Stud Welding Ferrule and Apparatus

A system for automatically identifying one or more welding site locations on a surface of a target metal marked with a plurality of welding site candidates, includes an imager configured to acquire an image of the surface of the target metal, wherein the acquired image includes a plurality of pixels each having a corresponding intensity value; and a processing circuit configured to: compare each intensity value to an intensity threshold, identify a plurality of pixel clusters, wherein each pixel cluster is made up of contiguous pixels that have intensity values that are equal to or greater than the intensity threshold, for each pixel cluster, determine whether a total pixel area of the pixel cluster is less than a threshold pixel area, and remove any pixel cluster from consideration as a welding site location if the total pixel area of the pixel cluster is less than the threshold pixel area.

FIELD

This present invention relates generally to arc welding equipment for manually or robotically welding studs to a beam, girder, embed plate or other base metal surface at a welding site, and in particular, to stud arc welders which incorporate a reusable ferrule for containing and molding the molten metal in addition to shielding the weld from atmospheric gases.

BACKGROUND

It is well known in the arc welding art that the process to weld a stud to a beam, girder or other base metal surface first begins by preparing the welding site by removing any surface contaminants which may include rust and paint. This process insures a clean metallic surface having good electrical conductivity and is usually accomplished by grinding the contaminant surface of the base metal. A conventional ceramic ferrule is then manually positioned on top of the cleaned welding site. The placed ferrule identifies the welding site location.

The head of the stud is then concentrically inserted into an electrically conducting collet either manually for a conventional welding gun or automatically for a robotically controlled welder. The collet and stud concentric combination are then vertically positioned over the ferrule. A downward force then moves the collet and stud concentric combination towards the ferrule. As the collet and stud combination moves in a downward direction, a ferrule alignment bracket first spring-ably engages the top of the ferrule concentrically aligning and fixing the position of the ferrule with respect to the collet and stud concentric combination.

The collet and stud continue with a downwardly directed vertical movement inserting the shank of the stud into the concentrically aligned ferrule. Downward vertical motion of the stud continues until the bottom surface of the shank is firmly and spring-ably pressed against the clean top surface of the base metal.

At this point the shank of the stud has been concentrically inserted into the ferrule and is firmly seated perpendicular to the clean base metal surface making a good electrical connection between the collet and stud combination and the base metal surface. The welder is then activated either by a welder operator depressing the welding gun trigger or automatically by the robotic welder.

Activating the welder initiates a pilot arc between the bottom area of the stud shank and the base metal surface for a short amount of time after which a large welding current is then permitted to flow.

As the large welding current flows a high temperature arc is produced which melts both the bottom of the stud shank and the surface of the base metal forming a pool of molten metal. The molten metal is confined around the base of the stud shank by the ferrule. The ferrule also concentrates the heat generated by the arc and additionally protects the molten metal from atmospheric gases which may cause oxidation of the molten metal. The stud is then slightly lifted and then downwardly forced into the pool of molten metal by the welder and allowed to solidify. After solidification, the stud and base metal are now welded together.

The ferrule is then removed from the base of the weld by manually fracturing the side of the ferrule with an object such as a hammer, or in the case of a robotic welder by automatically fracturing the ferrule with a mechanically operated hammer. With this current welding process one ferrule is consumed for each welded stud.

There are many disadvantages associated with using conventional ferrules during the welding process. The ferrule must first be positioned on top of the welding site before the welding process commences. This involves identifying the welding site, correctly orienting the ferrule over the welding site, and then placing the ferrule on top of the welding site. At this point it is assumed that the ferrule location is the same as the welding site location.

This process is time consuming and increases labor costs. Additionally, the ferrule is removed after each welded stud further increasing both the time and cost to complete a weld. A ferrule which can be repeatedly used (a reusable ferrule) is therefore very desirable and economically beneficial to the welding industry.

There are several factors to consider in the design of a reusable ferrule and include the working temperature and the mechanical strength of the ferrule material. A reusable ferrule must have material properties which can withstand repeated exposures to high arc welding temperatures. Additionally, the reusable ferrule must maintain sufficient mechanical strength at the high arc welding temperatures to allow a mechanism to repeatedly position the ferrule sections both around the shank of each stud and on top of the respective welding site.

To successfully replace the expendable ferrule, the reusable ferrule must be synergistically and cooperatively matched with the ferrule positioning mechanism. The reusable ferrule must also be economical to manufacture and easily replaceable in the field.

Another consideration in the design of a welding apparatus which incorporates a reusable ferrule is the method used to identify a suitable welding site. In the prior art and previously mentioned above, welding sites have been located by assuming that the location of the ferrule defines the location of the welding site. The welding site location is therefore assumed to be the same as the ferrule location. A misplaced ferrule on the base metal surface therefore erroneously gives an incorrect welding site location. Additionally, with a reusable ferrule, the welding site location is not defined by the ferrule location simply because the reusable ferrule is moved from welding site to welding site during the welding process and is not stationary on the base metal surface. Therefore, a different technique must be used to identify each welding site which does not use the ferrule location as welding site location.

Another consideration in the design of a welding apparatus using a reusable ferrule is the area of the ground welding site. A ground welding site which is too small to accommodate the diameter of the shank of the stud should not be used. Further, welding sites that have been placed too near each other will interfere with the placement of the ferrule positioning system between consecutive welds. Additionally, welding sites which are too close to the outside perimeter of the base metal tend not to produce good welds and should not be considered as a valid welding site.

Attempts to replace the expendable ferrule with a reusable ferrule (and along with a synergistic positioning mechanism) have been previously disclosed in the art and have only been partially successful in disclosing a welding apparatus incorporating a reusable ferrule for arc welding applications.

For example, U.S. Pat. No. 5,049,717 (September 1991) issued to Mikihiko Yoshida and Hiroski Yamada teaches a ferrule construction having two semi-cylindrical arc shields (semi-cylindrical and identical ferrule sections) which have been constructively configured to include a lug on the inside cylindrical surface. A metallic clamp having an inner and outer member grip the inside and outside surface of each arc shield lug and fixes each arc shield to their respective support members. The support members and respective semicylindrical arc shields are subsequently each attached to a rotatable lever. The two support members are joined via links and are manually activated by a handle joined to a rotatable lever to mechanically force the arc shields together and around the shank of the stud before the welding process begins. The support members along with their respective links and the manually rotatable lever in combination positions and closes the two arc shields around the shank of the stud to form a cylindrically shaped ferrule.

The welding apparatus described above still requires the operator to manually open and close the two semicylindrical arc shields before and after the welding process by rotatably raising and lowering the lever. This is awkward when the operator is attempting to hold the welding apparatus (gun) with one hand while operating the lever to close the ferrule halves and then again to open the ferrule halves after the welding process has completed. Also, completely autonomous robotic welders should not require human intervention and should be configured to automatically position the ferrule around the shank of the stud and automatically close and open the ferrule sections.

Yoshida and Yamada also suggest that the metallic clamp construction and placement minimizes the thermal stresses placed on the ferrule by the molten metal. However, thermally induced stresses are still present because of the significant differences in the thermal coefficient of expansion between the ceramic material and the metallic clamp. It is also disclosed that a ceramic containing not less than 20% weight boron nitride is able to withstand the thermal shock experienced during the welding process.

U.S. Pat. No. 5,135,154 (August 1992), also issued to Mikihiko Yoshida and Hiroski Yamada, teaches a similar welding apparatus as disclosed in U.S. Pat. No. 5,049,717 but uses a ferrule with superior thermal shock resistance property. The ferrule composition disclosed in the U.S. Pat. No. 5,135,154 patent is composed of not less than 40 weight % of boron nitride (BN). The results of their study were published in their disclosure and is summarized in the following table. Only those ferrule compositions exceeding 100 welding cycles are listed.

As indicated in the above table, ferrules constructed from boron nitride composites having a weight composition of 50% or more boron nitride successfully passed more than 100 welding cycles according to the Japanese Industrial Standard for arc welding test criteria (standard JIS B1198). Welding was conducted having 1,200-1,300 amps of welding current and an arc time of 800 msec.

For both of the above-mentioned patents, the welding sites are identified by the placement of the ferrule onto the base metal surface.

Boron nitride has a number of different grades depending upon the purity of the material and the binder type and includes pure boron nitride, boron nitride with a boric oxide binder system and boron nitride with a calcium binder system. Manufactures usually distinguish the different grades of boron nitride using their own symbology.

Solid boron nitride does not use any binder, is the purist form of boron nitride (>99%) and is recommended for extreme high-temperature and thermal shock applications and does not wet with most molten metals. However, it is a soft material and would not be a good candidate for reusable ferrule applications which experience mechanical stresses during the repeated positioning and closing cycles. Pure boron nitride is commonly referred to as hexagonal boron nitride [(h)BN], and has a maximum temperature of 2,000 degrees C. in inert environments.

Additionally, boron nitride may be combined with other materials to form composite ceramics with very distinct thermal, electrical, and mechanical properties. Boron nitride-based composites are usually also excellent electrical insulators making them a preferred choice for welding applications where large welding currents are utilized.

An example of a boron nitride composite which is an improvement over the composites listed in U.S. Pat. No. 5,135,154 is available from ESK Ceramics GmbH & Co. of Germany (now owned by 3M) and comprises a composite material of boron nitride, zirconium oxide and silicon carbide and is commonly referred to as ZSBN. This ceramic combines the non-wetting property of boron nitride with the refractoriness of zirconia and the high wear resistance of silicon carbide. The composite has the chemical symbol BN—ZrO2—SiC and is known under the tradename Mycrosint® SO. Other manufacturers such as Saint-Gobain Ceramics produce similar BN—ZrO2—SiC and other refractory ceramic composites.

The ZSBN ceramic also has good mechanical properties for stud welding applications having a Vickers hardness of 770 [HV0.5] and a Young's modulus of 80/35 [GPa].

Thermal properties include a thermal conductivity of 38/20 [W/mK] and a coefficient of thermal expansion of 3.5/8.5 [10−6/K]. For Young's modulus, thermal conductivity and coefficient of expansion, the higher number refers to a measurement perpendicular to the ceramic manufacturing pressing direction. Additionally, this material may be first pressed into a starting shape and then easily machined into a final form using commonly used metal working processes such as milling and drilling operations using carbide tooling.

According to ESK Ceramics, BN—ZrO2—SiC has an application working temperature of 800 deg C. in air and 2,000 deg C. in inert atmospheres. Degradation of the BN—ZrO2—SiC ceramic usually is the result of surface oxidation of the material, and an inert working environment minimizes this failure mode.

Other binding systems are common which change the properties of boron nitride composites. For example, some manufacturers form a boron nitride composite having 40% boron nitride and 60% silicon dioxide (SiO2) which has a maximum temperature of 1,000 degrees C. in inert environments.

For arc welding applications, the boron nitride prevents molten metal from wetting the ferrule surfaces during the welding process while additional materials such as zirconium and silicon carbide add mechanical strength and high wear resistance respectively to the ceramic composite. The BN—ZrO2—SiC ceramic material has sufficient structural strength to withstand the mechanical forces for both the closing and opening of the semi-cylindrical ferrule section and also has the toughness required to withstand the repeated forceful downward contact with the base metal surface.

Thus there is a need for an arc welding apparatus having a collet and ferrule support assembly which easily and automatically positions a reusable ferrule around the shank of the stud and on top of the welding site, the reusable ferrule being able to further repeatedly withstand the high temperatures associated with the arc-welding process without degradation while maintaining sufficient mechanical strength to synergistically cooperate with the ferrule positioning mechanism during repeated welding cycles. The ferrule material should also be economically manufacturable and have good machining properties.

There is also a need for a welding apparatus which incorporates a reusable ferrule and which can further easily identify each welding site to determine if there is sufficient welding site area to accommodate the bottom shank area of the stud, and to further determine if the distance between welding sites is sufficient to accommodate the repeated movement of the collet and ferrule support assembly from one welding site to a subsequent welding site without positional interference, and to prevent the welding of a stud in predefined no-weld areas.

SUMMARY

The deficiencies of the prior art are overcome in the present invention which provides in a first embodiment a welding apparatus having a three axis (x-y-z) stud positioning system having x-axis, y-axis and z-axis linear motion systems which automatically positions a collet and ferrule support assembly (having a stud inserted into the collet) over the welding site prior to the beginning of the welding process.

The collet and ferrule support assembly includes a ferrule support plate, a collet support plate and a cross-member support plate arranged in a stacked configuration. All of the above-mentioned plates are vertically aligned with each other using four support rods as vertical guides. The lower end of each support rods is threaded and affixed to the ferrule support plate. The ferrule support plate is positioned closest to the base metal surface followed by the collet support plate and lastly by the cross-member support plate.

Pivotally attached to the ferrule support plate are two oppositely disposed slanted L shaped ferrule brackets. Each ferrule bracket includes a vertical arm attached to a downwardly and inwardly slanted arm (hence the designation “slanted”). The included angle between the vertical and slanted arm of each slanted L shaped ferrule bracket is greater than ninety degrees.

The free upper end of each vertical arm has a cylindrically shaped boss having a through hole for pivotally mounting each ferrule bracket to the ferrule support plate with a removable pin. The ferrule support plate is constructively configured having two pairs of formed tabs, each pair of tabs further having a horizontal through hole for accepting the removable pin. Alignment of the boss and tab holes along with the inserted pin pivotally supports each ferrule bracket. The removeable pins (one for each boss) allow the operator to quickly change the ferrule brackets during normal servicing of the welder.

The non-attached (free) end of each slanted arm includes a semi-cylindrical ferrule section.

The ferrule support plate is positioned around the collet and stud combination and does not interfere with the vertical motion of the collet and stud combination. Thus, each ferrule bracket may rotate around the pin and swing towards or away from each other. With the ferrule brackets swung completely towards each other, the semi-cylindrical ferrule sections of each ferrule bracket mate and close to form a cylindrically shaped ferrule around the shank of the stud.

Each ferrule bracket is composed of a refractory ceramic composite such as BN—ZrO2—SiC ceramic.

Further connected to the upper end of the vertical arm of each ferrule bracket and located above the boss is one end of an extension spring having the other end of the extension spring attached to the ferrule support plate. Each spring biases their respective ferrule bracket to swing outward from the collet and stud combination and away from each other thereby opening the two semi-cylindrical ferrule sections without any other external forces.

Further attached to each vertical arm and below the boss of each ferrule bracket is a plunger of a solenoid. The body of the solenoid is attached to the ferrule support plate and is constructively configured to counter the force (when energized) of the extension spring. The solenoids are controlled by a computer, and when activated create a pulling force on the ferrule bracket.

When electrically energized, the solenoids force the two ferrule brackets to pivot towards each other. Thus, the closing of the brackets forms a complete cylindrically shaped ferrule which can be electrically controlled by activating the solenoid. With the solenoids deactivated, the brackets are forcibly opened and positioned away from each other by the force exerted by the extension springs. The shank of the stud passes through the center of the now formed closed cylindrically shaped ferrule during the welding process.

The solenoids could also be bi-directional capable of creating both a pulling and pushing force on the plunger. The extension springs would therefore not be required to separate the brackets.

Attached to the ferrule support plate are two limit switches for each ferrule bracket. The switches for each ferrule bracket are constructively configured to detect the opening and closing positional state for each ferrule bracket. Each of the four switches are in communication with the computer or a suitable input/output computer interface module (for example, a conventional peripheral component interconnect express, or PCIe, input and output card). Thus, the computer can query the switches and determine the opening and closing states of the ferrule brackets and therefore of the ferrule sections. The two switches for each ferrule bracket may be combined into a single switch (a conventional single pole double throw, or SPDT, switch for example) and housing.

A program is provided to control and synchronize the timing of the opening and closing of the ferrule brackets within the welding cycle.

Further affixed to the inside of a slanted arm of one ferrule bracket is a stud sensing transducer. The stud sensor transducer is in bi-directional communication with the computer via a conventional communication link and detects if a stud is inserted into the collet.

The collet support plate is located above the ferrule support plate and is spring-ably biased above the ferrule support plate with four compression springs concentric with the support rods. The springs are located between the top surface of the ferrule support plate and the bottom surface of the collet support plate. The collet support plate has a pressed bearing for each support rod. Thus, the collet support plate can spring-ably move in the z-direction with respect to the vertical position of the ferrule support plate.

A flange bearing pressed fitted an insulating sleeve of the collet support plate guides the vertical movement of a vertical collet support shaft. The lower end of the collet support shaft is attached to the top end of the collet, and the upper end of the collet support shaft extends above the top surface of the collet support plate.

A collet compression spring is disposed between the collet spring retaining ring mounted on the top of the collet and the bottom of the collet support plate. The z-direction travel of the collet support shaft is limited between the collet spring retaining ring and a collet retaining pin positioned through a horizontal hole located on the top end of the collet support shaft. The collet support plate is further affixed to a vertically positioned collet and ferrule assembly support bracket. The collet and ferrule assembly support bracket is attached to the z-axis motion system.

Thus, the downward vertical movement of the collet and ferrule assembly support bracket will cause the closed ferrule brackets to first spring-ably contact the base metal surface (by compressing the four springs located between the ferrule support and collet support plates) and then cause the stud to secondly spring-ably contact the base metal surface (by compressing the collet compression spring).

The cross-member support plate is positioned above the collet support plate and is adjustably affixed to the support rods. The vertical position of the cross-member support plate determines the vertical travel distance of, and amount of spring compression exerted on, the ferrule support plate by the four (support rod) compressions springs.

The concentrically aligned collet and stud combination is positioned over the welding site using a conventional computer-controlled servo-based robotic x-axis, y-axis and z-axis linear motion (rail) system as previously disclosed in U.S. Pat. No. 9,764,411, the contents of which are incorporated herewith as if set forth in full.

The x-axis positioning system includes two identical parallel linear motion systems disposed from each other and longitudinally positioned along the length of the surface of the base metal. The first x-axis linear motion system having a first and second saddle is driven by a brushless direct current (BLDC) motor-based servo system. The second x-axis linear motion system also includes a first and a second saddle. The saddles for the second x-axis linear motion system are not driven and are free to move along the x-axis of the second linear motion system.

The y-axis positioning system includes two identical parallel linear motion systems disposed from each other and laterally positioned across the width of the surface of the base metal. The first y-axis linear motion system having a first saddle is driven by a BLDC motor-based servo system. The second y-axis linear motion system also includes a first saddle. The saddle for the second y-axis linear motion system is not driven and is free to move along the y-axis of the second linear rail.

One end of the first y-axis linear motion system is connected to the first saddle of the first x-axis linear motion system, while the opposite end of the first y-axis linear motion system is connected to the first saddle of the second x-axis linear motion system. Similarly, one end of the second y-axis linear motion system is connected to the second saddle of the first x-axis linear motion system, while the opposite end of the second y-axis linear motion system is connected to the second saddle of the second x-axis linear motion system.

A support platform is positioned on top of the first and second y-axis linear motion systems and is attached to the first saddle of the first y-axis linear motion system and to the first saddle of the second y-axis linear motion system. Additional saddles may be used depending upon the vertical load.

The z-axis positioning system includes a single linear motion system positioned in the vertical direction and perpendicular to the base metal surface. The z-axis linear motion system is further attached to the support platform (mentioned previously) of the y-axis linear motion system. The z-axis linear motion system also includes a first and a second saddle and is similarly driven by a BLDC motor-based servo system. The first saddle of the z-axis linear motion system is positioned furthest from the base metal surface. Affixed to both z-axis saddles is the vertically positioned collet and ferrule assembly support bracket. An additional z-axis linear motion system may be added depending upon the vertical load and stability requirements.

Each x-axis, y-axis and z-axis servo system includes an axis controller and a BLDC servo motor having a feedback encoder. The driven linear motion systems may be included of a conventional ball and screw drive or belt drive which is connected to the driven axis saddles. Each axis controller is connected to and is in bi-directional communication with the computer.

Thus, the computer under software control can direct the x-axis and y-axis linear motion systems to move the collet and ferrule support assembly (along with the inserted stud) to a computed x-y position over the surface of the base metal. The computer under software control also controls the z-axis linear motion system to vertically move the collet and stud combination and ferrule brackets onto and off of the base metal surface. The x-y-z axis servo systems and computer includes an x-y-z stud positioning system and can position the stud at any location on the base metal surface.

Each of the driven x-axis, y-axis and z-axis linear motion systems additionally have two conventional limit switches positioned at the travel ends of the respective axis motion systems. The limit switches are in communication with and connected to the computer (or respective axis controller).

A conventional stud loader mechanism is provided which enables the stud welding positioning system to automatically load a stud into the collet during the welding process.

Located above the surface of the base metal is an imager having its imaging array parallel to the base metal surface. The imager is typically a conventional charge-coupled device (CCD) or complimentary metal oxide semiconductor (CMOS) camera having a lens optically focused to have a field of view (FOV) encompassing the entire surface of the base metal surface, welding sites and a registration marker located on the top surface of the base metal (embed) plate support structure. The imager is in communication with the computer via a universal serial bus (USB) or other communication channel. A light is also positioned above the base metal surface to illuminate the welding sites.

Connected to the support platform is a z-axis distance sensor to measure the vertical distance from the support platform (the support platform was previously described above) to the surface of the base metal. The distance sensor is in communication with the computer via a conventional communication link.

A welding control system is in bi-directional communication with, and is responsive to, the computer. The welding control system controls the actual welding process in response to a ‘Weld’ command from the computer. The welding control system also supplies the necessary welding current to generate both the pilot arc and welding arc.

Further connected to the computer is a conventional keyboard and liquid-crystal display (LCD). Using the keyboard and LCD, the operator may input and receive information from the computer.

The computer further incorporates programs to locate and identify valid welding sites by first identifying each potential ground welding site on the surface of the base metal using image threshold filtering and determining the center and radius of the maximum inscribed circle (MIC) contained within each identified welding site. The center of the maximum inscribed circle is used as a stud welding target location. The diameter of the maximum inscribed circle is used to ensure that sufficient ground welding site area is available for the weld and the distance between MIC centers is used to check for potential interference among nearest neighbor welding sites. Any welding sites having MIC areas less than the minimum required for welding are rejected. The computer also identifies and rejects any welding sites located within a predefined area around the perimeter of the base metal (such as an embed plate).

In operation, a base metal having pre-defined welding sites is placed underneath the x-y-z stud positioning system. In response to the operator pressing the ‘Begin Welding’ key on the keyboard, the computer first homes each axis, i.e., sets the location of the x-y-z axis at a known location (usually defined as [0,0,0] with respect to a conventional Cartesian coordinate system). It is assumed that the home position will not interfere with the imaging of the base metal surface.

The computer then sends a signal to the light to turn on which illuminates the base metal surface. The computer then commands the imager to image the base metal surface. The image data (image space data) is received by and subsequently stored in the memory of the computer.

The computer then inputs the raw image data, corrects the raw image for both lens and perspective distortions and stores the corrected image into computer memory. The computer also determines the image-space to object-space distance and area transformations and determines the image-space coordinates of a registration marker located on the top surface of the base metal (embed) plate support structure.

The computer then threshold filters the corrected image, removes salt and pepper and Gaussian noise, further processes the image to determine connected components (i.e., clusters of similar intensity valued pixels), and determines the area of all clusters and eliminates those clusters having an object-space area less than the minimum defined for welding a stud. The computer then further determines the area of the MIC and the center for each MIC and eliminates those clusters having an MIC area less than the minimum defined for welding a stud. These operations may be combined.

The computer then further calculates the center to center distances among all maximum inscribed circles and eliminates those maximum inscribed circles and associated clusters having distances less than the minimum distance required to weld the stud to prevent interference during the welding process (using the predetermined minimum spacing to accommodate the collet and ferrule support assembly with respect to previously welded studs), and then further eliminates those maximum inscribed circles and associated clusters intersecting a perimeter area defined by the operator to eliminate those clusters (and therefore welding sites) near the perimeter. The computer then creates a welding site coordinate table listing all the remaining MIC centers in both image-space and object-space.

The computer then controllably moves the collet and ferrule support assembly to the desired x-y-z location for loading a stud (for the first, and subsequent studs if any) and then checks the status of the stud loaded sensor. If the stud loaded sensor indicates that the stud is not loaded into the collet, the welding process stops, and the operator is notified. If a stud is loaded into the collet, the computer then controllably moves the ferrule and collet assembly to the x-y location specified in the welding site coordinate table.

The computer then controls the electrical activation of the solenoids and closes the ferrule brackets forming a cylindrical ferrule around the shank of the stud. The computer then checks the closed ferrule limit switches to ensure the ferrule sections have been closed. If the ferrule sections are not closed, the welding process stops, and the operator is notified.

If the ferrule sections are closed, the computer then reads the z-distance sensor and computes the necessary distance (offset corrected) to move the collet and ferrule support assembly. The computer then moves the collet and ferrule support assembly in a downward direction until the bottom of the ferrule sections engage the base metal surface.

At this position the four compression springs biasing the ferrule support plate in the vertical direction begin to compress increasing the contact force between the ferrule brackets and the base metal surface. The construction and arrangement of the ferrule brackets along with the downward force aids in the ferrule semi-cylindrical sections to forcibility close.

Downward motion continues until the bottom of the shank of the stud contacts the base metal surface thereby compressing the collet spring and increasing the contact force between the bottom of the shank and the base metal surface. The downward distances are calculated knowing the vertical lengths of the mechanical components, required offsets including the length of the stud, the z-axis sensor output, the desired amount of spring compressions and other factors.

At this position the ferrule sections are forcibly mated and closed around the shank and are forcibly contacting the base metal surface. The bottom of the shank of the stud is also forcibly contacting the base metal surface at the welding site target. The computer then opens the argon gas valve flooding the closed ferrule volume with argon gas.

At this point the computer then sends a ‘Weld’ signal to the welding control system. In response to the ‘Weld’ command from the computer, the welding control system first generates a pilot arc and shortly thereafter generates the welding arc. The high temperature welding arc then begins to melt both the end of the shank and the base metal forming a molten pool of material between the end of the shank and the top or the base metal surface.

After a predetermined time, the computer commands the z-axis controller to lift the stud a predetermined distance, dwell in this position for a predetermined time and then commands the z-axis controller to reverse direction of the stud thereby plunging the stud into the molten pool of material. Thereafter the welding control system removes the arc producing current and the weld is complete. The welding control system may send a ‘Weld Complete’ message back to the computer or the computer may time out after the ‘Weld’ signal is sent to the welding control system.

The computer then closes the argon gas valve.

The computer then commands the z-axis controller to lift the ferrule brackets off the base metal surface. A short distance above the base metal surface the computer de-energizes the solenoids and the two semi-cylindrical ferrule sections separate. The computer then checks the status of the open ferrule section limit switches. If the ferrule sections are not open, the welding process stops, and the operator is notified.

If the ferrule sections are open, z-axis controller continues to move the collet and ferrule support assembly vertically until reaching the z-home position. The computer then determines if there are any additional welding sites listed in the welding site coordinate table. If there are more available welding sites, the computer begins another welding cycle by controllably moving the collet and ferrule assembly to the desired x-y location for loading a stud.

A stud is then loaded into the collet and the entire cycle is then repeated for the remaining welding sites contained in the welding site coordinate table.

After the last stud has been welded and ferrule sections separated, the computer commands the x-axis, y-axis and z-axis servo controllers to move the collet and ferrule support assembly to the previously defined home position. The computer then shuts off the lights and awaits another operator command.

A system for automatically identifying one or more welding site locations on a surface of a target metal marked with a plurality of welding site candidates is provided. The system includes: an imager configured to acquire an image of the surface of the target metal including the plurality of welding site candidates, wherein the acquired image includes a plurality of pixels with each pixel having a corresponding intensity value; and a processing circuit configured to: receive the acquired image, compare each intensity value to an intensity threshold for pixel clustering, identify a plurality of pixel clusters, each pixel cluster corresponding to a different one of the plurality of welding site candidates, wherein each pixel cluster is a cluster of contiguous pixels that have intensity values that are equal to or greater than the intensity threshold, for each pixel cluster, determine whether a total pixel area making up the pixel cluster is less than a threshold pixel area, and remove any pixel cluster from consideration as a welding site location if the total pixel area of the pixel cluster is less than the threshold pixel area.

A system for automatically verifying a welding site location on a surface of a target metal marked with a welding site candidate is provided. The system includes: an imager configured to acquire an image of the surface of the target metal including the welding site candidate, wherein the acquired image includes a plurality of pixels with each pixel having a corresponding intensity value; and a processing circuit configured to: receive the acquired image, compare each intensity value to an intensity threshold for pixel clustering, identify a pixel cluster corresponding to the welding site candidate, wherein the pixel cluster is a set of contiguous pixels that have intensity values that are equal to or greater than the intensity threshold, determine whether a total pixel area making up the pixel cluster is less than a threshold pixel area, remove the pixel cluster from consideration as the welding site location if the total pixel area of the pixel cluster is less than the threshold pixel area, and verify the pixel cluster as the welding site location on a condition that the total pixel area of the pixel cluster is equal to or greater than the threshold pixel area.

A system for automatically verifying a welding site location on a surface of a target metal marked with a welding site candidate is provided. The system includes: an imager configured to acquire an image of the surface of the target metal including the welding site candidate, wherein the acquired image includes a plurality of pixels with each pixel having a corresponding intensity value; and a processing circuit configured to:

receive the acquired image, compare each intensity value to an intensity threshold for pixel clustering, identify a pixel cluster corresponding to the welding site candidate, wherein the pixel cluster is a set of contiguous pixels that have intensity values that are equal to or greater than the intensity threshold, determine a largest inscribed circle that is enclosed within the pixel cluster, compare a diameter of the largest inscribed circle with a threshold diameter corresponding to a dimension of a metal stud, remove the pixel cluster from consideration as the welding site location if the diameter of the largest inscribed circle is less than the threshold diameter, and verify the pixel cluster as the welding site location on a condition that the diameter of the largest inscribed circle is equal to or greater than the threshold diameter.

A system for automatically verifying a welding site location on a surface of a target metal marked with a welding site candidate is provided. The system includes: an imager configured to acquire an image of the surface of the target metal including the welding site candidate, wherein the acquired image includes a plurality of pixels with each pixel having a corresponding intensity value; and a processing circuit configured to: receive the acquired image, compare each intensity value to an intensity threshold for pixel clustering, identify a pixel cluster corresponding to the welding site candidate, wherein the pixel cluster is a set of contiguous pixels that have intensity values that are equal to or greater than the intensity threshold, determine a largest inscribed circle that is enclosed within the pixel cluster, determine a center of the largest inscribed circle, calculate a center-to-center distance to centers of other pixel clusters, remove the pixel cluster from consideration as the welding site location if the center-to-center distance to another pixel cluster is less than a distance threshold, and verifying the pixel cluster as the welding site location on a condition that the center-to-center distance to the centers of the each of the other pixel clusters is equal to or greater than the distance threshold.

A method for automatically verifying a welding site location on a surface of a target metal marked with a welding site candidate is provided. The system includes: acquiring an image of the surface of the target metal including the welding site candidate, wherein the acquired image includes a plurality of pixels with each pixel having a corresponding intensity value; comparing each intensity value to an intensity threshold for pixel clustering; identifying a pixel cluster corresponding to the welding site candidate, wherein the pixel cluster is a set of contiguous pixels that have intensity values that are equal to or greater than the intensity threshold; determining a largest inscribed circle that is enclosed within the pixel cluster; comparing a diameter of the largest inscribed circle with a threshold diameter corresponding to a dimension of a metal stud; removing the pixel cluster from consideration as the welding site location if the diameter of the largest inscribed circle is less than the threshold diameter; and verifying the pixel cluster as the welding site location on a condition that the diameter of the largest inscribed circle is equal to or greater than the threshold diameter.

Objects

To overcome the shortcomings of current arc welding technologies, a new apparatus and method for arc welding studs are provided.

A basic object of the invention is to provide an improved robotic stud welding apparatus for automatically welding studs at randomly placed ground welding sites on a base metal surface.

Another basic object of the invention is to provide an improved robotic stud welding apparatus for automatically welding studs at randomly placed ground welding sites on a base metal surface using a re-useable ferrule.

Another basic object of the invention is to provide an improved robotic stud welding apparatus for automatically welding studs at randomly placed ground welding sites on a base metal surface using a re-useable ferrule comprising two semi-cylindrical ferrule sections.

Yet still another basic object of the invention is to provide a re-useable ferrule composed of ceramic materials.

Another object of the invention is to provide a reusable ferrule composed of refractory ceramic materials.

Another object of the invention is to provide a reusable ferrule comprised of boron nitride (BN) based refractory material.

Another object of the invention is to provide a reusable ferrule comprised of a boron nitride based composite ceramic refractory material.

Another object of the invention is to provide a reusable ferrule comprised of an ultra-high-temperature ceramic (UHTC) material.

Another object of the invention is to provide a reusable ferrule composed of boron nitride, zirconium oxide, silicon carbide (BN—ZrO2—SiC) based refractory material.

Another object of the invention is to provide a reusable ferrule composed of boron nitride, zirconium oxide, silicon carbide (BN—ZrO2—SiC) based refractory material having heat dissipating fins.

Another object of the invention is to provide a reusable ferrule assembly composed of boron nitride, zirconium oxide, silicon carbide (BN—ZrO2—SiC) based refractory material and the like and having heat dissipating fins.

Another object of the invention is to provide a reusable ferrule assembly composed of boron nitride, zirconium oxide, silicon carbide (BN—ZrO2—SiC) based refractory material and the like and having integral heat dissipating fins.

Another object of the invention is to provide a reusable ferrule assembly composed of boron nitride, zirconium oxide, silicon carbide (BN—ZrO2—SiC) based refractory material and the like and having a current of air flowing over the integral heat dissipating fins.

Another object of the invention is to provide a reusable ferrule assembly composed of boron nitride, zirconium oxide, silicon carbide (BN—ZrO2—SiC) based refractory material and the like and having a controlled current of air flowing over the integral heat dissipating fins.

Another object of the invention is to provide a reusable ferrule assembly composed of a refractory material and the like and having a source of inert gas being supplied to the welding site and refractory material.

Another object of the invention is to provide a reusable ferrule assembly composed of a refractory material and the like and having a source of inert gas being controllably supplied to the welding site and refractory material.

Another object of the invention is to provide a robotic stud welder which automatically images the base metal.

Another object of the invention is to provide a robotic stud welder which automatically images the surface of a base metal.

Another object of the invention is to provide a robotic stud welder which automatically images the welding surface of a base metal.

Another object of the invention is to provide a robotic stud welder which automatically images welding sites.

Another object of the invention is to provide a robotic stud welder which automatically images welding sites located on the surface of a base metal.

Another object of the invention is to provide a robotic stud welder which automatically images welding sites located on the welding surface of a base metal.

Another object of the invention is to provide a robotic stud welder which automatically images ground welding sites.

Another object of the invention is to provide a robotic stud welder which automatically images the ground welding sites located on the surface of a base metal.

Another object of the invention is to provide a robotic stud welder which automatically images the ground welding sites located on the welding surface of a base metal.

Another object of the invention is to provide a robotic stud welder which automatically identifies welding sites.

Another object of the invention is to provide a robotic stud welder which automatically identifies welding sites located on the surface of the base metal.

Another object of the invention is to provide a robotic stud welder which automatically identifies welding sites located on the welding surface of the base metal.

Another object of the invention is to provide a robotic stud welder which automatically identifies ground welding sites.

Another object of the invention is to provide a robotic stud welder which automatically identifies ground welding sites located on the surface of the base metal.

Another object of the invention is to provide a robotic stud welder which automatically identifies ground welding sites located on the welding surface of the base metal.

Another object of the invention is to provide a robotic stud welder which automatically identifies welding sites from an image of the surface of a base metal.

Another object of the invention is to provide a robotic stud welder which automatically identifies welding sites located on the surface of the base metal from an image of the surface of a base metal.

Another object of the invention is to provide a robotic stud welder which automatically identifies welding sites located on the welding surface of the base metal from an image of the surface of a base metal.

Yet another object of the invention is to provide a robotic stud welder which automatically identifies welding sites which are in close proximity to the perimeter of an embed plate

Another object of the invention is to provide a robotic stud welder which automatically identifies ground welding sites from an image of the surface of a base metal.

Another object of the invention is to provide a robotic stud welder which automatically identifies ground welding sites located on the surface of the base metal from an image of the surface of a base metal.

Another object of the invention is to provide a robotic stud welder which automatically identifies ground welding sites located on the welding surface of the base metal from an image of the surface of a base metal.

Yet another object of the invention is to provide a robotic stud welder which automatically identifies welding sites which are in close proximity to the perimeter of an embed plate.

Another object of the invention is to provide a robotic stud welder which automatically classifies the welding sites which are in close proximity to the perimeter of an embed plate.

Another object of the invention is to provide a robotic stud welder which automatically classifies the identified ground welding sites.

Another object of the invention is to provide a robotic stud welder which automatically classifies ground welding sites according to the area of identified ground welding site.

Another object of the invention is to provide a robotic stud welder which automatically classifies the identified ground welding sites into categories.

Another object of the invention is to provide a robotic stud welder which automatically classifies the identified ground welding sites into a first category or a second category.

Another object of the invention is to provide a robotic stud welder which automatically classifies the identified ground welding sites into a first category or a second category based upon the area of the identified ground welding sites.

Another object of the invention is to provide a robotic stud welder which automatically determines connected welding site pixels in the image.

Another object of the invention is to provide a robotic stud welder which automatically determines connected welding site pixels in the image.

Another object of the invention is to provide a robotic stud welder which automatically determines connected welding site pixels and forms clusters of connected welding site pixels.

Another object of the invention is to provide a robotic stud welder which automatically labels the clusters of welding site connected pixels.

Another object of the invention is to provide a robotic stud welder which automatically classifies the labelled clusters of ground welding sites into a first category or a second category, the first category based upon the area of the labelled clusters of ground welding sites equal to or greater than a predetermined area and the second category based upon the area of the labelled clusters of ground welding sites less than a predetermined area.

Another object of the invention is to provide a robotic stud welder which automatically classifies the labelled clusters of ground welding sites into a first category or a second category, the first category based upon the area of the labelled clusters of ground welding sites equal to or greater than a predetermined area and the second category based upon the area of the labelled clusters of ground welding sites less than a predetermined area, whereas the predetermined area is the minimum acceptable area to weld a stud.

Another object of the invention is to provide a robotic stud welder which automatically classifies the labelled ground welding sites into a first category or a second category, the first category based upon the area of the labelled ground welding site equal to or greater than a predetermined area and the second category based upon the area of the labelled ground welding site less than a predetermined area, whereas the predetermined area is the minimum acceptable ground area to weld a stud.

Another object of the invention is to provide a robotic stud welder which automatically classifies the labelled ground welding sites into a first category or a second category, the first category based upon the area of the labelled ground welding site equal to or greater than a predetermined area and the second category based upon the area of the labelled ground welding site less than a predetermined area based upon the area of the ground welding sites, whereas the area of the labelled ground welding site is the area of an inscribed circle of the labelled ground welding site.

Another object of the invention is to provide a robotic stud welder which automatically classifies the labelled ground welding sites into a first category or a second category, the first category based upon the area of the labelled ground welding site equal to or greater than a predetermined area and the second category based upon the area of the labelled ground welding site less than a predetermined area based upon the area of the ground welding sites, whereas the area of the labelled ground welding site is the area of an maximum inscribed circle of the identified ground welding site.

Another object of the invention is to provide a robotic stud welder which automatically determines the center of the inscribed circle of the labelled welding sites in the first category.

Another object of the invention is to provide a robotic stud welder which automatically determines the center of the maximum inscribed circle of the labelled welding sites in the first category.

Another object of the invention is to provide a robotic stud welder which concentrically aligns a ferrule assembly automatically with the inscribed circle for the first category of ground welding sites.

Another object of the invention is to provide a robotic stud welder which concentrically aligns a ferrule assembly automatically with the maximum inscribed circle for the first category of ground welding sites.

Another object of the invention is to provide a robotic stud welder which concentrically aligns a re-useable ferrule assembly automatically with the inscribed circle for the first category of ground welding sites.

Another object of the invention is to provide a robotic stud welder which concentrically aligns a re-useable ferrule assembly automatically with the maximum inscribed circle for the first category of ground welding sites.

Another object of the invention is to provide a robotic stud welder which automatically determines the center of the inscribed circle of the identified welding sites in the first category.

Another object of the invention is to provide a robotic stud welder which automatically determines the center of the maximum inscribed circle of the identified welding sites in the first category.

Another object of the invention is to provide a robotic stud welder which concentrically aligns a ferrule assembly automatically with the inscribed circle of the first category of ground welding sites.

Another object of the invention is to provide a robotic stud welder which concentrically aligns a ferrule assembly automatically with the maximum inscribed circle of the first category of ground welding sites.

Another object of the invention is to provide a robotic stud welder which concentrically aligns a reusable ferrule assembly automatically with the inscribed circle of the first category of ground welding sites.

Another object of the invention is to provide a robotic stud welder which concentrically aligns a reusable ferrule assembly automatically with the maximum inscribed circle of the first category of ground welding sites.

Another object of the invention is to provide a robotic stud welder which welds a stud concentrically aligned with the maximum inscribed circle of the first category of ground welding sites.

Another object of the invention is to provide a robotic stud welder which welds a stud concentrically aligned with the maximum inscribed circle of the first category of ground welding sites using a ferrule.

Another object of the invention is to provide a robotic stud welder which welds a stud concentrically aligned with the largest inscribed circle of the first category of ground welding sites using a re-usable ferrule.

Another object of the invention is to provide a robotic stud welder which welds a stud onto the surface of the base metal, the stud concentrically aligned with the largest inscribed circle of the first category of ground welding sites using a re-useable ferrule.

Other objects and advantages of the present invention will become clearer following a review of the specification and drawing. It is to be understood that both the foregoing general description and the following detailed description are exemplary, but are not restrictive, of the invention.

DETAILED DESCRIPTION

Referring now to the drawing in which like reference numbers refer to like elements throughout the various figures that comprise the drawing,FIG. 1illustrates a first embodiment of the improved robotic stud welding apparatus10of the present invention and includes the x-y-z stud positioning system12, the computer14, the power supply15, the stud loading mechanism16, and the welding controller18having a conventional welding cable17. The purpose of the improved robotic stud welding apparatus10is to weld a conventional steel stud162onto the top surface120of an embed plate105(or beam, girder, or the like) at randomly placed previously ground welding sites110athrough110nsuch as ground welding site110iusing reusable ferrule brackets270and310.

For the following disclosure, axes directions are defined by a conventional right-hand Cartesian coordinate system19.

The improved robotic stud welding apparatus10, and in particular the x-y-z stud positioning system12, comprises a pair of parallel first and second x-axes positioning linear motion systems20and25respectively, a pair of parallel first and second y-axes positioning linear motion systems30and35respectively, and a single vertical z-axis linear motion system40.

The top surfaces22and27of the x-axis positioning linear motion systems20and25respectively are planar coincident and form an x-axis linear motion systems surface plane29(partially shown and noted by an enclosed dashed line).

The top surfaces32and37of the y-axis linear motion systems30and35respectively are also planar coincident and form a y-axis linear motion systems surface plane39(partially shown and noted by an enclosed dashed line).

The x-axis linear motion systems surface plane29and the y-axis linear motion systems surface plane39are parallel and vertically (z-direction) displaced from each other, and the x-axis linear motion systems20and25are perpendicular to the y-axis linear motion systems30and35respectively.

The z-axis linear motion systems40has a top surface42and is vertically positioned and normal to both x-axis linear motion systems surface plane29and the y-axis linear motion systems surface plane39. The x-axes, y-axes and z-axis linear motion systems are conventional in design and, for example, may include the models MF-K (Movoparts) ball guided screw driven linear systems manufactured by Thomson of Radford, Va., or the like.

The first x-axis linear motion system20is powered by a brushless DC motor45, the first y-axis linear motion system30is powered by a brushless DC motor50and the z-axis linear motion system40is powered by a brushless DC motor55. Other motor types such as a conventional brushed DC servo motor and the like may be used to power the linear motion systems.

The first x-axis linear motion system20has two separated and moveable first and second saddles51and52respectively. The saddles51and52are constrained to move along the top surface22of the linear motion system20in the x-direction (defined by the coordinate system19) and are attached to, and powered with, a ball and screw drive not shown (or a belt drive or the like) connected to motor45.

The second x-axis linear motion system25has two moveable first and second saddles54and56respectively similar to saddles51and52. Saddles54and56are constrained to move along the top surface27in the x-direction of the linear motion system25and are not powered. Saddle51is positionally aligned in the y-direction with saddle54and saddle52is positionally aligned in the y-direction with saddle56.

The first y-axis linear motion system30has a single moveable saddle60. The saddle60is constrained to move along the top surface32of the linear motion system30in the y-direction defined by coordinate system19and is attached to, and powered with, a ball and screw drive not shown (or by a belt drive or the like) connected to motor50.

The second y-axis linear motion system35has again a single moveable saddle62similar to saddle60. Saddle62is constrained to move along the top surface37in the y-direction defined by coordinate system19of the linear motion system35and is not powered. Saddle60is positionally aligned in the x-direction with saddle62. If necessary, the number of saddles for the y-axis linear motion systems30and35may be increased to support larger vertical loads.

The z-axis linear motion system40has two separated and moveable first and second saddles65and67respectively. Both saddles65and67are constrained to move along the top surface42of the z-axis linear motion system40and are attached to and powered by a ball and screw drive not shown (or by a belt drive or the like) connected to motor55. The two saddles65and67are used to provide for increased vertical stability.

The x-axis linear motion systems20and25are affixed to the factory floor mount (not shown) or another stable fixture and positioned above the factory floor83.

The first end of the first y-axis linear motion system30is affixed to saddle52and the second end of the first y-axis linear motion system30is affixed to saddle56. The first end of the second y-axis linear motion system35is affixed to saddle51and the second end of the second y-axis linear motion system35is affixed to saddle54.

A horizontal z-axis support plate80is conventionally affixed to the top surfaces of saddles60and62. Further mounted to the top surface82of plate80is the horizontal leg85of an L-shaped bracket84. The vertical leg86of the bracket84is further conventionally attached to z-axis linear motion system40.

The first and second x-axis linear motion systems20and25respectively are fixed (both are attached to the floor mount) but the y-axis linear motion systems30and35may move in unison along the x-direction, while the z-axis axis linear motion system40may move along the y-direction. Thus, the z-axis linear motion system40may be positioned at a desired x-coordinate (by controlling the x-axis linear motion systems20and25) and a desired y-coordinate (by controlling the y-axis linear motion systems30and35), offset adjusted to accommodate the location of the Cartesian coordinate system19.

Attached to z-axis linear motion system saddles65and67is the top end of vertically positioned collet and ferrule assembly support bracket87. Attached to the bottom end and top surface of bracket87is collet and ferrule assembly100. Further attached to the top surface of bracket87is a conventional blower309having a gas inlet port308. Collet and ferrule assembly100is more fully described with reference toFIGS. 2-7.

Motors45,50and55are electrically connected to motor controllers (not shown) via cables71,73and75respectively. The motor controllers (not shown) connect to the computer14via cables and are more fully described below with reference toFIG. 8.

Motors45,50and55each have a shaft encoder (not shown) which gives the angular position of the respective motor shafts and which may also be used to commutate the BLDC motors. This angular position data is transmitted back to the motor controllers98and can be accessed by computer14via busses (not shown).

Therefore, it is understood that the computer14can command x-y-z stud positioning system12to accurately position the collet and ferrule assembly100(along with the loaded stud162) within the range of motion of system12(knowing of course the ball-screw or belt drive rotation to linear motion parameters, motor encoder transformations etc.).

Attached at the first and second ends of the x-axis linear motion system25are the first and the second conventional positional limit switches88and89respectively, and further attached at the first and the second ends of the y-axis linear motion system35are the first and the second conventional positional limit switches90and91respectively. Also attached at the first and the second ends of the z-axis linear motion system40are the first and the second conventional positional limit switches92and93respectively. Limit switches88,89,90,91,92and93are electrically connected to their respective axis brushless DC motor controllers (not shown) or the computer14via wires94,95,96,97,98,99respectively. As used herein, the terms “wire,” “cable” and “bus” refer to a communication system that transfers data between components inside a computer, or between a computer and device. This expression covers all related hardware components including, but not limited to, wire, optical fiber and the like, and software, including communication protocol.

The limit switches may alternately be placed on the complementary axis of the respective linear motion systems. For example, limit switches88and89may be attached to the first x-axis linear motion system20instead of the second x-axis linear motion system25. The same is valid for the y-axes linear motion systems30and35.

Shown below the x-axes, y-axes and z-axis linear motion systems is a conventional embed plate105having fourteen randomly located, surface ground welding sites110a-110n. The welding sites110a-110nhave been previously manually ground and may therefore have different exposed metal surfaces areas. For example, ground site110ahas a larger ground area than ground site110d. The ground sites are usually manually ground with a hand-held grinder or the like and usually do not have equal areas because of the manually grinding process. The welding sites may also be robotically ground.

The embed plate105is usually supported by an embed support structure (not shown for clarity) which is attached to the factory floor83. Thus, the x-y-z stud positioning system12has a fixed geometric relationship for a given supported embed plate105. On the top surface of the support structure is a registration marker112having a conventional right-handed Cartesian x′-y′-z′ coordinate system122. The coordinate system122has the x′-axis123, the y′ axis124and the z′ axis121. The coordinate system122may be translationally and rotationally displaced from coordinate system19, although in most instances the x-y-z axes are parallel to the x′-y′-z′ axes respectively (only a translation relationship exists between the coordinate systems19and122as shown inFIG. 1). Coordinate transformations between different Cartesian coordinate systems are well known in the art.

The planar top surface120of the embed plate105is oriented to be parallel to the x-axes linear motion system surface plane29(and therefore also to y-axes linear motion system surface plane39), and is placed within the range of travel of the x-axes linear motion systems20and25and the y-axes linear motion systems30and35, and is placed vertically below the x-y-z stud positioning system12. Embed plate105is vertically supported by the embed support structure (not shown) which is attached to the factory floor83.

Embed plate105is the workpiece and is not part of the x-y-z stud positioning system12.

Further attached to the underside surface of z-axis support plate80is a z-axis directed laser-based distance sensor115having a vertically downward directed laser beam117which reflects off of the top surface120of the embed plate105at location119. The sensor measures the distance from the support plate80to the top surface120of the embed plate105and is used to calculate z-direction distances. For example, the z location of the collet and ferrule support assembly100with respect to the surface120of the embed plate105can be determined using laser beam sensor (not shown) that is offset adjusted, the encoder data of the BLDC motor55and other parameters. The cable118provides communication to computer14.

Located above the embed plate105is imager125having lens127. The imager125has a field of view which fully covers the entire surface of any size embed plate105placed within the range of travel of the x-axes positioning linear motion systems20and25and the y-axes positioning linear motion systems30and35.

It is assumed that the y-axes positioning linear motion systems30and35have been previously positioned (parked) along the x-axis so as not to obstruct the view when imager125is imaging the surface120of the embed plate105. The parked location may also be the homed position for the x-y-z stud positioning system12so as not to obstruct the field of view of imager125of the embed plate105. The homed position may be defined as the x-axes, y-axes, and z-axis travel extents for the respective linear motion systems.

Imager125particularly images ground welding sites110a-110nlocated on the top surface120of the embed plate105as welding site candidates and simultaneously images the registration marker112. The registration marker112is also registered with the (object space) x-y position of the x-axis and y-axis linear motion systems using conventional calibration methods. Thus, the registration marker has a known x-axis and y-axis position in both object-space and image-space.

Imager125is electrically connected to the computer14via the cable128.

Also positioned above the embed plate105is an obliquely positioned electromagnetic wave source, also referred to herein as a light source130which illuminates the top surface120of embed plate105. The light source130is fixed to an adjustable mount (not shown). The reflections of the light source130off the ground welding sites110a-110nare imaged by imager125.

The wavelength of light source130is not restricted and may include ultraviolet, visible, radio, x-ray and infrared wavelengths of electromagnetic radiation. The imager125is responsive to the wavelength of the light source130.

The position of source130is manually adjusted to maximize the reflections of the light source130off the ground welding sites110a-110n. Multiple light sources may be used to increase the intensity of the light reflections or to illuminate larger area embed plates. The light source130is connected to and controlled by the computer14via wire cable131.

The imager125may be a complementary metal oxide semiconductor (CMOS) based area scan camera and the like having a high dynamic range such as model number acA1440-73gc like series manufactured by Basler AG of Germany.

Additionally, shown inFIG. 1is the pressurized argon gas tank140. The outlet port141of the gas tank140is connected to the inlet port of a conventional gas regulator142. Gas regulator142regulates the flow of gas from the tank140through the electrically responsive gas valve146to the proximal ends of conduits143and144. During normal operation the tank140, gas regulator142, electrically responsive gas valve146and conduits143and144are in fluid communication with each other. The other distal ends of the conduits143and144are attached to the ferrule brackets270and310respectively and are more fully discussed with reference toFIGS. 6 and 7. Electrically responsive gas valve146is electrically connected to the computer14via the cable145.

The remaining features ofFIG. 1are discussed referring additionally now toFIGS. 2-7. Elements identified inFIGS. 1-7that are discussed in the specification in relation to one figure, and which do not differ from corresponding elements in other figures, may not be discussed in the specification in connection with the subsequent FIGS. The collet and ferrule support assembly100comprises the conventional collet156, the cross-member support plate150, the collet support plate155, the ferrule support plate160, and a first and second ferrule brackets270and310respectively.

Collet and ferrule support assembly100is further attached to bracket87(dotted line representation) via collet support plate155. As shown inFIGS. 1 and 2, a conventional steel stud162has been previously loaded into the collet156by the stud loading mechanism16.

The conventional steel stud162comprises an upper cylindrical head164and a lower shank166. The diameter of the head164is larger than the diameter of the shank166and is sized to be forcibly insertable into the lower section158of collet156and gripped by fingerlike grippers159.

A flux pellet168(shown explicitly inFIGS. 2B and 2C) is attached to the bottom surface170of stud162. Upon welding, the flux pellet168melts and quickly outgasses surrounding the area of the welding site with an oxidation preventative gas.

The collet156has formed an upper section157thread-ably affixed to the collet support shaft210. The lower section158of collet156has formed expandable finger-like grippers159for gripping and forcibly holding the head164of the stud162. Further formed on the upper section157of collet156is the collet spring retaining ring169.

The upper end of shaft210has a through collet retaining pin173for limiting the downward vertical movement of the shaft210and therefore the collet156.

Referring particularly toFIG. 3, rectangular shaped cross-member support plate150comprises four corner positioned rod support through holes151,152,153and154. The rod support through holes151,152,153and154are concentric with the support rods191,192,193and194(shown as dashed lines) respectively. The rod support through holes151,152,153and154also have a larger diameter than the rods191,192,193and194respectively which allows each rod to be slidably inserted through their respective hole.

The bottom ends of rods191,192,193and194are threaded and are more fully discussed with reference toFIG. 5.

The right-side wall174and oppositely disposed left-side wall175of rectangular support plate150each have two tapped holes176and177, and178and179, respectively. Threaded into each hole176and177, and178and179are bolts180and181, and182and183, respectively. With rods191,192,193and194inserted into holes151,152,153, and154respectively, tightening bolts180,181,182and183affixes each rod to plate150. Thus, the vertical position of plate150can be slidably affixed with respect to the vertical position of rods191,192,193and194.

The support plate further has a centrally located through hole184concentric with shaft210. The diameter of hole184allows an obstructive passage of shaft210and pin173. The plane of top surface185of plate150is parallel to plane29(and therefore also parallel to plane39).

Referring particularly toFIG. 4, the rectangular shaped collet support plate155has formed four corner-positioned through holes200,201,202and203. Press fitted into the through holes200,201,202and203are bearings205,206,207and208respectively which supports rods191,192,193and194respectively. Bearings205,206,207and208may be conventional sleeve bearings or ball bearings or the like.

Thus, collet support plate155can move in a vertical (z-direction) positionally guided by the support rods191,192,193and194. The top surface212and bottom surface213of plate155are parallel to plane39.

Collet support plate155is further attached to collet and ferrule assembly bracket87(shown in dotted lines) using bolts214and215which pass through respective holes in bracket87and thread into threaded holes217and218respectively (both not shown inFIG. 4, but hole217and bolt214are shown inFIG. 2C) positioned on the back side219(oppositely disposed from front surface216) of plate155. Collet support plate155therefore moves in the z-direction in response to the movement of bracket87within the range of motion of the z-axis linear motion system40.

Collet support plate155has further formed a through hole220. Press fitted into the through hole220is insulation bushing172. Bushing172has further an inserted and press fitted flange bearing209to support shaft210. Insulation bushing172electrically isolates the flange bearing209from plate155, and therefore the stud162, collet156and shaft210from collet support plate155. The upper end of shaft210has a through collet retaining pin173

Referring toFIG. 2C, the collet spring171is disposed between the bottom surface of insulating bushing172and the top surface of collet spring retaining ring169and concentrically positioned around the shaft210. The welding cable17is electrically and mechanically conventionally attached to the collet156using a bolt11.

Referring specifically toFIGS. 5 and 2B, the substantially rectangular shaped ferrule support plate160has four corner-positioned threaded through holes225,226,227and228for accepting the threaded bottom ends of the support rods191,192,193and194respectively. When threaded into their respective holes, support rods191,192,193and194are perpendicular to the top surface230of plate160and are all aligned with the z-direction. The top surface230(and also the bottom surface229) of plate160is parallel to plane29(and therefore also parallel to plane39).

In the embodiment illustrated inFIG. 5, the right side232of ferrule support plate160has formed a one ended opened slot234.

The front side236of the ferrule support plate160has formed the front side first ferrule mounting tab238and a front side second ferrule mounting tab240respectively, each tab having horizontally directed concentric through holes242and244having their respective axes parallel to the y-axis.

Similarly, the rear side246(disposed opposite of front side236) of the ferrule support plate160has formed rear side first and second ferrule mounting tabs248and250, each tab having horizontally directed concentric through holes252and254respectively and having their respective axes parallel to the y-axis. Tab pair238and240are mirrored about a plane256which is parallel to the front side236, is directed along the y-axis direction and bisects the plate160in the x-axis direction to form tab pair248and250.

Hole pair242and244and hole pair252and254are each sized accordingly to accept a conventional ring-grip quick release pin258aand258b(seeFIGS. 2A and 2C) respectively or the like.

Referring specifically toFIGS. 2C, 6A and 7A, tabs238and240, and tabs248and250, are further constructively configured to mate with cylindrical shaped bosses284and336of the ferrule brackets270and310, respectively.

The top surface230of ferrule support plate160further has formed a first ferrule bracket spring holding tab262having the through hole264whose axis is parallel to the x-axis. A second ferrule bracket spring holding tab266is mirrored through plane256having the through hole268whose axis is parallel to the x-axis. Holes264and268are concentrically aligned.

Referring specifically toFIGS. 1, 2A, 2B, and 2C, four compression springs221(not shown),222,223and224are placed around and concentric with rods191,192,193and194respectively and disposed between the bottom surface213of plate155and the top surface230of ferrule support plate160. Springs221(not shown),222,223and224extend-ably bias the ferrule support plate160(and the ferrule brackets270and310). As the bottom of the ferrule sections276and328of ferrule brackets270and310respectively contact the surface120, springs221-224compress thus forcibly holding the ferrule brackets270and310against the surface120.

Referring specifically toFIGS. 2A, 2B, and 2C, the collet spring171is disposed between the collet spring retaining ring169and the bottom surface of insulating bushing172. Collet spring171extend-ably biases the collet156(and loaded stud162). As the stud162comes into contact with surface120, spring171begins to compress.

Referring now toFIGS. 6A and 6B, andFIGS. 7A and 7B, the first ferrule bracket270is shown having an upper vertical arm272and an inwardly slanting (i.e., towards the loaded stud162) lower arm274. Further formed on the lower section of lower arm274is a semi-cylindrical ferrule section276of a conventional ferrule. Ferrule section276further comprises a partial semi-cylindrical shaped through hole278having a diameter exceeding the diameter of stud shank166.

As is discussed later in this disclosure, closing both ferrule brackets270and310will mate the ferrule section276of ferrule bracket270with the corresponding ferrule section328of ferrule bracket310thus forming a closed conventional ferrule around the shank of stud162. Thus, shank166can freely move through the completed hole formed with the mated ferrule sections276and328.

Gusset280is inwardly formed between the lower portion of the upper vertical arm272and the upward portion of lower arm274. Gusset280provides additional strength to ferrule bracket270, and may also dissipate heat generated in ferrule bracket270by the welding process.

Formed at the upper end282of the upper vertical arm272is a horizontally positioned cylindrically shaped boss284having a through hole286. Through hole286is sized accordingly to freely accept a conventional ring-grip quick release pin258a(seeFIG. 2A) or the like. The axis of through hole286is parallel to the y-axis of the Cartesian coordinate system19.

Also formed on the top surface of boss284is a vertical tab288having a through hole290. Further formed on the top inward surface292of the upper vertical arm272is tab294having through hole296. The axes of through holes290and296are parallel to the y-axis of the Cartesian coordinate system19.

Further mounted on the inside surface of lower arm274is a conventional steel stud sensor298having a cable299. Sensor298senses the presence of steel stud162and may incorporate optical or magnetic based sensing technologies, and communicates with computer14via stud sensor cable299.

Further formed on the outside surfaces of ferrule bracket270are heat dissipating heatsink fins300and302. The fins300and302are composed of the same material as the ferrule bracket270and will have the same coefficient of thermal expansion and will therefore minimize thermally induced internal stresses. Additional heatsinking fins may be added to the surfaces of ferrule bracket270.

A conventional blower309(as shown inFIG. 1) or fan or other air moving device or the like may also be mounted on collet and ferrule assembly support bracket87. Air or other gas (such as an inert gas such as argon) is forced into the inlet port308(seeFIG. 1) of blower309and exists under pressure through the outlet conduits311and312.

The current of gas from blower309via the conduit311is directed to flow across the surfaces of ferrule bracket270and especially the surfaces of heatsink fins300and302thereby dissipating any heat build-up produced in the ferrule bracket270by the arc welding process. The fins300and302are passive heat exchangers that transfer the heat generated in the ferrule bracket270by the arc welding process to the current of air flowing across the fins. The current of air may be replaced by a circulating fluid and the ferrule bracket270constructively configured to accommodate a liquid medium, or a combination of a current of air and fluid cooling could be used. The inert gas may also retard the surface oxidation of the ferrule bracket270.

The support clamp for affixing the conduit311to the ferrule bracket270is not shown for clarity.

Also shown inFIGS. 6A and 6Bis conduit143. The distal end of conduit143is attached to the lower arm274of the ferrule bracket270in close proximity to the semi-cylindrical ferrule section276. The distal end of conduit143is constructively configured to direct the argon gas flowing outwards from the distal end of conduit143into the volume bounded by the closed inside surfaces of the mated semi-cylindrical ferrule sections276and328, the surface120of the embed plate105(seeFIG. 1), and the shank166of the loaded stud162(seeFIG. 2C).

The argon gas inhibits the oxidation of the closed inside surfaces of the semi-cylindrical ferrule sections276and328during the welding of stud162extending the useful life of the ferrule bracket270(and310).

Referring toFIGS. 7A and 7B, the second ferrule bracket310is shown. The second ferrule bracket310is identical to the first ferrule bracket270except for the stud sensor298on first ferrule bracket270.

The second ferrule bracket310has an upper vertical arm324and an inwardly slanting lower arm326. Further formed on the lower section of lower arm326is a semi-cylindrical ferrule section328of a conventional ferrule. Ferrule section328further has formed a semi-cylindrical through hole330having a diameter exceeding the diameter of stud shank166.

As previously mentioned, closing both the first and second ferrule brackets270and310mates the ferrule sections276and328respectively thus forming a conventional ferrule and allowing shank166to freely move through hole created by the mated ferrule sections276and328.

Gusset332is inwardly formed between the lower portion of the upper vertical arm324and the upward portion of lower arm326. Gusset332provides additional strength to ferrule bracket310, and may also dissipate heat generated in ferrule bracket310by the welding process.

Formed at the upper end334of the upper vertical arm324is a horizontally positioned cylindrically shaped boss336having a through hole338. Through hole338is sized accordingly to accept a conventional ring-grip quick release pin258b(seeFIG. 2A) or the like. The axis of the through hole338is parallel to the y-axis of Cartesian coordinate system19.

Also formed on the top surface of boss336is a vertical tab340having a through hole342. Further formed on the top inward surface344of the upper vertical arm324is tab346having through hole348. The axes of the through holes342and348are parallel to the y-axis of Cartesian coordinate system19.

Further formed on the outside surfaces of ferrule bracket310are heatsinking fins350and352. The fins350and352are composed of the same material as the ferrule bracket310and will have the same coefficient of thermal expansion and will therefore minimize thermally induced internal stresses. Additional fins may be added to the surfaces of ferrule bracket310.

The current of gas from conduit312is directed to flow across the surfaces of ferrule bracket310and especially the heatsink fins350and352via the conduit312thereby dissipating any heat build-up produced in the ferrule bracket310by the arc welding process. The heatsink fins350and352are passive heat exchangers that transfer the heat generated in the ferrule310by the arc welding process to the current of air. The current of air may be replaced by a circulating fluid and the ferrule310constructively configured to accommodate a liquid medium. The inert gas may also retard the surface oxidation of the ferrule bracket310.

The support clamp for affixing the conduit312to the ferrule bracket310is not shown for clarity.

Also shown inFIGS. 7A and 7Bis conduit144. The distal end of conduit144is conventionally attached to the lower arm326of the ferrule bracket310in close proximity to the semi-cylindrical ferrule section328. The distal end of conduit144is constructively configured to direct the gas flowing outwards from the distal end of conduit144into the volume bounded by the closed inside surfaces of the semi-cylindrical ferrule sections276and328, the surface120of the embed plate105(seeFIG. 1), and the shank166of the loaded stud162(seeFIG. 2C).

Referring toFIGS. 6A and 6B, attached to the hole290of tab288of ferrule bracket270is one end of the extension spring320, the other end of the extension spring320is attached to the hole264of tab262of plate160(seeFIG. 2A). Likewise, referring toFIGS. 7A and 7Battached to the hole342of tab340of ferrule bracket310is one end of the extension spring322, the other end of the extension spring322is attached to the hole268of tab266of plate160(seeFIG. 2A).

Referring toFIG. 2C, mounted on the bottom surface229of plate160are solenoids354and356having moveable plungers358and360respectively. The distal ends of plungers358and360are conventionally connected to tabs262and266via pins362and364or by other means, respectively. Cables366and368connect solenoids354and356respectively to computer14. When solenoids354and356are electrically energized, plunger358and360are forcibly pulled into the bodies of their respective solenoids.

As previously mentioned, the solenoids354and356may be configured to provide both a pulling and pushing force. If the solenoids354and356are configured to additionally provide a pushing force, then the extension springs320and322are not required with the force required to separate (open) the ferrule sections276and328being supplied by the solenoids354and356respectively.

Additionally, ferrule bracket270and ferrule bracket310each have a “ferrule section opened” and “ferrule section closed” conventional limit switches370and371respectively (not shown for clarity). The limit switches324and371are mounted on plate160and constructively configured to be responsive to the rotatable positions of the ferrule's brackets270and310respectively.

The ferrule brackets270and310are composed of a high temperature, electrically insulating, non-wetting and heat conducting refractory material such as BN—ZrO2—SiC based ceramic composite or the like, including ultra-high-temperature ceramics (UHTC), such as those currently under consideration for use in the construction of hyper-sonic missiles.

The stud loading mechanism16, welding controller18, conventional keyboard369, conventional liquid crystal display (LCD)374, light source130, imager125, distance sensor115, stud sensor298, BLDC motor controller70, BLDC motor controller72, BLDC motor controller74, x-axis linear motion system25first and second limit switches88and89respectively, y-axis linear motion system35first and second limit switches90and91respectively, z-axis linear motion system40first and second limit switches92and93respectively, solenoid354, solenoid356, ferrule bracket270opened/closed limit switch370, ferrule bracket310opened/closed limit switch371, and argon gas valve146are in bi-directional communication with computer14and each other via local buses379,376,377,378,131,128,118,299,76,77,78,94,95,96,97,98,99,366,368,372,373,145, respectively, and master bus375.

Limit switches370and371each generate a signal when the ferrule sections276and328are fully closed (thereby signaling that a complete cylindrical ferrule is formed around and the shank166) or fully opened (thereby signaling that the ferrule sections276and328are fully separated from the shank166), respectively.

The limit switches370and371are connected to either a motor controller70,72or74(using the available standard input and output (I/O) port of the controller) or to a conventional input/output port of computer14using cables372and373respectively. The state of the limit switches370and371can be communicated to the computer14through any of the motor controllers70,72and74, or directly to the input/output port of the computer14.

The liquid crystal display374may include touch screen technology for entering data by the operator to the computer14.

The stud loading mechanism16is of conventional design and is constructively configured to accommodate the x-y-z stud positioning system12for loading a stud162into the collet156.

Referring toFIG. 9, a computer memory380block diagram is shown having the operating system390, program memory400and data memory420.

Operating system390is a conventional operating system for managing the hardware and software resources of computer14and may include a conventional Windows or Linux operating system software, a real time operating system (RTOS), or other operating systems and the like. The operating system390performs conventional operating system software functions and is capable of executing various programs stored in program memory400of computer14. The operating system390is well known technology in the art of computer science.

The program memory400comprises a number of software programs for performing tasks according to the preferred embodiment of the invention including the camera calibration program402, image correction program404, the image processing and analysis program406, the x-y-z servo positioning and control system program408, the ferrule control program410, the welding control program412, the peripheral sensors program414, the argon gas valve controller program416and other programs418.

The data memory420is conventional random-access memory (RAM) and stores variables and other data used by the other programs. For example, raw image data acquired by imager125and corrected image data are stored in data memory420. Data memory420may also include conventional non-volatile flash memory for storing constant variable and configuration data information.

The camera calibration program402determines the required correction parameters to correct raw image data for lens127distortion (pin cushion and barrel distortions and the like) and additionally determines the element valves of a homography matrix to correct images for perspective distortion.

The camera calibration program402first acquires raw images of a number of 2-D checkerboard patterns of different spatial orientations via imager125and lens127and stores these raw images in data memory420. One image includes having the 2-D checkerboard pattern oriented to be flat on the surface120and is tagged as the “flat-image”.

The flat image is used to correct the image for perspective distortion and to determine the element values of the homography matrix within the camera calibration program402. The flat image is also used by the image correction program404to determine the image-space to object-space and vice versa distance transformation values.

The 2-D checker-board raw image data, taken at different spatial orientations, along with a conventional lens distortion correction program, such as referenced in the “Camera Calibration Toolbox for MATLAB” and offered by The MathWorks, Inc. of Natick, Mass., then processes these raw checkerboard images and calculates the lens distortion parameters used to correct for the lens127distortion. There are many programs known in the art to correct images having lens distortion.

The camera calibration program then additionally determines the element values of a homography based transformation matrix to correct for any perspective distortion using the lens distortion corrected flat-image of the 2-D checkerboard placed flat on the embed surface120. The homography calculations are based upon the assumption that both the embed surface120and the image plane of the imager125maintain a planar relationship. Homography calculations to correct for perspective distortion is well known in computer vision technology.

The camera calibration lens distortion parameters and the element values of a homography based transformation matrix are stored in a configuration data file located in the non-volatile flash memory within data memory420or may be stored within the camera calibration program402or other programs.

Usually the camera calibration program402is executed infrequently since the lens127does not change and the planar relationship between the imager125image plane and the surface120plane remains constant for similar embed plates105.

Image correction program404first commands the imager125to acquire a raw image of the surface120(which includes the reflections from the welding sites110a-110nproduced by light source130) and then inputs the lens distortion parameters and homography transformation matrix element values from the configuration data file stored either in non-volatile memory or camera calibration program402program.

The lens and homography correction data from the configuration file are then used by the image correction program404to first correct the acquired raw images for lens distortion, and then secondarily correct the lens-corrected image for perspective distortion. The corrected image is then stored in memory420.

Image correction program404also undistorts (i.e., corrects for lens and perspective distortions) the flat-image of the 2-D checker-board raw image and determines the object-space to image-space distance transformation, and vice versa.

For example, the dimensions of the squares on the checker-board pattern are known in object space (the checkerboard may have alternating 1-inch black and white squares). From the corrected image of the checkerboard, a corresponding pixel count is determined for the imaged squares using well known techniques in the art, and the corresponding pixels per inch distance (the image-space to object-space distance transformation) and vice versa is determined.

Also, the image-space area of each pixel has an associated object-space area. For example, if the corrected image of the 1-inch black square yields 100 pixels within the black square image, then each pixel equates to 0.01 square inches (assuming square pixels).

Using the image-space to object-space distance transformation, the image-space coordinates of the image of the registration marker112can be calculated. Thus, every pixel has a unique u-v coordinate (in image-space) which maps to an equivalent object space x′-y′ coordinate referenced to the coordinate system122and vice versa. These values are also stored in the configuration data file.

The image processing and analysis program406then processes the corrected surface120image previously stored in memory420by image correction program404by first using a conventional thresholding filter.

Image processing algorithms including thresholding filters, image segmentation, image enhancement, morphological image operations and restoration methods are referenced in many texts including Rafael C. Gonzalez and Richard E. Woods, Digital Imaging Processing (2d ed., Prentice Hall, 2002), among others.

FIG. 10is an image representation of the field of view of the camera illustrating the imaged embed plate, the welding sites, and salt and pepper noise. A corrected image450of the area defined by the field of view of the imager125is shown and includes the image456of the embed plate105, the image452of the perimeter129(seeFIG. 1) of the embed plate105, and the images110a′-110n′ of the welding sites110a-110nrespectively. The welding sites110a-110nare markings (e.g., grind spots) on the embed plate105(i.e., the target metal for welding studs thereto) that are potential locations for a welding site. Accordingly, the welding sites110a-110nrepresent welding site candidates that are to be evaluated via imaging processing and verification to determine the viability of using such a welding site candidate as a welding site location for welding a metal stud thereto. Any welding site candidate that is validated as a viable welding site location can be used, whereas any welding site candidate that is determined not to be a viable welding site location can be removed from consideration such that it is not used for welding a metal stud at that location.

Image450further includes the image454of the registration marker112having a conventional superimposed image space u-v coordinate system458having u-axis460and v-axis462. The u-v coordinate system458defines the pixel coordinates with respect to the image454of the registration marker112. Also visible in the image450is salt and pepper noise pixels464(not all salt and pepper noise pixels are labelled for clarity). A small selected area463of image110i′ is also shown.

Referring additionally toFIG. 11A, the selected imaged area463of the imaged ground welding site110i′ is shown explicitly illustrating the rectangular (square) shaped pixels (for example, pixel500) and the respective 8-bit grayscale intensity values within the border of the individual pixels (for example, the intensity value 70 of pixel500is represented by502). Additionally, the imaged welding sites may be determined using artificial intelligence. Specifically, a trained convolutional neural network (CNN) may be used to determine the imaged welding sites.

Referring toFIG. 11B, the selected area463of the imaged ground welding site110i′ (as shown inFIG. 11A) is depicted after an intensity thresholding value of 100 has been applied. Any pixel grayscale intensity value less than 100 is set to 0 and any pixel value greater than or equal to 100 is set to 255 (maximum grayscale value for an 8-bit quantization). The grayscale intensity value502of pixel500inFIG. 11A(value is equal to 70) is now changed after thresholding to a grayscale intensity value504(value is equal to 0) inFIG. 11B. The pixels intensity values of 0 and 255 may be changed to the intensity values of 255 and 0 respectively using software.

Salt and pepper and Gaussian noise removal is next performed on the threshold corrected image using well known techniques in the image processing art. The images110a′-110n′ of the welding sites110a-110nare shown blackened against a white background for disclosure purposes even though the actual image would show the images of the welding sites110a-110nas whitened against a blackened background. Complementing pixel intensity valves is easily done in imaging processing software (see for example the MATLAB command “imcomplement”).

FIG. 12shows the image450after thresholding and noise removal (note that the welding site images110a′-110n′ have been slightly reduced in size and are a grayscale valve of 0 (black representation) and the salt and pepper noise464has been removed).

The image processing and analysis program406then further processes the threshold and noise mitigated image of both the surface120and welding sites110a-110nusing conventional image processing techniques and in particular imaging processing morphological operations as now discussed.

After mitigating the noise in the image, image processing and analysis program406may then use morphological operations to determine connected components (i.e., groups or clusters of similar valued pixels that are connected) using a decision rule of pixel connectivity (such as 4-connectivity or 8-connectivity), and further assigning a label to each group.

FIG. 13illustrates the image450having the connected components (clusters of pixels) defined by labels465(numeric labels 1 through 14).

An example of an algorithm for determining the connected components (groups of pixels) and labeling each distinct group is the Hoshen-Kopleman algorithm.

The number of pixels contained within each labeled cluster (pixel area) is then calculated and clusters having less pixel area than needed for welding the stud to surface120are eliminated (the equivalent pixel area in object-space area was previously determined in the image correction program404). For example, the number of pixels contained within each labeled cluster may be compared to a threshold number of pixels corresponding to the minimum acceptable total pixel area. If the number of pixels is less than the threshold number of pixels, the cluster can be removed from consideration. Alternatively, the number of pixels can be converted to a total pixel area and the total pixel area may be compared to a threshold pixel area. If the total pixel area is less than the threshold pixel area, the cluster can be removed from consideration. Those clusters that have at least the requisite number of pixels or requisite total pixel area are considered further as welding site locations by the algorithm. The minimum pixel area required is calculated based upon the operator inputting the shank diameter in inches (or the type of stud which has pre-stored the shank diameter) and using the object-space to image-space transformation values previously obtained in the image correction program404.

The image processing and analysis program406then calculates the area of the largest (maximum) inscribed circle (commonly referred to as MIC) and the center of each inscribed circle (in u-v coordinates) for each cluster. The maximum inscribed circle is the largest circle that can be completely enclosed within the pixel area of a pixel cluster (i.e., within the outer boundary of the pixel cluster) without overlapping with a pixel that has an intensity value that is less than an intensity threshold (e.g., an intensity threshold value of 100 in the above example). Clusters having “holes” within their respective perimeter are modified by creating a path from the perimeter to the hole (i.e., to open the hole to the exterior of the cluster). In other words, a low-intensity pixel falling below the intensity threshold may be completely surrounded by high-intensity pixels that meet the intensity threshold, thus appearing as a “hole”. In this case, pixel grayscale intensity value of high-intensity pixels that are located between the low-intensity pixel and a nearest outer perimeter of the cluster may be switched to 0, thereby creating a pathway of “0” value pixels from the hole to the nearest outer perimeter.

An iterative algorithm for performing this calculation is “Poles of Inaccessibility: A Calculation Algorithm for the Remotest Places on Earth” by Garcia-Castellanos & Lombardo, Scottish Geographical Journal vol. 123, No. 3, 227-233, September 2007, modified for pixelated data. Other algorithms are available, for example, “An efficient Algorithm to Calculate the Center of the Biggest Inscribed Circle in an Irregular Polygon” by Oscar Martinez, arxiv.org (web). Other programs utilize a Voronoi diagram, and still other programs iteratively solve for the MIC. Polygons can be formed using the u-v coordinates of the perimeter pixels.

The areas of each MIC for each cluster is then compared against the bottom shank surface area of the chosen stud. Clusters having MIC areas less than the bottom shank surface area are further eliminated from welding consideration.

As an example, and referring toFIG. 14A, a first cluster467of pixels representing the image110i′ and having the label “9” is shown. The calculated first maximum inscribed circle469is shown having a diameter470and having a center472(having u-v coordinates) defined in image-space. Also shown is an image-space representation of the minimum required circular area473to weld the stud162to surface120having diameter474and based upon the specification of stud162(i.e., the area of bottom surface170of shank166) and centered on the center472.

The first cluster467does meet the minimum area requirements for welding a stud162and will be further included for welding site consideration.

Referring now toFIG. 14B, a second cluster475of pixels representing the image110fand having the label “6” is shown. The calculated second maximum inscribed circle477is shown having a diameter479and having a center480defined by the image-space u-v coordinates. Also shown is an image-space representation of the minimum required circular area482to weld the stud162to surface120having image-space diameter484based upon the specification of stud162(i.e., the area of bottom surface170of shank166).

The second cluster475does not meet the minimum area requirements for welding a stud162and will be eliminated from further welding site consideration.

The centers of the MIC for those clusters having MIC areas larger than the bottom shank surface area are then used to calculate the distance (in u-v coordinates) between each MIC center. Those center-to-center distances less than the minimum distance required to weld the stud to the surface120are eliminated and their respective clusters are removed. In other words, both clusters are removed from consideration. This assures that the collet and ferrule support assembly100has sufficient room between the welding sites to weld the stud without interference from previously welded studs. Alternatively, one of the clusters may be removed from consideration while the other cluster remains in consideration. Which cluster of the two clusters that is selected for removal and which cluster is kept for further consideration may be based on one or more factors, including the one having the smaller total area or the smaller inscribed circle may be removed while the other cluster remains for consideration. Alternatively, which cluster has a smallest average center-to-center distance to other clusters may be removed while the other cluster remains for consideration.

Referring toFIG. 15, the image processing and analysis program406further calculates a second image-space perimeter, also referred to as an inside image perimeter133, inwardly offset by an image-space vertical distance134and an image-space horizontal distance135from the image132of the embed plate perimeter129. The u-v vertical distance134and the horizontal distance135are calculated from the object-space distance values (using the image-space to object-space transformation) input into the computer14via keyboard369by the operator. The area bordered by the outside image perimeter132and the inside image perimeter133defines a ‘No Weld’ image-space area137.

The image processing and analysis program406then determines if any of the minimum required welding area136(in image-space) (e.g., minimum required circular area473) centered on the MIC to weld the stud162would intersect the ‘No Weld’ area137. Any welding site candidate (i.e., pixel cluster) that corresponds to stud162having its respective minimum required image-space area intersect the area137is discarded from any further welding considerations and not listed in the welding table.

This prevents the welding of studs162too close to the perimeter129of embed plate105.

The centers for each MIC of the remaining welding sites (i.e., each of the remaining welding site candidates or pixel clusters) are then stored in a welding site table which lists the MIC center coordinates (in u-v coordinates) for each remaining cluster. The image-space u-v coordinates for each center are then transformed to object space x′-y′ coordinates and x-y coordinates using the object-space to image-space distance transformation calculated in the image correction program404and corrected for any offsets. Thus, any remaining welding site candidate that has not be eliminated based on not satisfying welding site criteria is used as a welding site location for affixing a metal stud thereat. All remaining welding site candidates may be used as welding site locations at which the controller (e.g., one or more controllers implementing control programs408,410, and412) automatically places a metal stud for welding. Alternatively, a user may have an option to select from the remaining welding site candidates to be used as welding site locations via manual input or based on a priority selection. It will be further appreciated that the evaluation stages that result in removal of pixels clusters from consideration as welding site locations may be performed in a different order. For example, the largest inscribed circle size could be performed prior to the total pixel area evaluation. Or the proximity evaluation with respect to a peripheral edge of the embed plate105may be performed first.

It is therefore understood that a table of x′-y′ coordinates (with respect to the registration marker112) of each welding site is determined from the raw image data of surface120. Conventional calibration techniques have previously calculated the offsets of the x′-y′-z′ coordinate system122to the coordinate system19, and therefore any x′-y′-z′ location is also known in the x-y-z coordinate system19. Coordinate transformations from one to another Cartesian coordinate system is well known in the art and may include translational and rotational transformations.

The x-y-z servo positioning and control system program408controllably moves the collet and ferrule support assembly100to a desired x-y-z location. The acceleration and speed profiles for the x-axis, y-axis and z-axis linear movement are controlled by the x-axis, y-axis, and z-axis motor controllers70,72and74respectively and are programmed by computer14.

For example, to position a stud over a particular welding site the x-y welding site coordinates stored in the welding site table is received by the x-y-z servo positioning and control system program408. Program408then sends the proper motion commands to the x-axis controller70and y-axis controller72for positioning the collet and ferrule support assembly100directly over the center of the respective MIC for that welding site. The x-y-z servo positioning and control system program408then receives the z-direction data and moves the collet and ferrule support assembly100to the desired z-axis coordinate to first have the ferrule brackets270and310forcibly contact the surface120and then to continue in a predetermined downward direction to forcibly have the flux pellet168of stud162contact the surface120.

The x-y-z servo positioning and control system program408may also receive x-y coordinates of the stud loading position. For the stud loading cycle, the x-y-z servo positioning and control system program408homes the z-axis and then sends the proper motion commands to the x-axis controller70and y-axis controller72to position the collet and ferrule support assembly100directly over the center of the head of the unwelded stud. The x-y-z servo positioning and control system program408then receives the z-direction data and moves the collet and ferrule support assembly100to the desired z-axis coordinate to load the stud162into collet156.

The z-direction distance for both the welding and loading of the stud is previously calculated knowing the stud162length, the z-direction distance sensor115input (offset corrected) and other parameters.

It is therefore understood that x-y-z positioning and control program408controls both the linear speed and acceleration of the x-axis, y-axis and z-axis linear motion systems for positioning the collet and ferrule support assembly100at a desired x-y-z position.

The ferrule control program410controls the of electrical activation of solenoids354and356via bus375and local buses366and368respectively. Electrically activating solenoids354and356results in a pulling force on tabs262and266of ferrule brackets270and310, respectively. This force mates the semi-cylindrical ferrule section276with the semi-cylindrical ferrule section328to form a cylindrical shaped ferrule around the shank166of stud162.

The welding control program412communicates with and controls the welding controller18and sends the welding parameters required by the welding controller18to successfully perform the stud welding function. For example, the welding current and welding time may be transmitted from computer14via bus376to the welding controller18. The welding parameters may be input into computer14by the operator using keyboard369or a touch screen activated liquid crystal display374, or previously stored in the configuration data file previously mentioned. Also, a “Weld Now” command is sent to the welding controller18which first initiates the pilot arc and then initiates the arc weld welding the stud162to the embed plate105.

The peripheral sensors program414interfaces with and receives z-axis distance data from sensor298via local bus118and master bus375. The peripheral sensor program414also interfaces with and receives data from stud sensor via local bus299and master bus375to indicate the presence or absence of a loaded stud162in collet156.

The argon gas valve controller program416controls the electrically responsive gas valve146. To open valve146, program416sends an “Open Valve” command via bus375and control cable145to the gas valve146which then allows the argon gas to flow through conduits143and144(and therefore to ferrule brackets270and310). To close valve146, program416sends a “Close Valve” command to the gas valve146via bus375and control cable145which stops the argon gas flow to conduits143and144(and therefore to ferrule brackets270and310).

The other programs418include programs not explicitly described above for providing the necessary functionality for the improved robotic stud welding apparatus10to achieve the stated objects.

Referring now toFIG. 16, a summary of the process steps for obtaining a list of valid welding sites from a raw image of the embed plate105is shown and begins with process step505.

Process step505obtains the raw image of the embed plate105from the imager (camera)125using program404.

Process step510corrects the raw image (bit map) for lens distortion using program404.

Process520corrects the lens corrected image for perspective distortion using program404.

Process step525threshold filters the lens and perspective corrected image using program406.

Process530removes noise from the threshold filtered image using program406.

Process535determines pixel connectivity and clusters of pixels and then further labels each cluster using program406.

Process540determines the number of pixels in each labelled cluster using program406.

Process545eliminates those clusters having their respective pixel areas less than the minimum required pixel area to weld a stud162using program406.

Process550calculates the maximum inscribed circle (MIC) area or diameter and center u-v coordinates for the remaining clusters using program406.

Process555eliminates those clusters having a MIC pixel area or diameter less than the minimum pixel area or diameter required to weld a stud162using program406.

Process560calculates the MIC center-to-center distance for the remaining clusters using program406.

Process step565eliminates those clusters not meeting the minimum MIC center-to-center clearance distance using program406.

Process570eliminates those clusters which have their stud162image-space welding area intersecting the ‘No Weld” area defined by the area between the image132of the embed plate105perimeter129and the inside offset perimeter image133defined by the operator using program406.

Process575then creates a welding site coordinate table in u-v, x′-y′, and x-y coordinates using program406.

Process580completes the welding site coordinate table by appending the z-direction distance data to the welding site coordinate table. The z-direction distance is calculated and offset corrected knowing the z-direction distance from the sensor115, the stud162length, and other parameters using program406.

The following operational disclosure assumes that the system has been calibrated for lens distortion and perspective distortion, and that the image-space to object-space transformation parameters have also been determined as previously determined by program404.

In operation and referring additionally toFIGS. 17A-17F, the operator begins the operation of the improved robotic stud welding apparatus10beginning with the START step600. Operational flow then continues via arrow605to step610.

In step610, electrical power is supplied to the improved robotic stud welding apparatus10by the operator (or other means) turning on power supply15. Operational flow continues via arrow615to step620.

In step620, the computer14performs a power-on-reset procedure which initializes all variables and tables, de-energizes the solenoids354and356(which opens the ferrule brackets270and310), commands the x-y-z stud positioning system12to move to the predefined ‘home’ position, turns on the blower309and the light source130, initializes the imager125, initializes the motor controllers70,72and74, initializes the stud loading mechanism for loading a stud162, and performs other tasks to place the improved robotic stud welding apparatus10in a condition for proper operation. Operational flow continues via arrow625to step630.

In step630, the operator inputs the required data via the keyboard369for welding a stud162to the embed plate105. This data includes the stud data (size, shank length and stud diameter), the peripheral offset distance to prevent welding studs162close to the embed plate105perimeter129, welding parameters such as desired welding current, dwell time and the like. The operator could input this data individually when queried or could select the stud162and other required data from a pull-down list or the like. After completing the data entry, operational flow continues via arrow635to step640.

In step640, the computer14instructs the motion controllers70,72and74to move the x-y-z stud positioning system12to the ‘park’ position opening an area under the positioning system12so that imager125has an unobstructed view of the entire embed support structure106. The park position and home position may be one in the same. Operational flow continues via arrow645to step650.

In step650, computer14instructs the operator to position an embed plate105on top of the embed plate support structure106and queries the operator if this task was accomplished. The manual process of positioning the embed plate105on top of the embed plate support structure106could also be automated. Operational flow continues via arrow655to step660.

In step660, the computer14waits for the operator's affirmative response that the embed plate105is properly positioned. If the embed plate105is not properly positioned, operational flow continues via arrow665back to step650. If the embed plate105is properly positioned, operational flow continues via arrow675to step680.

In step680, computer14checks the state of the ferrule bracket270and the ferrule bracket310limit switches370and371respectively to ensure the ferrule brackets270and310are both opened. If the ferrule brackets270and310are closed, operational flow continues via arrow685to step690which displays an error flag on liquid crystal display374and operational flow continues via arrow695to step700which stops further operation of the improved robotic stud welding apparatus10. If the ferrule bracket limit switches370and371indicate that the ferrule brackets270and310are both opened, operational flow continues via arrow705to step710(via ‘A’).

In step710, the computer14queries the operator if the arc welding process should begin. To begin the arc welding process, the operator selects the ‘Begin Welding’ command using the keyboard369or selectively chooses the command from the touch screen enabled liquid crystal display374. Operational flow continues back via arrow715to the beginning of step710until an affirmative response is input (or chosen) by the operator. Upon receiving the ‘Begin Welding’ affirmative response, operational flow continues via arrow725to step730.

In step730, the computer14commands the imager125to image the field of view image450containing the embed plate105(and therefore the embed plate perimeter129), the previously ground welding sites110a-110n, and the registration marker112. The field of view raw image450is subsequently stored in memory420. Operational flow continues via arrow735to step740.

In step740, the computer14corrects the field of view raw image450for lens distortion and perspective distortion using the image correction program404. The lens and homography correction data from the configuration file are used by the image correction program404to first correct the acquired raw images for lens distortion, and then secondarily correct the lens-corrected image for perspective distortion. At this point the image is fully corrected and subsequently stored in data memory420. Operational flow continues via arrow745to step750.

In step750, the computer14, using the image processing and analysis program406to correct the field of view image450and in particular the image of surface120stored in memory420, calculates a list of the permitted object-space x-y coordinates of the centers of the MIC for each welding site meeting the selection process. Operational flow continues via arrow755to step760.

In step760, the computer14commands the x-y-z stud positioning system12to move to the x-y stud loading position of the stud loading mechanism16. Note that the ferrule brackets270and310are in the opened position. Operational flow continues via arrow765to step770.

In step770, the computer14commands the x-y-z stud positioning system12to move the collet156from the present (parked) z-location downward to load the stud162into collet156. Operational flow continues via arrow775to step780(via ‘B’).

In step780, the computer14then checks the stud sensor298to make sure that the stud162is loaded into the collet156and held by the fingerlike grippers159. If the stud162is not properly loaded into collet156, operational flow continues via arrow795to step800which terminates the operation of the improved robotic stud welding apparatus10. An error flag is also displayed on the LCD374. If the stud is properly loaded into the collet156, operational flow continues via arrow785to step810.

In step810, the computer14then commands the x-y-z stud positioning system12to move in the upward z-direction and back to the parked z-location. At this point the stud162has been loaded into the collet and repositioned at the parked z-location. Operational flow continues via arrow815to step820.

In step820, the computer14commands the x-y-z stud positioning system12to move to the x-y location of the first welding site listed in the welding table. Note that there is no z-axis linear system movement40for this step. Operational flow continues via arrow825to step830.

In step830, the computer14sends electrical signals to energize the solenoids354and356forcing the ferrule brackets270and310inward towards each other and thus forming a cylindrical ferrule from the two touching semi-cylindrical ferrule sections276and328. Operational flow continues via arrow835to step840.

In step840, the computer14inputs the state of the limit switches370and371for ferrule brackets270and310respectively to ensure that the ferrule sections276and328are closed. If the ferrule sections are not closed, operational flow continues via arrow845to step850which stops the operation of the improved robotic stud welding apparatus10. If the ferrule sections are closed, operational flow continues via arrow855to step860(via ‘C’).

In step860, the computer14commands the x-y-z stud positioning system12to controllably move the collet and ferrule support assembly100in the downward z-direction a distance calculated from the input data to have the closed semi-cylindrical ferrule sections276and328contact the surface120.

This input data includes distance sensor115data, the stud data (for example stud length), the encoder data from the BLDC servo motor55, and other necessary data to controllably contact the bottom surfaces of the closed semi-cylindrical ferrule sections276and328with the surface120. All z-distance data is offset corrected, as necessary. As the z-direction motion continues, the ferrule sections276and328are spring-ably forced downward and held in place by springs221,222,223, and224. Operational flow continues via arrow865to step870.

In step870, motion continues in the z-direction until the stud162goes through the formed cylindrically shaped ferrule (formed when the ferrule brackets270and310are closed) and the pellet168contacts surface120. At this point the stud162is spring-ably biased and forcibly held in place by spring171and the z-direction motion is stopped. Operational flow continues via arrow875to step880.

In step880, computer14commands the gas valve146to open which allows the pressurized argon gas to flow via conduits143and144into the closed ferrule brackets270and310and around the shank166. The computer14further commands the welding controller18to begin the arc welding process. In response to the computer14commands, the welding controller18initiates the pilot arc followed by the large welding arc. A short time thereafter, computer14commands the x-y-z stud positioning system12to lift, dwell (pause) and then plunge the stud162into the molten metal produced by the welding arc. The lift and plunge distances and dwell time are known given a particular stud162, welding current and other parameters. Operational flow continues via arrow885to step890.

In step890, the welding controller18terminates current flow to the stud162extinguishing the welding arc and sends a ‘Weld Complete’ signal to the computer14indicating that the welding process has completed. Operational flow continues via arrow895to step900.

In step900, the computer14responds to the ‘Weld Complete’ signal from the welding controller18and commands the gas valve146to close stopping the flow of argon gas to the ferrule brackets270and310, and further commands the x-y-z stud positioning system12to move a short distance upward in the z-direction to enable the ferrule brackets270and310to open and clear the surface120. Operational flow continues via arrow905to step910(via ‘D’).

In step910, the computer14sends electrical signals to deenergize the solenoids354and356. Deenergizing the solenoids354and356causes the ferrule brackets270and310to pivotally open (separate) from each other in response to the spring action of springs320and322. Operational flow continues via arrow915to step920.

In step920, the computer14inputs the state of the limit switches370and371for ferrule brackets270and310. Operational flow continues via arrow925to step930.

In step930, the computer14determines if the ferrule sections276and328have opened from the limit switches370and371state input. If the ferrule sections276and328are not opened, operational flow continues via arrow935to step940which stops the operation of the improved robotic stud welding apparatus10. If the ferrule sections276and328are separated, operational flow continues via arrow945to step950.

In step950, the computer14commands the x-y-z stud positioning system12to move upward in the z-direction back to the parked z-location. Operational flow continues via arrow955to step960.

In step960, the computer checks if more studs162are to be welded. If no additional welding sites are available (i.e., there are no additional blank welding sites), operational flow continues via arrow965to step970.

In step970, the computer14commands the x-y-z stud positioning system12to move to the parked position. The improved robotic stud welding apparatus10then awaits a subsequent operator command. If additional welding sites are available for welding, operational flow continues via arrow975to step980(via ‘E’).

In step980, the computer14determines the x-y coordinates of the next available welding site from the list of permitted welding sites. Operational flow continues via arrow985back to step760(via ‘F’).

Although illustrated and described above with reference to certain specific embodiments and examples, the present invention is nevertheless not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the spirit of the invention. It is expressly intended, for example, that all ranges broadly recited in this document include within their scope all narrower ranges which fall within the broader ranges.