Method and apparatus for testing styli

A test apparatus for testing a capacitive playback stylus, which includes a stylus shoe which normally contacts a continuous spiral groove of a capacitive information disc record during playback and a stylus electrode which is used to recover information recorded in the capacitive information disc record by means of capacitance variations between the capacitive information disc record and the stylus electrode, wherein the test apparatus is employed to test the width or the symmetrical relationship of the stylus electrode within said groove and wherein the test apparatus comprises:

• (a) a test disc record which includes a continuous spiral groove arranged in groups of turns in a major surface adapted to receive said stylus for testing the width or the symmetrical relationship of said electrode in said groove;
• (b) a test signal recorded in one of said turns of each group of turns of said record, said signal having a known amplitude and frequency,
• whereby relative amplitude information of said signal recovered from each turn by measuring capacitance variations in each turn by said stylus electrode riding in said groove is an indication of the symmetry or width of said stylus electrode relative to said grooves,
• (c) means for contacting the stylus shoe of the stylus to be tested with the continuous spiral groove;
• (d) means for establishing relative motion between the stylus to be tested and the continuous spiral groove;
• (e) means for sensing a capacitive variation between the stylus and a disc record surface while the shoe is contacting the spiral groove and there is relative motion between the stylus and the spiral groove;
• and
• (f) means for processing the sensed capacitive variations so that the signal representative of the information recorded in the continuous spiral groove may be recovered to provide relative amplitudes of the recovered signals in each group of turns compared to signal amplitudes of adjacent groups.

A method for testing a capacitive playback stylus, which includes a stylus shoe which normally contacts a continuous spiral groove in groups of turns of a capacitive information disc record during playback and a stylus electrode which is used to recover information recorded in a capacitive information disc record by means of capacitance variations between the capacitive information disc record and the stylus electrode, in order to determine the stylus electrode width or the symmetrical relationship of the electrode relative to the groove comprising the steps of:

• (a) contacting the stylus shoe with a test disc record wherein the test disc record includes said continuous spiral groove in a major surface adapted to receive said stylus for testing the width or the symmetrical relationship of said electrode in said groove;
• (b) establishing relative motion between the stylus shoe and the test disc record continuous spiral groove;
• (c) sensing the capacitive variations between the stylus electrode and the continuous spiral groove while the shoe is contacting the spiral groove and there is relative motion between the spiral groove and the stylus shoe;
• and
• (d) processing the sensed capacitive variations so that signals representative of the information recorded in the continuous spiral groove may be recovered to provide relative amplitudes of the recovered signals in each group of turns compared to signal amplitudes of adjacent groups.

A method for lapping a capacitive playback stylus, which includes a stylus shoe which normally contacts a continuous spiral groove of a capacitive information disc record during playback and a stylus electrode which is used to recover information recorded in a capacitive information disc record by means of capacitance variations between the capacitive information disc record and the stylus electrode, comprising the steps of:

• (a) recording a test signal in one or more groove turns of a lapping disc record so that the amplitude information recovered from each groove as said stylus rides in the groove compared to the amplitude recovered in adjacent turns is an indication of the symmetry or width of the stylus electrode relative to the groove;
• (b) contacting the stylus shoe with said lapping disc record wherein the lapping disc record includes an abrasive, continuous spiral groove, in a major surface, which comprises a plurality of spiral groove turns wherein the width of a first spiral groove turn or portion thereof and the signal information which can be read out by capacitive means contained in a second spiral groove or portion thereof which is contiguous with the first spiral groove turn or portion thereof is used to test the width or symmetrical relative of the stylus electrode within the groove;
• (c) establishing relative motion between the stylus and the lapping disc record continuous spiral groove;
• (d) sensing the capacitive variations between the stylus electrode and the continuous spiral groove while the stylus is contacting the continuous spiral groove and there is relative motion between the continuous spiral groove and the stylus;
• (e) processing the sensed capacitance variations so that a signal representative of the information recorded in the spiral grooving may be recovered;
• and
• (f) lapping the stylus in the continuous spiral groove until the recovered signal indicates that the desired lapping results have been obtained.