1. Field of the Invention
The present invention is generally related to a testing and calibrating apparatus and, more particularly, to a portable apparatus that provides a target simulator to test and calibrate the operating condition of a sensor, such as a gear tooth sensor.
2. Description of the Prior Art
Many different types of machines use position sensors to determine the relative position of one component relative to another component. These position sensors can be used to determine the precise relative position of two components or, when used in conjunction with a timing device, can be used to determine the velocity of one component relative to another. When used in association with a rotatable component, such as a shaft of a machine tool, the sensor can be used to control the operating speed of the shaft.
Many different types of machine tools are known to those skilled in the art. U.S. Pat. No. 4,949,444, which issued to Kojima et al on Aug. 21, 1990, describes a machine tool machining method. A complex machine tool is provided with a single frame having a chip collector space at a center portion thereof. First and second spindle stocks are provided on the frame and are relatively free to move and drive in a Z axis direction while holding the chip collecting space therebetween. Workpiece spindles on the spindle stocks are free to rotate and drive while facing each other. Tool rests are also provided. The tool rests have turrets and can assume various kinds of movement. Complicated and varied types of machining can be performed by combining the rotation control of the workpiece spindles and the spindle stocks.
Gear tooth sensors are used in conjunction with machine tools and many other types of devices. Typically, the gear tooth sensor is associated with some type of rotatable component, such as a gear wheel, that has a number of irregularities that are sensed by the sensor. By knowing the number of irregularities in the circumferential surface of the rotatable member, the position of the shaft can be determined, along with its philosophy. U.S. Pat. No. 5,922,953, which issued to Payne et al on Jul. 13, 1999, describes a sensor apparatus with self-adjusting mechanism for minimizing airgap. The apparatus is useful for detecting the speed and/or position of an object moving along a defined path and more particularly to such an apparatus configured to minimize the spacing between a sensing face of the apparatus and a target surface on the object. Embodiments of the invention are particularly suited for sensing the speed of a rotating member, such as gear, by utilizing a sensor, such as a Hall-effect sensor, to detect the movement of each gear tooth moving past the sensor. The apparatus is configured to mount the sensor for adjustable positioning along a sensor path between an initial position and a final operational position. Movement of the sensor along the sensor path is restricted, for example by frictional engagement, but can be overcome by contact with the target surface so as to move the sensor to its final position with the spacing between the sensing face and the target face minimized.
U.S. Pat. No. 5,497,084, which issued to Bicking on Mar. 5, 1996, discloses a geartooth sensor with means for selecting a threshold magnitude as a function of the average and minimum values of a signal of magnetic field strength. The geartooth sensor is provided with a circuit which determines a threshold magnitude as a function of a minimum value of a first output signal from a magnetically sensitive component and an average output signal from a magnetically sensitive component. Circuitry is provided to determine the average signal. The minimum signal is than subtracted from the average signal and the resulting signal is doubled before being scaled to a predetermined fraction and then compared to the original output signal from the magnetically sensitive component. This circuit therefore determines a threshold signal as a function of both the minimum signal value and the average signal value and, in addition, enables the resulting signal to be scaled to a predetermined percentage of this difference for the purpose of selecting a threshold value that is most particularly suitable for a given application.
U.S. Pat. No. 5,304,926, which issued to Wu on Apr. 19, 1994, discloses a geartooth position sensor with two Hall effect elements. The position sensor has two magnetically sensitive devices associated with a magnet. The sensor is disposable proximate a rotatable member having at least one discontinuity in its surface. The two magnetically sensitive devices, such as Hall effect transducers, each provide output signals that represent the direction and magnitude of the magnitude field in which its respective transducer is disposed. An algebraic sum of the first and second output signals from the magnetically sensitive devices is provided as an indication of the location of the rotatable member that is disposed proximate the sensor.
U.S. Pat. No. 4,687,952, which issued to Capizzi on Aug. 18, 1987, describes a dynamic angular position sensor for a reference geartooth. A magnetic transducer is mounted on a turbine engine and forms a sinusoidal signal as the teeth of a gear attached to the engine shaft pass the head of the magnetic transducer. One tooth of the gear is a short tooth having its tip slightly shaved and acts as a reference point from which angular deviation is measured. The sinusoidal signal is first used to maintain the peak-to-peak amplitude of the sinusoidal signal within a predetermined range. A pulse generator forms a spike pulse each time the short tooth passes the magnetic transducer. A comparator circuit uses the spike pulse to enable a one shot creating a reference pulse of a specified length. A counter circuit, clocked by a zero axis detector, is provided for ensuring that only one reference pulse is generated for each rotation of the gear.
U.S. Pat. No. 4,074,196, which issued to Webster on Feb. 14, 1978, describes a speedometer and odometer apparatus. The apparatus comprises an encoding apparatus for generating pulses as a function of the distance a vehicle is moved, a calibrating apparatus and an indicating circuit means for visually indicating the distance and speed of the movement.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
The repair and maintenance of complicated machine tools often require the gear tooth sensors to be removed or replaced. When a new or repaired gear tooth sensor is again placed in its operating position relative to the machine tool, it is sometimes later determined that the gear tooth sensor or its related circuitry is faulty. If this problem is first discovered after the sensor is completely installed in the machine, subsequent removal of the defective sensor can be very time consuming and expensive. It would therefore be significantly beneficial if an individual gear tooth sensor could be tested and calibrated in an environment that simulates the actual machine tool, but which is easily portable and which affords the operator an opportunity to dynamically adjust and calibrate the sensor without having to dismantle the machine tool itself.
The present invention provides an apparatus for testing a sensor, in which the apparatus comprises the target simulator that is representative of a target located within the structure of a machine tool with which the sensor under test will eventually be used. The apparatus also comprises a motor that is attached to the target simulator for the purpose of causing the target simulator to move along a preselected path, such as a circular path. The apparatus comprises a source of electric power that is connectable in electrical communication with the sensor. The source of electric power, in a preferred embodiment of the present invention, is a power supply that provides a 15 volt DC current to the sensor under test. The apparatus also comprises a signal receiver that is connectable in signal communication with the sensor. The signal receiver is configured to annunciate one or more preselected signals transmitted from the sensor under test. In a particularly preferred embodiment of the present invention, the signal receiver can be a conventional oscilloscope of the type that is generally well known to those skilled in the art. The oscilloscope, which is also portable, can be connected to selected locations on a circuit board associated with the sensor. The apparatus of the present invention further comprises a holding fixture that is located at a preselected distance from the target simulator and is shaped to hold the sensor at a fixed distance from the target simulator when the motor causes the target simulator to move along the preselected path.
In a particularly preferred embodiment of the present invention, the motor is an air powered motor. The use of an air powered motor avoids electrical interference that might otherwise be generated by an electric motor. The electrical noise could otherwise interfere with the proper testing and calibration of the sensor under test. In a particularly preferred embodiment of the present invention, the target simulator is a rotatable component which comprises a plurality of surface discontinuities formed in the target simulator along its circumference. The surface discontinuities are movable past the sensor under test when the sensor under test is attached to the holding fixture of the present invention.
The present invention further comprises a speed control device for manually selecting a convenient operating speed of the air powered motor. In a preferred embodiment, the speed control device is a hand operated valve that controls the flow of air from an air pressure source to the air powered motor.
In most applications of the present invention, the sensor actually comprises an individual sensing head and an individual electronic circuit, wherein the electronic circuit is connected in signal communication with the sensing head. The electronic circuit is connectable in signal communication with the signal receiver of the present invention, when the sensor under test is being tested or calibrated.
The holding fixture of the present invention can comprise a first mounting fixture shaped to hold the sensing head and a second mounting fixture shaped to hold the electronic circuit. The signal receiver, which is an oscilloscope in a preferred embodiment of the present invention is connectable in signal communication with the sensor and, more particularly, with the electronic circuit associated with the sensing head of the sensor under test. The signal receiver, or oscilloscope, is typically configured to visually annunciate one or more preselected signals transmitted from the sensor to the signal receiver. In most applications of the present invention, the visually annunciated signals are sinusoidal in nature.