Mass velocity controller

• US 5,036,266 A
• Filed: 03/30/1990
• Issued: 07/30/1991
• Est. Priority Date: 01/17/1989
• Status: Expired due to Fees

• Current Assignee: Tektronix Incorporated (Fortive Corp.)
• Original Assignee: Tektronix Incorporated (Fortive Corp.)
• Inventors: Burke, Edward F.
• Primary Examiner(s): Shoop, Jr., William M.
• Assistant Examiner(s): BERGMANN, SAUL
• Application Number:
  US07/502,379
• Time in Patent Office: 487 Days
• Field of Search: 318/646, 318/615, 318/561, 318/618, 310/15, 400/322, 73/519, 73/651, 73/862.41, 73/862.42
• US Class Current: 318/646
• CPC Class Codes: G11B 5/5547 "Seek" control and circuits therefor G11B5/5556 takes precedence
• CPC Class Codes: H02P 23/16 Controlling the angular speed of one shaft H02P23/18 takes precedence

Abstract

A system (11) for monitoring and controlling the movement of a mass (12) along a predetermined path (14) by a motor-driven flexible member (20) is provided to modulate the motor drive output so that the actual velocity of the mass corresponds more closely to the desired target velocity profile. The system preferably employs a dual loop servo system wherein an outer servo loop uses conventional linear encoding techniques and is supplemented by an inner servo loop utilizing a sensor (27) that detects a physical characteristic of the flexible member representative of the relative velocity of the mass. Relative velocity transducers utilizing magnetic circuits and operating according to variable reluctance principles for generating relative mass velocity signals directly are disclosed.

Claims

1. A system for monitoring the movement of a mass driven by a flexible element comprising:

a mass moveable along a predetermined path;

a flexible element coupled to the mass;

a motor for driving the flexible element and thereby the mass along a predetermined path;

a transducer mounted on the mass and in communication with the flexible element capable of detecting a physical characteristic of the flexible element representative of velocity of the mass relative to velocity of the motor; and

means for generating a relative velocity signal therefrom.

2. A system according to claim 1, additionally comprising:

means for generating a target velocity signal in communication with the motor for controlling rotational output of the motor and thereby the velocity of the mass; and

means for combining the target velocity signal with the relative velocity signal and generating a mass velocity error signal.

3. A system according to claim 2, additionally comprising:

means for modifying the target velocity signal in accordance with the mass velocity error signal.

4. A system according to claim 1, wherein the mass is a shuttle carriage of an ink jet printer and the flexible element is a cable.

5. A system according to claim 1, wherein the relative velocity transducer utilizes a magnetic circuit operating according to variable reluctance principles to generate the relative velocity signal.

6. A system according to claim 5, wherein the relative velocity transducer comprises:

a base member having a support arm and a mounting arm extending therefrom, the mounting arm being connected to the flexible element, and the base member comprising an iron-containing rigid metallic material;

a magnet mounted on the support arm with its poles arranged in a predetermined orientation;

a pole piece mounted on the magnet having an extending portion extending toward the mounting arm and forming an air gap between its terminal end and a surface of the mounting arm; and

a coil wound around the extending portion of the pole piece.

7. A dual loop servo system for monitoring and controlling the movement of a mass moved along a predetermined path by a motor-driven flexible member comprising:

an outer servo loop employing linear encoder techniques to generate a signal indicative of the velocity of the mass; and

an inner servo loop employing a sensor that detects a physical characteristic of the flexible member representative of the velocity of the mass relative to the velocity of the motor to generate a relative velocity signal.

8. A dual loop servo system according to claim 7, wherein:

the sensor comprises a relative velocity transducer mounted on the mass and connected to the motor-driven flexible member.

9. A dual loop servo system according to claim 8, additionally comprising:

means for generating a target velocity signal in communication with the motor for controlling rotational output of the motor and thereby the velocity of the mass as it moves along its predetermined path;

means for combining the target velocity signal with the relative velocity signal and generating a mass velocity error signal; and

means for modifying the target velocity signal in accordance with the mass velocity error signal.

10. A dual loop servo system according to claim 8, wherein the relative velocity transducer utilizes a magnetic circuit operating according to variable reluctance principles to generate the relative velocity signal.

11. A dual loop servo system according to claim 7, wherein the mass is a shuttle carriage of an ink jet printer.

12. A dual loop servo system according to claim 7, wherein the mechanical stiffness of the sensor is significantly higher than that of the flexible member.

13. A dual loop servo system according to claim 8, wherein the relative velocity transducer comprises:

a base member having a support arm and a mounting arm extending therefrom, the mounting arm being connected to the flexible element, and the base member comprising an iron-containing rigid metallic material;

a magnet mounted on the support arm with its poles arranged in a predetermined orientation;

a pole piece mounted on the magnet having an extending portion extending toward the mounting arm and forming an air gap between its terminal end and a surface of the mounting arm; and

a coil wound around the extending portion of the pole piece.

14. A dual loop servo system according to claim 13, wherein the air gap formed between the terminal end of the pole piece and the surface of the mounting arm is from about 5 mils to about 50 mils in width.

15. A dual loop servo system according to claim 13, wherein the coil wound around the extending portion of the pole piece is a signal coil, and the system additionally comprises a bucking coil wound in the same direction as the signal coil around an opposite side of the pole piece and connected in series with the signal coil, but with opposed polarity.

16. A dual loop servo system according to claim 8, wherein the relative velocity transducer comprises:

a base member having a support arm and a mounting arm extending therefrom, the mounting arm being connected to the flexible element, and the base member comprising an iron-containing rigid metallic material;

a magnetic insulator mounted on the support arm;

a first pole piece mounted on the magnetic insulator having an extending portion extending toward the support arm and defining an air gap between its terminal end and a surface of the mounting arm;

a magnet mounted on the first pole piece generally aligned with the support arm, with its poles arranged in a predetermined orientation; and

a second pole piece mounted on the magnet and generally aligned with the first pole piece, the second pole piece having an extending portion extending toward the mounting arm and defining a second air gap between its terminal end and a surface of the mounting arm; and

a coil wound around the extending portion of the first pole piece.

17. A dual loop servo system according to claim 8, wherein the relative velocity transducer comprises:

a base member having a central mounting arm and two support arms extending therefrom, the central mounting arm being connected to the flexible element, and the base member comprising an iron-containing rigid metallic material;

a magnet mounted on each support arm with its poles arranged in a predetermined orientation;

a pole piece mounted on each magnet, each pole piece having an extending portion extending toward the mounting arm and defining an air gap between its terminal end and a surface of the mounting arm; and

a coil wound around the extending portion of each pole piece, the coils being wound in the same direction and connected in series with opposed polarity.

18. A dual loop servo system for monitoring and controlling the movement of a mass moved along a predetermined path by a motor-driven flexible member comprising:

a first servo loop employing linear encoder techniques to generate a mass velocity signal; and

a second servo loop employing a sensor that detects a physical characteristic of the flexible member representative of the velocity of the mass relative to the velocity of the motor.

19. A relative velocity transducer that senses velocity of a mass movable along a predetermined path by a motor-driven flexible element coupled to the mass relative to the velocity of rotational output of the motor utilizing a magnetic circuit operating according to variable reluctance principles.

20. A relative velocity transducer according to claim 19, comprising:

a base member having a support arm and a mounting arm extending therefrom, the mounting arm being connected to the flexible element, and the base member comprising an iron-containing rigid metallic material;

a magnet mounted on the support arm with its poles arranged in a predetermined orientation;

a pole piece mounted on the magnet having an extending portion extending toward the mounting arm and defining an air gap between its terminal end and a surface of the mounting arm; and

a coil wound around the extending portion of the pole piece.