Planar grinder

A sample grinder includes a base having a bowl and a rotatable drive plate to operably support a grinding wheel. A head is configured to support a specimen holder and has a first drive for rotational drive of the specimen holder and a second drive for moving the head and specimen holder toward and away from the drive plate. The head has a sleeve that is larger than the specimen holder. A cover is disposed over the bowl and has an opening larger than the sleeve so that the sleeve fits through the opening when the specimen holder is moved toward the rotatable drive plate. The grinding wheel is mountable to the plate in a single radial orientation only. A dressing system is operably connected to a controller to monitor the current of the drive plate motor and/or the head first drive actuates the dressing system based upon the current drawn by the drive plate motor and/or the head first drive motor falling below a predetermined value.

BACKGROUND

Grinders are in use in many industries. One type of grinder is used to prepare samples of materials such as metals, polymers, ceramics or the like for further examination, such as by microscopic examination.

Known grinders include a sample or specimen holder that is configured to rotate relative to a grinding media that is also configured to rotate. In this manner, there are two rotating motions occurring simultaneously. A fluid, such as water, is injected onto the grinding media to lubricate and cool the sample and media and to remove debris, such as grinding debris generated during the grinding process.

One known grinder/polisher, disclosed in Shewey, et al, U.S. Pat. No. 8,574,028, includes a head on which a sample holder is mounted for rotation of the sample. The sample is held against a rotating plate or platen in a base of the grinder. The plate or platen has an abrasive surface or an abrasive fluid media is introduces onto the platen to effect the sample preparation. Typically, the abrasive surface on the platen is an abrasive paper or other removable and replaceable media. The disclosure of Shewey, as well, the disclosures of Hart. U.S. Pat. No. 8,465,347 and Hart, U.S. Pat. No. 8,152,603 are commonly assigned with the present application and are incorporated herein by reference.

The head of the grinder/polisher of Shewey reciprocates (moves toward and away from the platen) to maintain a predetermined force between the sample and the platen. Reciprocating movement of the head is determined based, in part, on input from a load cell that is operably connected to the specimen holder (via a chuck and drive shaft).

When used as a grinder, a grinding wheel is mounted to the platen. In use, the abrasive particles that form the grinding wheel become worn as a result of contact with and grinding of the specimen. As a result, the grinding wheel must be “dressed” or resurfaced to continue to effectively prepare the sample. Dressing is carried out during the grinding operation using an arm that swings over an opposite side of the wheel that has a head mounted to the arm. The arm moves in an arc and contacts the wheel to remove the worn areas and expose fresh surfaces of the abrasive that more efficiently effect the grind. In known automated grinder systems, dressing is carried out on a timed basis, regardless of whether it is needed, or is overdue.

In addition, known grinders have a base in which the platen is positioned that has an open top. That is, the areas above the platen, surrounding the specimens on the holder are open to the environs. While this makes access to the wheel and/or platen and specimens readily available, it can also result in splashing and debris being ejected from the grinder during operation.

It is also common to, at times, change out wheels to carry out different grinding operations. For example, different materials to be prepared (such as steel and aluminum) may require that different types of grinding wheels (different wheel materials) be used. As such, a wheel for grinding steel may be removed and a wheel for grinding aluminum then installed in the grinder. When the steel grinding wheel is then reinstalled, it may require dressing or redressing to assure that the wheel surface is planar and normal to the specimen due to the orientation of the wheel as it is installed on the platen. Otherwise, the grind may not be flat due to high spots and low spots on the wheel relative to the specimen. This additional dressing to assure a planar surface on the wheel can be time consuming and can result in removing portions of the wheel that are not yet consumed or portions of the wheel that are still effective for grinding.

Accordingly, there is a need for an improved grinder. Desirably, such a grinder includes an automated system for dressing the grinding wheel based on need. More desirably, such a grinder includes a cover over the specimen to reduce the amount of splashing and debris ejection, but that permits ready access to the grinding wheel. More desirably still, such a grinder permits removing a grinding wheel and reinstalling that grinding wheel in such a way that the orientation of the wheel is maintained during reinstallation.

SUMMARY

A sample grinder includes a base having a bowl and a rotating drive plate to operably support a grinding wheel. A head is configured to support a specimen holder and has a first drive for rotational drive of the specimen holder and a second drive for moving the head and the specimen holder toward and away from the rotating plate. The head has a depending sleeve that has an inner outer periphery larger than the specimen holder.

A removable cover is disposed over the bowl and rotating drive plate. The cover has an opening having an inner periphery greater than the outer periphery of the sleeve, so that the sleeve traverses through the cover opening when the specimen holder is moved toward the rotating drive plate.

The cover has a top that is non-planar and slopes away, toward a front-side corner. The sleeve can be formed from a transparent or semi-transparent material.

The cover can include a fluid delivery manifold and a plurality of fluid dispensing nozzles in fluid communication with the fluid delivery manifold. The fluid delivery manifold can be formed as part of the cover and the fluid dispensing nozzles can be mounted to the cover over the fluid delivery manifold. The nozzles can be formed as openings in a plate and the plate mounted to an inside surface of the cover. The openings can be asymmetrically disposed generally along a line of the plate. A fluid delivery conduit in the base is in fluid communication with the fluid delivery manifold.

A grinding wheel has a central axis and is mountable to and coaxial with the platen. The grinding wheel mounts to the platen in a single radial orientation only and has one or more mounting elements thereon cooperating with the platen mounting elements to permit mounting the grinding wheel in the single radial orientation only. The grinding wheel is initially mounted to the platen, removed from the platen and remounted to the platen, and when the grinding wheel is remounted to the platen, it can be remounted in only the same radial orientation as initially mounted to the plate.

The platen mounting elements and the grinding wheel mounting elements can be, for example, cooperating projections and recesses. The cooperating projections and recesses can be pins and bores. The pins can be positioned on the platen and the bores formed in the grinding wheel.

In an embodiment, four pins are positioned on the platen, three of which are symmetrically disposed on the platen and the fourth pin is asymmetrically disposed on the platen relative to the three symmetrically disposed pins. The grinding wheel includes four bores positioned to cooperate with the four pins.

The sample grinder can also include a dressing system including an arm and a hardened face for contacting the grinding wheel to dress the grinding wheel. A monitor monitors the current of one or both of the drive plate motor and the head first drive. The sample grinder includes a controller.

The monitor monitors the current drawn by one or both of the drive plate motor and the head first drive, and the dressing system is actuated based upon a the current drawn by one or both of the drive plate motor and the head first drive motor falling below a predetermined value.

In an embodiment, the controller determines whether a grinder cycle has commenced, and once commenced, the controller initiates a dressing operation. When the controller determines that a dressing operation is in progress, the controller monitors and captures current data points, and when the controller determines that a dressing operation is not in progress, the controller determines the predetermined current value for the drive plate motor and/or the head first drive.

These and other features and advantages of the present invention will be readily apparent from the following detailed description, in conjunction with the claims

DETAILED DESCRIPTION

While the present device is susceptible of embodiment in various forms, there is shown in the drawings and will hereinafter be described a presently preferred embodiment with the understanding that the present disclosure is to be considered an exemplification and is not intended to be limited to the specific embodiment illustrated.

Referring now to the figures and in particular, toFIGS.1-5, there is shown a bench top planar grinder10. The grinder10includes, generally, a base12, a head14and a controller16in communication with a control panel18. The base12includes a casing20that encloses a rotating platen22and a drive system24for the platen22. Referring briefly toFIGS.9and10A-10C, the drive system24includes a drive motor26. In a present embodiment, the motor26is an AC motor operably connected to the platen22by a drive belt28.

The base12defines an upper lip30that forms the top edge of a bowl32. The platen22is positioned in the bowl32, above the bottom of the bowl, but below the lip30. The bowl32has a generally D-shaped profile to allow access to the platen22for maintenance, removal and the like. A grinding wheel34is positioned on the platen22. The D-shaped profile of the bowl32also allows ready access to the grinding wheel34for maintenance, removal and the like.

Referring toFIGS.4and14-15, the grinding wheel34is positioned on and mounted to the platen22for rotation with the platen22. The grinding wheel34and platen22are coaxial with one another (that is, share a common axis A) and are configured so that the grinding wheel34can be installed on or mounted to the platen22in only one orientation. This single orientation mounting configuration assures that when the wheel34is removed and reinstalled on the platen22, it is reinstalled in the exact same orientation each time. As will be appreciated by those skilled in the art, the ability to reinstall the wheel34at the same orientation each time eliminates the need to redress the wheel34each time it is installed on the platen22.

In a present embodiment the single orientation mounting system is provided by a plurality of locating pins36A-D, one of which36D is asymmetrically located and which are received in cooperating locating bores38A-D in the wheel34, one of which38D is asymmetrically located to receive the asymmetrically located pin36D. For example, the wheel34can include three pins36A-C located 120 degrees from one another spaced an equal distance from a center axis A of the wheel34and a fourth pin36D located at any location on the wheel34(such as in the illustrated embodiment, along a radial line of one of the three pins), and cooperating bores38A-D in the platen22for receiving the pins. Essentially, the asymmetric fourth pin36D provides an interfering mounting arrangement to prevent installing the wheel34at any orientation other than the one orientation in which all four pins36A-D will be accommodated in their respective, cooperating bores38A-D. A single fastener40, such as a countersunk threaded bolt can be used to secure the wheel34to the platen22.

There are a number of advantages to such a single-orientation mounting arrangement. For example, as noted above, once a wheel34is dressed, it can be removed from the platen22and reinstalled without further dressing or redressing, unless it is needed to resurface the wheel34. Moreover, the wheel34is readily and quickly installed, removed and reinstalled on the platen22with, for example, a single fastener40.

As illustrated inFIGS.1-4and11, the grinder10includes a cover42positioned over the bowl32. The cover42envelops the bowl32(including the wheel34) when in place. The cover42includes an opening44through which a specimen holder46moves to move the specimens into contact with the wheel34. A sleeve48is positioned on the head14, depending therefrom around and over a shaft50to which the specimen holder46is mounted. The sleeve48depends from the head14to a position just above the specimen holder46.

The sleeve48has an inner diameter that is slightly larger than the diameter of the specimen holder46and an outer diameter configured to allow the sleeve48to move through the cover opening44with the specimen holder46(the outer diameter of the sleeve48is just smaller than the diameter of the cover opening44). In this manner, a gap52between the sleeve48and the cover opening44is sufficiently small so as to reduce or eliminate splashing that may occur. As seen inFIGS.3and12, a front corner54of the cover42slopes downward to permit the head14(with the specimen holder46mounted thereto) to swing away from the cover42and wheel34for easy access to the holder46and wheel34. A seal56can be positioned around a lower edge of the cover42, where the cover42is positioned on the base12, to further seal the bowl32. The sleeve48can be formed from a transparent or semi-transparent material to permit viewing the specimen and wheel34.

In order to access the wheel34and platen22, the cover42is configured for easy removal from the base12. In a present embodiment, the cover42includes a slotted opening58in a rear of the cover that is positioned over the dressing arm housing60. The edges of the slotted opening58slide into a recess62in the dressing arm housing60to secure the cover42in place. The cover42can include clamps64that secure and lock the cover42to the base12and permit removing and installing the cover42without the use of tools.

When the cover42is in place on the base12, an opening66in the cover42is in communication with a fluid supply conduit68. The conduit68extends upwardly from the base12into the opening66. A seal70is positioned between the conduit68and the opening66. A fluid, such as water is provided from a supply, through the base12and into the opening66in the cover42.

As noted above, a cooling/lubricating fluid is needed for proper grinder10operation. The fluid supply conduit68, via a fluid delivery manifold72in the cover42, supplies the cooling/lubricating fluid to the wheel34. In an embodiment, the fluid delivery manifold72includes a plurality of openings or nozzles74that spray the fluid onto the wheel34. The nozzles74are positioned to provide a desired spray pattern of fluid onto the wheel34. In an embodiment, nine (9) nozzles74a-74iare arranged to spray fluid from the manifold72, with a first nozzle74anear to the fluid entrance (from the conduit68), a set of five adjacent nozzles74b-74fspaced from the first nozzle, a seventh nozzle74gspaced from the set of five nozzles, and a set of two nozzles74h,74iat about the end of the manifold72, nearest to the center of the wheel34. The nozzles74can be formed in a plate76that is positioned over and forms part of the manifold72.

Referring toFIGS.1-9the head14supports and rotates the specimens S. The head14is mounted to the base12by a telescoping support78. The head14contains two drive systems, one drive system80for rotation of the specimen holder46(seeFIG.8), and a height drive system82for up and down movement of the head14(seeFIGS.6-7) to move the specimen holder46and the specimens S toward and away from the wheel34. The movements, rotational and height, are provided by the separate drive systems80,82.

Referring toFIG.8, the rotational drive80is configured to rotate the specimen holder46in either a clockwise or counter clockwise direction. In a present grinder10, the drive system80is a gear drive, driven by a motor84, however, a direct drive, belt drive or the like can also be used. It will be understood that the head14is stationary as the specimen holder46rotational drive is operating. The drive system80includes a can-like housing86that has a gear88that engages a motor gear90to rotate the can-like housing86.

Referring toFIGS.6-7, the height drive82is a precision drive to precisely position the specimen holder46and the specimens S relative to the wheel34. The height drive82is fixedly mounted in the head14. The present grinder10uses a servomotor that is operably connected by a timing belt92to a pulley94(driven by the belt92). A lead screw96is mounted to the pulley94for rotation with the pulley94. The lead screw96is mounted to a fixed (relative to the base12and the support78) threaded receiving element98so that rotation of the lead screw96moves the head14up and down to move the specimen holder46toward and away from the wheel34.

A further enhancement to the grinder10is an automated dressing system100. As noted above, dressing is carried out to resurface or recondition the wheel34as the wheel34becomes worn, that is when the peaks on the abrasive are worn and the valleys between the peaks become filled with the specimen material (referred to as wheel loading). The dressing system100includes a head102mounted to an arm104that moves in an arc and contacts the wheel34to remove the loaded area (e.g., the worn and dulled areas or abrasive) and expose fresh surfaces of abrasive that more efficiently effect the grind. Dressing is carried out during the grinding operation by moving the arm104to swing over an opposite side of the wheel34from the location at which the grinding operation is carried out.

The dressing system head102has a hardened face106that contacts and removes the worn or dulled areas of the wheel34. One hardened face is a sacrificial diamond dressing face106. In the operation of known grinding systems, dressing is carried out at preset times, regardless of whether dressing is actually required or dressing is overdue. In the former instance, it will be appreciated that dressing too often removes portions of the wheel surface that are still effective for grinding. In the latter, overdue dressing can result in too much time spent grinding a sample or failure to properly grind. Moreover, the required dressing period is a function of many variables, such as specimen material, wheel composition, wheel speed, sample holder speed and the like.

In an embodiment of the present grinder10, dressing is carried out based upon measured operating conditions and comparing those operating conditions to a preset value. One such way in which to dress the wheel34based on operating conditions is to measure the resistance between the specimen S and the grinding wheel34and to dress the grinding wheel34when the resistance drops below a certain preset value.

The resistance can be monitored in a variety of ways. In one embodiment, resistance is related to the amount of power required to operate either the platen motor26or the head motor84(the two concurrently rotating elements). The power is related to the current drawn by the motors26,84. So, in application, one way in which to measure the resistance is to monitor the current drawn by with the platen motor26or the head motor84. When the current drops below a certain predetermined level, it is indicative of lowered resistance and dressing will automatically commence.

A flow chart of the automated dressing operation1000is illustrated inFIG.16. At step1002, the grinder cycle commences and at step1004, a dressing operation is initiated. At step1006, the controller monitors whether a dressing operation is in progress.

If a dressing operation is in progress, then at step1008, the (electrical) current data points (work load on the motor) are captured and stored in the controller and the operation returns to between steps1004and1006.

If a dressing operation is not in progress, then at step1010, the controller determines the optimal current trigger point to initiate the next dressing operation. The controller monitors whether the current load has reached a load trigger point at step1012. And, if the trigger point has been reached, the controller initiates a dressing operation at step1004. If the trigger point has not been reached, the controller continues to monitor whether the current load reaches the load trigger point at step1012.

In this manner, the dressing operation is initiated only when needed based on actual operating data (data as captured through monitoring the current load on the platen or the head motor), rather than on an arbitrary, time-based measurement. This feature provides an optimal work load with a minimized cycle time.

All patents referred to herein, are hereby incorporated herein by reference, whether or not specifically done so within the text of this disclosure.

From the foregoing it will be observed that numerous modifications and variations can be effectuated without departing from the true spirit and scope of the novel concepts of the present disclosure. It is to be understood that no limitation with respect to the specific embodiments illustrated is intended or should be inferred. The disclosure is intended to cover all such modifications as fall within the scope of the invention.