Surface property measuring apparatus and method for controlling the same

• US 9,921,044 B2
• Filed: 04/29/2014
• Issued: 03/20/2018
• Est. Priority Date: 05/01/2013
• Status: Active Grant

• Current Assignee: Mitutoyo Corporation
• Original Assignee: Mitutoyo Corporation
• Inventors: Nakayama, Tatsuki
• Primary Examiner(s): Fitzgerald, John
• Assistant Examiner(s): Frank, Rodney T
• Application Number:
  US14/264,416
• Publication Number:
  US 20140326057A1
• Time in Patent Office: 1,421 Days
• Field of Search: 73105
• CPC Class Codes: G01B 21/04 by measuring coordinates of points
• CPC Class Codes: G01B 21/047 Accessories, e.g. for positioning, for tool-setting, for measuring probes
• CPC Class Codes: G01B 3/002 Details
• CPC Class Codes: G01B 3/008 Arrangements for controlling the measuring force
• CPC Class Codes: G01B 5/20 for measuring contours or curvatures
• CPC Class Codes: G01B 5/201 for measuring roundness
• CPC Class Codes: G01B 5/28 for measuring roughness or irregularity of surfaces

Abstract

A surface property measuring apparatus includes a control unit, configured to control operations of a roughness measuring instrument and a relative moving mechanism, including: a measuring force command module configured to output a measuring command; and a measuring force control module configured to control the direction and magnitude of the measuring force, wherein the measuring force control module instructs a measuring force application unit of the roughness measuring instrument to generate therein the measuring force whose magnitude and direction are designated by the measuring force command when a displacement speed of a measuring arm is equal to or slower than a predetermined threshold, and the measuring force control module instructs the measuring force application unit to generate therein a force in a direction in which the distal end of the measuring arm is raised upwards when the displacement speed of the measuring arm exceeds the predetermined threshold.

Claims

1. A surface property measuring apparatus comprising:

a roughness measuring instrument configured to measure a surface property of a measured surface of a measured object by tracing the measured surface while being kept in contact with the measured surface, the roughness measuring instrument including;

a measuring arm supported so as to make an arc-like movement about a rotating shaft as a fulcrum;

a stylus provided at a distal end of the measuring arm;

a displacement detector configured to detect a displacement of the measuring arm which occurs as a result of the measuring arm having made an arc-like movement; and

a measuring force application unit configured to bias the measuring arm in a direction in which the measuring arm makes an arc-like movement to thereby apply a measuring force to the stylus;

a relative moving mechanism configured to move the roughness measuring instrument and the measured object three-dimensionally relative to each other so that the roughness measuring instrument traces the measured surface; and

a control unit configured to control operations of the roughness measuring instrument and the relative moving mechanism, the control unit including;

a measuring force command module configured to output a measuring command which designates a direction and a magnitude of the measuring force; and

a measuring force control module configured to control the direction and magnitude of the measuring force which is generated by the measuring force application unit by issuing a control signal to the measuring force application unit, wherein

the displacement detector outputs a displacement detection pulse whose frequency varies based on a speed of the measuring arm;

the measuring force control module monitors the detected displacement from the displacement detector and issues the control signal to the measuring force application unit, the control signal instructing the measuring force application unit to generate therein the measuring force,

the measuring force control module comprises a determination circuit which receives the displacement detection pulse from the displacement detector and determines whether or not a speed of the detected displacement of the measuring arm exceeds a predetermined threshold based on the frequency of the received displacement detection pulse,

the measuring force control module applies a feedback to the control signal so as to instruct the measuring force application unit to generate therein a force in a direction in which the distal end of the measuring arm is raised upwards when the determination circuit determines that the speed of the detected displacement of the measuring arm exceeds the predetermined threshold, and

the measuring force control module stops applying the feedback to the control signal when the determination circuit determines that the speed of the detected displacement of the measuring arm is equal to or slower than the predetermined threshold.

2. The surface measuring apparatus according to claim 1, wherein:

the measuring force control module further comprises;

a measuring force command voltage generation module configured to generate a measuring force command voltage which is a voltage signal according to a value of the measuring force command;

a feedback signal generation module configured to generate a feedback signal which is a voltage signal which instructs the measuring force application unit to generate therein a force in a direction in which the distal end of the measuring arm is raised upwards; and

a subtraction unit configured to subtract the feedback signal from the measuring force command voltage; and

the determination circuit inputs the feedback signal into the subtraction unit when the determination circuit determines that the displacement speed of the measuring arm exceeds the predetermined threshold.

3. The surface property measuring apparatus according to claim 2, wherein

the feedback signal generation module is made up of a frequency-voltage conversion circuit which generates a voltage signal according to a frequency value of the displacement detection signal from the displacement detector.

4. The surface property measuring apparatus according to claim 2, wherein:

a switch unit is provided between the feedback signal generation module and the subtraction unit; and

the determination circuit turns on the switch unit when the displacement speed of the measuring arm exceeds the predetermined threshold, whereas when the displacement speed of the measuring arm is equal to or slower than the predetermined threshold, the determination circuit turns off the switch unit.

5. The surface property measuring apparatus according to claim 1, wherein the measuring force control module stops applying the feedback to the control signal when the determination circuit determines that the speed of the detected displacement of the measuring arm is equal to or slower than the predetermined threshold in a state that the feedback is applied after the speed of the detected displacement of the measuring arm exceeds the predetermined threshold.

6. The surface property measuring apparatus according to claim 1, wherein

the determination circuit determines whether or not the frequency of the displacement detection pulse exceeds the predetermined threshold,

the measuring force control module applies the feedback to the control signal when the determination circuit determines that the frequency of the displacement detection pulse exceeds the predetermined threshold, and

the measuring force control module stops applying the feedback to the control signal when the determination circuit determines that the frequency of the displacement detection pulse is equal to or lower than the predetermined threshold.

7. A method for controlling a surface property measuring apparatus comprising:

a roughness measuring instrument having a measuring arm which is supported so as to make an arc-like movement about a rotating shaft as a fulcrum, a stylus which is provided at a distal end of the measuring arm, a displacement detector configured to detect a displacement of the measuring arm configured to occur as a result of the measuring arm making an arc-like movement, and a measuring force application unit configured to bias the measuring arm in a direction in which the measuring arm makes an arc-like movement to thereby apply a measuring force to the stylus; and

a relative moving mechanism configured to move the roughness measuring instrument and a measured object three-dimensionally relative to each other so that the roughness measuring instrument traces a measured surface of the measured object therealong, the method comprising;

outputting, by the displacement detector, a displacement detection pulse whose frequency varies based on a speed of the measuring arm;

controlling a direction and a magnitude of the measuring force which is generated by the measuring force generation unit by issuing a control signal based on a measuring force command which designates the direction and magnitude of the measuring force to the measuring force application unit;

monitoring the detected displacement from the displacement detector;

issuing the control signal to the measuring force application unit, the control signal instructing the measuring force application unit to generate therein the measuring force;

receiving the displacement detection pulse from the displacement detector;

determining whether or not a speed of the detected displacement of the measuring arm exceeds a predetermined threshold based on the frequency of the received displacement detection pulse;

applying a feedback to the control signal so as to instruct the measuring force application unit to generate therein a force in a direction in which a distal end of the measuring arm is raised upwards when the speed of the detected displacement of the measuring arm exceeds the predetermined threshold; and

stopping applying the feedback to the control signal when the speed of the detected displacement of the measuring arm is determined to be equal to or slower than the predetermined threshold.

8. The method according to claim 7, wherein the application of the feedback to the control signal is stopped when the speed of the detected displacement of the measuring arm is equal to or slower than the predetermined threshold in a state that the feedback is applied after the speed of the detected displacement of the measuring arm exceeds the predetermined threshold.

9. The method according to claim 7, wherein

the determining includes determining whether or not the frequency of the displacement detection pulse exceeds the predetermined threshold,

the applying includes applying the feedback to the control signal when the frequency of the displacement detection pulse exceeds the predetermined threshold, and

the stopping includes stopping applying the feedback to the control signal when the frequency of the displacement detection pulse is determined to be equal to or lower than the predetermined threshold.