Active damping vibration controller for use with cryocoolers

A cryocooler assembly including a cryocooler housing and a free-piston engine arranged within the housing, an absorber housing and a damper motor arranged within the absorber housing, and a controller housing rigidly coupled between the cryocooler and the active damper such that vibrations may pass through the controller. A controller mounted within the controller housing provides power to the cryocooler and monitors the phase and frequency of the power supplied to the cryocooler. The controller monitors the vibration of the cryocooler assembly and provides a damping signal to the active damper. The damping signal generated by the controller is based at least in part on the phase and frequency of the power supplied to the cryocooler and the monitored vibration of the cryocooler assembly.

BACKGROUND

The present invention is directed to vibration damping control cryocoolers including free-piston engines. More particularly, the invention is directed to an active damping vibration controller for use with a cryocooler where low-vibration levels are required.

Sunpower® Inc. produces a product line of crycoolers under the trade name Cryo Tel®. The system vibration levels of the Cyro Tel® cryocoolers are greatly influenced by the mass, configuration, and rigidity of the system in which the cryocooler is installed. Sunpower® Inc. provides a passive (reactive) balance absorber that is tuned to mitigate a primary drive frequency of the cryocooler. With generic production tuning, the resultant free-body vibration acceleration of the system is approximately 300-400 milli-g (acceleration). This level of vibration is tolerable in many applications.

When lower levels of vibration are required, Sunpower® Inc. offers three options for further reducing vibration levels. First, in-situ tuning of the primary passive absorber when the cryocooler is mounted in the customer's system allows for addressing and mitigating the effects of the system design on the total system vibration. Second, a harmonic passive absorber or a dual-frequency absorber assembly that includes a first and second harmonic absorber may be installed on the cryocooler resulting in vibration levels of 200 milli-g and lower. Finally, an active (powered) absorber may be attached to the back of the cryocooler. The active damper can be driven by a closed loop driver that reads a vibration signal and provides a drive signal to the absorber to counteract the vibration energy. Vibration levels on the order of 40 milli-g can be achieved. Sunpower does not provided the drive system for the active damper.

Infrared (IR) and photo detectors potentially benefit from operation under cryogenic conditions. However, system vibrations can render the use of a cryogenic cooling system undesirable if the vibrations produce more noise for the detectors than the system inhibits. Other detector and sensor types benefit from the invention.

U.S. Pat. Nos. 7,458,143; 7,266,947; 7,043,835; 6,782,700; 6,684,637; 6,446,336; 6,293,184; 6,199,381; 5,642,088; 5,642,008; and 5,525,845 are assigned to Sunpower Inc. and directed to aspects of the Cryo Tel® line of cryocoolers. All the above listed documents are incorporated by reference herein in their entirety.

BRIEF SUMMARY OF THE INVENTION

The present invention overcomes the aforementioned drawbacks by providing a controller that monitors the vibrational output of a cryocooler and communicates a tuned signal to an active damper to reduce the vibrational output of the overall system.

In one construction, the invention provides a controller for a cryocooler assembly including a cryocooler having a cryocooler housing, a free-piston motor positioned within the housing, and a cold head, and an active damper coupled to the cryocooler and arranged to control vibrations of the cryocooler assembly. The controller includes a wall that is rigidly coupled between the cryocooler and the active damper such that the vibration passes between the cryocooler, the controller, and the active damper. A power supply connector receives power, a cryocooler power connector is arranged to provide power to the cryocooler, a damping connector is arranged to provide power to the active damper, and a control connector receives signals indicative of system vibrations from a vibration detector. The controller monitors the phase and frequency of the power supplied to the cryocooler, the system vibrations, and sends a damping signal to the active damper to control the system vibrations. The damping signal is dependant on at least the monitored system vibrations and the monitored phase and frequency.

In another construction, the invention provides a cryocooler assembly that includes a cryocooler that has a cryocooler housing, a free-piston engine arranged within the housing, and a cold head, an active damper that has an absorber housing and a damper motor arranged within the absorber housing, and a controller that has a controller housing rigidly coupled between the cryocooler and the active damper such that vibrations may pass through the controller. The controller provides power to the cryocooler and monitors the phase and frequency of the power supplied to the cryocooler. The controller further monitors the vibration of the cryocooler assembly, and provides a damping signal to the active damper. The damping signal is generated by the controller based at least in part on the phase and frequency of the power supplied to the cryocooler and the monitored vibration of the cryocooler assembly.

In another construction, the invention provides a controller for a cryocooler assembly that includes a cryocooler and an active damper coupled to the cryocooler and arranged to control vibrations of the cryocooler assembly. The controller includes a controller housing that is configured to be rigidly coupled between the cryocooler and the active damper to transmit vibrations from at least one of the cryocoller and the active damper to the controller. A controller is located within the controller housing and is configured to monitor at least one of a phase and frequency of power supplied to the cryocooler, monitor vibration received through the controller housing from at least one of the cryocooler assembly and the active damper, and generate a damping signal based at least in part on the at least one of the phase and frequency of the power supplied to the cryocooler and the monitored vibration. The damping signal configured to be communicated to the active damper to control future vibrations.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be described in terms of one or more embodiments, and it should be appreciated that many equivalents, alternatives, variations, and modifications, aside from those expressly stated, are possible and within the scope of the invention.

FIGS. 1-3show a cryocooler assembly6that includes a free-piston type cryocooler10. For example, a Cryo Tel® brand cryocooler is an example of one cryocooler that may be used with the present invention. The cryocooler assembly6also includes an active damper motor in the form of an active absorber or damper14. One example, of an active damper14is offered by Sunpower® Inc. The cryocooler assembly6further includes a controller in the form of an active damping vibration controller18.

The cryocooler10includes a piston body22that houses a motor, a piston, and other components of the cryocooler10, as is understood in the art. The cryocooler10further includes a cold head26that acts as an interface for heat exchange with whatever system the cryocooler10is used with. Details of the function and internal components of the cryocooler10are well known and, as such, will not be discussed herein.

The cryocooler10includes a mounting plate30arranged to mount the cryocooler10to an installation (e.g., IR detector system), as desired. The piston body22includes a rear wall or plate34that defines mounting holes38(seeFIG. 2) and power leads in the form of passthroughs40. The rear plate34is rigidly mounted to the piston body22or formed as a part thereof The passthroughs40are arranged to communicate power to the cryocooler10.

The active damper14includes a mounting plate42with mounting holes46arranged to align with the mounting holes38of the piston body22, and a damper motor housing50. A damper motor56(seeFIG. 8) is mounted within the damper motor housing50and arranged to affect the vibration of the cryocooler10through the mounting plate42and receives power through damper power leads58(represented inFIG. 8).

With reference toFIGS. 4-7, the controller18includes a housing in the form of an adapter ring60and a main ring64. The adapter ring60includes a rigid sidewall68that defines a hole pattern72arranged for coupling the adapter ring60to the mounting holes38of the cryocooler10and a hole pattern76arranged for coupling to the main ring64. The illustrated sidewall68is a quarter inch thick aluminum sidewall. In other embodiments, the sidewall may be formed of other material and be of a sufficient thickness to provide rigidity and effective transfer of vibrations therethrough. The adapter ring64defines a substantially open central cavity.

The main ring64includes a rigid sidewall80that defines a hole pattern84arranged for coupling the main ring64to the mounting holes46of the active damper14and a hole pattern88arranged for coupling to the adapter ring60. The sidewall80may be a quarter inch thick aluminum sidewall. In other embodiments, the sidewall may be formed of other material and be of a sufficient thickness to provide rigidity and effective transfer of vibrations therethrough.

A printed circuit board92is mounted within the main ring64and includes an on-board controller96, a damping output100, a power supply connector104, a control connector108, and a cryocooler power connector112. The on-board controller96monitors the phase and frequency of the power supplied from a power supply116to the power supply connector104and passed to the cryocooler power connector112, provides a power output to the damping output100, and relays data to the control connector108.

The damping output100is connected to the active damper14such that the damper motor56is operated in response to the output relayed form the on-board controller96through the damping output100.

The control connector108is connected to a computer, data logging device, or external control device as desired to monitor or control the operation of the controller18. A sensor or vibration detector118(seeFIG. 8) is also connected to the control connector108either directly or through a network. The illustrated vibration detector118is a MEMS 3 axis accelerometer, though standard accelerometers or other detector types may be used. The vibration detector118is positioned to detect the vibration level transferred from the cryocooler assembly6to the installation and may be positioned on the printed circuit board92, on the cryocooler10, or in another location, as desired. In the illustrated embodiment, the control connector108is a USB port arranged to be connected to a computer. In other constructions, the control connector108may be an Ethernet port or another connection type (e.g., RS232, RS485, MODBUS, CANBUS, LonWorks, Wi-Fi, Bluetooth).

The illustrated cryocooler connector112includes an on-board clamp in the form of a socket that is arranged to engage the passthoughs40of the piston body22for providing power to the cryocooler10. Alternatively, the cryocooler connector112may include an external port.

In one construction of the invention, the controller18includes an on-board damping motor120(seeFIG. 5) that responds to activation by the on-board controller96to mitigate vibration and noise of the printed circuit board92itself. In some constructions, the on-board damping motor120may be removed.

To assemble the cryocooler assembly6, the cryocooler10is mounted to the installation with the mounting plate30. The adapter ring60of the controller18is then rigidly fastened to the rear plate34of the piston body with fasteners engaging the hole pattern72of the adapter ring60and the mounting holes38of the rear plate34.

The main ring64of the controller18is then aligned with the adapter ring60and the passthroughs40are aligned with the cryocooler connector112. The cryocooler connector112engages the passthroughs40and the main ring64is rigidly fastened to the adapter ring60by engaging fasteners with the hole pattern88of the main ring64and the hole pattern76of the adapter ring60. The controller18is then rigidly fastened to the cryocooler10such that vibrations are effectively translated therebetween.

The active damper14is then fastened to the controller18by engaging fasteners with the mounting holes46of the active damper14with the hole pattern84of the main ring64. The cryocooler10, the active damper14, and the controller18then form a rigid body through which vibration may readily pass. In some constructions, passive dampers may be employed in addition to the active damper14, as desired.

Once physically assembled, power is connected from the power supply116to the power supply connector104for powering the cryocooler assembly6. An external cable is routed from the damping output100to the active damper14, an external cable is routed from the control connector108to the computer, and the vibration detector118is connected either through a network or directly to the control connector108. Once assembled and connected, the cryocooler assembly6may be operated.

In operation, power passes from the power supply116to the power supply connector104on the controller18. The controller18monitors the phase, amplitude, and frequency of the power that is subsequently supplied to the cryocooler10. The illustrated controller18utilizes a current transformer. Other constructions include but are not limited to voltage measurement, either direct or across a current sense resistor, or Hall Effect current sensing.

The controller18also monitors the vibration of the cryocooler assembly6with the vibration detector118. The illustrated embodiment utilizes a programmable bandpass filter and peak detector. Other constructions include fixed filters with peak or root mean square (RMS) detectors, or analysis in the digital domain using techniques such as Fast Fourier Transforms (FFT).

The on-board controller96then conducts a tuning operation wherein a damping signal is generated based on the detected vibrations and sent to the active damper14to counter and mitigate the vibrations. The illustrated damping signal is a complex waveform generated by summing harmonics. Other constructions for generating the damping signal include, but are not limited to error signal inversions.

The damping signal is then provided to the active damper14to power the damper motor. The illustrated embodiment utilizes an H-Bridge pulse with modulator. Other constructions include but are not limited to an analog amplifier, a servo drive, or an inverter.

Because the controller18is monitoring the phase, amplitude, and frequency of the power supplied to the cryocooler10and the resultant vibration, a feedback or feedforward loop may be used to generate damping signals that are in-phase and in-frequency with the power signal sent to the cryocooler10such that a large number of harmonics may be tuned and the resultant vibrations may be reduced significantly. For example, five harmonic levels of the 60 Hz signal may be tuned to achieve a minimized vibration level. In other words, the damping signal is phase/frequency locked to the power signal sent to the cryocooler10.

Further, the damping signal is tuned to harmonics of the fundamental frequency of vibration of the cryocooler assembly6. For example, the damping signal may be tuned with the first five harmonics of the fundamental frequency. The phase, frequency, and amplitude of the vibrations of the cryocooler assembly6may be monitored and used to tune the system to minimize overall vibration.

The damping signal is not directly driven by the detected vibrations, but is rather calculated based on the entire environment of the cryocooler assembly6. The controller18takes into account the power signal sent to the cryocooler10, environmental vibrations, tuning vibrations provided by the active damper, and other noise to mitigate the overall vibration produced by the cryocooler assembly6.

This control arrangement leads to great reduction of vibration and noise produced as compared to current control schemes. For example, while zero milli-g's of vibration is theoretically possible, an upper limit of 10 milli-g's is fully attainable. Further, while tuning through the fifth harmonic, 5 milli-g's are attainable as an upper limit of vibration. Vibration levels under 10 milli-g's allows cryocoolers10to be utilized on a large number of projects where before cryocooler's10were not an acceptable solution, or no simple arrangement existed to use a cryocooler10. For example, IR detection requires a very low noise and vibration level. The current invention provides a solution whereby cryocoolers10may be utilized to their highest advantage without the drawbacks of current cryocooler technology (i.e., vibration and noise).

The position of the controller18between the active damper14and the cryocooler10allows the controller18to monitor the power supplied to the cryocooler10, the vibration levels, and the damping signal sent to the active damper14while transferring vibrations between the two components and providing the end user with an easy to assemble, service, and maintain assembly6. All electrical connections and cables are connected to a central area (i.e., connectors and ports of the controller18), providing a clean installation. Additionally, the illustrated controller18is relatively small and adds only about one or two inches of extension to the cryocooler assembly6. The minimal additional length allows the cryocooler assembly6to be installed in minimally smaller space than a non-controlled cryocooler that lacks the controller18.

The cooperation of the adapter ring60and the main ring64allow for rigid coupling of the assembly6together without the use of long fasteners passing from the active damper14directly to the cryocooler10. In other words, the two ring arrangement provides a more rigid and easy to assemble unit.

In other constructions, the connectors and communication ports could utilize wireless technology. For example, Bluetooth may be used.