Measuring stand for determining a measurement parameter of an optical test object

Abstract

A measuring stand (100) for determining a measurement parameter of an optical test object (X) comprises a receiving section (110) for receiving the test object (X), a linear guide unit (120) wherein the receiving section (110) is arranged at one end of the linear guide unit (120), a positioning carriage (130) for holding at least one measuring device (170) wherein the positioning carriage (130) is mechanically coupled to the linear guide unit (120) and is displaceable along the linear guide unit (120) relative to the receiving section (110), a drive unit (140) with coarse drive (142) and fine drive (144) wherein the drive unit (140) is mechanically coupled to the positioning carriage (130) and can be manually actuated to displace the positioning carriage (130) relative to the receiving section (110), a locking unit (150) which is mechanically coupled to the Positioning carriage (130) is coupled and trained,to lock the positioning carriage (130) on the linear guide unit (120) in an unactuated rest position and to release the positioning carriage (130) for movement along the linear guide unit (120) in a manually actuated release position, and a weight compensation unit (160) to compensate for a weight force of the positioning carriage (130), wherein the weight compensation unit (160) is mechanically coupled to the positioning carriage (130).

Description

[0001] The invention relates to a measuring stand for determining a measurement parameter of an optical test object according to the preamble of the independent claim.

[0002] In the field of optics, well-known measuring stands that can move a measuring system or device along a measuring axis utilize concepts such as dovetail guides with rack and pinion drives or lead screws. The drive for this movement can be achieved, for example, via gearboxes and rotary movements in coarse and / or fine adjustment. Typically, these rotary movements are initiated by handwheels or cranks. Alternatively, motors and controllers can be used instead of manual operation.

[0003] US Patent 2010 / 0231923 A1 describes an interferometric measuring device for measuring the shape of aspherical lenses or their surfaces. The interferometer can be moved manually in the Z-direction by means of a guide.

[0004] JP3193449 B2 describes a centering measuring device in reflection with autocollimator and two auxiliary lenses 35 and 36, cf. Fig. 11. Lenses 35 and 36 can be moved mechanically and manually along their optical axis using a gear drive. Handles 40 and 41 are provided for operation. Disclosure of the invention

[0005] Against this background, the approach presented here introduces an improved measuring setup for determining a measurement parameter of an optical test specimen according to the main claim. The measures listed in the dependent claims enable advantageous further developments and improvements of the device specified in the independent claim.

[0006] The approach presented here enables, in particular, a measuring stand that moves a measuring system or device along an optical or measuring axis with simple, intuitive, and ergonomic operation and high cost efficiency. In addition to ergonomic and simple operation, stable and positionally accurate focusing is also possible with this approach.

[0007] A measuring station for determining a measurement parameter of an optical test object includes the following features: a recording section for recording the examinee; a linear guide unit, wherein the receiving section is arranged at one end of the linear guide unit; a positioning carriage for holding at least one measuring device, wherein the positioning carriage is mechanically coupled to the linear guide unit and is displaceable along the linear guide unit relative to the receiving section; a drive unit with coarse and fine drive, wherein the drive unit is mechanically coupled to the positioning carriage and can be manually operated to move the positioning carriage relative to the recording section; a locking unit that is mechanically coupled to the positioning carriage and is configured to lock the positioning carriage to the linear guide unit in an unactuated rest position and to release the positioning carriage for movement along the linear guide unit in a manually actuated release position; and a weight compensation unit for compensating a weight force of the positioning carriage, wherein the weight compensation unit is mechanically coupled to the positioning carriage.

[0008] Application areas of the measuring stand can include centering testing, thickness measurement, and, additionally or alternatively, interferometers. The measuring device can also be designed and designated as a measuring system. Measuring systems can include, for example, autocollimators, combined front optics or focusing optics for centering measurement applications, various interferometers, or other length and direction sensors. The linear guide unit can have a linear axis or be designed as a linear axis. The linear guide unit can be designed as an elongated unit. The locking unit can be designed and designated as a brake or braking unit. The coarse drive can be designed and arranged to move the entire positioning carriage along the linear guide unit.The fine adjustment can be designed and arranged to move the entire positioning carriage or a relative position of a portion of the positioning carriage that can be coupled to the measuring device along the linear guide unit. The coarse adjustment is designed to position the positioning carriage within a first tolerance range, and the fine adjustment is designed to position the positioning carriage within a second tolerance range. These tolerance ranges can differ by at least one order of magnitude. For example, the coarse adjustment can be designed to position the positioning carriage in the centimeter range relative to the workpiece, and the fine adjustment can be designed to position the positioning carriage in the millimeter or sub-millimeter range relative to the workpiece.In other words, the fine adjustment offers the additional possibility of refining the positioning of the positioning carriage.

[0009] According to one embodiment, the coarse drive of the drive unit can have at least one handle for moving the positioning carriage along the linear guide unit. This handle can be attached to the positioning carriage. Such an embodiment offers the advantage of enabling simple, quick, and ergonomic movement of the entire positioning carriage, and thus also of any measuring device or measuring system coupled to the positioning carriage, over large travel distances in a structurally simple manner.

[0010] The fine adjustment mechanism of the drive unit can also include an adjusting screw, in particular a micrometer screw. The adjusting screw can be mounted on the positioning slide. Such an embodiment offers the advantage that fine adjustment of the entire positioning slide or of the relative position of a section of the positioning slide that can be coupled to the measuring device can be implemented simply, quickly, precisely, and reliably in a structurally simple manner.

[0011] Furthermore, the locking unit can be pre-tensioned into the rest position by an elastic means. Such an embodiment offers the advantage that secure locking of the positioning carriage in the rest position can be achieved, whereby the locking unit only needs to be actuated to move the positioning carriage into the release position.

[0012] According to one embodiment, the positioning carriage can have a changeover device that can be configured to hold several measuring devices and move one of them into an active measuring position at a time. The changeover device can have a turret mechanism. Such an embodiment offers the advantage of enabling a simple and quick changeover of the measuring devices currently in use.

[0013] Furthermore, the measuring stand can include a linear encoder for determining the position of the positioning carriage along the linear guide unit. Such an embodiment offers the advantage that the position of the positioning carriage relative to at least one other element of the measuring stand can be determined simply and reliably.

[0014] The measuring setup can also include a measuring device, which may incorporate an optical system. Optionally, the optical system can additionally include an interferometer. In particular, the optical system can be a measuring head of an interferometer, especially a low-coherence interferometer, for determining the midpoint thickness of the test specimen. Such an embodiment offers the advantage of enabling straightforward interferometric measurements on the test specimen.

[0015] Furthermore, the measuring stand can include the measuring device, which may have a tactile sensor or probe configured to detect a point on the surface of the optical test piece. Such an embodiment offers the advantage that the measuring stand is versatile and suitable for various types of measuring devices and methods, including tactile devices and methods.

[0016] According to one embodiment, the measuring stand can include a further measuring device, which can be fixedly arranged at an end of the linear guide unit facing away from the receiving section. The positioning carriage can be displaceable relative to this further measuring device. Such an embodiment offers the advantage that the measuring stand provides diverse application possibilities and is suitable for various types of measuring devices and measuring methods.

[0017] The measuring device can include an optical system, and the further measuring device can include another optical system. For example, the further optical system can include an autocollimator, and the optical system can include an attachment optic for the autocollimator. Such an embodiment offers the advantage that the position of a focal point of the attachment optic, which is mechanically connected to the positioning carriage, can be easily, quickly, and precisely adjusted along an optical axis of the autocollimator using the coarse and fine adjustment controls.

[0018] For example, a measuring stand with a focusing mechanism can be provided that is cost-effective and also quick and ergonomic to operate, especially compared to cheaper, state-of-the-art alternatives. For larger focus adjustments, only minimal travel distances are required, compared to a handwheel, for instance. Even when fine adjustments are required, the combination of coarse and fine adjustments allows for time-saving operation and optimal ergonomics. Furthermore, the adjustment via the drive unit can be performed quietly. The adjustable measuring stand presented here can enable precise focusing simply, intuitively, ergonomically, and quickly, while remaining cost-effective. The measuring stand can be operated simply, quickly, ergonomically, and intuitively.By combining coarse adjustment and fine adjustment, optionally also connected with a position encoder, a cost-effective measuring stand can be implemented in which even large presentations can be carried out manually with high accuracy.

[0019] Examples of the approach presented here are shown in the drawings and explained in more detail in the following description. It shows: Fig. 1 a schematic representation of an embodiment of a measuring stand for determining a measurement parameter of an optical test object; Fig. 2 an oblique view of an embodiment of a measuring stand for determining a measurement parameter of an optical test object; Fig. 3 a schematic representation of an embodiment of a measuring stand for determining a measurement parameter of an optical test object; Fig. 4 a partial representation of an embodiment of a measuring stand for determining a measurement parameter of an optical test object; Fig. 5 a partial representation of an embodiment of a measuring stand for determining a measurement parameter of an optical test object; Fig. 6 a rear view of a positioning carriage of an embodiment of a measuring stand for determining a measurement parameter of an optical test object; Fig. 7 a partial representation of an embodiment of a measuring stand for determining a measurement parameter of an optical test object; and Fig. 8 a partial representation of an embodiment of a measuring stand for determining a measurement parameter of an optical test object.

[0020] In the following description of favorable embodiments of the present invention, the same or similar reference numerals are used for the elements shown in the various figures and acting similarly, without repeating these elements.

[0021] Fig. Figure 1 shows a schematic representation of an embodiment of a measuring stand 100 for determining a measurement parameter of an optical test specimen X. The measuring stand 100 comprises a receiving section 110, a linear guide unit 120, a positioning carriage 130, a drive unit 140 with coarse drive 142 and fine drive 144, a locking unit 150, and a weight compensation unit 160. In the representation of Fig. Figure 1 also shows the examinee X.

[0022] The receiving section 110 is shaped to accommodate the optical test piece X. The linear guide unit 120 is connected to the receiving section 110 at one end. In other words, the receiving section 110 is arranged at one end of the linear guide unit 120. The positioning carriage 130 is mechanically coupled to the linear guide unit 120. Furthermore, the positioning carriage 130 is displaceable along the linear guide unit 120 relative to the receiving section 110. The positioning carriage 130 is shaped to hold at least one measuring device 170. In particular, the linear guide unit 120 defines an axis of movement for a displacement or translation of the positioning carriage 130 along the linear guide unit 120.

[0023] The drive unit 140 comprises the coarse drive 142 and the fine drive 144. The drive unit 140 is mechanically coupled to the positioning carriage 130. The drive unit 140 can be manually operated to move the positioning carriage 130 relative to the receiving section 110 or along the linear guide unit 120 relative to the receiving section 110. The locking unit 150 is also mechanically coupled to the positioning carriage 130. The locking unit 150 is designed to lock the positioning carriage 130 to the linear guide unit 120 in an unactuated rest position, or in other words, to lock or block the movement of the positioning carriage 130 along the linear guide unit 120. The locking unit 150 is designed to release the positioning carriage 130 for movement along the linear guide unit 120 in a manually operated release position.Thus, the locking unit 150 can be moved from the rest position to the release position by manual operation. The weight compensation unit 160 is also mechanically coupled to the positioning carriage 130. The weight compensation unit 160 is designed to compensate for the weight force of the positioning carriage 130. For illustrative purposes only, the weight compensation unit 160 includes a counterweight that is coupled to the positioning carriage 130 via a cable.

[0024] According to one embodiment, the measuring stand 100 comprises at least one measuring device 170. The measuring device 170 is arranged on or held on the positioning carriage 130. According to one embodiment, the measuring device 170 has an optical system. The optical system is, for example, an interferometer. According to another embodiment, the measuring device 170 has a tactile sensor or probe designed to detect a point on a surface of the optical test piece X.

[0025] According to one embodiment, the measuring stand 100 comprises at least one measuring device 170 and a further measuring device 180. The further measuring device 180 is arranged at an end of the linear guide unit 120 facing away from the receiving section 110. The further measuring device 180 is fixed with respect to any movement of the positioning carriage 130. Thus, the positioning carriage 130 is displaceable relative to the further measuring device 180. According to this embodiment, the measuring device 170 has an optical system, and the further measuring device 180 has a further optical system. The further optical system comprises an autocollimator, wherein the optical system includes an attachment optic of the autocollimator.

[0026] According to one embodiment, the positioning carriage 130 includes an exchange device configured to hold several measuring devices, such as the measuring device 170, and to move one of them into an active measuring position. Additionally or alternatively, according to one embodiment, the measuring stand 100 further includes a linear encoder for determining the position of the positioning carriage 130 and / or a measuring device 170 held by the positioning carriage 130 along the linear guide unit 120.

[0027] Fig. Figure 2 shows an oblique view of an embodiment of a measuring stand 100 for determining a measurement parameter of an optical test specimen. The measuring stand 100 in Fig. 2 corresponds to or resembles the measuring stand from Fig. 1. This includes Fig. Figure 2 of the measuring stand 100 shows, by way of example, only the receiving section 110, also referred to as the specimen holder, together with a specimen X held therein, the linear guide section 120, the positioning carriage 130, the measuring device 170, which according to the embodiment shown here is designed as an auxiliary lens or focusing lens, and the further measuring device 180, which according to the embodiment shown here is designed as an autocollimator. The positioning carriage 130 can thus be understood as a carriage for moving the focusing lens.

[0028] Fig. Figure 3 shows a schematic representation of an exemplary embodiment of a measuring stand 100 for determining a measurement parameter of an optical test specimen. The measuring stand 100 in Fig. 3 corresponds to or resembles the measuring stand from Fig. 1 and / or Fig. 2. In particular, it shows Fig. 3 a schematic representation of the measuring stand Fig. 2. This includes Fig. 3 of the measuring stand 100, by way of example only the recording section 110 together with a test specimen X recorded therein, the measuring device 170, which according to the embodiment shown here is designed as an auxiliary lens or focusing lens, the further measuring device 180, which according to the embodiment shown here is designed as an autocollimator, and an autocollimation lens 385 in a beam path between the further measuring device 180 and the measuring device 170 are shown.

[0029] Fig. Figure 4 shows a partial representation of an embodiment of a measuring stand 100 for determining a measurement parameter of an optical test specimen. The measuring stand 100 in Fig. 4 corresponds to or resembles the measuring stand from one of the figures described above. Fig. Figure 4 shows a sectioned view of part of measuring stand 100. In the partial view of Fig. Figure 4 shows a part of the linear guide unit 120, the positioning slide 130, the coarse drive 142 of the drive unit, the locking unit 150 and a part of the weight compensation unit 160, more precisely its counterweight, from the measuring stand 100.

[0030] According to the embodiment shown here, the coarse drive 142 of the drive unit comprises at least one handle for moving the positioning carriage 130 along the linear guide unit 120. For example, the coarse drive 142 comprises two handles arranged on opposite sides of the positioning carriage 130.

[0031] Fig. Figure 5 shows a partial representation of an embodiment of a measuring stand 100 for determining a measurement parameter of an optical test specimen. The measuring stand 100 in Fig. 5 corresponds to or resembles the measuring stand from one of the figures described above. In the partial representation of Fig. Figure 5 shows the linear guide unit 120, the positioning slide 130, the coarse drive 142 and the fine drive 144 of the drive unit, the locking unit 150 and the weight compensation unit 160 from the measuring stand 100.

[0032] According to the embodiment shown here, the coarse adjustment 142 of the drive unit comprises two handles for moving the positioning carriage 130 along the linear guide unit 120. Furthermore, the fine adjustment 144 of the drive unit comprises an adjusting screw. In particular, the adjusting screw is designed as a micrometer screw. The fine adjustment 144 enables the displacement of a mounting section 535 of the positioning carriage 130, designed to hold the measuring device, relative to other sections of the positioning carriage 130 and thus relative to the optical test specimen. The counterweight unit 160 comprises a counterweight that is connected to the positioning carriage 130 via two pulleys and a cable.

[0033] Fig. Figure 6 shows a rear view of a positioning carriage 130 and a locking unit 150 of an embodiment of a measuring stand for determining a measurement parameter of an optical test specimen. The positioning carriage 130 and the locking unit 150 correspond to or resemble those of the measuring stand shown in one of the figures described above. The positioning carriage 130 and the locking unit 150 are shown from the rear, which, in the assembled state of the measuring stand, faces the linear guide unit.

[0034] According to the embodiment shown here, the locking unit 150 comprises a scissor mechanism. Furthermore, the locking unit 150 comprises an elastic element 655. The elastic element 655 is designed to pre-tension the locking unit 150 into its rest position. The elastic element 655 is, for example, a coil spring.

[0035] Fig. Figure 7 shows a partial representation of an embodiment of a measuring stand 100 for determining a measurement parameter of an optical test specimen. The measuring stand 100 in Fig. 7 corresponds to or resembles the measuring stand from one of the figures described above. In the partial representation of Fig. Figure 7 shows the linear guide unit 120, the positioning carriage 130, the fine adjustment 144 of the drive unit, the locking unit 150, and the counterweight unit 160 of the measuring stand 100. Here, too, the counterweight unit 160 comprises a counterweight, two deflection pulleys, and a cable that runs over the deflection pulleys and is connected to both the counterweight and the positioning carriage 130. The fine adjustment 144 of the drive unit includes an adjusting screw, which is, for example, designed as a micrometer screw.

[0036] Fig. Figure 8 shows a partial representation of an embodiment of a measuring stand 100 for determining a measurement parameter of an optical test specimen. The measuring stand 100 in Fig. 8 corresponds to or resembles the measuring stand from one of the figures described above. In the partial representation of Fig. Figure 8 shows the linear guide unit 120, the positioning slide 130, the coarse drive 142 of the drive unit, the locking unit 150 and a lever 855 for manually actuating the locking unit 150 from the measuring stand 100.

[0037] According to the embodiment shown here, the coarse drive 142 of the drive unit comprises two handles for moving the positioning carriage 130 along the linear guide unit 120. By actuating the lever 855, the locking unit 150 is moved from the rest position to the release position. After actuation, the lever 855 is reset by the action of the elastic element, so that the locking unit 150 is returned to its rest position. The lever 855 is, for example, arranged adjacent to one of the handles of the coarse drive 142. The locking unit 150 comprises a scissor mechanism.

[0038] With reference to the figures described above, exemplary embodiments, backgrounds of exemplary embodiments and advantages of exemplary embodiments are summarized again below and presented in other words.

[0039] The drive unit 140 is divided into a coarse drive 142 and a fine drive 144. The coarse drive 142 is achieved by direct displacement along a guide axis, which is provided here by the linear guide unit 120. To ensure positioning and ergonomics, the positioning carriage 130 is equipped with both a brake in the form of the locking unit 150 and a weight force compensation unit in the form of the counterweight unit 160. For safety and ergonomic reasons, the brake is closed in the rest / normal state. The operator does not need to actively engage the brake, but releases it to change the measuring distance of the measuring system via a mechanism integrated into the handle. For example, the lever 855 and the elastic element 655 are mechanically linked via a wire and pulleys.The brake is neither electronic nor pneumatic, which reduces the system's cost and complexity. Fine positioning of the positioning carriage 130 is achieved via a separate linear precision axis. The weight force compensation is designed so that the operator does not need to apply any vertical force, thus enabling operation by any user. The (relative) position of the measuring system along the focus axis is determined by a length measurement encoder system that takes into account the movements of the coarse drive 142 and the fine drive 144. Within the framework of the drive concept, both the force applied to the brake and the choice of guide concept can vary according to different embodiments.

[0040] In Fig. Figure 3 shows a schematic representation of a centering measurement in reflection, where in Fig. Figure 2 shows an embodiment of the present invention. For adjusting or moving the auxiliary or focusing lens, i.e., the measuring device 170, along its optical axis or the optical axis of the autocollimator, an advantageous mechanism, according to the aforementioned embodiments, is provided. The lens or measuring device 170 is attached to the positioning carriage 130, which has a coarse adjustment 142 and a fine adjustment 144. In its rest position, the positioning carriage 130 is fixed by a brake or the locking unit 150 together with a weight force compensation or the weight compensation unit 160. The weight force compensation is effected by a tensioned belt in combination with at least one deflection pulley and a counterweight, as described in the Fig. 1, Fig. 5 and Fig.Figure 7 shows that the brake or locking unit 150 can be released via a tensioned wire using a lever 855, which is located laterally on the positioning carriage 130, and the positioning carriage 130 can be moved. When the lever 855 is released, the tensioned spring 655 actuates the brake and locks the positioning carriage 130 in its position without requiring any active adjustment. The fine adjustment 144 is implemented via a screw, e.g., a micrometer screw. The coarse adjustment 142 and the fine adjustment 144 form a common mechanism, which allows the focus position of the attachment optic or measuring device 170 to be adjusted easily and ergonomically by hand. The travel distance is determined by a linear encoder. In addition, the holder 535 for the attachment lens or measuring device 170 can be changed via an interchangeable mechanism (e.g.,The device features a turret mechanism, allowing lenses with different focal lengths to be swiveled into the beam path. Additionally or alternatively, the adjustment mechanism described here can be used to manually move other components or measuring tools. For example, the measuring head of an interferometer, particularly a low-coherence interferometer for determining the center thickness of an optical system, could be used as a measuring device. The aforementioned interchangeable mechanism can also be used to swivel another measuring tool, such as a low-coherence interferometer, into the beam path of the test specimen.

[0041] In other words, according to one embodiment, and as illustrated in the figures described herein, a measuring stand 100 is provided for determining a measurement parameter of a test specimen X, wherein the measuring stand 100 has a test specimen holder or a holding section 110 and a measuring system consisting of an optical system in the form of the further measuring device 180 attached to the measuring stand 100 and a manually movable optical system in the form of the measuring device 170. The drive or drive unit 140 of the movable optical system or the measuring device 170 is divided into the coarse drive 142 and the fine drive 144 and is configured to position the movable optical system or the measuring device in a vertical direction relative to the optical test specimen X along a linear axis. The movable optical system orThe measuring device 170 is mechanically connected to the positioning carriage 130, which is coupled to the measuring stand 100 and on which the coarse adjustment 142 and the fine adjustment 144 act simultaneously. The positioning carriage 130 is mechanically locked in a rest position and is equipped with a brake with weight force compensation in the form of the locking unit 150 and the weight compensation unit 160 for this mechanical locking. In particular, the optical system or the further measuring device 180 attached to the measuring stand 100 comprises an autocollimator, and the manually movable optical system or the measuring device 170 comprises an attachment optic of the autocollimator. The front optics are mechanically connected to the positioning carriage 130, so that the position of the focal point of the front optics along the optical axis of the autocollimator can be adjusted using the coarse drive 142 and the fine drive 144.

[0042] In another embodiment, and as illustrated in the figures described herein, a measuring stand 100 is provided for determining a measurement parameter of a test specimen X, wherein the measuring stand 100 comprises a test specimen holder or a holding section 110 and a measuring system consisting of a manually movable optical system or the measuring device 170. The drive unit 140 or the drive of the movable optical system or the measuring device 170 is divided into a coarse drive 142 and a fine drive 144 and is configured to position the movable optical system or the measuring device 170 in a vertical direction relative to the optical test specimen X along a linear axis. The movable optical system or the measuring device 170 is mechanically connected to a positioning carriage 130 coupled to the measuring stand 100, on which the coarse drive 142 and the fine drive 144 act simultaneously.The positioning carriage 130 is mechanically locked in a rest position and is equipped with a weight-compensated brake in the form of the locking unit 150 and the weight compensation unit 160 for this mechanical locking. In particular, the manually movable optical system or measuring device 170 comprises an interferometer that is mechanically connected to the positioning carriage 130, such that the position of the interferometer relative to the optical test object X can be adjusted using the coarse adjustment 142 and the fine adjustment 144. Alternatively, the manually movable optical system or measuring device 170 comprises a tactile sensor or probe, wherein the tactile sensor or probe is mechanically connected to the positioning carriage 130, such that a point on the surface of the optical test object X can be tactilely detected using the coarse adjustment 142 and the fine adjustment 144.

[0043] According to exemplary embodiments, and as illustrated in the figures described herein, at least one of the following features is optionally provided: a changing mechanism for the positioning carriage 130, so that various movable optical systems or measuring devices 170 can be mounted on the linear axis; a linear encoder for determining the travel distance of the manually movable optical system or measuring device 170; the brake or locking unit 150 of the positioning carriage 130 can be released by actively actuating a lever 855 laterally on the positioning carriage 130 and locked by releasing the lever 855, the lever 855 being mechanically coupled to the brake via a wire; and / or the fine adjustment 144 is implemented via a screw, in particular a micrometer screw. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 2010 / 0231923 A1

[0003] JP 3193449 B2

[0004]

Claims

[1] Measuring stand (100) for determining a measurement parameter of an optical test object (X), wherein the measuring stand (100) has the following features: a recording section (110) for recording the test subject (X); a linear guide unit (120) wherein the receiving section (110) is arranged at one end of the linear guide unit (120); a positioning carriage (130) for holding at least one measuring device (170), wherein the positioning carriage (130) is mechanically coupled to the linear guide unit (120) and is displaceable along the linear guide unit (120) relative to the receiving section (110); a drive unit (140) with coarse drive (142) and fine drive (144), wherein the drive unit (140) is mechanically coupled to the positioning carriage (130) and can be manually operated to move the positioning carriage (130) relative to the receiving section (110); a locking unit (150) which is mechanically coupled to the positioning carriage (130) and is configured to lock the positioning carriage (130) to the linear guide unit (120) in an unactuated rest position and to release the positioning carriage (130) for movement along the linear guide unit (120) in a manually actuated release position; and a weight compensation unit (160) for compensating a weight force of the positioning carriage (130), wherein the weight compensation unit (160) is mechanically coupled to the positioning carriage (130). [2] Measuring stand (100) according to claim 1, wherein the coarse drive (142) of the drive unit (140) has at least one handle for moving the positioning carriage (130) along the linear guide unit (120). [3] Measuring stand (100) according to one of the preceding claims, wherein the fine adjustment (144) of the drive unit (140) has an adjusting screw, in particular a micrometer screw. [4] Measuring stand (100) according to one of the preceding claims, wherein the locking unit (150) is pre-tensioned into the rest position by an elastic means (655). [5] Measuring stand (100) according to one of the preceding claims, wherein the positioning carriage (130) has an exchange device configured to hold several measuring devices (170) and to bring one of them into an active measuring position. [6] Measuring stand (100) according to one of the preceding claims, comprising a linear encoder for determining a position of the positioning carriage (130) along the linear guide unit (120). [7] Measuring stand (100) according to one of the preceding claims, with the measuring device (170), wherein the measuring device (170) comprises an optical system, and / or wherein the optical system comprises an interferometer. [8] Measuring stand (100) according to one of the preceding claims, with the measuring device (170), wherein the measuring device (170) has a tactile sensor or probe configured to tactilely detect a point on a surface of the optical test object (X). [9] Measuring stand (100) according to one of the preceding claims, with a further measuring device (180) which is fixedly arranged at an end of the linear guide unit (120) facing away from the receiving section (110), wherein the positioning carriage (130) is displaceable relative to the further measuring device (180). [10] Measuring stand (100) according to claim 9, wherein the measuring device (170) has an optical system and the further measuring device (180) has a further optical system, and / or wherein the further optical system has an autocollimator and the optical system has an attachment optic of the autocollimator.

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