Coordinate measuring apparatus having a stylus friction compensating means

• US 5,088,055 A
• Filed: 02/22/1990
• Issued: 02/11/1992
• Est. Priority Date: 02/22/1989
• Status: Expired due to Fees

• Current Assignee: Kabushiki Kaisha Okuma Tekkosho
• Original Assignee: Kabushiki Kaisha Okuma Tekkosho
• Inventors: Oyama, Hiroshi
• Primary Examiner(s): Dixon, Joseph L.
• Application Number:
  US07/483,461
• Time in Patent Office: 719 Days
• Field of Search: 364/560, 364/474.18, 364/474.35, 364/474.37, 364/571.01, 33/503, 33/504, 33/505, 33/546, 33/551, 33/553, 33/554, 33/702
• US Class Current: 702/168
• CPC Class Codes: G05B 19/4207 in which a model is traced or scanned and corresponding data recorded

Abstract

A digitize control apparatus having a measuring function of the present invention determines a correct contact point between a stylus and a model on the basis of the displacement vector of a stylus obtained by a scanning head and a position vector indicating a machine coordinate value obtained by a position detecting apparatus, and therefore the influence of friction generated between a stylus and a model can be removed, thereby reducing error in the measurements.

Claims

1. A coordinate measurement apparatus for determining contact points between a stylus and a model, said coordinate measurement apparatus comprising:

conveying means for conveying the stylus relative to a surface of the model while maintaining a constant magnitude of a displacement of the stylus;

scanning head means for detecting the displacement of the stylus;

position detecting means for detecting a relative position of the stylus;

tangent line vector calculating means for calculating a tangent line vector of the model which is tangent a trace of a first position vector indicating a center of the stylus, the first position vector corresponding to a sum of a displacement vector denoting the displacement of the stylus obtained by said scanning head means and a second position vector denoting the relative position of the stylus obtained by said position detecting means;

normal line vector calculating means for calculating a normal line vector which intersects normal to the tangent line vector at a magnitude in accordance with the displacement vector; and

means for calculating a third position vector denoting a contact point between the stylus and the model based on the displacement vector, the second position vector, the normal line vector and a radius of the stylus.

2. In an apparatus a claimed in claim 1, wherein said normal line vector calculating means determines said normal line vector based on a sum of said displacement vector and a vector obtained by multiplying said tangent line vector by a numeric value.

3. In an apparatus as claimed in claim 2, wherein said normal line vector calculating means determines the numeric value in accordance with the following equation, ##EQU6## where, k is the numeric value, ε

is the displacement vector, t is the tangent line vector.

4. An apparatus as claimed in claim 1, wherein said third position vector calculating means calculates said third position vector in accordance with the following equation, ##EQU7## where, G is the third position vector, P is the second position vector, ε

is the displacement vector, R is the radius of the stylus, and n is the normal line vector.

5. An apparatus as claimed in claim 2, wherein said third position vector calculating means calculates said third position vector in accordance with the following equation, ##EQU8## where, G is the third position vector, P is the second position vector, ε

is the displacement vector, R is the radius of the stylus, and n is the normal line vector.

6. An apparatus as claimed in claim 3, wherein said third position vector calculating means calculates said third position vector in accordance with the following equation, ##EQU9## where, G is the third position vector, P is the second position vector, ε

is the displacement vector, R is the radius of the stylus, and n is the normal line vector.