GB2263777A - Apparatus for remote eddy current and ultrasonic inspection of turbine generator rotor retaining rings - Google Patents

Abstract

The apparatus for inspecting large cylinders such as generator retaining rings, has sensors for simultaneously detecting flaws in inner and outer surfaces of the cylinder and in the body of the cylinder. The sensors are mounted on a scanner 22 which moves around the circumference of the cylinder and on which the sensors can move axially of the cylinder. The sensor outputs and sensor location signals are transmitted to a remote location 13, 16 and the apparatus is remotely controlled by computer 19. The sensors are eddy current and ultrasonic. The scanner has drive sprockets which engage chains placed round the cylinder and carries a platform which moves axially and on which the sensors are mounted. Position encoders act to accurately locate the sensors on the retaining ring. The retaining ring can be inspected while the rotor remains in place in the generator stator, or with the rotor removed. <IMAGE>

Description

APPARATUS FOR REMOTE EDDY CURRENT AND ULTRASONIC INSPECTION OF TURBINE GENERATOR RETAINING RINGS The invention relates to a system for the inspection of large cylindrical bodies, and more particularly to a combined eddy current and ultrasonic inspection system and method for turbine generator retaining rings.

Generator shaft retaining rings, which are mounted on the end of a generator shaft to retain rotor windings in place, need to be periodically inspected to identify any flaws which may have developed therein.

Generally, this requires that the utility owner remove the rotor from the generator stator in order to gain access to the retaining rings. Many times the rings are found to be acceptable for continued service and the rotor is reinstalled in the stator without the need for retaining ring change-out. Other times, cracks may have developed in the ring surface which contacts the rotor windings, and these cracks frequently start at locations on the inside diameter of the ring.

In order to prevent failure of the retaining rings from crack propagation, many utilities perform periodic inspections. Since removal of the ring is not always practical, an ultrasonic examination is typically performed, in which a high frequency ultrasonic signal is directed radially from the ring outer circumference toward the ring inner circumference. By monitoring the ultrasonic travel time, together with knowledge of the dimensional characteristics of the retaining ring, small cracks which have developed in can be detected. However, these prior methods generally require that the rotor be removed form the generator in order to perform these inspections.

This involves a time-consuming, detailed procedure in order to prevent any damage to the rotor or stator during removal. It is therefore desirable to have a system which is capable of doing the inspection without the need to remove the rotor.

It is a primary object of the present invention to provide a system for the inspection of large cylinders, without requiring removal of the cylinder form its regular location.

It is another object of the present invention to inspect generator retaining rings by simultaneously delivering eddy current and ultrasonic test sensors to the retaining ring from a remote location.

The above and other objects are attained by the present invention, according to which, briefly stated7 a system for inspecting generator rotor retaining rings having an outer diameter surface and an inner diameter surface, the inspection system characterized by: sensor means for simultaneously detecting flaws in the outer diameter surface, the inner diameter surfaces and in the body of the cylindrical object; scanner means for delivering said sensor means to the cylindrical object, wherein said scanner means is positionable about the circumference of the cylindrical object and axially along its length; position detecting means for determining the location of said scanner means on the cylindrical object; and means for controlling the operation of the inspection system from a remote location.

Various other objects, features, and advantages of the invention will become more apparent by reading the following detailed description in conjunction with the drawings, which are shown by way of example only, wherein: Fig. 1 is an overall schematic representation of the retaining ring inspection system of the present invention; Fig. 2 is an isometric view of the retaining ring scanner assembly of the present invention; Fig. 3 is a detailed view of the inner carriage assembly shown in Fig. 2; Fig. 4 is a detailed view of the eddy current ultrasonic transducer holder assembly shown in Fig. 2; Fig. 5 shows a detailed view of the ultrasonic transducer block assembly of the present invention; Fig. 6 shows a detailed view of the eddy-current block assembly of the present invention; Fig. 7 is a block diagram of the motion control mechanism for the present invention; and Fig. 8 is a schematic representation of the data acquisition and control of the inspection system transducers for the present invention.

Referring now to the drawings in detail, the retaining ring inspection system 10 of the present invention is shown in Figures 1 and 2. The inspection system 10 is comprised of ultrasonic instrumentation units 13 and eddy-current instrumentation units 16 operated via a computer control station 19. These apparatus operate from a remote location, the retaining ring scanner assembly 22 which is operably associated with a retaining ring 25 on a generator rotor 28. The rotor can be either installed in or removed from an electric generator (not shown). The retaining ring scanner comprises a first or circumferential carriage 31 and a second or linear carriage 34. The circumferential carriage 31 is rotated about the rotor 28 by means of a sprocket and chain drive system 37.The linear carriage is mounted to the circumferential carriage by means of two "U" channel side rails 40, and linearly moveable with respect thereto. The drive systems for these carriages will be discussed in more detail hereinafter.

The retaining ring scanner 22 drives around the full circumference of the retaining ring 25, by way of the circumferential drive system 37. Circumferential drive chains 43 are positioned around the rotor 28 in the area of the retaining ring 25. The chains 43 pass over the scanner via grooves in arch brackets 46. This permits the linear carriage 34 to travel unobstructed from end to end on the retaining ring, which allows the entire retaining ring 25 to be examined with one installation of the scanner. Drive sprockets 49 engage the chains 43 and are driven by circumferential drive motor 52. A circumferential position feedback transducer 55 provides information to the control station 19, as will be described more fully hereinafter.A hand-held belt spacer tool (not shown) is used when the scanner 22 is installed on the retaining ring 25 to set the chains at the proper axial location along the rotor. Axial alignment is provided t front 58 and back 61 nylon guide wheels. These guide wheels maintain the scanner at a fixed axial position with respect to a zero point bn the retaining ring. This point is commonly referred to as the retaining ring nose. The front guide wheels 58 are located on swing arms 64 due to the small radial assembly clearances. These swing down and lock onto the nose of the retaining ring-aftewLthe~ ~ scanner is placed at the proper axial location. The rear guide wheels 61 are then positioned and tightened. This scanner is similar to one described in U.S. Patent 4,970,890, entitled "Electric Generator Inspection System", which patent is assigned to the present assignee and is hereby incorporated by reference herein.

The linear carriage 34, shown in more detail in Figure 3, rides on eight pre--loaded ball bearings 67 which roll in the left and right "U" channel side rails 40 of the circumferential carriage 31. Cantilever springs 70 are bolted to the linear carriage 34 and they are preloaded against the bearings to eliminate radial play.

Pre-loading provides a very stable, vibration free scan at all speeds of carriage travel. Linear carriage 34 is driven back and forth along the retaining ring centerline by means of a DC drive motor 73, sprockets 76, and cablereinforced drive chain 79. Chain clamp 82 attaches the carriage 34 to the chain 79. A linear feedback transducer 85 is also provided.

Figure 4 shows the sensor holder assembly 88 utilized to mount the eddy current and ultrasonic transducers to the linear carriage 34. The ultrasonic (UT) 91 and eddy current (.E/C) 94 transducers are to be lightly spring loaded against the retaining ring 25 which allows them to float over any retaining ring irregularities such as paint bubbles and ring contour transitions. Transducer bracket gimballing and spring loading are accomplished in certain ways due to the limited space available for a rotor in place non-destructive examination (NDE) exam.

For certain retaining ring designs, the radial clearance is only 3.81 cm (1.5 in.) measured from the air-gap baffle ring (not shown) to the retaining ring nose outer diameter. Due to the limited space available, the gimballing mechanism must be constructed to the lowest possible radial height, which requires that the mechanism be spread out circumferentially and axially. One important feature of the apparatus of the present invention for performing semi-automatic eddy current and ultrasonic scanning relates to the self-alignig features of the transducer gimbals and spring loaded probe holders.

Figure 5 shows a typical UT wedge block 97. The wedge is manually positioned and clamped into an inner bracket clamp 100 by tightening finger nut 103 of UT clamp 106. Inner bracket clamp 100 is free to slightly rotate about the roll pivot line with respect to the UT clamp bracket 109. Also, the UT clamp bracket seats against the x-y compliance pin 112 which is the only contact point with the transducer "U" bracket 115. These two orthogonal gimbal points allow the couplant hydrodynamic pressure to align the ultrasonic transducer wedge block 97 tangent to the contact line on the retaining ring 25. This transducer "U" bracket 115 is part of the removable sensor holder 88 of the linear carriage 34.It should be noted that the UT clamp bracket 109 can be easily removed from the apparatus by simply lifting the transducer "U" bracket 115 to remove the sensor holder 88 from the linear carriage. The x-y compliance pin 112 is fixed to the UT clamp bracket 109. This feature permits a rapid changeout of ultrasonic blocks which is necessary for the many different scans required for the complete NDE of the retaining ring. Also the ultrasonic transducer wedge, which is preferably made of plexiglass, should always remain in direct contact with the retaining ring surface to promote optimum ultrasonic coupling thereto. Optimum coupling is accomplished by the design of the ultrasonic transducer wedge block 97. The support gimbal design is also important in maintaining the transducer wedge tangent to the retaining ring contact line.

Preferably, a nonhygroscopic ultrasonic couplant, such as Pyrogel, is pumped directly into the block 97 at each of the tapped holes 118, which connect with two 0.15 cm (0.06 in.) wide dispersal grooves 121. A nonhygroscopic couplant is preferred since any stress corrosion cracking which may be present in the retaining rings is catalyzed by the presence of moisture. Couplant is forced from these grooves 121 in all directions including the area beneath the ultrasonic transducer 91.

Tests have shown that this configuration of UT weiRge yields excellent sound coupling irrespective of the direction of motion on the retaining ring surface.

The eddy current probe holder block 124 is also spring loaded against the retaining ring 25 by means of four translation shafts 127 which bolt to the transducer "U" bracket 115 and by four compression springs 130 shown in Figure 6. The contact surface of the eddy current block 124 is machined to match the curvature of the retaining ring. To prevent retaining ring scratches the block is made from a non-marring material, preferably oil impregnated nylon. The transducer "U" bracket 115 is free to pivot about the left 133 and right 136 yaw pivots with respect to the removable "U" bracket 116 shown in Figure 3. In addition eddy current probe lift must be minimized.

The yaw pivot line is located near the retaining ring contact surface for maximum stability which allows the eddy current block 124 to pivot and thereby closely follow the various retaining ring contours, such as the nose area. The eddy current block 124 and inner bracket clamp 100 pivot and track independently which is essential for parallel eddy current and ultrasonic scans. Tests have shown that the Pyrogel ultrasonic couplant has no effect on eddy current lift-off and that the eddy current block 124 has no effect on the coupling action of the Pyrogel.

Parallel scanning saves a lot of time. Two independent eddy current probes are used to yield a 0.508 cm (0.2 in.) wide scan width, and additional eddy current probes could be added to increase the scan width to any desired value.

The removable "U" bracket 116 snaps into grooves (not shown) which are machined into a pivot arm assembly 139. This arm is free to pivot plus or minus fifteen degrees (+/- 15") with respect to the linear carriage 34.

The pivot arm 139 is spring loaded against the retaining ring by means of two tension springs 142 shown in Figure 3. Cables 145 connect to each spring and pass over tension pulleys 148 and connect to tension anchor points 148 which are integral to the linear carriage 34.

Pretension in the springs 142 is set by adjusting cable length, which, in turn, governs the ultrasonic and eddy current transducer force exerted on the retaining ring surface.

Retaining rings 25 occasionally have paint blisters and other surface irregularities that must be removed to facilitate optimal ultrasonic signal coupling and minimal sensor lift-off. To accomplish this, it is sometimes necessary to sand the retaining ring outer diameter with the air-powered sander 151 shown in Figure 2. The sander is attached to the linear carriage 34 by replacing the transducer "U" bracket 115 with a special bracket that holds the air sander 151. A simple vacuum hose is attached to the sander hood to collect debris. To visually inspect the surface after cleaning, a fiber optic video probe (not shown) such as the 6mm version manufactured by Welch Allyn has proven very effective.

Figure 7 shows the block diagram of the motion control section of the retaining ring inspection system 10. There are two axes of motion for the system that are mounted on the scanner; the circumferential drive motor 52 moves the retaining ring scanner 22 circumferentially around the retaining ring 25 and the linear carriage drive motor 73 moves the linear carriage 34 axially over the ring. The circumferential drive motor 52 also has an electric brake 154 attached to it which has two functions; one is to keep the motor from drifting when there is no power on the motor, and the other is to stop the motor from moving in an emergency situation.

Both axes have positional transducers (155,185) that are mounted on the retaining ring scanner 22 to give position information to a motion control module 157 of the computer control station 19. The circumferential ~position feedback transducer 55 is referenced to the belts that are used to hold the retaining ring scanner 22 on the retaining ring 25, and the linear drive position feedback transducer 85 is referenced to the belt drive that moves the linear carriage 34. Each transducer produces two pulse trains that are electrically 90 degrees out of phase from each other and whose frequency is proportional to velocity. The phase of the pulse train tells the motion control module 157 which direction the different axes are travelling, and the number of pulses along with the pulse frequency convey position, velocity, and acceleration information.

The linear carriage also has a front limit switch 160 and a rear limit switch 163 associated with it.

These limit switches send a signal to the motor interface module 166 to stop the linear carriage drive motor 73 from moving the linear carriage 34 too far and thus preventing any damage to the drive system. A circumferential drive motor voltage sensor 169 senses the voltage and a circumferential drive motor current sensor 172 measures the current associated with the circumferential drive motor 52. A linear drive voltage sensor 175 senses the voltage and a linear drive current sensor 178 measures the current associated with the linear carriage drive motor 73.

There are two modes for controlling the motion of each axis. One is control via the motion control module 157; this is a microprocessor based module that uses transducer information to control the motors and sends the proper control signals to the motor interface module 166. The other is a manual mode that provides control through the use of a remote hand held motion control unit 181. The auto/manual switch 184 indicates to the motor interface module 166 which mode has active control of the motors. The active control signals are sent to the circumferential drive motor amplifier 187 and the linear drive motor amplifier 190, which applies electrical power to move the motors.

Figure 8 shows a block diagram for the data acquisition and control of the system transducers. The ultrasonic transducer(s) 91 and the eddy current transducer(s) 94 are located in the linear carriage 34.

Couplant also flows through an outlet in the ultrasonic transducer mounting block 97 which is connected to the ultrasonic transducer(s) 91, and provides for proper transfer of sound energy into the retaining ring 25 being inspected. The couplant flow is regulated by a couplant delivery system 193 and it can be turned on or off by either the couplant on/off switch 196 or by the computer 19 via the digital I/O module 199.

The ultrasonic transducer(s) 91 sends its signal through a low noise coaxial cable 202 to the ultrasonic instrumentation 13 which has three types of output. Two analog outputs are provided, one of which is a representation of the reflected ultrasonic waveform, and the other is the peak amplitude of the reflected ultrasonic waveform within a time window. This signal is sampled by the analog-to-digital module 205. The other type of output is through a digital data bus 208 that enables the digital I/O module 199 to communicate with the ultrasonic instrumentation 13.

The eddy current transducers 94 in the linear carriage 34 are used to sense irregularities in the retaining ring 25 O.D. surface. Their signals are provided to the eddy current instrumentation 16. The eddy current instrumentation 16 has two analog outputs, an Xposition 211 and a Y-position 214 output for each transducer 94; these signals are read by the analog-to-digital module 205. The combination of the X- and Y- position output signals are used to characterize surface irregularities.

The analog clinometer 217 is used as an absolute positioning mechanism for the retaining ring scanner 22 in the circumferential direction. The analog output from this device corresponds to the position of the retaining ring scanner 22 relative to the twelve o'clock position.

The clinometer 217 uses the gravitational field as a reference to produce this output. The absolute position is needed because the circumferential position feedback transducer 55 gives a relative position only. The displacement transducer 220 is used to correctly identify the position of the linear carriage 34 relative to the front of the retaining ring scanner 22.

Operation of the apparatus and electronic system described above can be implemented by any suitable computer software. A functional description of computer software particularly useful with the preferred embodiment is provided below, from which suitable computer programs can be readily generated by one skilled in the art. The system 10 can be operated generally in ten modes: Initialization Mode, Home Mode, Time-of-Flight Table Mode, Calibration mode, Jog Mode, Auto Mode, Scan Mode, Post Processing Mode, Diagnostics Mode, and Utilities Mode.

The program includes a top level mode, main, from which the operator can choose one of the ten system modes for the active mode. After system start-up, the computer 19 displays a main menu offering the operator selection of one of the ten system operating modes.

Upon entry into the Initialization Mode, the computer 19 presents a data entry form on CRT 223. The operator is given the opportunity to enter the following information via keyboard 226: 1. UTILITY NAME 2. UTILITY SITE LOCATION 3. OPERATOR NAME 4. UTILITY SITE PHONE NUMBER 5. JOB ORDER NUMBER 6. TURBINE-GENERATOR UNIT NUMBER 7. RETAINING RING DRAWING NUMBER 8. RETAINING RING MATERIAL CLASSIFICATION 9. GENERATOR ROTOR END ON WHICH THE INSPECTION IS TO BE PERFORMED 10. ADDITIONAL COMMENTS AND INFORMATION Additionally, the computer 19 reads the drawing file specified by item (7) from magnetic storage media 229 into its random access memory (RAM). The drawing file contains critical dimensions for a generic retaining ring of the type to be inspected.Two of these dimensions, the ring outside diameter and the ring length are of general use and are displayed on CRT 223 for the operator. A third dimension, the ring nose length, is shown on CRT 223 and may be altered from the nominal ring nose length read from the drawing file. The actual ring nose length for a specific generator rotor is measured at the job site, and the entry field for this value may be changed by the operator. If the retaining ring drawing or these dimensions are otherwise unavailable, the device disclosed in U.S. Patent 5,029,476 which issued to Metala et al., and assigned to the assignee hereunder, may be used and the dimensions entered into RAM. The '476 patent is hereby incorporated by reference herein.

As part of the Initialization Mode, the operator has the ability to indirectly enter the shear sound wave (transverse wave front) velocity for the retaining ring 22 to be inspected. This is accomplished by using commercially available ultrasonic pulse-echo instrumentation, along with an ultrasonic transducer 91 that produces a zero degree shear wave front normal to the inspection surface. The echo filter section of the instrumentation 13 is set to match the resonant frequency of the ultrasonic transducer, which is the same as the nominal resonant frequency of the ultrasonic transducer(s) used for the retaining ring inspection. The operator positions the ultrasonic transducer in contact with a portion of the retaining ring to be inspected that is parallel to the axis of the generator rotor 28, and at an axial location with a known retaining ring radial thickness.The operator subsequently records the time required for the ultrasonic sound wave to traverse the radial thickness of the retaining ring, reflect from the retaining ring inside diameter surface and return to the ultrasonic instrumentation 13. This value, t, is entered into the Initialization Mode data entry form. The computer 19 calculates the measured shear wave velocity using the following relationship: Vs = 2X/t x 106 WHERE Vs = Shear wave sound velocity in the retaining ring (centimeters/second) X = Ring thickness taken from the drawing (inches) t = Time in microseconds for the shear sound wave to travel to the retaining ring inside diameter and return to the ultrasonic instrumentation 13.

The computer 19 displays the calculated sound wave velocity on CRT 223 and stores this value in RAM for later use. If the operator exits the Initialization Mode, the computer 19 stores information from the data entry form into RAM and onto magnetic storage media 229.

Upon entry into the Home Mode, the computer 19 displays an operator interface form on CRT 223. The home mode is for defining the zero position for both the circumferential axis and the axial axis of the retaining ring scanner 22. The operator can home the axial axis by moving the linear carriage 34 to the home position on the nose end of the retaining ring 25. Motion is accomplished using the hand held motion control unit 181, and continues until the front limit switch 160 is met and motion is stopped. Due to positional errors in determining exactly where the linear carriage stops when the front limit switch 160 is met, a displacement transducer 220 detects more accurately where the linear carriage 34 is with respect to the front of the retaining ring scanner 22.

The operator signals the computer 19 via keyboard 226 that the linear carriage has reached the home position.

To home the circumferential axis the operator moves the retaining ring scanner 22 to the twelve o'clock position. The output of the analog clinometer 217 is sampled by the analog-to-digital module 205 and transferred to computer 19 for display on CRT 223 to indicate the twelve o'clock position for the operator. At this point the operator signals the computer 19 via keyboard 226 that the retaining ring scanner 22 has reached the circumferential home position.

The next step is to produce a calibration factor for the circumferential position feedback transducer 55.

This has to done for each retaining ring 25 primarily due to variations in ring diameters and chain lengths. From the zero position, the operator moves the retaining ring scanner 22 three hundred sixty degrees (360") around the retaining ring until it reaches the same point it started from. At this point the operator signals the computer 19 via keyboard 226 that the retaining ring scanner 22 has gone 360". The computer 19 will calculate the proper calibration factor for the circumferential position feedback transducer 55 based upon the difference between home position feedback and 360" position feedback.

The Time-of-Flight Table Mode is used to create a table of retaining ring inspection parameters from the retaining ring drawing dimensions and sound velocity measurement recorded in the Initialization Mode. The computer 19 determines the inspection parameters that are optimal for the ring to be inspected. The inspection parameters include transducer positions, transducer wedge angles, and precise ultrasonic wave travel times necessary to examine any location on the retaining ring I.D.

surfaces. The table of inspection parameters is stored by the computer 19 in RAM for optional use in the Scan Mode.

The operator is given the option of producingJ aoprintout~ of the table on hard copy output device 232.

Upon entering the Scan Mode, the computer 19 displays a Scan Initialization Submenu on CRT 223. The operator can select a desired area of the retaining ring to inspect from this submenu. Based on the operators selection from the Scan Initialization Submenu, the computer 19 displays a Scan Initialization data entry form on CRT 223 appropriate for the exam to be performed.

Optimal scan parameters for the selected exam produced in the Time-of-Flight Table Mode are extracted from RAM. The computer 19 displays these parameters on CRT 223. The operator has the option to edit these parameters. The operator may also supplement the base ultrasonic examination, which entails inspection of the retaining ring I.D.

surfaces, with an eddy-current examination, which entails inspection of the retaining ring O.D. surfaces, or other examinations using additional sensors 235. Upon completion of the Scan Initialization data entry form, the operator may signal the computer 19 via keyboard 226 to begin an automated examination. If the computer 19 receives the signal to begin an automated examination, the following scan setup and motion sequence will be performed: 1. The computer 19 transmits ultrasonic instrumentation setup information for the examination to be performed to the ultrasonic instrumentation 13, unless the operator has disabled this option in the Scan Initialization Submode.

2. The computer 19 transmits scan data acquisition setup information to the analog-todigital module 205 for the examination to be performed based upon RAM data produced in the Scan Initialization Submode.

3. Appropriate motion control parameters to position the retaining ring scanner 22 for the examination to be performed are extracted from RAM data produced in the Scan Initialization Submode by computer 19. This data is transmitted to the motion control module 157.

4. The computer 19 signals the motion control module 157 to begin a specific motion sequence for the examination to be performed.

5. The ultrasonic instrumentation 13 provides an analog representation df the return sound echo(s) from the ultrasonic transducer(s) 91 to the analogto-digital module 205.

6. The eddy-current instrumentation 16 provides an analog representation of the response from the eddy-current transducers 94 to the analogto-digital module 205.

7. The computer 19 communicates periodically with the motion control module 157 to determine when the retaining ring scanner 22 has reached the next position in the motion sequence appropriate to signal the analog-to-digital module 205 to sample one or more of the signals presented to the analog-todigital module 205 in steps (5) and (6). The next position in the motion sequence appropriate to signal the analog-to-digital module 205 is determined from the retaining ring O.D. stored in RAM during the Initialization Mode and an experimentally developed criteria for adequate ring coverage for the present examination.

8. The computer signals the analog-to-digital module 205 to sample and digitize the appropriate analog signals provided in steps (5) and (6).

9. Depending on the examination being performed, the analog-to-digital module 205 may transfer digitized data produced in step (8) to RAM for use by the computer 19.

10. The computer 19 acquires digitized data produced in step (8) in one of the two ways, depending on the examination being performed: a) Data is transmitted from the analog-to digital module 205 to the computer 19 via a common data bus shared by the computer 19 and the analog-to-digital module 205.

b) Data is transmitted from the analog-to digital module 205 to RAM. The computer 19 extracts the data from RAM for its use.

11. The computer 19 displays the status of the present examination on CRT 223. The default display option consists of a segregated display of near realtime representation(s) of the data extracted in steps (7) and (10). Additionally, the computer 19 displays operator input options on CRT 223.

12. The computer .19 communicates periodically with the motion control module 157 to determine when the retaining ring scanner 22 has reached the next position in the motion sequence appropriate to transfer data acquired in step (10) to magnetic media 229 for permanent storage.

13. The computer 19 periodically checks the digital I/O module 199 for various system shutdown inputs.

14. Steps (1) through (13) may or may not be repeated depending on the examination being performed. The scan sequence continues until one of the following occurs: a) The computer 19 receives a shutdown signal during step (13), at which time the operator is given control of the system.

b) The computer 19 satisfies scan duration requirements specified in the Scan Initializa tion Submode, at which time the operator is given control of the system.

c) The computer 19 receives an operator input via keyboard 226 to suspend the scanning sequence. The operator can suspend the present scan sequence temporarily, at which time manual motion control of the retaining ring scanner 22 via the hand held motion control unit 181 is possible. Additionally, the computer 19 reads the present position of the retaining ring scanner 22 from the motion control module 157 and stores this data in RAM. The computer 19 monitors position of the retaining ring scanner 22 from the motion control module 157 and displays this information on CRT 223.The operator may signal the computer 19 via the keyboard 226 to resume the present examination, at which time the computer 19 disables the hand held motion control unit 181 and transmits appropriate motion control parameters to the motion control module 157 to resume the examina tion in progress, including the last position of the retaining ring scanner 22 stored in RAM.

The operator may also abort the present examina tion, at which time the computer 19 returns control to the operator and displays the Scan Initialization Submenu. At this point, the operator may select a new examination or return to the main menu via keyboard 226.

Upon entering the Calibration Mode, the computer 19 displays a Calibration Submenu on CRT 223. The computer 19 reads the operator's selection from the Calibration Submenu via keyboard 226. The Calibration Submenu provides the operator with various calibration options; in two of the options the computer 19 displays a data entry form on CRT 223 for operator entry of various instrumentation settings for the ultrasonic instrumentation 13 and eddy-current instrumentation 16. A third option allows the operator to calibrate the eddy current transducers 94. To do this, the "U" bracket 116 is removed from the retaining ring scanner 22 and attached to the "U" bracket calibration adapter 238. To perform the calibration test, the "U" bracket calibration adapter 238 is moved over the calibration reflectors 241 on the eddy current calibration standard 244.During this motion, the calibration adapter position transducer 247 gives positional information to the motion control module 157, and the analog-to-digital module 205 reads the X- and Yposition output 211,314 produced by the eddy current instrumentation 16 at the same sample rate to bemused during the actual scan of the retaining ring 25.

The eddy current calibration standard 244 contains artificial and/or natural reflectors 241 with known dimensions, and is made of the same type of material as the retaining ring 25. The data from the calibration scan is stored by computer 19 on magnetic storage media 229. This data will be compared later with data collected on the retaining ring 25.

Upon entry of the Auto Mode, the computer 19 displays various operator options and status items on CRT 223. Status items include the current position of both axes. The Auto mode allows for movement of the retaining ring scanner 22 to a specified axial and/or circumferential position on the retaining ring 25. ThevXperator- may enter a desired position and speed of travel for each axis via keyboard 226, and signal the computer 19 to begin motion of the retaining ring scanner 22.

Upon entry of the Jog Mode, the computer 19 displays various operator options and status items on CRT 223. Status items include the current position of both axes. The Jog mode enables the operator to jog the retaining ring scanner 22 manually through the use of the hand held motion control unit 181. The speed of motion for both the circumferential and axial drives can be varied by using the arrow keys on keyboard 226. The front limit switch 160 and the rear limit switch 163 will stop the linear carriage 34 from going too far in the axial direction. When one of the limit switches are met, the computer 19 displays a status signal on CRT display 223.

When the emergency stop push-button 250 is pressed on the hand held motion control unit 181, the computer 19 disables motion on both axes, and activates the circumferential drive motor electric brake 154. The computer 19 displays a status signal for the emergency stop condition on CRT display 223.

Upon entering the Post Processing Mode, the computer 19 displays a Post Processing Submenu for the operator on CRT 223. Upon operator selection of the Combine Segment Files Submode from the Post Processing Submenu via keyboard 226, the computer 19 displays a data entry form on CRT 223 for setup and combination of segmented scan data files. Segmented scan data files are data files that contain a circumferential quadrant of retaining ring inspection data less than 360 degrees. The Combine Segment Files Submode is a facility for combining quadrant data to form a full 360 degree scan file for a particular examination. Segmented scan data files are created during the Scan Mode whenever a segmented scan is specified by the operator in the Scan Initialization Submode. A segmented scan must be specified for in-place inspection of generator retaining rings in cases where a full 360 degree scan of the retaining ring is not possible, or in other cases of limited ring access. The operator is given the opportunity to enter the following information via keyboard 226: 1. QUADRANT SCAN ROTATION STARTING DIRECTION.

2. PERIOD IN DEGREES PER SAMPLE AT WHICH ANALOG SCAN DATA WAS SAMPLED.

3. FILENAMES FOR THE QUADRANT FILES TO COMBINE.

4. QUADRANT SIZE IN DEGREES FOR EACH FILENAME ENTERED IN (3).

The operator may signal the computer 19 via keyboard 226 to display on CRT 223 a filename directory of appropriate files stored on magnetic media 229. The computer 19 calculates the circumferential scan length of each file specified in step (3) using the following relationship: s=qxP WHERE s = Circumferential scan length of the file in samples.

q = Quadrant size in degrees for the file entered in (3).

P = Sample period in degrees per sample entered in (2).

The computer 19 displays the circumferential scan length for each filename on CRT 223 following operator entry of items (3) and (4). The operator may signal the computer 19 via keyboard 226 to commence combination of the segmented scan data files. Upon receipt of this signal, the computer 19 validates the data files entered in step (3), and, if successful, assembles scan lines of lengthnL- from each filename entered in step (3) in the proper sequence to produce a scan file whose scan length is equal to the sum of s values calculated for each segmented scan data file. The computer 19 stores the combined scan file on magnetic media 229.

Upon operator selection of the Combined Exams Submode from the Post Processing Submenu via keyboard 226, the computer 19 displays a data entry form on CRT 223 for setup and combination of 360 degree scan files stored on magnetic media 229. Three hundred sixty degree scan files from various examinations may be combined to produce an output file whose data represents the entire retaining ring I.D. or O.D. surface. The operator is given the opportunity to enter the following information via keyboard 226: 1. OUTPUT FILE TYPE 2. CIRCUMFERENTIAL ZERO REFERENCE OFFSET 3. AXIAL ZERO REFERENCE OFFSET 4. PERIOD IN DEGREES AT WHICH SCAN DATA WAS SAMPLED 5. FILES TO BE COMBINED 6. REFRACTED SOUND BEAM ANGLE USED DURING THE RETAINING RING INSPECTION, IF APPLICABLE FOR THE OUTPUT FILE TYPE SPECIFIED IN STEP (1).

The computer 19 computes the scan length of the 360 degree scan files using the relationship given in the Combine Segment Files Submode description and displays this value on CRT 223 for the operator following step (4). Additionally, the computer 19 calculates the number of scans present in each file entered in step (5) by determining the number of data samples in each file and dividing this number by the calculated scan length. The computer 19 subsequently displays on CRT 223 the number of scans per file following the entry of each filename in step (5).

The operator may signal the computer 19 via keyboard 226 to display a directory of appropriate filenames for step (3) contained on magnetic storage media 229. The operator may signal the computer 19 via keyboard 226 to commence combination of files specified in step (5) to produce an output file of the type specified in step (1). Upon receipt of this signal, the computer 19 will validate the filenames entered and combine scan lines in the proper sequence from each of the valid files into one file. The computer 19 will additionally adjust scan data as appropriate for the following: a) Missing scan files required to produce a complete output file of the type specified in step (1).

b) Scan file data alignment to reference zero positions on the retaining ring inspected based upon the offsets entered in steps (2) and (3), the refracted sound beam angle entered in step (6) (if applicable), and mechanical offset constants of transducers 91 and/or 94 (if applicable) in retaining ring scanner 22.

Upon operator selection of the Plot Submode from the Post Processing Submenu via keyboard 226, the computer 19 displays a data entry form on CRT 223 for setup and plotting of combined exam files produced in the Combined Exams Submode. The computer 19 retrieves applicable text data from RAM entered in the Initialization Mode and displays this information on CRT 223. The operator may enter a filename representing a combined exam file to plot via keyboard 226. The operator may edit text data and other plot parameters via keyboard 226. Upon receipt of the appropriate signal from the keyboard 226, the computer 19 reads the data file to be plotted from magnetic storage media 229 and displays a color representation of the data on CRT 223.The computer 19 compresses the data read from the file as necessary to plot the data within an acceptable boundary, preferably in an 8-1/2 x 11 inch format. Compression of the data is accom > plotting the highest data sample amplitude for every x data samples, where x is a scale factor based upon the data file size. Additionally, the computer 19 displays appropriate scales for the axial, circumferential, and amplitude information contained in the data file. The computer 19 also displays appropriate text information for the particular data set. Upon receipt of the appropriate signal from keyboard 226, the computer 19 transmits a representation of the image displayed on CRT 223 to hard copy output device 232.

Upon entering the Diagnostics Mode, the computer 19 displays a Diagnostics Submenu on CRT 223. From this menu, the operator may select various options, which upon selection will cause the computer 19 to execute system diagnostic tests and displays the results of the tests on CRT 223.

Upon entering the Utilities Mode, the computer 19 displays a Utilities Submenu on CRT 223. From this menu, the operator may select various options related to file manipulation, magnetic media formatting, setting time and date for computer 19, and other utility functions common to computer operating system software.

IDENTIFICATION OF REFERENCE NUMERALS USED IN THE DRAWINGS LEGEND REF. NO. FIGURE ULTRASONIC INSTRUMENTATION 13 8 EDDY-CURRENT INSTRUMENTATION 16 8 MOTION CONTROLLER MODULE 157 7 MOTOR INTERFACE MODULE 166 7 MOTOR AMPLIFIER 187 7 MOTOR AMPLIFIER 190 7 COUPLANT DELIVERY SYSTEM 193 8 DIGITAL I/O MODULE 199 8 ANALOG TO DIGITAL MODULE 205 8

Claims (10)

CLAIMS:

1. A system for inspecting generator rotor retaining rings having an outer diameter surface and an inner diameter surface, the inspection system characterized by: sensor means for simultaneously detecting flaws in the outer diameter surface, the inner diameter surfaces and in the body of the cylindrical object; scanner means for delivering said sensor means to the cylindrical object, wherein said scanner means is positionable about the circumference of the cylindrical object and axially along its length; position detecting means for determining the location of said scanner means on the cylindrical object; and means for controlling the operation of the inspection system from a remote location.

2. The inspection system of claim 1, wherein said sensor means is further characterized by an eddy current probe for detecting flaws in the outer diameter and an ultrasonic transducer for detecting flaws in the inner diameter surface and the body of the cylindrical object.

3. The inspection system of- claim 1 or 2, wherein said scanner means is characterized by a first carriage having a longitudinal axis and means for rotating the first carriage about the circumference of the cylindrical object, and a second carriage attached to the first carriage, the second carriage including means for trans lating the second carriage along the longitudinal axis of the first carriage.

4. The inspection system of claim 3, wherein said means for rotating the first carriage is characterized by a drive chain securable about the circumference of the cylindrical object, a circumferential drive system coupled to the first carriage, the circumferential drive system further comprising a first drive motor secured to the first carriage, the first drive motor having a sprocket operably attached thereto, the sprocket being engaged with the drive chain such that the first carriage is caused to rotate about the circumference of the cylindrical object when the first drive motor is operated.

5. The inspection system of claim 3, wherein the first carriage is characterized by a pair of generally U-shaped channels associated therewith and briented along the longitudinal axis thereof, and said means for translating the second carriage comprises a bracket adapted to slidably engage said U-shaped channels, a linear drive chain generally disposed along the longitudinal axis of the first carriage, a chain clamp having one portion secured to the linear drive chain and another portion secured to the second carriage, and means for driving the linear drive chain along the longitudinal axis of-the first carriage whereby the second carriage is translated along the longitudinal axis of the first carriage.

6. The inspection system of claim 5, wherein the second carriage is characterized by means for mounting said sensor means thereon, said mounting means comprising: a pivot arm assembly connected to the second carriage so as to be pivotable about an axis normal to the longitudinal axis of the first carriage and adapted to cause said sensor means to contact the surface of the cylindrical object; a first bracket removably attachable to the pivot arm assembly; a sensor holder assembly adapted to be secured to the first bracket, t-he sensor holder assembly being pivotable with respect to the first bracket such that said sensor means mounted thereon are held against the cylindrical object.

7. The inspection system of claim 6, wherein said sensor means comprises an eddy current probe for detecting flaws in the outer diameter and an ultrasonic transducer for detecting flaws in the inner diameter surface and the body of the cylindrical object.

8. The inspection system as recited in any of claims 1 to 7, characterized by: a drive chain securable about the circumference of the cylindrical object; a circumferential drive system coupled to the first carriage, the circumferential drive system further comprising a first drive motor secured to the first carriage, the first drive motor having a sprocket operably attached thereto and operably engaged with the drive chain such that the first carriage is caused to rotate about the circumference of the cylindrical object when the first drive motor is operated; a pair of generally U-shaped channels on either side of the first carriage and oriented along the longitudinal axis thereof; the second carriage having a bracket adapted to slidably engage said U-shaped channels; a linear drive chain generally disposed along the longitudinal axis of the first carriage;; a chain clamp having one portion secured to the linear drive chain and another portion secured to the second carriage; a second drive motor for driving the linear drive chain along the longitudinal axis of the first carriage whereby the second carriage is translated along the longitudinal axis of the first carriage; and said position detecting means for determining the location of said scanner means on the cylindrical object comprises a circumferential position feedback transducer operably connected to the circumferential drive system and a linear position feedback transducer operably associated with the linear drive motor, whereby output signals from the circumferential and linear position feedback transducers is supplied to said control means for determining the position of said first and second carriages of said scanner means.

9. The inspection system of claim 8, wherein the sensor holder assembly is characterized by a U-bracket removably attachable to the first bracket, the U-bracket being pivotable with respect to the first bracket on an axis normal to the longitudinal axis of the first carriage, a first mounting block adapted to receive an eddy current probe, the first mounting block being attached to the U-bracket by compression springs, and a second mounting block secured to the U-bracket and being orthogonally pivotable with respect thereto, the second mounting block adapted to receive an ultrasonic transducer.

10. The inspection system of claim 9, further characterized by means for delivering a couplant to the cylindrical object for use with the ultrasonic transducer, wherein the second mounting block includes a first means for receiving the couplant from a couplant supply and a second means for delivering the couplant to the cylindrical object.