Patent Application
20230150043
The present invention is directed to an apparatus. The apparatus comprises a first frame, a second frame and a plurality of drive assemblies. The first frame comprises a first cylindrical rail and a second cylindrical rail. The second cylindrical rail is parallel to and spaced apart from the first cylindrical rail.
The second frame comprises a plurality of drive assemblies, each comprising a motor and a roller rotatably attached to the motor. Each roller in the plurality of drive assemblies has an external concave profile complementary to a portion of the first cylindrical rail. The second frame is supported on the first frame at each roller of the plurality of drive assemblies.
In another aspect, the invention is directed to an assembly for driving a second frame along a first frame. The first frame comprises vertically offset first and second cylindrical rails. The assembly comprises a first drive member and a first preloading member.
The first drive member comprises a motor, a roller, a bearing assembly, and a position sensor. The roller is coupled to the motor and has a concave profile complementary to a surface of the first cylindrical rail. The bearing assembly comprises inner and outer portions. The inner portion rotates relative to the outer portion and the outer portion does not rotate relative to the second frame. The position sensor is configured to determine a position of the second frame along the first frame.
The first preloading member comprises a roller and a biasing member. The roller has a concave profile complementary to the surface of the second cylindrical rail. The biasing member is configured to force the first preloading member in a direction toward the second cylindrical rail and away from the first cylindrical rail.
In another aspect, the invention is directed to an apparatus having three degrees of linear freedom. The apparatus comprises a first pair of drive-guide assemblies, a second pair of drive-guide assemblies, and a third pair of drive-guide assemblies. The first pair of drive-guide assemblies is adapted to move a work tool in a first direction along a corresponding first set of linear rails. The second pair of drive-guide assemblies is adapted to move a work tool in a second direction along a corresponding second set of linear rails. The third pair of drive-guide assemblies is adapted to move a work tool in a third direction along a corresponding third set of linear rails. Each set of linear rails comprises opposed pairs of first and second rails. The first direction, second direction, and third direction are each perpendicular to each of the other directions.
Each of the drive-guide assemblies comprises a drive roller assembly, a support guide assembly, and a loaded guide assembly. The drive roller assembly comprises a motor and a roller. The roller is coupled to the motor and has a concave radial surface conforming to a first member of a selected one of the first, second, and third linear rails.
The support guide assembly comprises a support roller having a concave radial surface conforming to the first member of a selected one of the first second and third set of linear rails. The loaded guide assembly comprises a loaded roller and a biasing member. The loaded roller has a concave surface conforming to a second member of the selected one of the first, second, and third linear rails. The biasing member is configured to bias the loaded roller towards the second member of the selected one of the first, second, and third set of linear rails and away from the first member of the selected one of the first, second, and third set of linear rails.
Traditional gantry systems are typically large and heavy metal assemblies. The primary purpose of these gantry systems is to control the movement of tools and other attachment pieces throughout machining and/or assembly processes. These gantry systems can be situated overhead or on the ground. Notably, these gantry systems consist of separate drive and guide systems. The separate drive and guide systems result in axes of contact at each location of a drive member. Such separate systems have known limitations in accurate placement of a tool, due to the inherent tendency towards backlash and runout in these systems.
Drive systems are configured to power movement and “drive” whatever is attached to the gantry-often cutting/machining tools or assembly tools. The most common drive systems for large motion platforms are gear systems. These gear systems usually comprise a toothed gear rack and at least one pinion gear configured to fit inside the gear rack. The pinion may be driven by a gearbox, in which many gears may allow the alteration of a gear ratio in order to meet mechanical need. These gear systems experience backlash, however, which results in increased margins of error and higher machining tolerances. As more gears are added, the overall amount of backlash increases. Backlash can cause issues in later phases of production, such as misaligned holes or unanticipated gaps between machined pieces. It is therefore ideal to reduce backlash as much as possible in order to increase accuracy and efficiency.
Some artisans have attempted to eliminate backlash by creating pre-loaded pinion gears that manipulate against each other. However, even preloaded pinions wear over time, resulting in increased gap tolerances and eventually backlash. Therefore, even contemporary pre-loaded pinion gears do not completely eliminate backlash.
Other forms of drive systems have provided half-measures against backlash and often possess other limitations. For example, ball-nut drive systems are common in industrial settings. These ball-nut drive systems typically comprise a threaded rod with a spiral trapezoidal groove, and a plurality of balls that are preloaded inside of the nut to fit inside the grooves and allow the nut to slide up and down the rod. However, these ball-nut drive systems often wear down over time, resulting in increased gaps and, again, backlash. Moreover, these ball-nut systems are limited in size because the necessary rods are only manufactured up to a certain length. Thus, all current drive systems possess notable flaws.
While guide systems are separate from drive systems, they often experience similar backlash and accuracy issues. Guide systems are designed to support the weight of machining or tooling assemblies and provide axial limitations in the movement of the assemblies. These guide systems sit on top of drive systems, providing a second point of contact between the gantry and the machining or assembly tool.
Both box linear guideways and profile linear guideways contain recirculating rollers or balls that allow movement of the gantry system. These recirculating elements, however, often wear down, which leads to backlash and other inaccuracies during operation. Additionally, the surface that these guideways sit on are often unforgiving, resulting in extra forces exerted on the system.
Thus, there is a current industry need for both drive and guide systems that do not experience backlash or other inefficiencies.
Turning now to the figures,
The gantry 10 comprises a work tool assembly 12 which is supported in three dimensions, and rotational about three axes, due to components of the gantry 10. This tool 12 may be a probe, a milling tool, a waterjet cutting head, or any other tool for use in machining, inspection or assembly of large parts. The identity of the tool 12 is not limiting on the present invention.
The gantry 10 comprises a plurality of rails, each of which extends about a longitudinal axis. A first set of rails 14 is supported by one or more stationary frames 16. As shown, the stationary frames 16 are spaced apart, but it should be understood that these frames may be joined at one or more points for added rigidity.
The first set of rails 14 define a first longitudinal direction that is parallel to the longitudinal axis of each of the first set of rails. For the purposes of this disclosure, the first longitudinal direction is defined as “x”, though naming conventions are not limiting on this invention.
As shown, the first set of rails 14 is suspended some distance above the ground by the stationary frame 16, and supported by one or more beams extending in the first longitudinal direction. The first set of rails 14, alternatively, may be placed near to the ground level with a vertical offset allowing the operation of the gantry 10. It should be understood that the first set of rails 14 includes all rails on the gantry 10 which extend in the “x” direction.
A movable frame 20 is supported on the first set of rails 14. The movable frame 20 is movable along the first set of rails 14 in the first longitudinal direction. The movable frame 20 comprises a second set of rails 22. The second set of rails 22 define a second longitudinal direction, wherein the second longitudinal direction is perpendicular to the first longitudinal direction. For the purposes of this disclosure, the second longitudinal direction is defined as “y”.
As shown, the first longitudinal direction and second longitudinal direction define a plane which is parallel to a surface of the ground. A third longitudinal direction, therefore, is defined as “z” and is vertical - that is - perpendicular to both the first and second longitudinal directions.
A tool holding frame 30 is supported on the movable frame 20. The tool holding frame 30 comprises a third set of rails 32 (
The movable frame 20 comprises a drive-guide system 40 disposed at each of its ends. The drive-guide system 40 interacts with the first set of rails 14 to support and drive the movement of the movable frame 20 (and thus the tool 12) in the x direction. Likewise, a drive-guide system 40 is disposed on each side of the tool holding frame 30, and moves the tool holding frame in the y direction along the second set of rails 22. And further, a drive-guide system 40 is fixed in position on a tool frame 38 relative to the work tool 12 and interacts with the third set of rails 32 on the tool-holding frame 30, allowing movement in the z direction.
Each drive-guide system 40 is substantially identical, with a set of rollers, as described below, which interact with a selected one of the first, second and third set of rails 14, 22, 32 to move the work tool 12 in a corresponding x, y, or z direction.
As best shown in
While the term “frame” is used to describe the elements on a gantry 10, it should be appreciated that each frame which provides a separate degree of freedom to the work tool 12 is accurately described as an “axis stage”. In a gantry 10, each axis stage may indeed be a separate frame. However, other, non-frame structures may be used with other machine tools to provide degrees of linear freedom to a work tool 12. These alternative structures may also utilize the drive-guide system 40 of the present invention without departing from the spirit thereof.
The drive-guide system 40 comprises a support guide assembly 42, a drive roller assembly 44, and a loaded guide assembly 46. Each of the support guide assembly 42, drive roller assembly 44, and loaded guide assembly 46 are shown in the figures with reference to a single side of the movable frame 20, but substantially identical drive-guide systems 40 are provided with the tool frame 38 and the tool holding frame 30. Thus, an identical set of assemblies 42, 44, 46 is provided at a second end of the movable frame 20 and engage with the first set of rails 14 disposed on that portion of the secondary frame 16. Preferably, the movable frame 20 is only supported at the drive-guide system shown, and does not have additional guide members disposed elsewhere on the gantry 10 for supporting the movable frame 20.
As shown in
With reference to
The motor 102 may be a rotational drive motor having one or more intermediate rotor pieces 110 between the motor 102 and the roller 108. The motor 102 is mounted on the frame upon which the drive-guide system is supported, here, the movable frame 20. The adaptor 104 is connected to non-rotating components of the motor 102 and is sized to connect via pins 112 to the bearing assembly 106.
The bearing assembly 106 has a rotating race or portion 114 and a non-rotating race or portion 116. Preferably, the bearing assembly 106 is a cross-roller bearing. In a cross-roller bearing, rollers between the rotating 114 and non-rotating 116 portions of the bearing assembly 106 alternate at a ninety degree angle to adjacent rollers within a substantially “v” shaped groove. This allows the bearing assembly 106 to have radial and axial loading.
The non-rotating portion 116 is connected to the adaptor 104. The rotating portion 114 is connected to the motor 102 at its intermediate rotor pieces 110. The rotating 114 and non-rotating 116 portions abut at a sliding surface, where ball bearings, cylinder bearings or other bearing devices (not shown) disposed between the portions 114, 116 allow for relative rotation between them. Preferably, the bearing assembly 106 is preloaded and constrained in the axial direction to provide accurate and repeatable linear motion.
The drive roller assembly 44 is preferably connected to the movable frame 20 at a position close to its end, with as little of a drive roller assembly 44 extending from the frame 20 as possible. As shown in
The roller 108 is attached to the rotating section 114 and other rotating components 110 by large pins 118. These pins 118 should be of sufficient strength and length to carry forces exerted on the roller 108 by the weight of the frame it carries. For example, a plurality of drive roller assemblies 44 adapted to move the movable frame 20 along the first set of rails should be able to carry its weight, even as the tool holding frame 30 is moved along the second set of rails 22 to different locations.
A ring 119 is provided at which a micrometer (not shown) or other instrument may be attached to measure the runout of any individual drive roller assembly 44. Further, an encoder 130 may be carried by a flange 109 on the stationary bearing of the bearing assembly 106 to measure the position of the drive roller assembly 44 along a scale 132 which is attached to an element of the frame supporting the rail 14, 22, 32 along which the drive roller assembly 44 is moving.
The roller 108 has a concave surface 120 which largely conforms to the cylindrical rail 122 shown. The cylindrical rail 122 shown here may represent the first 14, second 22 or third 32 set of rails, and is sectioned for clarity. If magnets 36 are in use, the roller 108 will not center on the cylindrical rail 122, but rather will be offset due to the magnetic force associated with the field of the magnets 36. (
The amount of axial force 105 (
An example of how pre-loaded forces affect the position of the roller 108 is shown in
As shown in
In
The relative profiles of
With reference to
The support guide assembly 42 has a flat portion 160 at which the assembly may be attached to frame elements. As with the roller 108 of drive roller assembly 44, roller 150 has a concave surface 162 which conforms to an outer surface of a cylindrical rail.
While one support guide assembly 42 is shown as a part of the drive-guide system 40, multiple support guide assemblies 42 may be utilized to provide additional support to the particular frame being guided. It should be appreciated that if more than one is used, the additional support guide assemblies should be carefully aligned such that the drive-guide system will interact with the applicable set of rails 14, 22, 32 at each point. Alternatively, as in the Figures, one and only one support guide assembly 42 is used with each drive roller assembly 44 to provide two and only two points of contact on the lower rail 14a.
It may be preferable to allow the bearing assembly 152 of the support guide assembly 42 to float axially - that is, in a direction along the longitudinal axis of the assembly 42 and perpendicular to each of the first set of rails 14. The drive roller assembly 44 will be fixed in axial position and not allowed to float, which will maintain a preferred position of the assemblies 42, 44 relative to the rail. Allowing axial float in the roller 150 through the bearings 152 allows for mounting on imperfect surfaces without the drive-guide system 40 getting in a bind.
With reference to
The loaded guide assembly 46 comprises a roller 180, a bearing assembly 182, and a biasing assembly 184. The bearing assembly 182 is allowed to float axially for the same reasons as bearing assembly 152. The non-moving portion of the bearing assembly 182 is fixed to the biasing assembly 184, which allows the selective positioning of the roller 180 relative to the movable frame 20 by adjusting the distance between the engagement point of roller 180 and that of rollers 108, 150.
The biasing assembly 184 comprises a plate 186, a frame attachment point 188, and one or more pre-load nuts 190. The loaded guide assembly 46 is attached to the movable frame 20 (or other frame 30, 38 as the case may be) at the attachment point 188. Adjustment of the one or more nuts 190 adjusts the distance between the plate 186 and the attachment point 188. Preferably, a plurality of springs 191, such as disc springs, are utilized to provide the biasing force. Linear guideways 194 allow the plate 186 to slide, which carries the bearing assembly 182 and roller 180 to provide radial force.
As the roller 180 and bearing assembly 182 are movable with and supported on the plate 186, adjustment of the nuts 190 also adjusts the resultant force between the roller 180 and rollers 108, 150. Thus, adjusting the nuts 190 to force the roller 180 away from the lower rail 14a increases the load applied to the first set of rails 14, or radial force 103 (
As with the roller 108 of drive roller assembly 44 and roller 150 of the support assembly 42, roller 180 has a concave surface 192 which conforms to an outer surface of a cylindrical rail. In this instance, the cylindrical rail is upper rail 14b.
For drive-guide systems 40 engaging the first set 14 and second set 22 of rails, the biasing assembly adjusts a “z” distance between the roller 180 and rollers 108, 150. For drive-guide systems 40 engaging the third set of rails, the biasing assembly 184 adjusts either an “x” or “y” distance between these elements, depending upon the orientation of the drive-guide systems on the tool frame 38.
Components, such as the rollers 108, 150, 180, rings 119, 158, bearing assemblies 106, 152, 182 and the like may be identical between the described assembly, or may include differences between them without departing from the spirit of the invention. For example, the roller 180 of the loaded guide assembly 46 may be shaped similarly to roller 108A as shown in
In addition to the linear systems above, a radial adjustment mechanism may use similar rollers and rails. In some applications, such a radial adjustment mechanism may be disposed on the tool frame 38. However, depending upon the type of apparatus, linear guides may be provided between rotary systems.
The radial adjustment mechanism comprises a radial drive motor and one or more bearing assemblies. Each of the radial drive motor and the bearing assemblies are disposed about a disc having a circular outer profile. Rollers are provided with each of the radial drive motor and bearing assemblies which engage the disc. It is preferable to have three points of contact on the disc - the radial drive motor and bearing assemblies are approximately 120 degrees apart.
The drive motor may be mounted on a radial pre-load system 210 which provides force to the disc to ensure a proper frictional connection between the rollers and the disc.
The tool frame may have three or more radial adjustment mechanisms. For example, a first mechanism a rotates a bottom portion of the tool frame 38 about a substantially vertical axis. The second mechanism rotates the tool 12 about a substantially horizontal axis.
The third adjustment mechanism rotates the tool 12 relative to the tool frame 38 itself. The third adjustment mechanism is rotatable about an axis which is perpendicular to the substantially horizontal axis of the second mechanism, but its orientation relative to the directions “x”, “y”, and “z” is adjusted due to the operation of the second adjustment mechanism. Additional degrees of rotational freedom may be added, and various arrangements may be utilized depending upon the type of machine.
The gantry 10 thus can manipulate the tool 12 accurately along three perpendicular axes, and can rotate the tool 12 about three additional axes.
Given that the above system does not utilize any gear boxes nor does it provide a guide system separated from its drive system, backlash and runout are both significantly reduced. Total volumetric accuracies in large machine tools utilizing existing guide/drive systems may be as large as 0.03″ or 750 microns. The present gantry 10, due to the near-elimination of backlash and runout, may be able to achieve accuracy that is one hundred times greater, with total volumetric accuracy in the five to fifteen micron range.
Used in this specification and the claims, the phrase “complementary to the profile” or “conforms to” when discussing the interface of the cylindrical rail and roller 108,150,180, means that the roller is optimized to fit the rail. For example, a rail having a diameter of approximately five centimeters has an ideal complementary concavity on an associated roller. If the diameters too closely match, frictional resistance between the rollers and rail will cause problems. Conversely, if the diameters are too disparate, axial position of the roller relative to the rail will not be maintained, which can cause inaccuracies and unfavorable stress profiles.
If the diameter of the concavity of the roller and rail substantially match, more resistance to lateral (axial) movement will exist, and load capacity will increase. At a 14 degree roller pressure angle on a 49.983 millimeter rail, a 2.91 millimeter gap would exist between the roller and the rail, as the roller would have a concavity with a diameter of 75 mm.
Analytical tools reveal a best mode for a 49.983 millimeter rail being a roller with a 50.1 millimeter edge diameter. The roller pressure angle in this instance is 22.5 degrees with a gap of one one-thousandth of an inch between the rail and roller. This tight tolerance effectively reduces lateral movement and wear. While this is the best relationship between rail and roller diameter, it should not be construed as limiting. The example shown with a 75 millimeter diameter concavity may work in many applications, without departing from the scope and spirit of these claims.
The various features and alternative details of construction of the apparatuses described herein for the practice of the present technology will readily occur to the skilled artisan in view of the foregoing discussion, and it is to be understood that even though numerous characteristics and advantages of various embodiments of the present technology have been set forth in the foregoing description, together with details of the structure and function of various embodiments of the technology, this detailed description is illustrative only, and changes may be made in detail, especially in matters of structure and arrangements of parts within the principles of the present technology to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.
| Number | Date | Country | |
|---|---|---|---|
| 63279466 | Nov 2021 | US |
