ARM FOR A HEAD FOR THE LINEAR DIMENSION CHECKING OF MECHANICAL PIECES AND HEAD INCLUDING SAID ARM

Abstract: A gauging, or measuring, head for the linear dimension checking of mechanical pieces with a casing (1), a movable arm-set (3) and an arm (7), carrying a feeler (9) and coupled to the movable arm-set (3), the arm (7) including an element made of bent sheet (11) with two longitudinal, separate, portions (17, 19) arranged side by side and a portion (25) for coupling the two longitudinal portions (17, 19). A threaded coupling and adjustment device (33) enables the coupling of arm (7) to the movable arm-set (3) and the adjusting of its position with respect to the casing (1) in a direction (z).

Description: DESCRIPTION «ARM FOR A HEAD FOR THE LINEAR DIMENSION CHECKING OF MECHANICAL PIECES AND HEAD INCLUDING SAID ARM» Technical Field The present invention relates to an arm for a head for the linear dimension checking of mechanical pieces, the head including a casing and a movable arm-set, the arm having a first end for the coupling to the movable arm-set and a second end for supporting a feeler. The invention also relates to a head including a similar arm. Background Art There are known gauging or measuring heads for the linear dimension checking of mechanical pieces that comprise a casing, a movable arm-set, an arm, coupled to the movable arm-set and carrying a feeler, and a transducer for providing a signal responsive to the position of the feeler. A head of this type is disclosed, for example, in international patent application published under WO 98/20297. In the known heads the arms, that can be more or less long depending on the type of application, are typically made of steel and have circular, square or rectangular cross- sections. The arms must be considerably rigid and relatively light. These requirements are particularly important in the dynamic checkings, in other terms when the checking is carried out under the conditions of mutual motion between the head and the piece. One of the most severe dynamic checking applications regards the checking of pieces with an interrupted surface, for example grooved pieces, in the course of the machining in grinding machines . The pieces and the grinding wheel rotate at high speeds and are subject to a flow of coolant, that can stress the arm. In consideration of the trend to increase the speeds and in general the productivity of the machinings, and concurrently reduce the tolerances of the machined pieces, it is understood how, in some applications, it can be difficult to manufacture gauging heads with adequate repeatability and accuracy. Disclosure of Invention An object of the present invention is to provide a gauging or measuring head for the linear dimension checking of mechanical pieces, that guarantees high standards of repeatability and accuracy, and utilizes a sufficiently rigid and light arm, therefore an arm that is particularly suitable for withstanding the stresses of the coolant flow and being applied for the checking of pieces with an interrupted surface, made of even soft material. Another object of the present invention is to manufacture, in an extremely simple and rapid way without involving expensive and lengthy mechanic machinings, an arm for a gauging or measuring head that has the above mentioned features. Yet another object of the present invention is to provide a gauging or measuring head in which the position of the arm relative to the head can be adjusted in a simple and rapid way. These and other objects are achieved by an arm for a head for the linear dimension checking of mechanical pieces according to claim 1, and a head for the linear dimension checking of mechanical pieces according to claim 8. Brief Description of the Drawings The invention is now described in more detail with reference to the enclosed sheet of drawings, given by way of non limiting example, wherein: figure 1 is a side view of a gauging head provided with an arm according to the invention; figure 2 is a plan view of an arm and a threaded coupling and adjustment device of the head of figure 1; figure 3 is a cross-sectional view, taken along line III-III, of the arm and the threaded coupling and adjustment device shown in figure 2. Best Mode for Carrying Out the Invention The head shown in figure 1, more specifically a gauging head, includes a substantially parallelepipedon-shaped, steel casing 1, that forms a support element and defines a longitudinal geometrical axis. A movable arm-set 3 is partially housed in casing 1 and carries, at the end portion that protrudes from casing 1, a support element 5 for an arm 7. Arm 7 defines a first end 13 for the coupling to the movable arm-set 3 and a second end 15, that supports a feeler 9, for contacting a piece to be checked. Arm 7 includes an element 11 made of bent sheet, for example titanium sheet, with two longitudinal, separate portions 17 and 19, arranged side by side and a portion 25 for coupling the two longitudinal portions 17 and 19 at the first end 13. The two longitudinal portions 17 and 19 have free ends, at the second end 15, to which there is coupled a coupling device for coupling feeler 9 to arm 7, including an element, or small plate, 31 for supporting feeler 9, and a bolt with nut 29 traversing a pair of facing holes in the two free ends and a corresponding hole in plate 31. By screwing the nut into bolt 29, the free ends of the longitudinal portions 17 and 19 are clamped to plate 31. For the purpose of enhancing the rigidity of arm 7, the longitudinal portions 17 and 19 are coupled to each other by means of stiffening elements 21 and 23, as, for example, rivets, inserted in corresponding pairs of facing holes, obtained in the two longitudinal portions 17 and 19. The portion 25 for coupling the two longitudinal portions 17 and 19 can be elastically strained so as to enable the coupling of the sheet element 11 to the movable arm-set 3 in the hereinafter described manner. A threaded coupling and adjustment device 33 includes an internally threaded bushing 35, an adjustment screw 44 and an elastic safety ring 45. The adjustment screw 44 is secured to element 11 at the coupling portion 25, by means of the elastic safety ring 45 that engages in a slit 47, formed in the coupling portion 25, in such a way that by screwing or unscrewing screw 44, the latter can rotate but not translate with respect to the coupling portion 25. Screw 44 engages in the threaded hole of bushing 35. The threaded coupling and adjustment device 33 enables to couple arm 7 to movable arm-set 3 and adjust its position with respect to casing 1, in a direction z, as indicated by the arrows in figure 3. As far as the coupling of arm 7 to movable arm-set 3 is concerned, the unit formed by element 11, adjustment screw 44 and bushing 35, assembled as previously described, is coupled to support 5 by inserting bushing 35, that has an annular relief 37, in a hole of support 5, until annular relief 37 abuts against a surface 39 of support 5, and bushing 35 is clamped to support 5 by means of a screw 41 and a washer 43. Once arm 7 has been coupled to support 5, it is possible to adjust its position relative to the head by operating adjustment screw 44. As adjustment screw 44 can rotate but not translate with respect to arm 7, by screwing/unscrewing screw 44, by means of a set screw wrench, and keeping element 11 stationary - in order to prevent it from rotating together with screw 44 - arm 7 is displaced in order to approach to/move away from support 5, in other terms, with reference to figure 1, effect the lowering/raising of the arm with respect to the head. Once arm 7 has reached the desired position, the latter is fixed by locking element 11 to bushing 35 by means of a bolt with nut 32 inserted in a pair of facing holes, obtained in the two longitudinal portions 17 and 19, thereby causing the elastic deformation of the coupling portion 25. In order to perform subsequent adjustments, it is sufficient to loosen bolt 32, adjust the position of arm 7 by means of the adjustment screw 44 and tighten bolt 32 again. Thus, the threaded coupling and adjustment device 33 enables to secure arm 7 to movable arm-set 3 and position it in an extremely simple and rapid way within a suitable zone for subsequently effecting the electric zero-setting of the head in a known way. The main advantage that the present invention provides consists in the particular shape of the arm, that enables to reduce its cross-section to one third with respect to the traditional arms, at an equal standard of performance. The stresses, caused by the coolant flowing on the arms according to the invention, are thus considerably reduced as the surface area of the arm that is subject to this flow is smaller. The particular type of material that is preferably utilized, titanium, provides an optimum ratio between modulus of elasticity and specific weight and enables to achieve rigid arms with low inertia. The low inertia of the arm is particularly important when the head is applied for checking pieces with an interrupted surface. In these cases, the impact occuring between the feeler and the piece when the' surface changes from a protruding portion to a recessing causes the arm to bounce of an amount proportional to the arm inertia. Furthermore, when a heavy arm falls onto the piece after having bounced, it could damage it, especially if the piece is made of a soft material . In applications of this type, even the rigidity of the arm is a feature of particular importance. In fact, a not too rigid arm could deform itself as a consequence of impacts occurring between the feeler and the piece. A further advantage is provided by the manufacturing simplicity of the arm, that can be manufactured by cutting (for example by laser cutting machines) a sheet strap, bending it and thereafter shearing it to obtain the necessary holes. In this way it is possible to avoid welding, that, as known, is a process that can contribute to increase the thermal drift effect, i.e. the deformations of the mechanical parts due to temperature variations that can cause measurement errors. The arm can be manufactured by utilizing materials that differ from titanium, as, for example, steel. The manufacturing process is furtherly simplified in the event there is utilized a stainless material, like titanium or stainless steel, as in these cases it is not necessary to carry out any final antioxidizer treatments.

Claims: CLAIMS 1. Arm (7) for a head for the linear dimension checking of mechanical pieces, the head including a casing (1) and a movable arm-set (3) , the arm (7) having a first end (13) for the coupling to the movable arm-set (3) and a second end (15) for supporting a feeler (9) , characterized in that it includes an element (11) made of bent sheet with two longitudinal, separate portions (17,19) arranged side by side and a portion (25) for coupling the two longitudinal portions (17,19), at said first end (13). 2. An arm (7) according to claim 1, wherein said longitudinal portions (17,19) arranged side by side have associated free ends adapted for being coupled to each other so as to carry an element (31) for supporting said feeler (9) . 3. An arm (7) according to claim 1 or claim 2, wherein said longitudinal portions (17,19) arranged side by side are coupled to each other by means of stiffening elements (21,23) . 4. An arm according to claim 3, wherein said stiffening elements include rivets (21,23) . 5. An arm (7) according to one of claims from 1 to 4, wherein said coupling portion (25) is elastically deformable and suitable for being coupled to a support element (5) coupled to the movable arm-set (3) . 6. An arm (7) according to claim 5, wherein said longitudinal portions (17,19) are adapted for housing a bolt (32) for elastically deforming said coupling portion and fixing the arm (7) to the movable arm-set (3) . 7. An arm (7) according to one of claims from 1 to 6, wherein said sheet element (11) is made of titanium. 8. Head for the linear dimension checking of mechanical pieces, characterized in that it includes an arm (7) according to one of claims from 1 to 7. 9. A head according to claim 8, including a feeler (9) and a coupling device for coupling the feeler to the arm, the coupling device including a plate (31) for supporting the feeler (9) and adapted for being placed between said longitudinal, separate portions (17,19) and a bolt (29) for clamping said separate longitudinal portions (17,19) to said plate (31) . 10. A head according to claim 8 or claim 9, including a threaded coupling and adjustment device (33) for said arm (7), that includes a threaded bushing (35), coupled to the movable arm-set (3) , an adjustment screw (44) , an elastic safety ring (45) coupled to the screw (44) and the coupling portion (25) for enabling rotations of the screw (44) and preventing it from translating with respect to the coupling portion (25) , the threaded bushing (35) being coupled to the adjustment screw (44) for coupling the arm (7) to the movable arm-set (3) and adjusting its position with respect to the casing (1) of the head, in a direction (z) .

Inventors: DALL AGLIO CARLO, DALL'AGLIO, CARLO
Applicants: DALL AGLIO CARLO, MARPOSS SPA, DALL'AGLIO, CARLO, MARPOSS SOCIETA' PER AZIONI
Application year: 1999
Main classification: G01B5
IPC codes: G01B1, G01B5