Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23B—TURNING; BORING
  • B23B31/00—Chucks; Expansion mandrels; Adaptations thereof for remote control
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23B—TURNING; BORING
  • B23B31/00—Chucks; Expansion mandrels; Adaptations thereof for remote control
  • B23B31/02—Chucks
  • B23B31/10—Chucks characterised by the retaining or gripping devices or their immediate operating means
  • B23B31/12—Chucks with simultaneously-acting jaws, whether or not also individually adjustable
  • B23B31/16—Chucks with simultaneously-acting jaws, whether or not also individually adjustable moving radially
  • B23B31/16233—Jaws movement actuated by oblique surfaces of a coaxial control rod
  • B23B31/16254—Jaws movement actuated by oblique surfaces of a coaxial control rod using fluid-pressure means to actuate the gripping means
  • B23B31/16258—Jaws movement actuated by oblique surfaces of a coaxial control rod using fluid-pressure means to actuate the gripping means using mechanical transmission through the spindle
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23Q—DETAILS, COMPONENTS, OR ACCESSORIES FOR MACHINE TOOLS, e.g. ARRANGEMENTS FOR COPYING OR CONTROLLING; MACHINE TOOLS IN GENERAL CHARACTERISED BY THE CONSTRUCTION OF PARTICULAR DETAILS OR COMPONENTS; COMBINATIONS OR ASSOCIATIONS OF METAL-WORKING MACHINES, NOT DIRECTED TO A PARTICULAR RESULT
  • B23Q17/00—Arrangements for observing, indicating or measuring on machine tools
  • B23Q17/002—Arrangements for observing, indicating or measuring on machine tools for indicating or measuring the holding action of work or tool holders
  • B23Q17/005—Arrangements for observing, indicating or measuring on machine tools for indicating or measuring the holding action of work or tool holders by measuring a force, a pressure or a deformation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23Q—DETAILS, COMPONENTS, OR ACCESSORIES FOR MACHINE TOOLS, e.g. ARRANGEMENTS FOR COPYING OR CONTROLLING; MACHINE TOOLS IN GENERAL CHARACTERISED BY THE CONSTRUCTION OF PARTICULAR DETAILS OR COMPONENTS; COMBINATIONS OR ASSOCIATIONS OF METAL-WORKING MACHINES, NOT DIRECTED TO A PARTICULAR RESULT
  • B23Q2717/00—Arrangements for indicating or measuring
  • B23Q2717/003—Arrangements for indicating or measuring in lathes

Definitions

• the invention relates to a method for monitoring the clamping force in machine tools according to the preamble of claim 1.
• the workpiece to be machined is clamped in a workpiece holder.
• a certain clamping force must be observed. If the tension is too low, devastating consequences can occur. So there is the possibility that the workpiece from the workpiece would be thrown out, which poses a significant risk of accidents for people in the area. The workpiece itself and other objects can also be damaged. If, on the other hand, the clamping force is too great, the workpiece or the workpiece holder is deformed.
• the required clamping force is applied hydraulically by exerting a force on the inside of the clamping jaws, which are movably mounted in a chuck body.
• This force is e.g. Introduced via an actuating rod which engages with the clamping jaws via a conical gear.
• the sliding surfaces formed between the clamping jaws on the one hand and the chuck body and the gear on the other hand require lubrication so that the frictional forces are reduced and material corrosion is avoided.
• the invention has for its object to improve a method for monitoring the clamping force of machine tools in such a way that an automatic measurement of the clamping force is made possible so that the operating personnel can be warned in time of an excessive decrease in the clamping force.
• the basic idea of the invention is based on determining the clamping force applied to the workpiece by means of the clamping jaws via the clamping work or the travel pressure or the travel path which is carried out during the hydraulic actuation (it should be expressly mentioned that the term "travel pressure" means both Individual pressures in the cylinder chambers of a double chamber cylinder as well as the differential pressure is included). As a result, it is possible to determine the critical state of friction without great effort and to the operating personnel Signal condition so that cleaning and lubrication can be carried out immediately.
• the clamping jaws are acted upon by a prestressing force which exerts an increased normal force on the sliding surfaces and thereby causes a significant increase in friction when contamination and reduced lubrication occur. It is thus achieved that the proportion of the frictional force caused by contamination and decreasing lubrication increases compared to the proportion of the other frictional forces.
• the frictional forces artificially increased by the increased normal force now lead to a clearer influence on the clamping work performed, the travel pressure and the travel path. Therefore, these measurements allow an improved statement about the clamping force.
• a further development of the invention provides that the clamping jaws are continuously subjected to the prestressing force and the clamping work is also measured continuously.
• Another alternative provides that the prestressing force is only applied to the clamping jaws at predetermined time intervals and that the clamping work or the travel pressure or the travel path is measured in these time intervals.
• the amount of the preload force with which the clamping jaws are acted upon can expediently be such that it corresponds to the nominal value of the clamping force for clamping a workpiece.
• the measurement can also be carried out without clamping a workpiece, so that e.g. the measurement can be carried out during a changeover without disturbing the workflow.
• the invention further relates to a device for monitoring the clamping force of machine tools according to the preamble of claim 6.
• the workpiece holder comprises a chuck body with clamping jaws guided therein.
• the prestressing device consists of spring bodies which are supported on the clamping jaws on the one hand and the chuck body on the other.
• the prestressing force acts in exactly the same direction as the prestressing force and also acts at the same point as the prestressing force.
• the hydraulic actuating device consists of an actuating rod which is coupled to the clamping jaws via a gear and a piston which is connected to the actuating rod and is guided in a double-chamber cylinder.
• the measuring device for the hydraulic clamping work consists of a displacement transducer and a pressure transducer, which are assigned to the double chamber cylinder, and a computer.
• the clamping work can be calculated in a simple manner, namely via the integral of the pressure difference p on the piston, multiplied by the area a of the piston over the displacement path s.
• the area of the piston is assumed to be given, so that the signals determined by the displacement transducers and pressure transducers can be evaluated directly in the computer to calculate the clamping work W.
• FIG. 1 shows a longitudinal section through a hydraulically actuated workpiece holder of a lathe
• FIG. 1 shows a model of a hydraulically operated chuck
• FIG 3 shows a cross section through a chuck body of a lathe with a pretensioning device according to the invention
• Fig. 1 is a longitudinal section through a hydraulic actuated workpiece holder 10 of a lathe shown.
• a spindle 34 of the lathe is rotatably supported in spindle bearings 36.
• a workpiece holder 10 consisting of a chuck body 18 firmly connected to the spindle 34 and clamping jaws 12 guided therein.
• the clamping jaws 12 are mounted in, for example, double-T grooves of the chuck body 18 and are radially adjustable.
• the clamping jaws 12 are adjusted by means of a gear 22 which is conical and also engages with the inside of the clamping jaws 12 via double-T grooves.
• a longitudinal movement of the gear 22 to the right in the plane of the drawing expands the jaws 12 while they are compressed in the opposite direction.
• the transmission 22 is connected via an actuating rod 24 to a piston 28 which is guided in a double cylinder 26.
• This double chamber cylinder 24 is supplied with hydraulic fluid from a hydraulic source (not shown) via hydraulic lines 38.
• the hydraulic lines 38 are connected to a pressure sensor 32, which has the differential pressure p between one and the other chamber of the double-chamber cylinder 26 recorded.
• the actuating rod 24 is still led out of the double chamber cylinder 26 in the drawing.
• There is a displacement transducer 30 which determines the travel path s.
• the signals from the displacement transducers 30 and pressure transducers 32 arrive at a computer, not shown here, which determines the clamping work W from the values supplied for the travel path s and the pressure difference p. If we also take into account the area a of the piston 28, so that the following calculation formula results:
• Fig. 2 shows a model of a hydraulically operated chuck, in which the representation of the workpiece holder is limited to the parts that are involved in the creation of frictional forces. Arrows 1 to 5 point to the surfaces between which frictional forces occur.
• the pretensioning device according to the invention can be used to artificially exert an increased normal force on the surfaces 1, 2 and 3. This normal force multiplied by the friction factor increases the friction force if the friction factor increases due to increasing wear, reduced lubrication or increasing contamination.
• the desired consequence is that the proportion of the frictional forces between the surfaces 1, 2 and 3 increases compared to the proportion of the frictional forces between the surfaces 4 and 5 and can thus be evaluated even better in terms of measurement technology.
• the relationship between the clamping force and the clamping work can be determined even better with increasing friction forces on surfaces 1, 2 and 3.
• FIG. 2 Two alternatives are shown in FIG. 2 as pretensioning device 14.
• the one alternative shows a spring element 40 that between the mass m2 and an abutment is attached. With this spring element 40 a biasing force is constantly generated, so that a continuous monitoring of the tensioning work is possible.
• the other alternative shows a spring element 42, which is attached between the mass m2 and an abutment, but in contrast to the spring element 40, is not constantly in contact with the mass m2.
• a prestressing force is generated with the spring element 42 at certain time intervals by either moving the mass m2 towards the spring element 42 or, conversely, moving the spring element 42 towards the mass m2.
• Fig. 3 shows a cross section through a chuck body 18, e.g. is shown in Fig. 1.
• the three jaws 12 and a chuck heart 44 can also be seen.
• the pretensioning device 14 in the form of spring bodies 40 or 42. These can be supported continuously or if necessary between the clamping jaws 12 and the chuck body 18. Instead of the spring body 42, an elastic deformation ring can also be used.
• FIG. 4 shows a graphical representation Position of the temporal relationship between the clamping force Fsp and the clamping work W.
• the travel pressure p is also specified, which corresponds to the clamping work W here.
• the clamping work W and the travel pressure increase with time due to decreasing lubrication and increasing contamination.
• the tension force Fsp decreases.
• the threshold corresponds to a value of the clamping force Fsp at which a secure clamping of the workpieces is no longer guaranteed.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Gripping On Spindles (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=6393281

Family Applications (1)

Country Status (3)

Families Citing this family (6)

Family Cites Families (7)

• 1989
  • 1989-11-10 DE DE3937466A patent/DE3937466A1/de active Granted
• 1990
  • 1990-11-09 WO PCT/DE1990/000866 patent/WO1991007245A1/de not_active Application Discontinuation
  • 1990-11-09 EP EP90916237A patent/EP0500617A1/de not_active Withdrawn

Non-Patent Citations (1)

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