Counterbalanced coordinate-measuring instrument

• US 4,964,221 A
• Filed: 06/19/1989
• Issued: 10/23/1990
• Est. Priority Date: 07/07/1988
• Status: Expired due to Fees

• Current Assignee: Carl-Zeiss-Stiftung
• Original Assignee: Carl-Zeiss-Stiftung
• Inventors: Starp, Franz, Breyer, Karl-Hermann
• Primary Examiner(s): Cuchlinski, Jr., William A.
• Assistant Examiner(s): Wirthlin, Alvin
• Application Number:
  US07/367,777
• Time in Patent Office: 491 Days
• Field of Search: 33/503, 33/504, 33/1 M, 172/506, 212/195, 160/189
• US Class Current: 33/503
• CPC Class Codes: G01B 5/0016 due to weight on machine tools B23Q11/001
• CPC Class Codes: G01B 5/008 using coordinate measuring machines

Abstract

A coordinate-measuring instrument has a purely mechanical device (14) to compensate for the weight of a vertically displaceable spindle (9). The compensation device consists of a helical-coil spring having a working range which is small as compared with its length in relaxed condition, and a belt transmission interposed between the spring and the spindle (9). The belt transmission is preferably developed in the manner of a block and tackle. A first or drive pulley engages and drives the belt for Z-axis positioning of the spindle, and a second or belt-tension pulley applies weight-compensating tension to the belt.

Claims

1. A coordinate-measuring instrument having a vertically displaceable measurement slide, a drive for the measurement slide, and a device to compensate for the weight of the measurement slide;

the device for weight compensation comprising a helical spring (31) having a working range which is small as compared with its length in relaxed sate, a stepdown belt transmission (21-23) interposed between the spring (31) and the measurement slide (9), the drive (15-17) and the spring (31) being connected to a pulley (22/23) of the belt transmission;

means to compensate for variation in spring force within the working range of the spring (31), said means comprising an eccentrically mounted pulley (123) of the belt transmission.

2. A coordinate-measuring instrument having a vertically displacement measurement slide, a drive including an electric motor (17) and control-electronics (35) therefor for displacing said measurement slide, and a device to compensate for the weight of the measurement slide;

the device for weight compensation comprising a helical spring (31) having a working range which is small as compared with its length in relaxed state, a stepdown belt transmission (21-23) interposed between the spring (31) and the measurement slide (9), the drive (15-17) and the spring (31) being connected to a pulley (22/23) of the belt transmission;

means to compensate for variation in spring force within the working range of the spring (31), said means comprising a feedback-control circuit for spring-counterbalancing control of said control electronics, said feedback-control circuit including an elongate scale on said measurement slide and a fixedly mounted scale-reading device producing a position-indicating electric signal in accordance with displacement of said slide, said feedback-control circuit being a closed loop supplying said control electronics continuously with current to apply a residual force proportional to the difference between gravitational weight of said slide and a preload force of said spring, as a function of the instantaneous position-indicating output of said scale-reading device.

3. In a coordinate-measuring instrument, (i) wherein a spindle is displaceable in a vertical guide above a work-supporting table, said guide being at a fixed elevation above said table, (ii) wherein a vertical-displacement electric-motor drive system and control electronics therefor is connected to determine spindle position in the vertical guide, and (iii) wherein a weight-compensation system is provided to offset the gavitational weight of the spindle and thus to reduce load imposed on the vertical-displacement drive system, the improvement (a) wherein the spindle is suspended by one end of a belt via a pulley carried by the vertical guide, (b) wherein the other end of the belt is fixedly anchored with respect to the vertical guide, (c) wherein a helical-coil spring is fixedly referenced at one end with respect to the vertical guide and has a belt-tension pulley connecting its other end to said belt, the spring being so stressed in application of tension to said belt as to substantially compensate for the suspended gravitational weight of the spindle, (d) wherein said vertical-displacement drive system includes a drive pulley operatively engaged to said belt, and (e) wherein means including a feedback-control circuit is provided for further counter-balancing control of said control electronics;

said feedback control circuit including an elongate scale carried with said spindle and a fixedly mounted scale-reading device producing a position-indicating electric signal in accordance with displacement of said slide, said feedback-control circuit being a closed loop supplying said control electronics continuously with current to apply residual force proportional to the difference between gravitational weight of said spindle and a pre-load force of said spring, as a function of the instantaneous position-indicating output of said scale-reading device.

4. In a coordinate-measuring instrument, (i) wherein a horizontal guide provides horizontally displaceable guidance to a cantilevered horizontal boom at a fixed elevation above a work-supporting table, (ii) wherein a spindle is displaceable in a vertical guide at the cantilevered end of said boom, (iii) wherein a vertical-displacement drive system and control electronics therefore is connected to determine spindle position in the vertical guide, and wherein a weight-compensation system is provided to offset the gravitational weight of the spindle and thus to reduce load imposed on the vertical-displacement drive system, the improvement (a) wherein the spindle is suspended by one end of a belt via a pulley carried at the cantelivered end of the boom, (b) wherein the other end of the belt is fixedly anchored at a horizontal location along said boom, (c) wherein a helical-coil spring is horizontally oriented above the boom and is fixedly referenced at one end to a horizontal location along the boom, said coil spring having a belt-tension pulley connecting its other end to said belt;

with the spring so tensed in application of tension to said belt as to effectively compensate for the suspended gravitational weight of the spindle, (d) wherein said vertical-displacement drive system is carried by the boom and includes a drive pulley operatively engaged to said belt, and (e) wherein means including a feedback-control circuit is provided for further counterbalancing control of said control electronics;

said feedback control circuit including an elongate scale carried with said spindle and a fixedly mounted scale-reading device producing a position-indicating electric signal in accordance with displacement of said spindle, said feedback-control circuit being a closed loop supplying said control electronics continuously with current to apply a residual force proportional to the difference between gravitational weight of said spindle and a preload force of said spring, as a function of the instantaneous position-indicating output of said scale-reading device.