Patent ID: 7256713
Filing Date: 2007-08-14
Classification: G01D

Abstract:
1. An absolute angle detecting device comprising: a first rotary disk connected to a rotating body that performs multiple rotation; a first code pattern row provided on a circle of the first rotary disk; a first detecting element group composed of a plurality of detecting elements that are arranged opposite to the first code pattern row; a second rotary disk that is connected to the rotating body via a reduction gear mechanism and rotating at a reduced speed in relation to the rotating body; a second code pattern row and a third code pattern row provided on each of different circles of the second rotary disk; a second detecting element group composed of a plurality of detecting elements being arranged opposite to the second code pattern row; a third detecting element group composed of a plurality of detecting elements being arranged opposite to the third code pattern row; a plurality of sectors formed by dividing an angle detecting area of the rotating body at even amount; a Gray code string for angle detection that detects a rotating angle in each sector of the plurality of sectors at a predetermined resolution, the Gray code composed of a combination of codes supplied from the first detecting element group; and a first code string for sector identification and a second code string for sector identification that identifies each of the sectors, composed of a combination of codes supplied from the second detecting element group and the third detecting element group, wherein the Gray code string for angle detection is configured to have a relationship to vary by one bit at each step in each of the sectors, and to vary by one bit from a first code to a last code in each of the sectors, and wherein a code in each of the sectors deviates by one digit every predetermined number of steps, and codes at the steps at a same position in each of the sectors are configured to be equivalent, and wherein the first code string for sector identification is configured such that when a maximum deviation angle between the code of the same and the code of the gray code string for angle detection caused by the reduction gear mechanism is defined as α, and an angle assigned to one code is defined as β, β is found by a following equation: β=n·α (where n is an integral number equal to 3 or more), and the number of the steps of the first code string for sector identification is equal to or more than a total number of the plurality of sectors, and wherein the second code string for sector identification is configured such that when an angle assigned to one code is defined as γ, γ is found by following equation: γ=m·α (where m is an integral number equal to 3 or more), and following inequality is satisfied: γ≦l·β (l is an integral number from 1 through 4.), and the number of the steps of the second code string for sector identification is equal to or less than a total number of the plurality of sectors, and wherein the first and second code strings for sector identification are formed of a Gray code whose code varies by one bit between each of the adjoining steps, and wherein a relative angle difference between a changeover portion of each of the sectors and a changeover portion of each of the steps constituting the first code string for sector identification, and a relative angle difference between the changeover portion of each of the sectors and a changeover portion of each of the steps constituting the second code string for sector identification are set to a value obtained from multiplying α by an integral number equal to zero or more.