preceding claim, wherein two or more of the extendable arms (103b, 103c) are located at positions offset relative to each other along the axis of the cylinder (101).

10. The apparatus (100) of any preceding claim, wherein each extendable arm (103a-d) has a wheel assembly (111) at the radially outward end to contact the internal surface (105).

11. The apparatus (100) of any preceding claim, wherein the wheel assembly (111) allows for movement of the extendable arm (103a-d) relative to the internal surface (105) in a direction parallel with the rotation axis (201) and in a direction around the axis (201).

12. A method of acquiring measurements of an internal surface (105) of a hollow cylinder (101) using the apparatus according to any preceding claim, the method comprising the steps of:

i) locating the apparatus (100) within the hollow cylinder (101) such that the radially outward ends of each of the plurality of extendable arms of the carrier frame contact the internal surface;

iii) taking a position measurement using the linear position sensor;

iv) retracting the linear position sensor from the internal surface;

5 vi) repeating steps iii) to v) until a plurality of position measurements have been taken around the internal surface;

vii) moving the carrier frame in a direction parallel with the rotation axis; and viii) repeating steps iii) to vii) until a plurality of position measurements have been taken around the internal surface and along the axis of the hollow bore of the

10 cylinder.

13. A computer program comprising instructions to cause a computer to perform the method according to Claim 12.