Patent Application
20200271160
Carriages are used in a variety of functions to support, carry or transport equipment or material. Image forming apparatuses, such as two or three dimensional (2D or 3D) printers, sometimes include such carriages that are to be moved over or across a print bed to enable components included in the carriages to perform various operations during formation of an object. e.g. a 3D object. The carriages may be independently movable over the print bed and are to move along an axis or shaft.
Shafts are sometimes fitted with housings which may employ linear guides, such as bearings or sliders, in contact with the shaft to reduce stresses between the shaft and the housing.
In some image forming apparatuses, such as 3D printers, carriages are fitted with guides employing housings with multiple contact guiding elements to linearly guide the shafts when the image forming apparatus is in function.
Some non-limiting examples of the present disclosure are described in the following with reference to the appended drawings, in which:
The various pieces of the multi-bearing housing 100, namely the housing 105, the pins 120A, 120B, 120C and the bearings 115A, 115B, 115C, as well as the shaft 112 introduced in the opening, may be made of different materials. Each material may have a different thermal coefficient. When in use, the various pieces may heat up and expand unequally, each piece expanding according to its expansion coefficient (the expansion being a factor of its thermal coefficient and of its length). Thus contact between the shaft and one of the bearings of the “bearing-shaft-bearing” system may be lost. This may cause instability to the carriage and loss of accuracy. Some linear guides may use a preload mechanism, such as a spring 107 attached to the housing 105 The spring 107 may be in contact and push one of the pins, e.g. pin 120A, to generate a preloading force F in order to keep all the bearings in touch with the shaft during different temperatures as thermal coefficients of all the materials may not be the same and the materials may unequally expand.
Such a preloading force F may be applied constantly and may thus increase the Hertzian contact stresses, i.e. the stresses between the bearings and the shaft, and the Von Misses stresses, i.e. stresses used to predict yielding of materials under complex loading from the results of uniaxial tensile tests. By using spring 107, the preload force may be up to +100% of the force required with a system without preload. The linear guide 100 with preload may limit the acceleration of the carriage because the contact forces may reach the yield stress of the shaft 112 or of the bearing 115A.
The thermal compensation block 230 may be distributed in two parts 230A and 230B along the pin on both sides of the respective bearing, one block part per side of the bearing. On one side of the bearing, the thermal compensation block 230A, 2308 may comprise a first portion 235A, 2358, respectively in contact with the pin. The first portion 235A, 2358 may be made of a material, e.g. steel, with a tensile strength higher than the tensile strength of the pin, to reduce stress on the pin. The thermal compensation block 230A, 230B may comprise a second portion 240A, 2408, respectively in contact with the first portion 235A, 2358, respectively. The second portion 235A, 2358 may be made by a material, e.g. zinc, with a thermal or expansion coefficient different than the thermal or expansion coefficient of the first portion's material. However, other materials with a thermal or expansion coefficient different than the thermal expansion coefficient of the first portion's material may be used.
During a heating event, the total elongation of the plate portion between the outer side of pin 120A and the outer side of block 230 may be calculated as:
TE1=t*Ch(a+b+c+d+e) (Eq. 1)
In Eq. 1 t is the temperature, Ch is the thermal coefficient of the housing,
b=d3,
d=d4, e=d5, wherein d1 is the diameter of the pin, D2 is the radius of a bearing, d3 is the diameter of the shaft and d4 is the width of the first portion of the plate.
During the same event, the total elongation of the respective portion of parts on the plate (i.e. the pins, the bearings, the shaft and the block) may be calculated as:
TE2=t*(a*Cbr+b*Csh+c*Cbr+d*C1p+e*C2p) (Eq. 2)
Accordingly, Cbr is the thermal coefficient of the bearing, Csh the thermal coefficient of the shaft. C1p the thermal coefficient of the first portion of the block and C2p the thermal coefficient of the second portion of the block.
Assuming TE1=TE2 then d5 may be calculated as
Thus the size (i.e. the distance between proximal side and distal side of the second portion) of the second portion of the thermal compensation block may be calculated by knowing the various diameters and/or distances and thermal coefficients. The linear guide is thus modified in order to substitute the preloading spring, with a material that thermally compensates the dilatations between the housing and the system “bearing-shaft-bearing”, Thus the bearings may maintain contact with the shaft during the thermal event.
The thermal compensation block 430 may comprise a first portion 430A in contact with the pin. The first portion 430A may be made of a material, e.g. steel, with a tensile strength higher than the tensile strength of the housing 405. The thermal compensation block 430 may comprise a second portion 430B in contact with the first portion 430A, respectively. The second portion 430B may be made of a material, e.g. zinc, with a thermal or expansion coefficient different than the thermal or expansion coefficient of the first portion's material. However, other materials with a thermal or expansion coefficient different than the thermal expansion coefficient of the first portion's material may be used. When the shaft is introduced in the opening, the slider 415A, the shaft 412 and the slider 4158 may be arranged in a straight line to form a “slider-shaft-slider” system. Similar calculations may thus be performed, as the ones performed for calculating the size of thermal compensation block in the example of
All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the operations of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or operations are mutually exclusive.
Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise.
Although a number of particular implementations and examples have been disclosed herein, further variants and modifications of the disclosed devices and methods are possible. For example, not all the features disclosed herein are included in all the implementations, and implementations comprising other combinations of the features described are also possible. As such, representative examples of the present disclosure have utility over a wide range of applications, and the above discussion is not intended and should not be construed to be limiting, but is offered as an illustrative discussion of aspects of the disclosure. What has been described and illustrated herein is an example of the disclosure along with some of its variations. The terms, descriptions and figures used herein are set forth by way of illustration only and are not meant as limitations. Many variations are possible within the spirit and scope of the disclosure, which is intended to be defined by the following claims—and their equivalents—in which all terms are meant in their broadest reasonable sense unless otherwise indicated.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2017/061314 | 11/13/2017 | WO | 00 |
