Patent Application
20070030619
The present invention generally relates to position measurement of an actuation device and, more specifically, to methods and apparatus for sensorless position measurement of an actuation device using inductance variation.
There is a broad range of solenoid-based actuation devices used in the aerospace industry. The prime purpose of these devices is either to deliver motion or to use the mechanical stroke for controlling secondary electric, gas or fluid substances. The motion results from energizing the coil of the solenoid with current. One class of these devices has the relatively simple task associated with only two end positions. Other devices have to maintain accurate position at any point between the end positions. Regardless of the system implementation in most of the cases, the actual position of the actuation device is required to be known and fed back to the controller. In many applications, this information is vital to proper system operation. Furthermore, the knowledge of the position is often a matter of safety concerns.
There are numerous applications in which the exact position of an actuation device is required for control or protection. Conventional measurement methods use position-sensing devices that have different levels of complexity and cost. These conventional devices require additional hardware, such as interface cables for signal transfer to the controller and supply lines for sensor excitation. Additional signal condition and interface connectors are also required. This additional hardware increases the cost of the systems, reduces reliability and limits the applicability of these devices due to environmental constraints on the sensors.
There are a broad range of solenoid-based actuation devices. Linear actuators are used for linear positioning or transfer of linear force. Rotary actuators are used for rotary positioning or transfer of force. Contactors are used for control and protection purposes of high-power electric substances. Relays are used for control and protection of low-power electric substances. Valves are used for control and protection of gasses and fluids. Electromechanical brakes are used for many applications, including airplane brakes. Electromechanical clutches are devices used for mechanical engagement and disengagement of rotating shafts. The above list of solenoid-based actuation devices covers the commonly used devices.
Referring to
U.S. Pat. No. 5,583,434, issued to Moyers et al., discloses methods and apparatus for monitoring armature position in direct current solenoids. A special device and circuit are used in order to generate and introduce alternating current required for the measurement. Moreover, the method of the '434 patent uses sinusoidal measurements, thereby requiring two sensors to measure current and voltage. Furthermore, in order to get the desired data, complex calculations are required of the measured values.
As can be seen, there is a need for an improved position measurement method and apparatus for actuation devices. Furthermore, there is a need for an improved actuation device position measurement method and apparatus that eliminates the need for a dedicated sensor and the associated interfaces within the controller.
In one aspect of the present invention, a method for determining position of a solenoid-based actuation device, the method comprises applying a modulated voltage to a coil of a solenoid to produce a control current in the coil; measuring changes in a solenoid ripple current; and calculating a correlation between the measured changes in solenoid ripple current and the position of the actuator controlling a substance.
In another aspect of the present invention, a method for the sensorless measurement of a controlled substance, the method comprises applying current to a solenoid of an actuator device; measuring the current ripple produced by the solenoid; and correlating the measured current ripple with the position of the actuator.
In yet another aspect of the present invention, a device for measuring the state of a controlled substance comprises an actuator device; a solenoid within the actuator device; a controller; a solenoid control feeder for supplying a modulated voltage to the solenoid; and a feeder return for determining a ripple current in the solenoid.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.
The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.
Broadly, the present invention provides methods and apparatus for a sensorless position measurement for solenoid-based actuation devices using inductance variation. Unlike conventional position measurement methods which use various position sensing devices, the present invention may eliminate the need for a dedicated sensor and the associated interfaces within the controller. The method of the present invention may be based on indirect measurement of the solenoid inductance that varies with the air-gap for the device. Thus, a correlation between the position and measured inductance is found. The excitation lines for the solenoid may be used for obtaining the information for the solenoid inductance. The present invention may find use in many applications where the various types of actuators may be used, including applications in the aerospace industry.
The present invention may eliminate the need for a position sensor within the actuator device, resulting in increased reliability, reduced cost, reduced volume, reduced weight, no need for additional supply, improved system efficiency and improved EMI environment. The present invention may eliminate the cable interface between the controller and the sensor, including insulated wire, shielding, connectors with EMI back-shells, mating connectors on the device and a mating connector on the controller. Moreover, internal interfaces in the actuator device and in the controller may be eliminated. The present invention may be useful in a variety of challenging environments, such as a broad temperature range, broad shock and vibration signature, and broad radiation susceptibility.
The operation of the solenoid-based actuation type device may be based on the magneto-motive force created as a result of current flow in the winding of a solenoid. The current may create flux that flows in a magnetic circuit. The electromagnetic law postulates that the lines of the flux have a tendency to shorten. Therefore, a force may be created in the area where the air gap is located. This force is used for an actuation motion. The stroke of the actuation motion may be equal to the maximum air-gap. A combination of electromechanical and control devices may comprise an actuation system. The actuation system may be able to position the target object to any desirable position within the predefined stroke. A, simple case is when only two end positions are required.
The regulation of the current in the solenoid may be provided by linear or switching dc/dc converters and regulators. The switching converters may be the desirable solution since they may provide much better efficiency. There are a great variety of switching converters and modulation schemes that can be applied for controlling the current in a solenoid.
By means of a non-limiting example, one such scheme will be discussed to verify the viability of this method. In this scheme, an H bridge comprising two switches and two diodes with a capacitor across the dc supply will be used as a converter. A two-state modulation scheme will be applied. That is, both switches will be simultaneously modulated with a constant frequency. When the switches are on, the solenoid is connected to the voltage supply and the current increases per Formula 1. Vdc is the supply voltage. L is the solenoid inductance.
di/dt=Vdc/L (1)
When the switches are off, the solenoid is connected to the voltage supply in the opposite direction and the current decreases per Formula 2.
di/dt=−Vdc/L (2)
The peak value of the current ripple ipp is defined in Formula 3. The modulation frequency is f.
ipp=−Vdc/(2*L*f) (3)
A simulation program was created to verify the concept for the position measurement method. The model provided parallel calculation and accounts for solenoid electrical parameters and realistic semiconductor devices.
The parameters of a clutch device used for mechanical engagement and disengagement are used to check the viability of the concept. The clutch is a part of a universal actuator.
Table 1 summarizes the major parameters involved. The air gap varies from close to zero to about 0.03 in. The inductance varies approximately four times for the entire stroke resulting in a current ripple variation from about 2.5 to about 10 milliamps.
Modulation Frequency: 5000 Hz
Supply Voltage: 120 Vdc
Referring now to
A solenoid control feeder 56 and a feeder return 58 may electrically connect the actuator device 52 with a controller 60. In one embodiment of the present invention, the controller 60 may be located at a position separately from the actuator device 52. Unlike conventional designs, there is no need for separate sensor cables to connect the actuator device 52 and the controller 60 (see, for example, sensor cable 22 in
A switching regulator 62 may be used in the controller 60 to regulate the current in the solenoid 54. By means of a non-limiting example, the current may be delivered to the switching regulator 62 via a current regulator 64 and a pulsewidth modulation controller 66. Other modulation means, such as two-state modulation, three-state modulation and bang-bang control may be used to control the current delivered to the solenoid 54.
The feeder return 58 may provide return current from the solenoid 54 to a current sensor 68 within the controller 60. By means of a non-limiting example, the sensed current may be processed by an analog/digital converter 70, with the processed current monitored by a peak detector 72 to determine the ripple current. This determined ripple current may be used as an input for a look up table 76 to determine the state of the controlled substance 74. Other signal conditioning methods may be used to extract information from the current ripple correlated to the air gap.
Referring to
The method of the present invention may allow for both analog and digital implementations. If analog electronics are used, a small signal conditioning circuit, as is known in the art, may be required. If digital electronics are used, no additional hardware may be required.
The method of the present invention may eliminate the need for a dedicated position sensor and associated interfaces with the controller. The method of the present invention is based on indirect measurement of the solenoid inductance, which varies with the air gap of the device. Hence, an adequate correlation between the position of the device and measured inductance may be found. By combining the advantages of solenoid-based actuation devices with the position sensing scheme of the present invention, one can envision positive changes in the perspective of actuation utilization.
It should be understood, of course, that the foregoing relates to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.
