US 5,710,426 AGranted

Dynamic and thermal mechanical analyzer having an optical encoder with diffraction grating and a linear permanent magnet motor

AssigneeTA Instruments, Inc.

InventorsKevin J. Reed, Robert L. Danley, John R. Reader, Jr., John W. Schaefer

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Abstract

A dynamic and thermal mechanical analyzer incorporating a slide driven vertically in an air bearing guidance system with a large displacement capacity, very low friction and low mass. The position of the slide is measured by digitizing and interpolating two quadrature output signals generated by an optical encoder with very high spatial resolution and a long stroke. A force is applied to the slide using a linear permanent magnet motor with high force, high force linearity and low sensitivity to temperature variations. Position signals derived from the digitized and interpolated quadrature output signals are analyzed as a function of the applied force to calculate viscoelastic properties of a sample of material.

Claims53

Dependent claims

A mechanical analyzer comprising:

(a) a frame;
(b) a linear permanent magnet motor comprising a fixed permanent magnet and a moving coil, wherein the fixed permanent magnet is attached to the frame of the mechanical analyzer;
(c) a slide having a first end and a second end, wherein the moving coil is rigidly attached to the second end of the slide, and wherein current applied to the coil causes the moving coil to apply a drive force to the slide;
(d) means for determining the magnitude of the drive force applied to the slide;
(e) an optical encoder comprising a diffraction grating attached to the slide, a light source attached to the frame, and a photodetector system attached to the frame, wherein a light beam produced by the light source is reflected by the diffraction grating back at the light photodetector system, such that the photodetector system detects two maxima and two minima per period of the diffraction grating as the slide moves vertically relative to the frame;
(f) a first plurality of bottom air bearings attached to the frame and a second plurality of top air bearings attached to the frame, wherein the bottom air bearings and the top air bearings cooperate to guide the slide within the air bearings such that it moves only in the vertical direction;
(g) a drive rod having a second end attached to the first end of the slide and a first end;
(h) a moving sample clamp assembly rigidly attached to the first end of the drive rod;
(i) a fixed sample clamp assembly rigidly attached to at least one vertical support, wherein said vertical support is attached to the frame at its second end;
(j) means for receiving electronic signals output by the photodetector system and combining the electronic signals to produce two quadrature output signals;
(k) means for converting the two quadrature output signals into digital angle and magnitude signals;
(l) means for receiving the digital angle signals and counting the maxima that have been detected, and means for keeping track of the direction of movement of the diffraction grating at each maximum;
(m) means for using the magnitude signals to match the magnitude of the two quadrature output signals to each other;
(n) means for interpolating the digital angle signals to calculate an interpolated position for the slide;
and
(o) means for calculating material properties of the sample based upon the interpolated positions of the slide as a function of the magnitude of the drive force applied to the slide.

13 more elements

A mechanical analyzer comprising:

(a) a frame;
(b) a linear permanent magnet motor comprising a fixed permanent magnet and a moving coil, wherein the fixed permanent magnet is attached to the frame of the mechanical analyzer;
(c) a slide having a first end and a second end, wherein the moving coil is rigidly attached to the second end of the slide, and wherein current applied to the coil causes the moving coil to apply a drive force to the slide;
(d) means for determining the magnitude of the drive force applied to the slide;
(e) an optical encoder comprising a diffraction grating attached to the slide, a light source attached to the frame, and a photodetector system attached to the frame, wherein a light beam produced by the light source is reflected by the diffraction grating back at the light photodetector system, such that the photodetector system detects two maxima and two minima per period of the diffraction grating as the slide is moved vertically relative to the frame;
(f) a first plurality of bottom air bearings and a second plurality of top air bearings, wherein the bottom air bearings and the top air bearings allow the slide to move in only the vertical direction;
(g) a drive rod having a second end attached to the first end of the slide and a first end;
(h) a moving sample clamp assembly rigidly attached to the first end of the drive rod;
(i) a fixed sample clamp assembly rigidly attached to at least one vertical support post, wherein said at least one vertical support post is attached to the frame at its second end;
(j) means for processing the signals output by the photodetector system to determine successive positions of the slide as the slide moves under the applied drive force with a resolution of at least four nanometers;
and
(k) means for calculating material properties of the sample based upon the determined positions of the slide as a function of the magnitude of the drive force applied to the slide.

9 more elements

A mechanical analyzer comprising:

(a) a frame;
(b) a linear permanent magnet motor comprising a fixed permanent magnet and a moving coil, wherein the fixed permanent magnet is attached to the frame of the mechanical analyzer;
(c) a slide having a first end and a second end, wherein the moving coil is rigidly attached to the second end of the slide, and wherein current applied to the coil causes the moving coil to apply a drive force to the slide;
(d) means for determining the magnitude of the drive force applied to the slide;
(e) an optical encoder comprising a diffraction grating attached to the slide, a light source attached to the frame, a grating reticle attached to the frame, and a photodetector system attached to the frame, wherein a light beam produced by the light source is modulated and reflected by the diffraction grating back at the photodetector system, and modulated and transmitted by the grating reticle, such that the photodetector system produces a modulated output signal as the slide is moved vertically relative to the frame;
(f) a first plurality of bottom air bearings and a second plurality of top air bearings, wherein the bottom air bearings and the top air bearings allow the slide to move in only the vertical direction;
(g) a drive rod having a second end attached to the first end of the slide and a first end;
(h) a moving sample clamp assembly rigidly attached to the first end of the drive rod;
(i) a fixed sample clamp assembly rigidly attached to a plurality of vertical support posts, wherein said vertical support posts are attached to the frame at their second ends;
(j) means for receiving the modulated output signal from the photodetector system and combining the electronic signals to produce two quadrature output signals;
(k) means for converting the two quadrature output signals into digital angle and digital magnitude signals;
(l) means for adjusting the amplitude of the two quadrature output signals such that they match each other;
(m) means for interpolating the digital angle signals to calculate an interpolated position for the slide;
and
(n) means for calculating material properties of the sample based upon the interpolated positions of the slide as a function of the magnitude of the drive force applied to the slide.

12 more elements

A mechanical analyzer comprising:

(a) a frame;
(b) a linear motor comprising a fixed magnet and a moving magnet, wherein the fixed magnet is attached to the frame of the mechanical analyzer, and wherein at least one of the fixed and moving magnets is an electromagnet having a coil;
(c) a slide having a first end and a second end, wherein the moving magnet is rigidly attached to the second end of the slide, and wherein current applied to the coil causes the coil to apply a drive force to the slide;
(d) means for controlling the magnitude of the drive force applied to the slide by controlling the current applied to the coil;
(e) means for determining the magnitude of the drive force applied to the slide;
(f) an optical encoder comprising a light source attached to the frame, an optical modulator attached to the slide, and a photodetector system attached to the frame, wherein a light beam produced by the light source is modulated by the optical modulator and directed to the photodetector system, such that the photodetector system produces a modulated output signal as the slide is moved relative to the frame;
(g) at least one air bearing, wherein the at least one air bearing constrains the slide such that it can slide in only one direction;
(h) a drive rod having a first end and a second end, wherein the second end of the drive rod is attached to the slide;
(i) a moving sample clamp assembly rigidly attached to the first end of the drive rod;
(j) a fixed sample clamp assembly rigidly attached to a support structure, wherein said support structure is attached to the frame;
(k) means for receiving the modulated output signal from the photodetector system and combining the electronic signals to produce output signals and for converting the output signals into digital angle and digital magnitude signals;
(l) means for interpolating the digital angle signals to calculate an interpolated position for the slide;
and
(m) means for calculating material properties of the sample based upon the interpolated positions of the slide as a function of the magnitude of the drive force applied to the slide.

11 more elements

Dependencies are inferred from the claim text.

Facts

Application: 08/609,547Filed 1 Mar 1996
Granted: 20 Jan 1998
Term ends: Not estimatedThe source records don’t support an estimate.

Classification12 codes

G01N 3/18
By applying steady tensile or compressive forces: performing tests at high or low temperatures
F27B 5/16
Details, accessories or equipment specially adapted for furnaces of these types: arrangements of air or gas supply devices
F27B 17/02
Furnaces of a kind not covered by any of groups F27B1/00 - F27B15/00: specially designed for laboratory use
F27D 1/0006
Linings or walls: linings or walls formed from bricks or layers with a particular composition or specific characteristics