Coupling mechanism

Abstract: A mechanism for clamping a tool (e.g. a probe) and a shank together comprises a clamping pin (144), which bears against an annular lip (142) in the rear face of the probe. A shaft (148) of the pin (144) extends into the shank (150), and two diametrically opposite, radially extending clamping bolts (160) supported by the shank (150), bear against a frusto-conical clamping surface (158). The action of the bolts (160) on the surfaces (158) urges the probe and shank together. The probe and shank are adjusted laterally relative to each other by four adjusting bolts (166) supported in the annular lip (142) which bear against a flange (152). The flange (152) is provided on the shank (150) and extends into the probe (140).

Description: The present invention relates to a coupling mechanism according to the preamble of claim 1 (see DE-U-8633959). Such a coupling mechanism may be used for example, in coupling a tool to a shank for supporting the tool in a head of a coordinate positioning machine, e.g. a machine tool or coordinate measuring machine. It is known to releasably couple a tool such as a probe or cutting tool (eg. a boring bar) to a shank, which supports the tool in a machine tool. This enables replacement of a faulty, worn, or broken boring bar for example without replacement of the shank as well, and thus is more cost effective. However, releasable coupling mechanisms have the disadvantage that, during coupling the axis of the tool may be displaced by a small distance from the axis of the shank as a result of lateral forces in the coupling mechanism. This source of error is undesirable, and particularly so where the device to be coupled to the machine is a touch or other probe. It is known, (for example from DE-U-8633959), to provide a tool and shank coupled together by an axial clamping force which is generated by a radially extending clamping screw acting on an inclined surface of a clamping shuttle. Adjustment of the alignment transverse to the axis of the tool and shank is provided by four radially extending adjusting screws. It is also known, from US 4776734 to attach a tool holder to a spindle fixture by axially extending screws. The axial alignment of the spindle fixture and tool holder is adjusted by a radially extending screw, carried in a rotatable ring provided on the spindle fixture, which bears against the tool holder. The present invention provides an alternative arrangement. According to the present invention there is provided a coupling mechanism for coupling a tool to a shank comprising a bore provided on one of the tool and shank, the bore defining an axis; a shaft provided on the other of the tool and shank, the shaft being movable in said bore in a direction transverse to said axis; a clamping element supported on the shaft in a manner enabling relative movement of the element and shaft in a direction transverse to said axis, the clamping element having a clamping surface inclined at an angle to the axis; means for applying a force to said clamping surface thereby to generate a clamping force acting parallel to said axis; characterised in that: the clamping element is in slidable engagement with the bore, thereby to enable axial movement of the clamping element in the bore upon the generation of a said clamping force, and to restrict any movement of the clamping element in the bore in a direction transverse to said axis. An embodiment of the invention will now be described, by way of example, and with reference to the accompanying drawing which shows a section through a shank and probe retained by a coupling mechanism embodiying the present invention. Referring now to the sole Figure a probe 100 has, at its rear face a shaft 102 into which a retaining pin 104 is embedded. Both the shaft 102 and the pin 104 lie inside the retaining bore 106 in the taper shank 108. The retaining pin 104 is sleeved by a clamping element in the form of a cylindrical collar 110; the collar 110 sleeves the pin 104 sufficiently loosely to allow relative movement of the pin 104 and collar 110 perpendicular to the axis D of shank 108. The head 112 of the retaining pin 104 bears against the collar 110 via a Belleville washer 114. The collar 110 has a conical side face 116 and the largest diameter edge of the collar 110 fits closely into bore 106. The entire assembly of shaft 102, pin 104, collar 110 and washer 114 comprises a projection which lies inside the recess (in this case, a bore 106) provided in the shank 108. A clamping bolt 118 projects into the retaining bore 106, in a direction radial to the axis D. The end face of the clamping bolt 118 is conical, and bears against the conical face 116 of the collar 110. Since the largest diameter of the collar 110 is adjacent the head 112 of the pin 104, inward radial movement of the clamping bolt 118 will cause the collar 110 to move away from the body of the probe 100, and therefore bear (via the Belleville washer 114), more strongly against the head 112 of the pin 104. Thus, force applied to the collar by inward radial movement of the bolt 118, produces a resultant clamping force which clamps the taper shank 108 and the probe 100 together. Radial adjustment of the relative alignment of the probe 100 and taper shank 108 is accomplished by means of four adjusting bolts 120, each of which is supported in the body of the taper shank 108 and extends radially into retaining bore 106 to bear against the shaft 102. A coupling, and adjustment operation is thus performed as follows: the clamping bolt 118 is first tightened to cause the probe 100 to bear against the shank 108 with sufficient force to provide friction against relative radial movement of the two parts. The relative radial positions of probe 100 and shank 108 are then adjusted using the four adjusting bolts 120. Once this has been completed, the clamping bolt 118 is fully tightened, thus drawing the probe 100 more firmly against the shank 108, without destroying the recently adjusted relative alignment of the two parts. The provision of three or more adjusting screws prevents relative movement of the tool and the shank (radially with respect to each other) when the tool and the shank are being clamped axially. Moreover, if the tool is to be used in conjunction with a tool change apparatus which grasps the shank to remove the tool from a magazine and insert it into a spindle, then the continual jarring of the tool during changing may cause misalignment between the tool and the shank. The provision of three or more radially extending adjusting screws helps to reduce this undesirable effect. It is not essential that the shaft (i.e. the fixed shaft provided by the probe or shank as appropriate) is cylindrical. For example, it may be desirable to provide a square or triangular shaft (depending upon the number of adjusting, and clamping bolts employed). Typically, the touch probe illustrated will be a touch trigger probe or an analogue touch probe.

Claims: A coupling mechanism for coupling a tool (100) to a shank comprising a bore (106) provided on one of the tool and shank, the bore (106) defining an axis (D); a shaft (102) provided on the other of the tool and shank, the shaft (102) being movable in said bore (106) in a direction transverse to said axis; a clamping element (110) supported on the shaft (102) in a manner enabling relative movement of the element and shaft in a direction transverse to said axis (D), the clamping element (110) having a clamping surface (116) inclined at an angle to the axis; means (118) for applying a force to said clamping surface thereby to generate a clamping force acting parallel to said axis (D); characterised in that: the clamping element (110) is in slidable engagement with the bore (106), thereby to enable axial movement of the clamping element in the bore upon the generation of said clamping force, and to restrict any movement of the clamping element in the bore in a direction transverse to said axis (D). A coupling mechanism according to claim 1 comprising a retaining pin (104) connected to the end of the shaft (102), the retaining pin (104) extending through an aperture provided in the clamping element (11) wherein said aperture is sufficiently large to allow movement of said clamping element relative to said retaining pin (104) in a direction transverse to said axis (D). A coupling mechanism according to claim 1 or claim 2 wherein said bore (106) has a cylindrical cross-section and the clamping element (110) has a cylindrical outer surface which contacts the bore (106), thereby to provide said sliding engagement. A coupling mechanism according to claim 2 or claim 3 wherein the clamping element (110) is resiliently urged into contact with the end of the shaft (102). A coupling mechanism according to any one of the preceding claims comprising a plurality of adjusting bolts (120), provided on said one of the tool and shank, for bearing against the shaft (102). A coupling mechanism according to any one of the preceding claims comprising a clamping bolt (118) provided on said one of the tool and shank, extending transversely to said axis (D) and bearing against said clamping surface.

Inventors: MCMURTRY DAVID ROBERTS, SPIVEY MARTIN PHILLIP, TRULL STEPHEN JAMES, MCMURTRY, DAVID ROBERTS, SPIVEY, MARTIN PHILLIP, TRULL, STEPHEN JAMES
Applicants: RENISHAW PLC
Application year: 1990
Main classification: B23B31
IPC codes: B23B31