Incremental encoder position interpolation
AssigneeE1Ectr0N, Inc.
InventorScott L. Baker
Life of this patent
Estimating the term…
Abstract
An interpolated position of an incremental encoder is provided. A first signal and a second signal having a quadrature relationship are received from the incremental encoder. A coarse position of the incremental encoder at a first time is produced using the quadrature relationship between the first signal and the second signal. An arcsine or arccosine value based on the first signal at the first time is determined using a lookup table and a fine position of the incremental encoder is calculated using the determined value. The interpolated position of the incremental encoder, based on both the coarse position and the fine position, is then provided.
Claims13
A method to provide an interpolated position of an incremental encoder, the method comprising:
- receiving a first signal from the incremental encoder;
- establishing a first zero-crossing value for the first signal;
- obtaining a digital value of the first signal at a first time;
- ascertaining a quadrant of the first signal at the first time;
- in response to the ascertaining that the quadrant of the first signal at the first time is in a first half of a cycle of the first signal, computing a lookup address by subtracting the first zero-crossing value from the digital value;
- in response to the ascertaining that the quadrant of the first signal at the first time is in a second half of the cycle of the first signal, computing the lookup address by subtracting the digital value from the first zero-crossing value;
- producing a coarse position of the incremental encoder and the lookup address based on the first signal;
- retrieving a lookup value representing an arcsine or an arccosine of a value of the lookup address from a lookup table;
- calculating a fine position of the incremental encoder using based on the lookup value and the quadrant;
- and
- providing the interpolated position of the incremental encoder based on both the coarse position and the fine position.
An apparatus to provide an interpolated position of an incremental encoder, the apparatus comprising:
- at least one input configured to receive first information related to a first signal and second information related to a second signal;
- a quadrature state machine coupled to the at least one input and configured to track a quadrature relationship of the first signal and the second signal, the quadrature state machine providing a quadrant output and counter control lines;
- a coarse position counter coupled to the counter control lines and configured to increment and decrement under control of the quadrature state machine;
- address calculation circuitry, coupled to the at least one input and the quadrant output of the quadrature state machine, and configured to generate a lookup address output;
- circuitry coupled to the at least one input and configured to provide the first information on a first output;
- circuitry coupled to the first output and configured to capture a local maximum and a local minimum of the first information and provide a local maximum output and a local minimum output;
- an adder coupled to the local maximum output and the local minimum output;
- a subtraction circuit coupled to the first output and an output of the adder;
- a multiplier coupled to an output of the subtraction circuit and a scaler output, the multiplier having a multiplier output,
- a memory having an address input coupled to the multiplier output and storing arcsine or arccosine values of corresponding lookup addresses, the lookup address output coupled to a multiplier output;
- circuitry to generate the interpolated position of the incremental encoder based on both an output of the coarse position counter and an output of the memory.
Dependencies are inferred from the claim text.