Optical or magnetic scale with selectable zero thermal expansion point

Abstract

The present invention relates to optical or magnetic scales with selectable zero thermal expansion points. An optical or magnetic scale for making linear measurements is provided, the optical or magnetic scale comprising: a scale frame integral with a fixed or moving component of a machine tool; and a scale grating support housed inside the scale frame and scanned by a transducer integral with the fixed or moving component of the machine tool. The scale frame and the scale grating support are respectively fixed to the machine tool and the scale frame at a single fixed position, the single fixed position forming respective FEPs of the scale frame and the scale grating support, and the FEPs are independently selectable among a plurality of predetermined positions. The scale frame and the scale grating support are further respectively fastened to the machine tool and the scale frame at one or more additional free longitudinal sliding positions.

Description

Technical Field

[0001] This invention relates to an optical or magnetic scale having a selectable zero thermal expansion point position, also known as a fixed expansion point, or simply FEP. Background Technology

[0002] As those skilled in the art will know, optical or magnetic scales are frequently used on tool machines and operating machine tools (hereinafter collectively referred to as "machine tools") to measure the linear movement of carriages and tables with high accuracy.

[0003] Other indirect measurement systems associated with the rotation of a ball screw (e.g., rotary encoders) are less accurate due to errors caused by the motion drive screw, which may experience localized heating, expansion, and wear due to its frequent movement. Conversely, measurement systems that directly detect the position of a carriage or table in a machine tool in a closed loop are unaffected by the play, reversal error, thermal changes, and inaccuracies of the motion drive system. This means that the accuracy of optical or magnetic scales is unaffected by external factors and maintains a high degree of accuracy over time.

[0004] In optical scales, a micro-engraved scale grating is mounted on a steel or glass support. This support is scanned by a position transducer, which converts alternating reflected / diffuse or transparent / opaque marks encountered while moving along the same scale grating into electrical signals. In magnetic scales, a magnetic strip support carrying a series of north / south poles detected by the position transducer is also made of steel. For the sake of brevity, the following description will focus specifically on optical scales with scale grating supports made of steel; however, it should be clearly noted that the invention is also intended for both types of scales: optical scales with scale grating supports made of steel or glass and magnetic scales with magnetic strip supports made of steel.

[0005] Considering the application areas and harsh operating conditions of optical scales, the scale gratings need to be protected from impact and dust by being housed in a robust aluminum casing, referred to below as a scale holder. This holder also serves as a guide and support for the scale grating and as a means of securing the optical scale to the machine tool. Although magnetic scales are much less sensitive to dust than optical scales, they are also typically housed and protected within a scale holder.

[0006] As is known, with very few exceptions, all materials expand according to their linear coefficient of thermal expansion λ and their temperature. The linear thermal expansion value of a material is expressed by the following formula: ΔL = λ x 10 -6 ℃ -1 Traditionally, the materials used to manufacture optical scales are aluminum for the scale support and steel or glass for the scale grating support. These materials have significantly different coefficients of thermal expansion: aluminum is 23.0, steel is 10.6, and glass is 8.0, respectively. Length measurement is conventionally referred to as measurement at 20°C in metrology; in practice, length measurements are performed under these conditions, and a technical certificate is issued to highlight the errors affecting the measurement system. For example, a rod 1,000,000 mm long at 20°C, heated to 25°C and stabilized at that temperature, will increase in length by 115 μm when made of aluminum, 53 μm when made of steel, and 40 μm when made of glass. Such differences (especially between the aluminum of the scale frame and the steel or glass of the scale grating support) are undoubtedly significant in metrology, as well as in the machining of the workpiece and the final measurement of the machined workpiece.

[0007] When a machine tool equipped with a measuring system can operate in an air-conditioned environment with a temperature close to 20°C, there will be no adverse effects because the thermal differences and the resulting linear thermal expansion are irrelevant and negligible. Conversely, when the machine tool operates at temperatures that almost always differ from the 20°C reference temperature by as much as 8°C / 10°C or more within a positive or negative range (day / night, summer / winter), it is clearly absolutely necessary to employ technical solutions that can compensate for the thermal expansion differences of the various components of the measuring system and the machine tool, or at least significantly reduce the adverse effects caused by such thermal expansion differences.

[0008] Modern cutting tool machines and CNC machining centers employ temperature sensors and software for correcting measurement errors, which are periodically reset. However, such systems are expensive, require time for reset operations, and cannot be applied to every type of machine tool. Therefore, even for state-of-the-art machine tools, the effective solution is to use optical scales with steel scale grating supports, especially when the scale grating is quite long (over 2 to 3 meters). In practice, the optical scale is typically fixed to a carriage, table, or mechanical structure. These machine tools are made of steel and cast iron, so their linear thermal expansion coefficient is similar to that of steel (λ = 10.6). In this case, the linear thermal expansion of the machine tool axis and the linear thermal expansion of the measurement system follow each other and tend to zero.

[0009] On the other hand, it must be considered that the scale holder is made of aluminum, and therefore its coefficient of thermal expansion (λ = 23) is significantly different from that of steel, as mentioned above. Therefore, to avoid any distortion in the measuring system that could lead to misalignment, the scale holder must be allowed to stretch and shorten according to room temperature, thus freely expanding its thermal expansion, which is very different from the thermal expansion of machine tool components where scale holders are typically used. Furthermore, the scale holder must be perfectly integrated with the machine tool at least at one point, as it is unacceptable that over time the scale holder might "migrate," dragging the scale grating and causing it to take a position different from the initial zero setting of the measuring system.

[0010] Current embodiments of optical scales provide a scale holder that is fixed directly or by means of an intermediate support rod to various rigid fastening points on a machine tool, the support rod also typically being made of aluminum. However, a solution that provides fixing the scale holder to a single rigid fastening point on the machine tool is more appropriate (this single fastening point is typically positioned at a central location and forms a constant positional reference between the scale holder and the machine tool), while all other fastening points have sufficient elasticity to allow the scale holder to freely expand its thermal expansion longitudinally in the direction opposite to this single fastening point, referred to as the zero thermal expansion point or FEP, as mentioned above.

[0011] Currently available optical scales do not specify that the field excavation point (FEP) of the scale holder and the field excavation point of the scale grating must be specifically positioned where the machine tool's field excavation point (FEP) is located. The machine tool's FEP is not always centered because its position clearly depends on the type of machine tool and the machining process being performed, as will be seen below. Therefore, when installing known measuring systems, this becomes a very important aspect that is often overlooked: the direction of thermal expansion of the scale holder, scale grating, workpiece, and machine tool. The resulting adverse effect is that linear thermal expansion expands uncontrollably and often inconsistently, which is clearly detrimental to accurate machining of the workpiece.

[0012] Therefore, the technical problem solved by the present invention is to provide a measurement system, in particular an optical scale, wherein a scale grating can be fixed to a scale holder, and the scale holder can be fixed to a machine tool in such a way that the scale grating and the scale holder can both expand freely in a mutually independent manner and in a mutually consistent direction (as a result of temperature changes), and wherein the operator can easily adapt the optical scale to a specific type of machine tool on which the optical scale is mounted, and to a specific machining process being performed.

[0013] US-5375338 (1994) first disclosed a partial answer to this technical problem, providing a method for fixing the scale frame and the scale grating support to each other at a first fixed point (scale grating FEP), and simultaneously fixing the scale frame to the machine bed at a second fixed point (scale frame FEP). The patent then provides a method for fixing the scale grating support and the scale frame at other points using a degree of elasticity to accommodate deformation caused by thermal expansion due to temperature changes.

[0014] Specifically, in addition to the FEP fixing points mentioned above, the scale grating support is integrally formed with the scale frame using an elastic adhesive layer, and the scale frame is fixed to each discrete point of the machine tool using a screw clamp with partial shape elasticity.

[0015] However, the solution disclosed in US-5375338 only exhibits acceptable performance for small, one-piece optical scales (in fact, as is the case with most optical scales used at the time of the aforementioned patent filing), but for both larger-length one-piece and modular optical scales (which are now particularly required and used due to their great versatility and ease of transport and assembly), where the optical scale is formed only during final assembly from multiple modules associated with each other, and the scale grating support is formed from a flexible metal strip. Indeed, the elastic adhesive and shape-resilient fixing screw clamps disclosed in prior art patents can only accommodate minimal deformation without causing significant drawbacks. In fact, when the length change due to thermal expansion of the scale grating support or scale frame exceeds the elastic deformation capacity of the elastic adhesive or shape-resilient fixing screw clamp, drawbacks such as detachment or breakage of the elastic adhesive layer or deformation of the scale frame occur.

[0016] In any case, even before these drawbacks occur, the elastic adhesive and the shape-elastic retaining screw clamp exert an elastic reaction force on the scale grating support and scale holder, which is proportional to the degree of thermal expansion. Therefore, these components do not expand freely but undergo gradual compression due to the elastic reaction force of their fasteners, with the compression being significantly greater the longer the optical scale. Moreover, this elastic reaction force varies with temperature and time (due to the aging of the adhesive and the hysteresis or fatigue of the shape-elastic retaining screw clamp), making it impossible to accurately assess the final deformation of the scale grating and scale holder at a given temperature; this ultimately leads to random measurement errors, thus reducing the quality of high-precision machining operations.

[0017] Therefore, the object of the present invention is, in addition to providing the FEP points of the scale grating and the scale holder, to provide multiple other fastening devices located at multiple points between the scale holder and the machine tool, and between the scale grating and the scale holder. These fastening devices should easily and stably ensure the correct lateral position of these components, while allowing them free longitudinal sliding under thermal expansion. The linear thermal expansion of the scale grating and the scale holder can occur independently of each other without any adverse interference from the fastening devices.

[0018] Next, another object of the present invention is to provide a special method for selecting different possible FEP points of a scale grating support, wherein (in contrast to the method provided in the prior art cited above), enabling the selected FEP point does not require preventive drilling of the scale grating support or preventive alignment of the scale grating support relative to the scale frame. Summary of the Invention

[0019] One aspect of the present invention relates to an optical or magnetic scale for performing straight-line measurements, the optical or magnetic scale comprising: a scale holder (P) integral with a fixed or moving part of a machine tool; and a scale grating support (2, 2v) housed within the scale holder (P) and scanned by a transducer (T), wherein the transducer (T) slides along the scale holder (P) and is integral with the fixed or moving part of the machine tool, the scale... The scale frame (P) and the scale grating support (2, 2v) are respectively fixed to the machine tool and the scale frame (P) at a single fixed position, the single fixed position forming a corresponding fixed expansion point FEP of the scale frame and the scale grating support, and the FEP can be independently selected among a plurality of predetermined positions (6, 9), wherein the scale frame (P) and the scale grating support (2, 2v) are further respectively fastened to the machine tool and the scale frame (P) at one or more additional free longitudinal sliding positions.

[0020] The scale holder (P) includes a mechanical connection with an elastic thrust comparison device having a constant lateral load that does not change due to thermal expansion during the longitudinal sliding of the scale holder (P) relative to one or more free longitudinal sliding positions of the machine tool.

[0021] One or more free longitudinal sliding positions of the scale grating support (2, 2v) relative to the scale frame (P) include mechanical connections with degrees of freedom in the longitudinal direction of the scale grating support.

[0022] The mechanical connection with the elastic thrust comparison device having a constant lateral load includes: a through slot (6) spanning the scale frame (P) and an elastic thrust screw clamping fastener (7) housed in the through slot and screwed into the machine tool.

[0023] The mechanical connection having a degree of freedom in the longitudinal direction of the scale grating support comprises: a plurality of spherical or cylindrical components (4, 5), which are fixed to the edge of the scale grating support (2, 2v) and accommodated in an open section groove (1) formed longitudinally in the scale frame (P), the open section at least partially matching the section of the spherical or cylindrical components (4, 5), and the mechanical connection having sufficient clearance to allow the degree of freedom in the longitudinal direction of the scale grating support.

[0024] A single fixed position of the scale grating support is formed at a selected threaded through hole among a plurality of threaded through holes (9), the plurality of threaded through holes being arranged across the scale frame (P) and terminating inside the scale frame, wherein a pressure pin (10) is screwed into the selected threaded through hole until the pressure pin intercepts the scale grating support (2, 2v) and locks the scale grating support (2, 2v) in place against the wall of the scale frame (P).

[0025] The scale frame (P) is made of aluminum, and the scale grating support (2, 2v) is made of steel or glass. Attached Figure Description

[0026] In summary, further features and advantages of the optical scale according to the invention will become more apparent from the following detailed description of its preferred embodiments, which are given by way of non-limiting example and illustrated in the accompanying drawings, wherein:

[0027] Figure 1 This is a schematic three-dimensional view of the worktable of a vertical milling machine, with an optical scale fixed on the front side of the worktable;

[0028] Figure 2A and Figure 2B These are schematic side views of a press, in which an optical scale is mounted along the vertical axis Y on a movable press head and a gooseneck-shaped side plate.

[0029] Figure 3 This is a perspective view of the length of the optical scale according to the present invention;

[0030] Figure 4 yes Figure 3 A front view of the length of the optical scale;

[0031] Figure 5 yes Figure 3 The edge of the optical scale Figure 4 A cross-sectional view taken from the VV line;

[0032] Figure 6 This is a schematic three-dimensional diagram of a guide rail and support system with a magnetic strip support made of steel.

[0033] Figure 7 This is a schematic three-dimensional diagram of the guide rail and support system of the scale grating support component made of glass;

[0034] Figure 8 This is a schematic side view of a dual-chuck CNC machine tool. Detailed Implementation

[0035] As is known from the prior art documents cited above, the optical scale of the present invention provides easy selection of the FEP position according to the machine tool to which the optical scale is mounted, thereby allowing optimization of the accuracy of processes performed at temperatures different from the reference temperature of 20°C.

[0036] There are countless types of machine tools, each with specific behaviors that need to be properly considered to identify where the FEPs (which are usually different from each other) of a single axis of the machine tool are positioned, and thus better suited for positioning optical scale FEPs (both scale gratings and scale holders); the specific process being performed also needs to be considered.

[0037] For example, such as... Figure 1 As shown in the diagram, in a vertical milling machine, the FEP (Flexible Printed Edge) is positioned at the center of both the longitudinal and transverse axes; therefore, it is correct that the optical scale FEP is also centered. Conversely, the FEPs on the vertical and descent axes of the milling spindle are transversely positioned. For better machining accuracy, it is preferable that the optical scale FEP is also in a transverse position, i.e., that this position coincides with the FEP position on the machine tool.

[0038] This also applies to the longitudinal and transverse axes of a parallel lathe. The workpiece is actually held by the chuck jaws, and the longitudinal guideways and workpiece undergo thermal expansion from the chuck towards the tailstock. Therefore, the FEP (field edge extension) of the longitudinal axis of the parallel lathe is "under the head," that is, corresponding to the chuck holding the workpiece. Depending on whether the optical scale is mounted on the front / rear of the machine tool, the FEP of this optical scale, which measures the displacement of the carriage moving along the guideways that undergo the same thermal expansion as the workpiece, should correspond to the chuck, that is, be laterally positioned on the left / right side. Therefore, a conventional optical scale with a centrally located FEP will not thermally expand in accordance with the thermal expansion of the machine tool and the workpiece. On the other hand, the FEP of the transverse axis of the parallel lathe is centrally located, that is, coincides with the rotation center of the chuck and the workpiece, and therefore, in this case, an optical scale with a centrally located FEP is suitable for measuring the position of the machining tool along this axis.

[0039] Figure 2A , Figure 2B A synchronous hydraulic press brake is shown, wherein the descent of the press head A is driven by two hydraulic cylinders, and the descent of the press head A is controlled by two optical scales R mounted along the two press columns Y (these two optical scales are located on...). Figure 2A , Figure 2B (They are overlapped in the side view). The position information sent to the CNC by the two optical scales R is used to lower the indenter A parallel to the worktable below until the indenter reaches the maximum descent point, which allows for obtaining a bending angle in the workpiece with good accuracy.

[0040] In this manufacturing process, it is preferable to precisely position the FEP of the optical scale at such a bend point so that the accuracy of the bend angle remains constant and independent of temperature changes. In fact, the linear thermal expansion of the optical scale extends in the opposite direction to the descent of the indenter A, thus not deviating from the final descent point of the indenter and therefore not affecting the bend angle. The optical scale R is typically fixed to the plane of the indenter A, such as... Figure 2A As shown schematically, but they are also usually modified to be fixed to a gooseneck plate, such as Figure 2B As shown. Regardless of the mounting method, the FEP of the optical scale R should be positioned towards its side, as shown in the figure.

[0041] Based on this consideration, the optical scale of the present invention was developed, wherein the position of the FEP of the scale holder P and the position of the FEP of the scale grating support can be easily set after selecting one of the positions set along the entire optical scale for this purpose, and wherein the scale grating support and the scale holder are further secured to the scale holder and the machine tool respectively at one or more free longitudinal sliding positions. As used herein, "free longitudinal sliding" refers to a type of constraint that generates a reaction force sufficient to hold the secured components in a laterally stable and correct position, however, said reaction force is constant with the thermal expansion of the secured components, i.e., independent of said thermal expansion.

[0042] According to this innovative solution, in the optical scale according to the invention, not only can the position of the FEP be easily set according to the machine tool model to which the optical scale is applied and the manufacturing process being performed, but the position of the FEP can also be changed freely and easily. However, most importantly, as the machine tool temperature conditions change, the scale grating support and the scale holder can expand their thermal expansion without any limitation of the FEP, thereby allowing for accurate measurement regardless of any length changes caused by thermal expansion, and at the same time avoiding any possible deformation or distortion of the scale grating support and the scale holder.

[0043] The following reference Figures 3 to 7 A detailed description of a preferred embodiment of the optical scale according to the present invention is given.

[0044] The scale grating support is a steel strip 2, which can also be quite long (in which case it is rolled up for transport). The upper edge of the steel strip 2 is inserted into an inner groove 1 of the scale frame P, which has a circular cross-section and extends longitudinally along the entire length of the scale frame P; the groove 1 is open towards the interior of the scale frame to allow the upper edge of the steel strip 2 to be inserted therein. The steel strip 2 is held in place inside the groove 1 by ball bearings 4, which are pressed in an interference manner into corresponding gauged holes 3 set at a constant pitch C along the entire length of the steel strip 2. Figure 6 The particularly simple and efficient insertion system of the steel strip 2 is described in detail in European Patent Application No. 21195800.4 filed by the same applicant, which can be consulted for more complete information.

[0045] For the case of magnetic scales, a similar steel strip 2 is used, on which a magnetic strip with a series of north / south poles is applied ( Figure 6 ), while for optical scales with a scale grating support of 2v made of glass ( Figure 7A cylindrical cursor 5 with a circular cross-section is glued to the upper edge of the support, set with the same constant pitch C as the calibration hole 3, and adapted to be inserted into the groove 1 with clearance.

[0046] The aluminum ruler frame P comprises one or more modules M, each of which is transportable in length and is assembled on-site in a known manner. Figure 3 The length of the optical scale, consisting of a portion of the first complete module M1 and the second module M2, is shown. Through-slots 6 are positioned on the upper part of the scale holder P and span the scale holder P, and are set at equal intervals along the entire length of the scale holder P, for example, according to the same pitch C of the calibration holes 3 of the steel strip 2. Except for the through-slots where the FEP of the scale holder P must be positioned, the remaining through-slots 6 allow the scale holder P to be secured to the machine tool by means of elastic thrust screw clamping fasteners 7 that engage with each through-slot 6. The screw clamping fasteners 7 apply a lateral elastic thrust provided by spring-contrast means, which is sufficient to ensure that the scale holder P rests continuously on the worktable and prevents any movement in either lateral direction, thereby ensuring that the alignment tolerances between the individual modules M of the optical scale are maintained over time. On the other hand, the tightening of the elastic thrust clamping fastener 7 is adjusted so that the final elastic thrust is sufficient to allow the scale holder P to slide freely in the longitudinal direction, thereby expanding its linear thermal expansion (which differs significantly from the thermal expansion of the machine tool due to the different materials of the scale holder and the fastener) when the ambient temperature changes, without causing distortion or misalignment of the scale holder P itself. Conversely, the rigid screw clamping fastener 8 is fitted into the through slot 6 intended to determine the FEP position of the scale holder P (the rigid clamping fastener precisely fits into the through slot 6, thereby rigidly fixing the scale holder P to the machine tool table), thereby determining the point at which the scale holder P is fixedly engaged with the machine tool under any temperature conditions. Depending on the various possible scenarios, as illustrated above, the rigid screw clamping fastener 8 can be positioned to correspond to the central through slot 6 or the side through slot 6, or to any other position between the central and side through slots that typically corresponds to the FEP of the machine tool on which the optical scale is mounted (even if specific situations (such as those mentioned above) may require different positioning). Thus, the thermal expansion of the scale holder P and the machine tool can freely expand in the directions imposed by their geometry without any mutual interference.

[0047] Furthermore, corresponding to the steel strip 2 forming the scale grating support, a threaded through-hole 9 is provided across the scale frame P, which terminates inside the scale frame P, as shown in... Figure 5As clearly seen in the cross-sectional view, through-holes 9 are set on the entire scale frame P at a constant pitch C, which can be the same as the pitch of the through slot 6. A pressure pin 10 is screwed into a selected through-hole of the through-holes 9 until the steel strip 2 is intercepted by the tip of the pressure pin 10 and locked in place against the scale frame wall located behind it; this position thus becomes the scale grating FEP. In the case of the glass support 2v, the pitch of the through-holes 9 is equal to the pitch C between the cylindrical verniers 5 glued to the scale grating glass support, so that the tip of the pressure pin 10 impinges on the steel body of the vernier 5, but not on the glass support 2v, and the position of the pressure pin 10 thus becomes the scale grating FEP on the glass support 2v.

[0048] The steel strip 2 or glass support 2v is effectively rigidly locked in this position, while still remaining completely free to slide along the scale frame P in the permissible longitudinal direction to expand thermally; that is, expanding thermally towards the opposite end when the FEP is in the lateral position, and expanding thermally towards the right / left side when the FEP is in the center position, or in any other intermediate position defined by the through-hole 9. All other unused through-holes 9 are protected by corresponding waterproof caps 11 to prevent liquids or contaminants from entering the interior of the scale frame P.

[0049] This method of fixing the scale grating FEP is particularly effective and advantageous compared to the known techniques illustrated above. In fact, this FEP fixing method eliminates the need for any preventative drilling of the scale grating support to accommodate the fixing screw. Furthermore, this FEP fixing method can be quickly activated under any circumstances, even when the scale grating support and scale holder are under thermal expansion, whereas in prior art devices, under the same conditions, the through holes on the scale grating support and scale holder to accommodate the fixing screw may no longer be aligned with the selected FEP position.

[0050] Optical scales typically provide a centering point (FEP) for both the scale holder P and the scale grating. However, their positions can always be easily modified if needed. In fact, it is sufficient to move the rigid screw clamping fastener 8 into a different through slot 6, move the pressure pin 10 by placing it in the through hole 9 corresponding to the new position of the rigid clamping fastener 8, and move the associated cap 11 to the previous position of the pressure pin 10, so that the FEP of the scale holder P coincides with the FEP of the scale grating in the new desired position. Moreover, any other arrangement of the FEP is possible when it is deemed useful for improving the machining accuracy of the machine tool. In fact, the optical scale of the present invention provides maximum flexibility in setting the positions of the FEPs of both the scale support P and the scale grating, which can therefore be in the same or different positions. The entire operation can be performed in minutes without any special equipment.

[0051] Test Example

[0052] Various machining tests were conducted to verify the reliability and effectiveness of the new optical scale with selectable FEP position. Here, we report on the situation on the dual-chuck CNC machine tool, such as... Figure 8 As illustrated schematically, in the first series of tests, the axes X1 and X2 of the optical chuck CNC machine tool were controlled by conventionally manufactured optical scales (i.e., optical scales with a center-positioned FEP F1).

[0053] Over a period of one month, temperature variations of approximately 6°C / 8°C caused a difference of up to 12 μm in the turning diameter of the workpiece along the two axes X1 and X2 of the machine tool. 8 μm of this 12 μm is clearly due to the linear thermal expansion of the measuring system, as the workpiece B rotates with different diameter values ​​as the temperature changes. In fact, both optical scales R exhibit thermal expansion from their center position (i.e., FEP in F1) towards their ends, thus causing the tool to move up / down, resulting in undesirable changes in the turning diameter.

[0054] In the second series of tests, the two optical scales R were replaced with a pair of optical scales with a transverse FEP F2 that coincides with the rotation axis of the chuck: the machining accuracy of workpiece B was no longer affected by temperature changes, and was therefore more stable and precise.

[0055] The optical scale of the present invention has been described with reference to a preferred fastening system for a scale grating or magnetic band support within the scale frame P. However, all the basic features of the present invention can also be applied to optical scales with different fastening systems for the support, provided that such a fastening system includes a single fixing point for the support, wherein the support is integrally formed with the scale frame, for example by means of a screw or other mechanical fastening system or a non-elastic adhesive, and the remaining components of the support are held in place within the scale frame P by means of a free longitudinal sliding device.

[0056] In any event, it should be understood that the present invention should not be considered limited to the arrangements illustrated above, which are merely exemplary embodiments of the invention. However, different variations are possible, all of which are within the scope of those skilled in the art and do not depart from the protection scope of the invention, which is defined only by the appended claims.

[0057] Figure Labels

[0058] A = Pressure Head

[0059] B = workpiece

[0060] C = constant pitch

[0061] F1, F2 = FEP position

[0062] M1, M2 = Optical scale frame module

[0063] P = ruler frame

[0064] R = Optical scale

[0065] T = Transducer

[0066] X1, X2 = Machine tool axis

[0067] Y = Press column

[0068] 1 = Groove

[0069] 2 = Steel strip

[0070] 2v = Glass support

[0071] 3 = Standard Hole

[0072] 4 = Ball bearing

[0073] 5 = Vernier

[0074] 6 = slot

[0075] 7 = Elastic thrust clamping fastener

[0076] 8 = Rigid clamping fasteners

[0077] 9 = Through hole

[0078] 10 = Pressure pin

[0079] 11 = hat

Claims

1. An optical or magnetic scale for performing straight-line measurements, said optical or magnetic scale comprising: A scale holder (P), which is integrated with a fixed or moving part of the machine tool; and a scale grating support (2, 2v), which is housed inside the scale holder (P) and scanned by a transducer (T), wherein the transducer (T) slides along the scale holder (P) and is integrated with the fixed or moving part of the machine tool, the scale holder (P) and the scale grating support (2, 2v) are respectively fixed to the machine tool and the scale holder (P) at a single fixed position, the single fixed position forming a corresponding fixed expansion point FEP of the scale holder and the scale grating support, and the FEP can be independently selected among a plurality of predetermined positions (6, 9), characterized in that the scale holder (P) and the scale grating support (2, 2v) are further respectively fastened to the machine tool and the scale holder (P) at one or more additional free longitudinal sliding positions.

2. The optical or magnetic scale according to claim 1, wherein, The scale holder (P) includes a mechanical connection with a spring-loaded device with a constant lateral load that does not change due to thermal expansion during the longitudinal sliding of the scale holder (P) relative to the machine tool at one or more free longitudinal sliding positions.

3. The optical or magnetic scale according to claim 1, wherein, The one or more free longitudinal sliding positions of the scale grating support (2, 2v) relative to the scale frame (P) include a mechanical connection with degrees of freedom in the longitudinal direction of the scale grating support.

4. The optical or magnetic scale according to claim 2, wherein, The mechanical connection of the device with a constant lateral load relative to the elastic thrust spring includes: a through slot (6) that spans the scale frame (P); and an elastic thrust screw clamping fastener (7) that is received in the through slot and screwed into the machine tool.

5. The optical or magnetic scale according to claim 3, wherein, The mechanical connection having a degree of freedom in the longitudinal direction of the scale grating support comprises a plurality of spherical or cylindrical components (4, 5) fixed to the edge of the scale grating support (2, 2v) and accommodated in an open section groove (1) formed longitudinally in the scale frame (P), the open section groove (1) at least partially matching the cross section of the spherical or cylindrical components (4, 5), and the mechanical connection having sufficient clearance to allow the degree of freedom in the longitudinal direction of the scale grating support.

6. The optical or magnetic scale according to claim 5, wherein, The single fixed position of the scale grating support is formed at a selected threaded through hole among a plurality of threaded through holes (9), the plurality of threaded through holes being arranged across the scale frame (P) and terminating inside the scale frame, wherein a pressure pin (10) is screwed into the selected threaded through hole until the pressure pin intercepts the scale grating support (2, 2v) and locks the scale grating support (2, 2v) in place against the wall of the scale frame (P).

7. The optical or magnetic scale according to any one of claims 1 to 6, wherein, The scale frame (P) is made of aluminum, and the scale grating support (2, 2v) is made of steel or glass.

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