FIELD OF THE INVENTION
The present invention relates in general to assessing health of a DC motor, and in particular to a uniquely constructed non-intrusive real-time system for monitoring and assessing the health of a DC motor using high speed acquisition and processing of images of the sparks formed at the commutator brush area of the motor.
BACKGROUND OF THE INVENTION
The steel making process starts with smelting reduction of iron ore where it is simultaneously reduced from oxide to metal and melted. This liquid iron is further subjected to refinement processes in which it is converted to steel which is then cast into different basic shapes like slabs, billets etc. The slabs are the feed stock for flat products like strips and plates.
To obtain flat products, steel slabs is first passed through hot rolling mill and then depending upon need for further treatment, through cold rolling mill. The Hot Rolling Mill, also known as Hot Strip Mill handles a product mix dominated by high value steel qualities such as micro alloyed grade, pipe line grade and dual phase steel. During hot rolling, steel slab is first heated to around 1200 °C. This slab first passes through a rolling process known as roughing, which causes bulk reduction in the slab thickness. Further downstream, the Finishing Mill carries out fine rolling to reduce the work piece to target thickness of around 2-20 mm. The steel coil then passes through the run-out table which cools it to around 500 – 600 °C. The product is then coiled into a compact form, packaged and dispatched for delivery.
Evidently in this entire value chain, the greatest deformation occurs in the Roughing mill, where slab thickness is reduced from 210-250 mm to around 30 mm. this process requires enormous amount of energy. The top and bottom rolls in roughing mill are driven by two DC motors. The motors have a maximum capacity of 7500 horsepower (hp) and require an input voltage of 1000 volts DC. The motors have twenty poles and a commutator diameter of around 2.5 meters.

There are many factors which might cause varying degrees of damage to these motors. Whenever one of more of these factors comes into play, the motor health deteriorates. A prominent indicator of this damage is sparking between the brush and commutator surface. It is first important to understand the concept of motor commutation. In a DC motor, commutation is the process of periodically reversing the current flowing in individual armature coils in order to maintain unidirectional torque as the armature coils move under alternate field poles. The commutator must reverse current through armature coils which left the influence of one field pole and are approaching the influence of an alternate field pole. The motor brush then contacts more than one commutator segment and an armature loop is momentarily shorted. If the short has a difference of potential across its ends, severe sparking can occur between the brush and the commutator. This leads to erosion of commutator surface and reduction of brush life. It is thus necessary to ensure that voltage is not induced in the commutator loop at the time of the momentary short. For this, the electrical neutral of the motor must be set properly. Another reason for sparking might be a shift in Magnetic Neutral Axis (MNA) of the DC motor. The carbon brushes are always placed on the MNA. Misalignment of MNA causes strengthening of flux at the leading pole tips and weakening of flux at trailing pole tips. This might lead to non-uniform rotation which may damage the motor shafts and disturb the rolling cycle. One of the major factor which might distort the neutral setting is overloading of motor, or in other words, increased current loading within short period of time. This can happen for instance due to sudden increase in mill speed. This can also happen in case of erroneous mill schedule, wherein motor was expecting a lower steel grade but instead got harder steel grade. Sparking and erosion can also be caused by other motor set up conditions or mechanical problems such as the brush neutral setting, interpole strength, low brush spring pressure, poor brush seating, high mica, commutator eccentricity etc.
Due to the critical role played by these motors in the entire process, extreme care must be taken to ensure their smooth operation. Any action to the contrary would have enormous costs associated with it which could be understood by the fact that the Hot Strip Mill is responsible for around 4 million tons of annual steel

production in a steel plant as big as Tata Steel. This translates to more than 500 coils of various grades produced daily. Roughing Mill is the critical link in this chain. As an example, a 24 hour downtime would lead to significant losses in the production. On top of this, the non-production causes problems upstream as extra space must be created to store the oncoming slabs. Moreover, the correction effort required in case something goes wrong with the motors is enormous. With a workspace volume of around 125 m3, each motor is huge in size and hence has large replaceable parts. Also, roughing mill is located deep inside the hot strip mill complex. This implies that transporting this large replacement part would involve huge complications and would be time consuming. And since these motors are specialized, these parts would have to be imported and the additional time overhead would lead to increased losses. Lastly, in the worst-case scenario, the replacement cost of the entire motor along with added downtime loss would exceed multiple crores in Indian currency.
Further, the present practice in typical steel plants for upkeep of the Main Mill Motors is primarily preventive. For example, every day the motors are visually observed once in a shift by the shift officer for sparking phenomenon. This visual check and requires reasonably experienced person to carry out task. Next level of maintenance involves a short time shutdown once every month for about 24 hours, wherein overall inspection of motor is done during normal shutdowns to check the health status of the commutator brushes with respect to erosion status, placement etc. Thus, the current maintenance practices may be categorized as preventive maintenance at periodic frequencies. The impediments associated with manual maintenance are due to narrow entrance of the motor, region of observation having poor lighting conditions and the region being extremely loud, temperature inside motor cover exceeding 50 °C, thus making entire process of manual observation of sparks is extremely unsafe. At the same time, it is inaccurate and prone to human bias. And since the observation is taken only once or twice per shift, there is a high chance that leads indicators might be easily missed and corrective action delayed.

In light of the aforesaid shortcomings, there is therefore a need to move towards safer and more accurate practices. There is a dire need to develop a device for predictive maintenance having efficient data-capturing and analyzing capabilities so that the health of the motor can be assessed with numeric certainty, thereby overcoming all of the shortcomings associated with aforesaid discussed conventional practices.
OBJECTS OF THE INVENTION
It is therefore an object of the invention is to overcome the aforementioned and other drawbacks existing in prior art arrangements for motor health assessment.
It is a primary object of the present invention to provide a spark monitoring system for DC motor health assessment using real-time imaging.
Still another object of the present invention is to provide a spark monitoring system which is non-intrusive in its application.
Yet another object of the present invention is to provide a unique motor cover unit strategically designed according to an embodiment of the present invention for allowing placement of an array of machine vision cameras on the sleeve of the motor cover unit.
Further object of the present invention is to provide a unique camera mounting unit for facilitating accurate adjustments in positioning of the cameras according to an embodiment of the present invention.
Still further object of the present invention is to provide a system for facilitating high speed data transfer and processing.
These and other objects and advantages of the present invention will be apparent to those skilled in the art after a consideration of the following detailed

description taken in conjunction with the accompanying drawings in which a preferred form of the present invention is illustrated.
SUMMARY OF THE INVENTION
In an aspect, the present application discloses a system for non-intrusive spark monitoring system for DC motor health assessment using real-time imaging. In an embodiment, the system includes: a cover unit for a DC motor having a top part, a right shoulder, and a left shoulder, said DC motor having a commutator and a plurality of brushes (b3, b4, b5, b6, b14, b15, b16, b17), an optimum number of camera mounting units positioned across the right shoulder and the left shoulder of the cover unit, each of said camera units constructed with a U-shaped channel having a base defined with rectangular slots, a U-shaped plate fixed to side wall of the U-shaped channel, an inverted L-shaped plate defined with a base and a trunk with the base of the inverted L-shaped plate movably attached to the U-shaped plate, a plurality of cameras (c3,c4,c5, c15, c16, c17) with each of the cameras (c3,c4,c5, c15, c16, c17) being mounted on upper side of the trunk of the inverted L-shaped such that point of focus (F1) of the camera is a radial mid-point in between two adjacently defined brushes (b3-b4, b4-b5, b5-b6, b14-b15, b15-b16, b16-b17), a spark monitoring unit which in an embodiment is configured to receive and store captured video frames from the camera, extract image feature data from the captured video frames, and processing the extracted image feature. Further, the system includes a display unit for displaying the processed image features extracted for the each of the camera mounted optimally on the camera mounting unit.
The above and additional advantages of the present invention will become apparent to those skilled in the art from a reading of the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The above brief description, as well as further objects, features and advantages, of the present invention can be fully appreciated by reference to the following detailed description. These features of the present invention will become more apparent upon reference to the drawings, wherein:
Figure 1 (a): is the Front view of original bottom roll DC motor cover assembly.
Figure 1 (b): is the Back view of original bottom roll DC motor cover assembly excluding the top part, showing the interior of motor including commutator and brush.
Figure 2: shows to-scale construction of left and right shoulders of bottom roll DC motor with three modifications.
Figure 3 (a): an exemplary embodiment showing optimum position of six cameras and their rectangular slots corresponding to the DC motor brushes.
Figure 3 (b): shows a rectangular slot at the base of U-shaped channel for facilitating appropriate field of view to camera.
Figure 4: shows a detailed view of a camera monitoring two brushes.
Figure 5: shows a camera mounting which allows axial and radial movement of camera with respect to motor cover unit.
Figure 6: shows the network architecture for carrying camera streams to spark monitoring unit.

DETAILED DESCRIPTION OF THE INVENTION
Although the disclosure hereof is detailed and exact to enable those skilled in the art to practice the invention, the physical embodiments herein disclosed merely exemplify the invention which may be embodied in other specific structure. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims.
It will be apparent, however, to one of ordinary skill in the art that the present invention may be practiced without specific details of the well known components and processes. Further specific numeric references should not be interpreted as a literal sequential order. Thus, the specific details set forth are merely exemplary. The specific details may be varied from and still be contemplated to be within the scope of the present invention. The features discussed in an embodiment may be implemented in another embodiment.
Moreover, occasional references to the conventional systems are made in order to better distinguish the present inventive disclosure discussed later in greater detail. Few of the details pertaining to said system/process/construction are well-known in the art and therefore, are described herein only in the detail required to fully disclose the present invention while unnecessarily obscuring the present invention. The present invention will be described in detail below with reference to embodiments as shown in the drawings.
Construction of Motor Cover Unit
The two Roughing Mill DC motors are each covered by a motor cover unit 1. Figure 1 (a) shows the front view of the original cover assembly for one of the motors. It consists of three parts: top part, the right shoulder and the left shoulder. The right and left shoulders are symmetric. The entire assembly resembles a shape of a pentagon and is made from mild steel sheets of thickness 6 mm and 8 mm. The purpose of this cover assembly is to block any object from reaching inside the motor, as it might lead to short-circuiting and cause catastrophic damage. It also serves to confine noise generated due to motor

operation and provide suitable vent for convective heat transfer with air. On the cover unit 1 are configured the cameras in order to get good visibility of the brush area without hampering normal maintenance activities of the motor. Figure 1 (b) illustrates the interior view of original cover assembly from the back¬side, excluding the top part. It shows the motor commutator and brushes. Upon careful inspection, an L-shaped plate is observed to be connected to the inner side of the cover assembly. This plate surrounds the commutator 2 radially. It would be ideal if cameras could be placed on this L-plate. But since the plate lies inside the motor, there’s a danger of parts falling onto the commutator 2. Alternatively, Figure 1(b) shows a plane “P” passing through the commutator 2, the L-shaped plate and the cover assembly. The intersections are highlighted in sky blue color. The location “L” where plane “P” intersects the cover assembly was found to be the best location for camera placement. This location provided two¬fold advantage of all cameras being radially equidistant from brushes thereby allowing standardization of camera specification. Secondly, the cameras could be placed on the outer side of motor cover, which would ensure that no object from outside would fall inside the motor through the cover.
To create space for camera mounting, a to-scale replica of left and right shoulders of bottom roughing mill motor were fabricated, albeit with certain unique modifications to suit the purpose of the invention. These are shown in Figure 2. In the first modification the L-shaped plate was expanded by “m” mm towards the motor door, i.e. the front of the motor. This was done to make some space for camera fitment. The second modification was that the L-shaped plate was converted into a U-shaped plate and corresponding radial material was removed from the outer part of cover assembly. In effect, this created a U-shaped channel overlooking the commutator assembly radially. This U-shaped channel has the added advantage that it acts as an added enclosure to cameras. The third modification was change in position of mounting hooks of the crane to account for change in center of gravity of new cover assembly. All these modifications are labelled suitably in Figure 2.

One constraint, as stated before, was that the camera should be placed outside the U-shaped channel to minimize risk of falling parts inside the motor. For the same reason, the viewing window of the camera could not be very wide. Hence, one camera could only monitor one brush at the very best. The optimum configuration of a camera “C1” would be such that it’s point of focus “F1” is the exact radial mid-point between two brushes “b1” and “b2”. As illustrated in Figure 3 (a), camera “C3” monitors the leading edge of brush “b3” and lagging edge of brush “b4”. Figure 3 (a) also shows the radial positions of six cameras “C3-C5” & “C15-C17” monitoring brushes “b3 – b6” and “b14-b17” respectively. The above considerations make sure that the number of cameras chosen is such that the number of brushes covered by the cameras is optimum without comprising on the efficiency of the overall system.
Corresponding to radial positions of the cameras, the invention involved cutting out rectangular slots at the base of U-shaped channel to create viewing window for cameras. The size of the rectangular slot was chosen such that the field of view of the camera was unobstructed. The slot was covered by a scratch resistant and optically transparent glass of 4 mm thickness, which was put in place using a heat resistant adhesive. Figure 3 (b) shows a rectangular slot in greater detail.
Lens Specification
Figure 4 shows camera “C1” monitoring brushes “b1” and “b2” in more detail. The field of view “FOV1” of camera “C1” has length “L1” and width “W1”. Further, the corresponding imaging sensor inside the camera has length and width “l” and “w” respectively. Let “D0” be the minimum working distance and “D1” be the actual working distance of camera “C1”. Also, let “D*“be the maximum working distance of camera “C1”. Since, camera cannot go inside the U-shaped channel; “D0” is constrained to be “F1H1”. Also, the camera can’t be placed beyond the outer-most point of U-shaped channel (denoted by “U1”). Hence “D*” is the distance “F1U1”.


Secondly, the width “W1” is the linear center distance between brushes “b1” and “b2”, or in other words, “B1B2” (where B1 and B2 denote centers of brushes b1 and b2 respectively). Wt = B1B2

If “f is the focal length of the lens chosen, then “f is given by:

A camera lens can either be a fixed focal length lens or a variable focal length (or zoom) lens. But in a rough industrial setting and under large vibrations, a zoom lens can lose its point of focus with time. Hence a fixed focal length lens was preferred for this invention. These lenses come with a standard focal length range such as 12mm or 15mm etc. To fix the working distance, D1 is varied from D0 to D* and corresponding value of f is computed to the nearest integer. The value of “D1” for which “f” equals a standard focal length range is the acceptable value of the working distance of camera “C1”. Due to radial symmetry, this distance value is same for all cameras.
The technical specification of camera itself is based on two parameters: the image resolution and frame rate. The smallest feature “µ” which can be detected by the camera should be represented by at least one pixel. Hence the minimum number of pixels (or image resolution in mega pixels) for a field of view of L1xW1 is given by:


Secondly, the sparking phenomenon inside a DC motor could be very short lived in nature, much like lightening during a thunderstorm. If “υ” milliseconds are the minimum duration of a spark that is captured by the camera, then requisite frame rate is given by:

Other considerations that went into camera selection are small form factor, availability of all color channels and a facility of power over Ethernet (PoE), which would allow the ethernet cable to double down as data transfer and power supplying conduit for the camera.
Camera mounting units
For fixed focal length camera, the radial working distance is kept constant. But some arrangement is required to make small adjustments to position of camera in radial and axial direction. The invention provides a novel mounting unit 3 to achieve the aforesaid object. This mounting unit 3 is a combination of a U-shaped plate and an inverted L-shaped plate. Both these plates are made of stainless steel and are of 1 mm thickness. The U-shaped plate is welded fix to the side wall of the U-shaped channel of motor cover. The base of L-shaped plate is connected to U-shaped plate using a nut-bolt arrangement. This allows movement of L-shaped plate with respect to U-shaped plate. The trunk of the inverted L-shaped plate, which lies perpendicular to the base contains an axial channel. The camera is connected to the upper side of the trunk using the nut-bolt arrangement. An Aluminium heat sink is also attached in between the L-shaped plate and the camera. In totality, the camera mounting unit 3 allows movement of camera with respect to L-shaped plate. The combined effect of this mounting is that the camera can be moved in both lateral and radial direction with respect to the fixed U-shaped plate. Further, Figure 5 illustrates the mounting.

Further, in an embodiment, the video data collected from all the cameras are efficiently transferred to spark monitoring unit 4 for processing. In an embodiment, spark monitoring unit 4 may be implemented by one dedicated hardware processors. In an embodiment, the video data is transferred through high bandwidth ethernet communication. Further, the acquisition rate for a single camera is calculated using the formula below:
Acquisition Rate = Resolution X 106 X Frame Rate XnX 10-9 GigaBits per second
Where “n” is the pixel bit depth;
The minimum required uplink bandwidth of the ethernet switch is then given by:
Minimum Uplink Bandwidth = Acquisition Rate x N
Where “N” represents total number of cameras installed.
As shown in Figure 6, the ethernet switch at the motor end collects data coming from all the cameras and transfers it through a single Fibre Optic (FO) cable. This cable carries data over long distances (around hundred meters) to the processing stations kept in the operator room. Another ethernet switch kept in the operator room converts the FO cable input back to individual video streams, which are then transferred to the processing stations using one ethernet cable per stream. The suitable choice of ethernet switch thus provides a constriction-free path from acquisition point to the processing station. The data processing computers have state-of-the-art graphical processing units for real-time computations.
Further, the one or more spark monitoring units 4 carry out video acquisition, processing, storage and display of sparking features. A spark monitoring unit 4 consists of a processing application, a client server application and a graphical user interface application. The processing application constructs two threads for one camera. One thread acquires incoming video frames and pushes it into a concurrent queue of frames. This thread also stores these frames in form of video files. A second thread extracts frames from the said concurrent queue, performs

processing operation and extracts useful features. The features we chose to extract were the sparking size and its color intensity distribution. For instance, for four cameras eight threads would be constructed out of which four would acquire & store images, and four would process it.
Furthermore, a server application for TCP/IP communication is developed to get the slab status from a client application running on Level 2 roughing mill computer (not part of the invention). The roughing mill computer (client) sends telegram messages at specific events of slab entry and slab exit to spark monitoring computer (server). The server application creates a shared memory and maps the slab status data onto that memory. This data is instantaneously and continuously read by a separate thread (called the shared memory thread) created in the spark monitoring application.
A switching is said to occur when slab status changes from “Entered” to “Exited” or vice versa. When switching occurs, the shared memory thread copies extracted image feature data into text files/database. The main thread of the processing application acts as the thread for responding to user inputs and interacts with all the threads to update the graphical user interface using the signal and slot mechanism. In this manner features extracted from videos are displayed as well as stored for future use by an integrated multithreaded application.
The display unit 5 which in an embodiment is a graphical user interface displays real-time features for a camera in form of graphs and trends. The GUI can display both short-term (over period of two slabs) feature trends and long-term (over period of a day, week and month) feature trends. This allows the user to correlate the sparking phenomenon to material grades, mill pacing or any other parameter in mill setup. It also generates an alarm signal in case sparking crosses a threshold and displays the details of alarms.
Thus, the proposed system is non- intruding to the equipment / process it is monitoring and designed for capturing and processing images at extremely high

frequency (25 frame per second) and thus recording short lived sparks in the range of 40 milliseconds. The extracted features from each image frame is stored and subjected to analysis to assess health of the equipment as well as to alert the personnel about abnormal behaviour of the equipment.
The foregoing is considered as illustrative only of the principles of the invention. Furthermore, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims.

We claim:
1. A non-intrusive spark monitoring system for DC motor health assessment
using real-time imaging, the system comprising:
a cover unit (1) for a DC motor having a top part, a right shoulder, and a left shoulder, said DC motor having a commutator (2) and a plurality of brushes (b3, b4, b5, b6, b14, b15, b16, b17);
a plurality of camera mounting units (3) positioned across the right shoulder and the left shoulder of the cover unit (1), each of said camera units (3) constructed with a U-shaped channel having a base defined with rectangular slots, a U-shaped plate fixed to side wall of the U-shaped channel, an inverted L-shaped plate defined with a base and a trunk with the base of the inverted L-shaped plate movably attached to the U-shaped plate;
a plurality of cameras (c3,c4,c5, c15, c16, c17) with each of the cameras (c3,c4,c5, c15, c16, c17) being mounted on upper side of the trunk of the inverted L-shaped such that point of focus (F1) of the camera is a radial mid-point in between the two adjacently defined brushes (b3-b4, b4-b5, b5-b6, b14-b15, b15-b16, b16-b17);
one or more spark monitoring units (4) with each configured to:
receive, process and store captured video frames from the camera; and
extract image feature data from the captured video frames;
a display unit (5) for displaying the processed image features extracted for the each of the camera.
2. The system as claimed in claim 1, wherein between the inverted L-shaped plate and the camera an aluminium heat sink is attached.
3. The system as claimed in claim 1, wherein the camera mounted on upper side of the trunk of the inverted L-shaped plate is configured to move both in lateral and radial directions with respect to the U-shaped plate.

4. The system as claimed in claim 1, wherein the inverted L-shaped plate and the U-shaped plate is made of stainless steel having thickness of 1mm.
5. The system as claimed in claim 1, wherein the right and the left shoulders are symmetric.
6. The system as claimed in claim 1, wherein the rectangular slot is covered with a scratch resistant and optically transparent glass of 4 mm thickness.
7. The system as claim in claim 1, wherein the camera has a small form factor, supports all color channels and is of POE (power over Ethernet) IP type.
8. The system as claimed in claim 1, wherein the extracted image features are sparking size, shape and color intensity distribution.
9. The system as claimed in claim 1, wherein the spark monitoring unit (4) comprises two threads for each camera, wherein a first thread receives and stores the captured video frames, and wherein a second thread extracts and processes the extracted image feature.
10. The system as claimed in claim 1, wherein when the processed extracted image feature representing spark crosses a threshold level an alarm signal is generated with details of the alarm displayed by the display unit (5), wherein the display unit (5) is a graphical user interface.
11. The system as claimed in claim 10, wherein when the spark is generated an SMS is sent to a registered user.