A non-contact passive ranging system wherein a first imager on a platform is focused on a first object and a second imager on the platform is also focused on the first object. The optical path from the first object to the first imager is configured to be shorter than the optical path from the object to the second imager. Processing circuitry is responsive to an output of the first imager and an output of the second imager as relative motion is provided between the platform and the first object and is configured to calculate the distance from the platform to the object.
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13. A method of determining the distance between a platform and an object, the method comprising:
focusing a first optical motion sensor on the platform at the object;
focusing a second optical motion sensor on the platform at the same object;
arranging the optical path from the first object to the first optical motion sensor to be shorter than the optical path from the object to the second optical motion sensor;
providing relative motion between the platform and the object; and
calculating the distance from the platform to the object based on a slower velocity different velocity output by the first optical motion sensor than the second optical motion sensor and based on the different optical path lengths of the first and second optical motion sensors.
1. A non-contact passive ranging system comprising:
a first optical motion sensor on a platform focused on a first object;
a second optical motion sensor on the platform also focused on the first object;
the optical path from the first object to the first optical motion sensor shorter than the optical path from the first object to the second optical motion sensor; and
processing circuitry responsive to an output of the first optical motion sensor and an output of the second optical motion sensor as relative motion is provided between the platform and the first object and configured to calculate the distance from the platform to the object based on a slower velocity different velocity output by the first optical motion sensor than the second optical motion sensor and based on the different optical path lengths of the first and second optical motion sensors.
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This subject invention relates to distance measuring systems.
Numerous distance measuring systems are known in the art and, by extension, so are systems which are able to resolve the motion of an object. Systems such as sonar, lidar, radar, and the like involve active emission of energy from a sensor to the object and thus such systems are often complex, expensive, and power intensive. The processing requirements underlying such systems are also typically intensive. Also, many prior systems may be fairly slow to acquire range information.
In fields such as robotics and portable navigation systems, fast, inexpensive, and low power ranging systems are desired.
It is therefore an object of this invention to provide a non-contact ranging system which is passive.
It is a further object of this invention to provide such a ranging system which does not involve intensive processing requirements.
It is a further object of this invention to provide such a ranging system which quickly acquires range information.
It is a further object of this invention to provide such a ranging system which is inexpensive.
It is a further object of this invention to provide such a ranging system which is low power in operation.
It is a further object of this invention to provide such a ranging system which is readily configurable to operate in different environments, for example in robotics, in vehicle based systems, and in portable navigation systems such as helmet or head mounted systems.
It is a further object of this invention to provide such a ranging system which is readily extensible to provide complete motion data.
The subject invention results at least in part from the realization that a viable non-contact passive ranging system, in one example, employs optical motion sensors configured so one is further away from an object than the other in which case the object will, to the sensors, appear to move at two different rates. Since the position of the two sensors is known, their outputs enable a processor to readily calculate the distance to the object. By extension, additional pairs of motion sensors allow the processor to fully calculate the motion of any platform the sensors are attached to.
The subject invention, however, in other embodiments, need not achieve all these objectives and the claims hereof should not be limited to structures or methods capable of achieving these objectives.
This subject invention features a non-contact passive ranging system. Typically, a first imager on a platform is focused on a first object and a second imager on the platform is also focused on the first object. The optical path from the first object to the first imager is designed to be shorter than the optical path from the object to the second imager. Processing circuitry is responsive to the output of the first imager and the output of the second imager as relative motion is provided between the platform and the first object and is configured to calculate the distance from the platform to the object.
In one embodiment, each imager is an optical motion sensor each outputting a velocity. The platform may be mobile. Also, there may be a beam splitter in the optical path of both the first and second imagers.
In another embodiment, there is a third imager and a fourth imager on the platform both focused on a second object. The optical path from the second object to the third imager is shorter than the optical path from the second object to the fourth imager. Now the processing circuitry is also responsive to an output of the third imager and an output of the fourth imager as relative motion is provided between the platform and the second object and is configured to calculate the distance from the platform to the second object. The processing circuitry may be further configured to calculate the linear velocity of the platform, and also the angular velocity of the platform.
In another embodiment, there is a fifth imager and a sixth imager both focused on a third object and the optical path from the third object to the fifth imager is shorter than the optical path from the third object to the sixth imager. Now the processing circuitry is also responsive to an output of the fifth imager and an output of the sixth imager as relative motion is provided between the platform and the third object and is configured to calculate the distance from the platform to the third object. The processing circuitry can be further configured to calculate the velocity of the platform in more than one direction and the angular velocity of the platform about more than one axis. Typically, the optical axes of the fifth and sixth imagers are orthogonal to the optical axes of the third and fourth imagers which are orthogonal to the optical axes of the first and second imagers.
The subject invention also features a method of determining the distance between a platform and an object. The method typically includes focusing a first imager on the platform at the object, focusing a second imager on the platform at the same object, and arranging the optical path from the first object to the first imager to be shorter than the optical path from the object to the second imager. Relative motion is provided between the platform and the object and the distance from the platform to the object is calculated based on reference and sample frames imaged by the first and second imagers. Providing relative motion may include moving the platform. Typically, the first imager outputs a first velocity xA of the platform and the second imager outputs second velocity xB of the platform. Calculating the distance h is a function of xA, xB and the position of the first and second imagers on the platform.
Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in which:
Aside from the preferred embodiment or embodiments disclosed below, this invention is capable of other embodiments and of being practiced or being carried out in various ways. Thus, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. If only one embodiment is described herein, the claims hereof are not to be limited to that embodiment. Moreover, the claims hereof are not to be read restrictively unless there is clear and convincing evidence manifesting a certain exclusion, restriction, or disclaimer.
In one example, sensors A and B are preferably optical motion sensors commonly used in optical computer mice. See U.S. Pat. No. 6,995,748 incorporated herein by this reference. Further away imager A captures a reference frame of object 12 at time t1 and then a sample frame of object 12 at time t2 as relative motion is provided between platform 10 and object 12. Similarly, closer imager B captures a reference frame of object 12 at time t1 and then a sample frame of object 12 at time t2. As shown in
Processor 14,
As shown in
where XA and XB are the velocity outputs of imagers A and B, respectively, when reference location 30 is moving with linear velocity μ relative to object 12.
By the addition of imagers C and D both imaging object 32 in a manner similar to the way imagers A and B image object 12, the distance h2 from reference location 30 to object 32 and also the full motion of platform 10 can be resolved by processing circuitry (14,
h1 is then:
h2 is:
q can now be solved:
By adding another pair of imagers focused on a third object (e.g., the floor beneath platform 10), additional motion data can be ascertained.
In accordance with the subject invention, no radiation other than ambient illumination or contact is required and the processing time is minimal with low latency and rapid update rates. The subject invention is not limited to optical sensing devices in the form of the optical motion sensors discussed above, however. The optical sensing devices could be cameras with separate processing units that calculate the frame to frame motion of a video sequence. In accordance with this configuration, it is possible to not only derive a single distance, but to also create a range map which provides readings to all points within the field of view of one of the imagers. In this configuration, it is also possible to derive the motion of the object on which the cameras are mounted.
When cameras are used instead of simple optical motion sensors, the solution of the depth map of the mutually overlapping portions of the two images is possible. With a sufficiently wide field of view and/or pairs of cameras aimed in different directions, it also becomes feasible to measure the full motion.
The combination of three pairs of such devices in which the optical axis of the three pairs are orthogonal to each other yields the ability to not only measure the three distances but also to derive the full motion of the object on which the sensors are mounted. In one example, an optimal combination of five optical navigation sensors arranged with three in a plane and subtending two orthogonal axes and two more vertically offset allow for the sensing of motion, height, and attitude relative to a reference plane. Such an arrangement might be mounted to a ground vehicle such as an automobile and used to measure the sway and tilt of the vehicle in addition to its turn rate and velocity relative to a plane. Two optical sensing devices could be separated vertically both pointing in the same direction but offset slightly horizontally. In this arrangement, there will be no optical apparatus to split the images and the two devices would be focused on different images but in certain situations this would still function adequately. The two optical sensing devices could be separated vertically and offset slightly horizontally but angled slightly towards each other as well. There could also be other optical apparatus to create the vertical separation between the two devices.
There are numerous other possible applications for the subject invention. Robotic applications include those requiring image and range mapping. 3-D model capture in situations involving relative motion between a sensor and an object being imaged are also applications. The subject invention can be used to sense motion of a moving vehicle or machine. Altitude sensing for small unmanned aircraft or rotorcraft is possible as is measurement of motion relative to a flat plane, for example crane operations, farm equipment navigation, and automobile navigation.
As shown in
In one example, it can be assumed that lC=iB=l, and lF=lE=lh, where lh is the distance from B to E or C to F, and l is the distance from A to B or A to C.
Other definitions are as follows:
xA, xB, xC, xE, xF are the X outputs of each optical sensor and yA, yB, YC, yE, yF are the Y output of each optical sensor. α is the angle between the vector (BA) and the projection of that vector onto the image plane, γ is the angle between the vector (C
A) and the projection of that vector onto the image plane, h is the distance from A to the image plane measured perpendicularly to the plane (A, B, C), hB is the distance from B to the image plane measured perpendicularly to the plane (A, B, C), and hC is the distance from C to the image plane measured perpendicularly to the plane (A, B, C). u is the linear velocity of A in the direction (B
A), v is the linear velocity of A in the direction (C
A), p is the rotational velocity of A about the axis (B
A), q is the rotational velocity of A about the axis (C
A), and r is the rotational velocity of A about the axis (B
A).
Thus,
Then,
mx is the distance on the focal plane that the image point has moved (output of the optical sensor system), f is the pin-hole equivalent focal length of the optical lens system employed, lA is the distance from the navigated point on the body in motion to the aperture of the optical system, Δx is the linear motion of the body in motion as measured at the navigated point, Δθ is the angular motion of the body in motion as measure at the navigated point, and h is the distance from the navigated point to the image point being tracked at the time of the initial image.
Then,
Then, assuming small angles, (i.e. tan θ=θ),
This implies that an assumption of small angles and small distances holds true for:
(Δx+lAΔθ)Δθ<<h−lA (35)
Although specific features of the invention are shown in some drawings and not in others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. The words “including”, “comprising”, “having”, and “with” as used herein are to be interpreted broadly and comprehensively and are not limited to any physical interconnection. Moreover, any embodiments disclosed in the subject application are not to be taken as the only possible embodiments. Other embodiments will occur to those skilled in the art and are within the following claims.
In addition, any amendment presented during the prosecution of the patent application for this patent is not a disclaimer of any claim element presented in the application as filed: those skilled in the art cannot reasonably be expected to draft a claim that would literally encompass all possible equivalents, many equivalents will be unforeseeable at the time of the amendment and are beyond a fair interpretation of what is to be surrendered (if anything), the rationale underlying the amendment may bear no more than a tangential relation to many equivalents, and/or there are many other reasons the applicant can not be expected to describe certain insubstantial substitutes for any claim element amended.
Zervoglos, Nicholas, DeBitetto, Paul, Rasmussen, Scott
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