Patent Description:
Obstacle and collision avoidance systems are useful to mitigate damage to vehicles and other property due to collisions. Various technologies regarding obstacle and collision avoidance systems can be incorporated into vehicles at a reasonable cost. Some technologies include sensors and digital cameras for sensing and monitoring areas around the vehicle. In some cases, cameras can increase safety by being mounted in locations that can give drivers access to alternative perspectives, which are otherwise diminished or unavailable to the driver's usual view through windows or mirrors. <CIT> discloses an ultrasonic lens cleaning system with current sensing. <CIT> discloses a lens cleaning apparatus. <CIT> discloses an on-board optical sensor cover and on-board optical apparatus. <CIT> discloses a cleaning apparatus for a mirror. <CIT> discloses an optical apparatus having dust off function.

One example not according to the claimed invention includes a control system for a sensor that includes a contaminant detection subsystem that measures a resonant frequency of the sensor assembly, the sensor assembly including a housing, an actuator and a sensor both disposed in the housing, and a housing cover that enables sensing by the sensor therethrough, the contaminant detection subsystem detects contaminants on an exposed surface of the housing cover and provides a detection signal identifying contaminants on the housing cover based on the resonant frequency of the sensor assembly, and a cleaning subsystem that provides a cleaning control signal to the actuator to expel the contaminants from the housing cover in response to the detection signal.

Another example includes a contaminant sensing system that includes a sensor assembly disposed on an exterior of a vehicle, the sensor assembly including an actuator and a sensor both disposed in a housing that enables sensing by the sensor through the housing, a contaminant detection subsystem that measures a resonant frequency of the sensor assembly, the contaminant detection subsystem to provide a detection signal in response to detecting contaminants on an exposed surface of the housing, a cleaning subsystem that implements expelling the contaminants from the exposed surface in response to the detection signal, and a temperature regulating device that regulates power to the actuator based on a temperature of the actuator. In a preferred embodiment, the contaminant sensing system further comprising a fault detection device to detect faults in the sensor assembly based on a change in the frequency response of the sensor assembly at different voltage excitation levels to determine whether the resonant frequency of the sensor assembly is present at the different voltage excitation levels, to determine whether the sensor assembly is faulty, and to disable the system start signal if a fault is detected. In another preferred embodiment, the contaminant detection/identification subsystem includes a frequency measurement circuit to measure a change in the resonant frequency of the sensor assembly to determine a presence or non-presence of the contaminants on the exposed surface. In a further preferred embodiment, the contaminant detection/identification subsystem includes a frequency response measurement circuit to measure a change in frequency response of the sensor assembly to determine a type of the contaminants and the amount of contaminants disposed on the exposed surface. In yet another embodiment, the temperature regulating device is arranged to determine whether the actuator temperature exceeds a temperature threshold based on a change in the frequency response of the sensor assembly, and wherein the temperature regulating device is arranged to disable the cleaning process and initiate a cooling procedure if the actuator temperature exceeds the temperature threshold.

Another example not according to the claimed invention includes a method of expelling contaminants from a sensor that includes measuring a change in a resonant frequency of a sensor assembly to detect contaminants on an exposed surface of the sensor assembly, measuring a change in the frequency response of the sensor assembly to determine the presence and amount of contaminants on the exposed surface, determining a cleaning mode based on the amount of contaminants on the exposed surface, determining a cleaning phase based on the amount of contaminants on the exposed surface, and generating a cleaning control signal to an actuator of the sensor assembly to expel the contaminants from the exposed surface. In a preferred embodiment not according to the claimed invention, the method further comprises determining whether the actuator is faulty based on the change in the frequency response of the sensor assembly at different voltage levels and disabling a start signal if the actuator is faulty.

This description relates generally to a sensing and signaling control/monitoring system for sensors (sensor assembly) disposed externally on a vehicle. More specifically, this description relates to a sensing and signaling control/monitoring system for identifying contaminants, cleaning, temperature detection/regulation, fault detection, power regulation, etc. relating to sensors disposed externally on the vehicle. Ultrasound excitation for cleaning sensors provides a more cost effective and efficient approach than water sprayers, mechanical wipers, or air jet solutions. Thus, the sensing and signaling control/monitoring system utilizes an actuator that vibrates the sensor assembly and consequently, drives a contaminant (e.g., water, mist, ice, dirt, mud, etc.) deposited on an exposed surface of a sensor assembly at its resonant frequency so as to facilitate the removal of the contaminant from the exposed surface. More specifically, when the actuator is excited by the proper periodic waveform, the actuator will vibrate the sensor assembly. Properly adjusting the frequency and amplitude of the vibration will expel the contaminant from the exposed surface. Because different contaminant amounts and types result in different resonant frequencies, the actuator can provide a frequency in a range of frequencies that encompass the resonant frequencies of the combined sensor assembly and the amount of contaminant deposited on the exposed surface. Some example actuators include a piezoelectric transducer, a voice coil actuator, etc..

The sensing and signaling control/monitoring system can be utilized with any sensor device disposed externally on the vehicle. For example, some sensor devices include camera systems (e.g., camera monitoring systems (CMS), surround view systems (SVS)), photodetectors, external mirrors, reflectors, lasers (LiDAR). Other types of sensor devices may include short-range and long-range radar, near-field transceiver, acoustic sensors or the like. Accordingly, the housing for the lens of cameras or other devices can include an exposed lens cover surface (such as camera, reflector, sensor, etc.). Similarly, other types of sensors (different from optical sensors or cameras) also include an external housing to protect the sensing devices from the environment. Each housing has an associated surface through which the signaling and/or sensing are provided to implement the corresponding sensing function (imaging, radar, LiDAR, near-field sensing, etc.). The sensing and signaling control/monitoring system not only cleans the housing, as described hereinabove, but also includes components to monitor other environmental or operating parameters for the sensor assembly. Examples of the environmental and operating parameters include temperature detection, fault detection (e.g., monitor the integrity and functionality of the exposed surface), power regulation, etc. The sensing and signaling control/monitoring system thus can extend the mechanical life of the sensor assembly and maintain its surface substantially free of contaminants. The sensing and signaling control/monitoring system may also provide early warnings for potential failures for the sensor assembly.

<FIG> illustrates an example sensing and signaling control/monitoring system <NUM> and <FIG> is an example sensor assembly <NUM> that can be used with the sensing and signaling control/monitoring system <NUM>. The sensing and signaling control/monitoring system <NUM> includes a contaminant detection subsystem <NUM> that measures a resonant frequency of a sensor assembly, a fault detection subsystem <NUM> that detects faults in the sensor assembly based on the change in the frequency of the sensor assembly, a cleaning subsystem <NUM> that provides a cleaning control signal to an actuator in the sensor assembly to expel contaminants from exposed surfaces of the sensor assembly, and a temperature monitoring/power regulation device <NUM> that monitors a temperature of the actuator. A controller <NUM> is provided to control the subsystems and devices via a bus <NUM>.

The example sensor assembly <NUM> illustrated in <FIG> is an example camera lens assembly for use on a camera. The sensor assembly <NUM> includes a housing <NUM> attached to a camera body <NUM>, a sensing device (e.g., camera lens) <NUM> disposed in the housing <NUM>, a transparent housing cover <NUM> disposed at an open end of the housing <NUM>, and an actuator <NUM>. The actuator <NUM> is disposed in the housing <NUM> and is attached to the housing cover <NUM>. The actuator <NUM> includes electrodes <NUM> that allow the actuator <NUM> to be connected to the controller <NUM> via a circuit interface <NUM>. In the example camera lens assembly, the actuator <NUM> can be a transducer (e.g., piezoelectric cylindrical or ring type transducer) that when excited by proper signaling, will vibrate the housing cover <NUM>. As described herein, by correctly adjusting the frequency and/or the amplitude of the vibration the contaminants can be expelled from an exposed surface <NUM> of the housing cover <NUM>.

Referring to <FIG>, <FIG>, <FIG> and <FIG>, the contaminant detection subsystem <NUM> detects and identifies contaminants disposed on an exposed surface of a sensor assembly (e.g., an exposed surface of a housing/lens cover) and can include a timer <NUM>, a frequency measurement circuit <NUM>, a frequency response measuring circuit <NUM>, and a comparator <NUM>. In one example, the contaminant detection subsystem <NUM> can be configured via the timer <NUM> to periodically check for contaminants based on various factors such as an amount of time the vehicle is in motion, a speed of the vehicle, direction of the vehicle (e.g., forward, reverse, turning), etc. The wait period can be dynamically updated (i.e. increased, decreased, no change) during the detection process. In another example, the contaminant detection subsystem <NUM> can be triggered manually (e.g., switch, push button, etc.) by an occupant of the vehicle. In yet another example, the contaminant detection subsystem <NUM> can be triggered by the sensor assembly if the sensor assembly senses that contaminants may be on the exposed surface. Thus, the triggering of the contaminant detection subsystem <NUM> can come from one of multiple sources.

Referring to <FIG>, the frequency measurement circuit <NUM> monitors a change in a resonant frequency of the sensor assembly to detect the presence of contaminants disposed on the exposed surface of the sensor assembly. A shift in the resonant frequency indicates that contaminants are present on the exposed surface of the sensor assembly. Specifically, the sensor assembly has a resonant frequency referred to as a natural frequency ωn and is defined by Equation (<NUM>): <MAT> where k is the effective stiffness of a mechanical system (sensor assembly) expressed in N/m and m is the effective mass of the mechanical system expressed in kg. When contaminants are detected on the exposed surface, the resonant frequency changes from the resonant (natural) frequency of the sensor assembly to a resonant (natural) frequency of both the sensor assembly and the contaminants disposed on the exposed surface. A change in the natural frequency Δωn due to the contaminants disposed on the exposed surface can be represented mathematically by Equation (<NUM>): <MAT> where <MAT> is a normalized change in natural frequency and <MAT> is a normalized change in mass both of which are unitless.

<FIG> is an example plot <NUM> that illustrates a change in the normalized natural frequency versus a change in the normalized mass, as described hereinabove. The change in normalized natural frequency is very sensitive to a small change in normalized mass. In the example in <FIG>, a change in normalized mass of about <NUM>% results in a change in normalized natural frequency of about <NUM>%. Thus, the sensitivity of the change in the resonant or natural frequency is effective in detecting the presence of contaminants on the exposed surface. Detection of the contaminants can be detected at a first resonant frequency, a second resonant frequency, etc..

Referring to <FIG>, the frequency response measurement circuit <NUM> measures a frequency response of the sensor assembly or any part thereof at a given resonant frequency to identify the type of contaminant and the amount of contaminant on the exposed surface. The frequency response of the sensor assembly plus the contaminants correlates to a specific amount of mass for contaminants on the exposed surface. For example, <FIG> is an example frequency response, which shows the impedance magnitude response curve <NUM> for an example sensor assembly. The peak is a pole of the impedance magnitude response and the valley is a zero of the impedance magnitude response. The pole-zero pair represent a resonant frequency of the example sensor assembly. More specifically, the pole represents a parallel resonant frequency and the zero a series resonant frequency. The term parallel resonant frequency refers to a resonance between the parallel combination of the mechanical subsystem and the dielectric whereas the term series resonance frequency refers purely to a resonance of the mechanical subsystem. <FIG> illustrates example impedance magnitude response curves <NUM> as a function of frequency for the example sensor assembly of <FIG> for different water droplet volumes ranging from 0µL to 200µL disposed in the center of the exposed surface of the example sensor assembly.

As illustrated in <FIG>, a given resonant frequency will shift by different amounts based on the amount of water (or other contaminants) disposed on the exposed surface. The amount of frequency shift from the resonant frequency of the sensor assembly correlates to an amount of mass on the exposed surface. Thus, in order to identify the type and amount of the contaminant on the exposed surface, the contaminant detection subsystem <NUM> can be calibrated with the resonant frequencies and frequency responses of the sensor assembly and any and all likely contaminant mass levels that may come in contact with the exposed surface. This information can be stored in a database <NUM> and the comparator <NUM> compares the measured resonant frequencies and frequency responses with the stored resonant frequencies and frequency responses to determine the amount and/or type of contaminants on the exposed surface of the sensor assembly. Identification of the contaminants can be initialized at a first resonant frequency, a second resonant frequency, etc..

Referring to <FIG>, <FIG> and <FIG>, the fault detection subsystem <NUM> performs system checks when the cleaning system <NUM> has not detected any appreciable mass on the exposed surface. System checks are performed by comparing a frequency response for a non-faulty, functional actuator and corresponding sensor assembly to a frequency response for a faulty, non-functional actuator and corresponding sensor assembly. For example, <FIG> shows the impedance magnitude response for an example non-faulty, functioning (healthy) actuator and corresponding sensor assembly for different voltage excitation levels at around <NUM>. The response has a zero between <NUM> and <NUM> and a pole between <NUM> and <NUM>, depending on the voltage excitation level. <FIG>, on the other hand, shows the impedance magnitude response for an example faulty or damaged actuator and corresponding sensor assembly for different voltage excitation levels at around <NUM>. In this case, the zero near <NUM> no longer has a resonant effect when the voltage level increases to the required level to excite the actuator. As a result, the impedance magnitude response of the sensor assembly can be monitored periodically during the life of the actuator. If the response indicates that the resonant frequency is no longer present, then the actuator is faulty and the fault detection subsystem <NUM> disables a system start signal (described further hereinbelow).

One example of a faulty actuator that the fault detection subsystem <NUM> can detect by a frequency response is the de-polarization of the piezoelectric material in a piezoelectric transducer when the transducer overheats. This failure occurs when the temperature of the material exceeds its Curie temperature and occurs when too much current is driven thru the sensor assembly during the cleaning process. Other example failures may include a cracked or broken lens, transducer cracking, seal failure, epoxy failure, etc. Thus, as described in the previous paragraph, the frequency response for the faulty actuator can be compared to the frequency response when the actuator is not faulty. The frequency response(s) for non-faulty actuators can be stored in a database <NUM> and accessed to compare the faulty actuator frequency responses to the non-faulty actuator frequency responses.

Referring again to <FIG>, the cleaning subsystem <NUM> initiates a cleaning process based on the identification of the contaminants by the contaminant detection subsystem <NUM>. The cleaning subsystem <NUM> includes a cleaning mode selector <NUM>, a cleaning phase selector <NUM>, and a signal generation device <NUM>. The cleaning mode selector <NUM> includes multiple cleaning modes (<NUM>, <NUM>. N) and selects a cleaning mode based on the type of contaminant disposed on the exposed surface as determined by the contaminant detection subsystem <NUM> described hereinabove. For example, a first cleaning mode may be implemented in response to determining the type of contaminants that correspond to mist, a second cleaning mode may be implemented in response to determining the type of contaminants that correspond to water droplets, a third cleaning mode may be implemented in response to determining the type of contaminants that correspond to ice, etc. Additional cleaning modes may correspond to other types of known (or unknown) types of contaminants such as dirt, mud, leaves, etc..

The cleaning phase selector <NUM> selects a cleaning phase from multiple cleaning phases (A, B. N) within a given cleaning mode based on the amount (e.g., size, mass, weight, volume, etc.) of contaminant disposed on the exposed surface as determined by the contaminant detection subsystem <NUM> described hereinabove. Thus, each cleaning mode can include one or more different cleaning phases depending on the amount of contaminants. Each cleaning phase within a given cleaning mode can provide a different level, intensity or process of cleaning based on the amount of contaminants on the exposed surface. Specifically, each cleaning phase can include one or more different parameters (i, ii. n) that define the cleaning process. The cleaning parameters can be defined as a frequency and/or voltage level that excites the actuator at specific resonant frequencies and/or amplitudes, which in turn vibrates the exposed surface thereby expelling contaminants from the exposed surface. Other parameters can include a time period (duration), heat drying, etc. Cleaning the exposed surface with ultrasonic systems and methods is disclosed in co-pending <CIT>, entitled METHODS AND APPARATUS USING MULTISTAGE ULTRASONIC LENS CLEANING FOR IMPROVED WATER REMOVAL.

As described hereinabove, each cleaning phase can provide a different process of cleaning. For example, larger amounts of contaminants disposed on the exposed surface require a more aggressive cleaning than smaller amounts. For example, if the cleaning mode selector <NUM> selects a cleaning mode that corresponds to water, the phase selector <NUM> selects the cleaning phase that includes an appropriate number of cleaning parameters to efficiently expel the water from the exposed surface. More specifically, a first parameter can correspond to a first (high) frequency (e.g., about <NUM>) that vibrates the actuator and hence, the exposed surface to atomize large water droplets. A second parameter can correspond to a second (lower) frequency (e.g., about <NUM>) that vibrates the actuator to further expel smaller water droplets. A third parameter can correspond to using the transducer as a heating device to heat dry the remaining water droplets. Thus, during the cleaning process, as the amount of the contaminant on the exposed surface changes (decreases/increases), the cleaning phase and/or the cleaning parameter can change accordingly, (e.g., from a more aggressive cleaning process to a lesser aggressive cleaning process (or vice versa)) to efficiently remove the contaminant from the exposed surface. In other words, the voltage and/or frequency or any other parameter can vary during the cleaning process.

The signal generation device <NUM> generates a cleaning control signal <NUM> to an actuator via an actuator interface <NUM>. The cleaning control signal <NUM> drives the actuator or other cleaning parameter based on the selected cleaning phase and/or cleaning parameters. The cleaning signal may have a predetermined frequency and/or voltage level that drives the actuator at the resonant frequency and/or amplitude to efficiently expel or dissipate the contaminants from the exposed surface. The cleaning signal can dynamically change as the cleaning mode, the cleaning phase, and/or the cleaning parameters dynamically change. As the contaminants begin to dissipate from the exposed surface, the resonant frequency of the exposed surface including the remaining contaminants changes. Thus during dissipation, the resonant frequency is essentially constantly changing. Therefore, as the resonant frequency changes, the cleaning mode, the cleaning phase and/or the cleaning parameters can change to continue efficient dissipation of the contaminants from the exposed surface that corresponds to the changing resonant frequency. In addition, the cleaning signal can be initiated at a first resonant frequency, a second resonant frequency, etc..

Referring to <FIG>, <FIG>, <FIG> and <FIG>, the temperature monitoring device <NUM> monitors a temperature of the actuator and can also serve as a power regulation device to regulate power to the actuator. Because the actuator is connected (e.g., mechanically coupled) to the exposed surface, the temperature monitoring device consequently monitors a temperature of the exposed surface. If the temperature of the actuator and/or exposed surface exceeds a threshold temperature the cleaning process is stopped until the actuator and/or exposed surface cools to ambient temperature or below the threshold temperature. Cooling can be passive cooling (e.g., air cool) or active cooling (e.g., air jets, water spray, etc.). In some examples, the temperature can be monitored by an external device, such as a thermocouple, infrared sensor, etc..

In another example, the temperature can be monitored internally by the sensor assembly. For example, the temperature monitoring device <NUM> can determine the temperature of the actuator and/or sensor assembly by measuring a frequency response of the sensor assembly for different temperatures. <FIG> illustrates an example impedance magnitude response <NUM> for an example sensor assembly at different temperatures. The magnitude of the impedance response at a particular frequency (e.g. <NUM>) can be used to determine the temperature of the transducer. This information can be stored and can be accessed to determine the temperature of the actuator and if the temperature of the transducer exceeds a temperature safety threshold. If so, the cleaning process is stopped until the actuator and/or exposed surface cools to a safe operating temperature, which is below the threshold temperature.

<FIG> shows a close-up view of the impedance magnitude response <NUM> from <NUM> to <NUM>. Given that the change in the impedance magnitude is uniform for a constant step changes in frequency, the temperature can easily be determined from the impedance data. In this example, the linear equation describing the temperature as a function of impedance magnitude for this example transducer is given by Equation (<NUM>): <MAT> that has a coefficient of determination value of R<NUM> = <NUM>. As this value approaches unity, the variance between the estimated value using the linear equation and the actual value is minimized.

<FIG> shows a plot <NUM> that compares the temperate estimate using the linear equation and the actual temperature from the impedance magnitude plots. The maximum error in the estimated temperate is approximately <NUM>. Thus, once an impedance magnitude value is known, the temperature of the actuator can be accurately estimated using a simple linear equation.

Referring again to <FIG>, the controller <NUM> includes a microprocessor (microcontroller) <NUM> for executing instructions and/or algorithms to carry out the process of the sensing and signaling control/monitoring system <NUM>. The microprocessor <NUM> can be embedded in a smart amplifier in a way such that the control system can be integrated into a single chip or can be comprised of multiple chips that are connected via bond wires. Logic control for the controller <NUM> can be software based (instructions executable by a processor core) or implemented as hardware, such as an arrangement of logic gates.

The controller <NUM> may further include a data storage device <NUM> that may store data and/or instructions such as executable program code that is executed by the microprocessor <NUM>. The data storage device <NUM> may store a number of applications and data that the microprocessor <NUM> can execute to implement at least the functionality described herein. The data storage device <NUM> may comprise various types of memory modules, including volatile and nonvolatile memory. For example, the data storage device <NUM> can include one or more of random-access memory (RAM) <NUM>, read-only memory (ROM) <NUM>, flash solid state drive (SSD) (not shown), and a database <NUM>. Additional devices and/or circuits <NUM>, such as but not limited to pulse-width (PWM) switching controller(s), PWM pre-driver(s), amplifier(s), analog-to-digital convertor(s), multiplexor(s), etc. that facilitate execution of the signals regarding the actuator may be included.

<FIG> is flow diagram <NUM> illustrating an example method of expelling the foreign contaminants from the exposed surface of the sensor assembly. The process begins in the contaminant subsystem described hereinabove. At <NUM>, the sensing and signaling control/monitoring system waits a period of time (e.g., waits for the system start signal) before beginning the process. At <NUM>, after the wait period has expired, the frequency measurement device monitors the resonant frequency to determine whether contaminant(s) are present on the exposed surface. If no material is detected, then at <NUM>, the process proceeds to the fault detection subsystem where the sensing and signaling control/monitoring system undergoes a system check. At <NUM>, a decision is made to determine whether the sensor assembly or any other component is faulty. If the system is faulty, then at <NUM>, the cleaning process stops. If the system is not faulty, the process loops back to <NUM> and the process starts again.

If at <NUM> material is detected, the contaminant detection subsystem <NUM> generates a material detection signal, then at <NUM> the frequency response measurement circuit identifies the type of contaminant disposed on the exposed surface. At <NUM>, the process proceeds to the cleaning subsystem and the cleaning process is performed, which is further described below with reference to <FIG>. At <NUM>, the temperature of the actuator is measured. At <NUM>, a decision is made to determine whether the temperature of the actuator exceeds a temperature threshold. If "YES," the process proceeds to the temperature monitoring subsystem where at <NUM>, the cleaning process is disabled. At <NUM>, cooling of the actuator and/or exposed surface is initialized. At <NUM>, a decision is made to determine whether the actuator temperature still exceeds the temperature threshold. If "YES," then at <NUM> the cooling continues and the process loops back to <NUM>. If "NO," then the process starts again at <NUM>.

If at <NUM> the actuator temperature does not exceed the temperature threshold, then at <NUM>, a decision is made to determine whether the cleaning process is complete. If "YES," then the process starts again at <NUM>. If "NO," then at <NUM> the cleaning signal duration is updated and the process loops back to <NUM>.

<FIG> is flow diagram illustrating an example cleaning process represented as <NUM> in <FIG>. At <NUM>, the cleaning mode is determined based on the type of contaminant disposed on the exposed surface, as described hereinabove. At <NUM>, the cleaning phase is determined based on an amount of contaminants disposed on the exposed surface. At <NUM>, the cleaning parameters are set based on the phase selection. At <NUM>, the cleaning signal is generated to thereby initialize the cleaning process.

<FIG> is a flow diagram illustrating another example cleaning process represented as <NUM> in <FIG>. Prior to this process, it was determined that the contaminant identified on the exposed surface is ice and/or water. At <NUM>, the temperature of the actuator is determined, which in turn determines the temperature of the exposed surface. At <NUM>, a decision is made to determine whether the temperature is below freezing, which is an indication that ice has formed on the exposed surface. If "YES," then a heating signal is generated to heat the exposed surface to thereby melt the ice. If "NO," then at <NUM> a decision is made to determine whether the amount of contaminant should be reduced. If "YES," then at <NUM> a cleaning signal is generated to excite the actuator at a resonant frequency of the exposed surface plus any contaminants on the exposed surface. If "NO," then at <NUM> a decision is made to determine whether drying is required based on the amount of contaminant. If "YES," then at <NUM> a heat signal is generated thereby heating the exposed surface of the sensor assembly. If "NO," then the process loops back to <NUM> and starts the process over again.

Claim 1:
A control system (<NUM>) for a sensor assembly (<NUM>), the system (<NUM>) comprising:
a contaminant detection subsystem to measure a resonant frequency of the sensor assembly (<NUM>),
a sensor assembly (<NUM>) disposed on an exterior of a vehicle, the sensor assembly (<NUM>) including a housing, an actuator (<NUM>) and a sensor both disposed in the housing, and a housing cover to enable sensing by the sensor therethrough, the contaminant detection subsystem being arranged to detect contaminants on an exposed surface (<NUM>) of the housing cover and to provide a detection signal identifying contaminants on the housing cover based on the resonant frequency of the sensor assembly (<NUM>); and
a cleaning subsystem to provide a cleaning control signal to the actuator (<NUM>) to expel the contaminants from the housing cover in response to the detection signal;
wherein the contaminant detection subsystem includes a frequency response measurement circuit to measure a change in the frequency response of the sensor assembly (<NUM>) to determine a type of the contaminants and the amount of contaminants on the housing cover; and
further comprising a temperature regulating device to regulate power to the actuator (<NUM>) based on a temperature of the actuator (<NUM>).