Laser distance measuring system with a shutter mechanism

A laser distance measuring system includes an object lens, a beam splitter, a transmitter, a receiver, and a shutter mechanism. The beam splitter is disposed at one side of the object lens. The transmitter emits a laser beam that is split by the beam splitter into a measurement beam and a reference beam. The measurement beam passes through the object lens, and is reflected by an object to result in a reflected measurement beam passing through the object lens. The receiver is disposed to receive the reflected measurement beam and the reference beam. The shutter mechanism includes a beam masker operable to move to either block path of the reflected measurement beam to the receiver or path of the reference beam to the receiver.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority of Taiwanese application no. 095129380, filed on Aug. 10, 2006.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a laser distance measuring system, more particularly to a laser distance measuring system with a shutter mechanism.

2. Description of the Related Art

U.S. Patent Application Publication Number 2001/0013929A1 discloses a device for optoelectronic distance measurement that includes two transmitters and two receivers. Two emitted light beams are respectively reflected internally and externally before being received by the receivers, respectively, thereby resulting in two measurement values. The difference between the two measurement values is then processed using analgorithm to result in a measured distance value. However, the device disclosed in this publication utilizes a large number of components, which results in complicated mechanical and circuit constructions, higher manufacturing and material costs, and a larger size. Moreover, there are inherent differences between the two transmitters and between the two receivers. Even if the two transmitters or the two receivers come from the same batch fabricated by the same manufacturer, there is no guarantee that the two transmitters or the two receivers will have identical characteristics. Therefore, measurement errors are unavoidable in the device disclosed in this publication.

U.S. Patent Application Publication Number 2004/0105087A1 discloses a laser distance measuring device that includes a transmitter and two receivers. An emitted light beam is split by a beam splitter to result in a reference light beam and a measurement light beam to be reflected by an object. The reflected measurement light beam and the reference light beam are received by the receivers, respectively, to result in two measurement values. The difference between the two measurement values is then processed using an algorithm to result in a measured distance value. However, although the measurement light beam and the reference light beam come from the same transmitter, measurement errors are still unavoidable since the measuring device includes two receivers. In particular, aside from the fact that there are inherent differences between the two receivers, one of the receivers receives the reference light beam under more ideal conditions, while the other receiver receives the reflected measurement light beam that is weaker and that has been subjected to some interference. Therefore, a bias voltage for the other receiver that receives the reflected measurement light beam is required to be larger to achieve higher gain for amplification. The difference between the bias voltages required by the two receivers is also a source of measurement error.

FIG. 1shows a device for distance measurement that is disclosed in U.S. Patent Application Publication Number 2005/0083512A1.FIG. 2shows an electro-optical distance measuring system that is disclosed in U.S. Pat. No. 6,781,675B2. Each of the device ofFIG. 1and the system ofFIG. 2includes a transmitter101and a receiver102. Two shutter mechanisms11are further included in the device ofFIG. 1. Through switching of the two shutter mechanisms11between two positions, a measurement beam for external reflection and a reference beam for internal reflection can be generated from the same light source for use in obtaining a measured distance value. However, the structure and operation of the device ofFIG. 1are difficult to realize since a change in the optical path of the reference beam can occur if the positions of the two shutter mechanisms11are imprecise, which can affect measurement accuracy. Moreover, the two shutter mechanisms11and the relevant driving mechanisms for the same will result in the disadvantage of a larger size. On the other hand, in the system ofFIG. 2, the reference beam is obtained from a reflecting surface12. In theory, the optical path of the reference beam is shorter and that of the measurement beam is longer such that the reference beam and the reflected measurement beam are received by the receiver102at earlier and later time points, respectively. However, in view of the response speed of the receiver102and the transient response of subsequent circuits, and in view of the fact that the speed of light is very fast, the late-arriving signal is likely to be affected by the early-arriving signal and is thus distorted, which leads to inaccurate measurement, especially when measuring short distances.

SUMMARY OF THE INVENTION

Therefore, the object of the present invention is to provide a laser distance measuring system that can be manufactured at a relatively low cost, that has a relatively simple construction, and that can provide accurate measurement results.

According to the present invention, there is provided a laser distance measuring system adapted for measuring distance between the system and an object. The laser distance measuring system comprises an object lens, a beam splitter, a transmitter, a receiver, and a shutter mechanism.

The beam splitter is disposed a tone side of the object lens. The transmitter is disposed at one side of the beam splitter opposite to the object lens, and is operable to emit a laser beam that is split by the beam splitter into a measurement beam and a reference beam. The measurement beam passes through the object lens to reach the object, and is reflected by the object to result in a reflected measurement beam that passes through the object lens. The receiver is disposed at said one side of the object lens to receive the reflected measurement beam passing through the object lens and the reference beam from the beam splitter. The shutter mechanism is disposed adjacent to the receiver, and includes a beam masker that is operable to move between a first position, where the beam masker blocks path of the reflected measurement beam to the receiver, and a second position, where the beam masker blocks path of the reference beam to the receiver.

When conducting a laser distance measuring operation, through blocking of the reflected measurement beam by the beam masker, the receiver is able to receive the reference beam that is not affected by the reflected measurement beam. After a response time of the receiver, the beam masker is switched to block the reference beam such that the receiver receives the reflected measurement beam that is not affected by the reference beam, thereby ensuring signal processing accuracy of subsequent circuits. In other words, this invention makes it possible to compute pure reference beams and pure reflected measurement beams to obtain a precise measurement result. This invention also achieves manufacturing requirements of a lower manufacturing cost and a simpler construction.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring toFIGS. 3 to 5, the preferred embodiment of a laser distance measuring system200according to the present invention is shown to be adapted for measuring distance between the system200and an object (not shown) The laser distance measuring system200comprises an object lens20, a beam splitter30, a transmitter40, a receiver50, and a shutter mechanism60.

The beam splitter30is disposed at a rear side of the object lens20.

The transmitter40is disposed at a rear side of the beam splitter30opposite to the object lens20, and is operable to emit a laser beam400. The transmitter40is a laser diode. The laser beam400is guided by a first reflector71toward the beam splitter30, and is split by the beam splitter30into a measurement beam401and a reference beam402. The reference beam402is guided by a second reflector72toward the receiver50. The measurement beam401passes through the object lens20to reach the object, and is reflected by the object to result in a reflected measurement beam401′ that passes through the object lens20. The reflected measurement beam401′ is guided by a third reflector73toward the receiver50.

The receiver50is disposed at the rear side of the object lens20to receive the reference beam402coming from the beam splitter30and guided by the second reflector72, and the reflected measurement beam401′ passing through the object lens20and guided by the third reflector73. The receiver50is an avalanche photo diode (APD) in this embodiment.

The shutter mechanism60is disposed adjacent to the receiver50and includes a beam masker61and an electromagnetic actuator62.

The beam masker61is operable to move between a first position (seeFIG. 5), where the beam masker61blocks path of the reflected measurement beam401′ to the receiver50, and a second position (seeFIG. 4), where the beam masker61blocks path of the reference beam402to the receiver50. Moreover, the beam masker61includes a pivot rod611that is pivotable about an axis thereof, a masking member612extending from the pivot rod611and disposed to block and unblock the paths of the reflected measurement beam401′ and the reference beam402to the receiver50, and a driven rod613extending from the pivot rod611and coupled to the electromagnetic actuator62.

The electromagnetic actuator62has an electromagnet therein, and includes an extensible arm621and a coupling ring622connected to the arm621and sleeved on the driven rod613. When the electromagnetic actuator62is not excited, the masking member612is at the second position (seeFIG. 4). When the electromagnetic actuator62is excited, the arm621pulls the driven rod613through the coupling ring622, thereby causing the beam masker61to pivot about the pivot rod611so as to move the masking member612to the first position (seeFIG. 5).

When conducting a laser distance measuring operation, through blocking of the reflected measurement beam401′ by the beam masker61, the receiver50is able to receive the reference beam402that is not affected by the reflected measurement beam401′. After a response time of the receiver50, the beam masker61is switched to block the reference beam402such that the receiver50receives the reflected measurement beam401′ that is not affected by the reference beam402, thereby ensuring signal processing accuracy of subsequent circuits (not shown). In other words, the system200of this invention makes it possible to compute pure reference beams402and pure reflected measurement beams401′ to obtain a precise measurement result.

Compared to the conventional devices described hereinabove, the system200of this invention only needs one transmitter40and one receiver50for distance measurement. In practice, the first, second and third reflectors71,72,73may be omitted through alignment between the transmitter40and the beam splitter30, and through simultaneous alignment of the receiver50with the beam splitter30and the object lens20. The system200of this invention thus has a simpler construction and can be manufactured at a lower cost to meet industry requirements and to result in a better competitive edge in the market.