Rotary encoder having a sensor activation controller

• US 6,031,223 A
• Filed: 03/11/1998
• Issued: 02/29/2000
• Est. Priority Date: 03/11/1997
• Status: Expired due to Term

• Current Assignee: Nikon Corporation
• Original Assignee: Nikon Corporation
• Inventors: Morishita, Akihiko
• Primary Examiner(s): Le, Que T.
• Application Number:
  US09/038,055
• Time in Patent Office: 720 Days
• Field of Search: 250/231.13, 250/231.16, 250/231.18, 250/237 G, 341/13
• US Class Current: 250/231.13
• CPC Class Codes: G01D 5/2451 Incremental encoders G01D5/2454 takes precedence

Abstract

A rotary encoder comprising a code plate having an optical pattern, first sensor group A1 through An for detecting the rotational angle of the code plate by detecting the optical pattern, second sensor group B1 through Bn for detecting the rotational angle of the code plate by detecting the optical pattern. Each of the first sensors is associated with one of the second sensor, and the second sensor is positioned 180 degrees opposite to the associated first sensor along the circumference of the code plate. The rotary encoder further comprises a determination unit which determines if the output of the currently processed first or second sensor is in the first state, in which the rotational speed of the code plate relative to the currently processed first or second sensor is greater than a predetermined value, or in the second state, in which the rotational speed of the code plate relative to the currently processed first or second sensor is smaller than or equal to the predetermined value. If it is determined that the output is in one of the first and second states which was defined in advance, a controller activates either the first group sensors or the second group sensors. If it is determined that the output is in the other state, then the controller activates both the first and second group sensors.

Claims

1. A rotary encoder, comprising:

a code plate having an optical pattern thereon;

one or more first sensors for detecting the rotational angle of the code plate by detecting the optical pattern;

one or more second sensors for detecting the rotational angle of the code plate by detecting the optical pattern, each of the second sensors being associated with one of the first sensors and being positioned 180 degrees about the code plate (opposite to) its associated first sensor;

a determination unit for determining whether an output of a currently processed sensor is in a first state, in which the rotational speed of the code plate relative to the currently processed first or second sensor exceeds a predetermined value, or in a second state, in which the rotational speed of the code plate relative to said currently processed sensor is smaller than the predetermined value or in other state in which the rotational speed of the code plate relative to said currently processed sensor is equal to the predetermined value; and

a controller for activating only one of the first and second sensors when it is determined that the output of the currently processed sensor is in either first or second state, and for activating both the first and second sensors when it is determined that the output of the currently processed sensor is in the other state.

2. A rotary encoder according to claim 1, wherein one of the first and second sensors is connected to the first signal processing line which includes an amplifier for amplifying the output signal from said first or second sensor, a square pulse generator for converting the output signal into a pulse wave, and a counter for counting the number of pulses of the pulse wave, and the other sensor is connected to the second signal processing line which includes an amplifier for amplifying the output signal from the other sensor.

3. The rotary encoder according to claim 2, wherein the determination unit receives a counter value which is the number of pulses counted by the counter in a predetermined period of time, and compares the counter value with a prescribed number.

4. A rotary encoder, comprising:

a code plate having an optical pattern;

one or more first sensors for detecting the rotational angle of the code plate by detecting the optical pattern;

one or more second sensors for detecting the rotational angle of the code plate by detecting the optical pattern, each of the second sensors being associated with one of the first sensors and being positioned 180 degrees opposite to the associated first sensor;

a determination unit for determining whether the rotational speed of the code plate relative to the currently processed first or second sensor is smaller than a predetermined minimum value, greater than a predetermined maximum value, or in the range between the minimum and the maximum values; and

a controller for activating only one of the first and second sensors when it is determined that the rotational speed of the code plate relative to the currently processed first or second sensor is smaller than the minimum value or greater than the maximum value, and for activating both the first and second sensors when it is determined that the rotational speed of the code plate relative to the currently processed first or second sensor is in the range between the minimum and the maximum values.

5. A rotary encoder according to claim 4, wherein one of the first and second sensors is connected to the first signal processing line which includes an amplifier for amplifying the output signal from said first or second sensor, a square pulse generator for converting the output signal into a pulse wave, and a counter for counting the number of pulses of the pulse wave, and the other sensor is connected to the second signal processing line which includes an amplifier for amplifying the output signal from the other sensor.

6. The rotary encoder according to claim 5, wherein the determination unit receives a counter value which is the number of pulses counted by the counter in a predetermined period of time, and compares the counter value with a prescribed number.