Laser radar device and laser radar system
Technical Field
The utility model relates to the field of laser technology, concretely relates to laser radar device and laser radar system based on vertical cavity surface emitting laser.
Background
The market of laser radar (LiDAR) is rapidly growing in the field of automobile automatic driving, and autonomous navigation and driving assistance are mainly realized by utilizing a 905nm semiconductor laser with a near infrared band to emit laser pulses and then utilizing a silicon-based Avalanche Photodetector (APD) to collect reflected light signals to create a point cloud picture of the surrounding environment of an automobile.
The famous Velodyne company in the U.S. owns three specifications of 16, 32 and 64-line mechanical fast scanning laser radars, wherein the measurement range of the 64-line laser radar with the highest specification can reach 120m, the measurement precision is about 20mm, but the price is even up to 7.5 ten thousand dollars, the laser radar is very expensive and bulky, and cannot be popularized in the field of assistant driving. At present, major manufacturers of lidar such as Velodyne and Quanergy are developing and producing all-solid-state lidar with small volume, light weight and low price.
At present, edge-emitting 905nm semiconductor lasers and silicon-based near-infrared detectors are commonly used in all-solid-state laser radars. However, the 905nm laser is not a laser radar light source safe to human eyes, and the quality of the light beam of the edge-emitting laser is poor. In addition, the high integration of a semiconductor laser, a near-infrared detector, a micro lens, a control circuit and analysis software in the all-solid-state laser radar is the mainstream direction of the laser radar, however, the laser and the detector in the current all-solid-state laser radar are respectively and independently packaged into modules, so that monolithic integration cannot be realized, and the high integration is difficult to realize. Moreover, most of laser beams emitted by the existing laser radar are in a divergent shape, the proportion of the laser beams actually projected onto a target object is small, the proportion of the laser beams returned to a detector is smaller, the laser utilization rate is lower, the power consumption is larger, and the sensitivity of the laser radar is greatly reduced.
SUMMERY OF THE UTILITY MODEL
Therefore, the utility model discloses the technical problem that solve is: in the prior art, the integration level of the laser radar is low.
In order to solve the technical problem, the utility model discloses a technical scheme as follows:
an embodiment of the utility model provides a laser radar device, include:
the signal transmitting module is used for transmitting a laser signal to a target object;
the signal receiving module and the signal transmitting module are integrated on the same laser radar main board and are used for receiving the laser signals reflected by the target;
the light path adjusting module is arranged on a light path where the laser signal is located and used for adjusting the light path of the laser;
and the data processing module is connected with the signal receiving module and is used for analyzing and processing the laser signal reflected by the target object.
Optionally, the signal emitting module is a number of Vertical Cavity Surface Emitting Laser (VCSEL) arrays.
Optionally, the signal receiving module is a number of Avalanche Photodiode (APD) arrays.
Optionally, the signal receiving modules are distributed around the signal transmitting module with the signal transmitting module as a center.
Optionally, the optical path adjusting module comprises a first lens assembly with a convex surface facing the signal emitting module, and a second lens assembly with a convex surface facing the target object;
the orthographic projection of the first lens assembly on the laser radar main board is coincided with the orthographic projection of the signal transmitting module on the laser radar main board, and the orthographic projection of the second lens assembly on the laser radar main board is coincided with the orthographic projection of the signal receiving module on the laser radar main board.
Optionally, the first lens assembly is a micro lens array, and the micro lens array is used for shaping the laser emitted by the signal emission module into parallel light to be emitted to the target object;
the second lens component is a micro lens array or a Fresnel lens, and the micro lens array or the Fresnel lens is used for shaping the laser reflected by the target into parallel light and transmitting the parallel light to the signal receiving module.
Optionally, the wavelength of the laser signal is greater than or equal to 1400 nm.
Optionally, the data processing module includes:
the signal conversion sub-module is connected with the signal receiving module and is used for converting the received laser signal reflected by the target object into an electric signal;
and the data processing submodule is connected with the signal conversion submodule and is used for processing the electric signals obtained by the signal conversion submodule.
Optionally, the method further comprises:
the image generation module is connected with the data processing module and generates an image signal according to an analysis result of the data processing module;
and the output module is connected with the image generation module and used for outputting the image signal generated by the image generation module to a terminal.
The embodiment of the utility model provides a laser radar system is still provided, including above-mentioned laser radar device and scanning control device, scanning control device is used for adjusting laser radar device's direction of deflection.
The technical scheme of the utility model, have following advantage:
the embodiment of the utility model provides a laser radar device, including signal transmission module, signal reception module, light path adjusting module and data processing module, signal transmission module is used for launching laser signal to target object, the target object has the reflex action to laser signal, signal reception module is used for receiving the laser signal that the target object reflects back, data processing module then carries out analysis processes to the received laser signal that reflects back of signal reception module, and then obtains target object distance to laser radar, detection results such as relative motion rate and spatial position relation. The embodiment of the utility model provides an in, signal transmission module and signal receiving module are integrated on same laser radar mainboard, and to a great extent has simplified the structure of this laser radar device, has reduced current laser radar device's volume, has improved the integrated level, accords with current laser radar's miniaturized development trend. In addition, a light path adjusting module is further arranged on a light path where the laser signal is located, the light path adjusting module is used for adjusting the emitted laser light path and the reflected laser light path, high collimation performance when the laser reaches a target object and enters a signal receiving module is further improved, and sensitivity and precision of the laser radar device are improved.
The embodiment of the utility model provides a laser radar device, signal transmission module are Vertical Cavity Surface Emitting Laser (VCSEL) array. The optical resonant cavity of the vertical cavity surface emitting laser is vertical to the laser radar main board substrate, laser emission on the surface of the laser radar main board can be realized, the laser radar main board substrate has the advantages of low threshold current, no Catastrophic Optical Damage (COD), long service life, stable single-wavelength work, high modulation rate, small divergence angle, low coupling efficiency and the like, and the light beam quality is far higher than that of an Edge Emitting Laser (EEL) and an LED, so that the vertical cavity surface emitting laser has higher application value in the technical fields of high-speed optical communication, laser radar, three-dimensional sensing and imaging and the like. Therefore, the embodiment of the present invention provides a vertical cavity surface emitting laser array as a signal emitting module, which effectively enhances the performance of the signal emitting module.
The embodiment of the utility model provides a laser radar device, signal reception module are avalanche photodiode (APD array) advantages such as Avalanche Photodiode (APD) have sensitivity height, small and fast, according to the selection of material, avalanche photodiode's response wave band can reach 900nm-1700nm, and peak wavelength is at 1550nm, is applicable to high-speed, high sensitivity photoelectric detection, and the wide application is in long distance optical communication field.
The embodiment of the utility model provides a laser radar device, signal receiving module use signal emission module as the center, distributes around signal emission module. On one hand, the arrangement mode is beneficial to enabling the signal receiving module and the signal transmitting module which are integrated on the same laser radar main board to have compact structures, reducing the volume of the whole laser radar device to the maximum extent and realizing miniaturization; on the other hand, the distribution rule of the transmitting light path and the reflecting light path of the laser is met, and the detection effect of the laser radar is ensured.
The embodiment of the utility model provides a laser radar device, light path adjusting module include convex surface towards the first lens subassembly of signal emission module to and convex surface towards the second lens subassembly of target object; orthographic projection of the first lens assembly on the laser radar main board coincides with orthographic projection of the signal transmitting module on the laser radar main board, and orthographic projection of the second lens assembly on the laser radar main board coincides with orthographic projection of the signal receiving module on the laser radar main board.
That is, the first lens assembly corresponds to the signal emitting module in position, and after the signal emitting module emits a laser signal, the laser light is corrected by the angle of the first lens assembly to form parallel light, and then the parallel light is irradiated on a target object in the form of the parallel light. The second lens component corresponds to the signal receiving module in position, and laser reflected from a target object is collimated and enters the signal receiving module after being corrected by the angle of the second lens component. Therefore, the arrangement of the first lens component and the second lens component obviously improves the collimation directivity and the luminous efficiency density of the emergent light, and increases the probability, the optical intensity and the sensitivity of the reflected light entering the signal receiving module.
Meanwhile, the interference and noise caused by environment stray light to the detection process are avoided, and the anti-interference capability of the laser radar device is improved.
The embodiment of the utility model provides a laser radar device, first lens subassembly are microlens array, and second lens subassembly is microlens array or fresnel lens. Namely, the first lens component and the second lens component both adopt a micro lens array, or the first lens component adopts a micro lens array and the second lens component adopts a Fresnel lens. The setting mode is comparatively nimble, can set up according to the actual demand. The micro-lens array has the advantages of low cost, wide application, light and thin Fresnel lens and good light condensation effect.
In addition, the micro lens array is used for shaping the laser emitted by the signal emitting module into parallel light to be emitted to a target object, and the micro lens array or the Fresnel lens is used for shaping the laser reflected by the target object into parallel light to be emitted to the signal receiving module.
Compared with the traditional laser radar device, the embodiment of the utility model provides a divergent light shaping that the laser radar device launches through the microlens array is the parallel light for the vast majority of light can shine to the target object, and has improved the proportion of the laser that is reflected back by the target object; laser shaping reflected by a target object is transmitted to the signal receiving module in a parallel mode through the micro-lens array or the Fresnel lens, most of laser reflected can be received by the signal receiving module, the utilization rate of the laser is effectively improved, meanwhile, the power of the laser radar device is reduced, and the power consumption is reduced.
The embodiment of the utility model provides a laser radar device, laser signal's wavelength more than or equal to 1400 nm. According to the research of human eye physiology and optical structure, the light with the wavelength of more than or equal to 1400nm can not be transmitted into retina, and the human eye can not be damaged even if higher power output is adopted. Therefore, the long-wavelength signal emitting module with the wavelength being more than or equal to 1400nm is used as a laser light source, and the longer detection distance, the higher resolution and the higher safety can be realized.
The embodiment of the utility model provides a laser radar system, including above-mentioned laser radar device and scanning control device, scanning control device is used for adjusting the direction of deflection of laser radar device. Therefore, under the control of the scanning control device, the laser radar device can emit laser in different directions, so that the scanning function is realized, and the road condition and the surrounding environment can be detected and identified in a large range.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the embodiments or the technical solutions in the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
Fig. 1 is a schematic structural diagram of a laser radar apparatus according to an embodiment of the present invention;
fig. 2 is a schematic block diagram of a laser radar apparatus according to an embodiment of the present invention;
fig. 3 is a schematic application diagram of a laser radar apparatus according to an embodiment of the present invention;
reference numerals:
1-a target; 2-laser radar main board; 3-a signal transmitting module; 31-an emission light path; 4-a signal receiving module; 41-reflection light path; 5-an optical path adjusting module; 51-a first lens assembly; 52-a second lens assembly; 6-a data processing module; 61-a signal conversion submodule; 62-a data processing submodule; 63-an image generation module; 64-an output module; 7-a control module; 8-a timing module; 9-terminal.
Detailed Description
The technical solution of the present invention will be described clearly and completely with reference to the accompanying drawings, and obviously, the described embodiments are some, but not all embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by a person skilled in the art without creative work belong to the protection scope of the present invention.
In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplification of description, but do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
In the description of the present invention, it is to be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; the two elements may be directly connected or indirectly connected through an intermediate medium, or may be communicated with each other inside the two elements, or may be wirelessly connected or wired connected. The specific meaning of the above terms in the present invention can be understood in specific cases to those skilled in the art.
Furthermore, the technical features mentioned in the different embodiments of the invention described below can be combined with each other as long as they do not conflict with each other.
Example 1
An embodiment of the utility model provides a laser radar device, as shown in fig. 1 and fig. 2, including signal transmission module 3, signal reception module 4, light path adjusting module 5 and data processing module 6. Wherein,
the signal transmitting module 3 is used for transmitting a laser signal to the target object 1; the signal receiving module 4 and the signal transmitting module 3 are integrated on the same laser radar main board 2 and used for receiving laser signals reflected by the target 1; the light path adjusting module 5 is arranged on a light path where the laser signal is located and used for adjusting the light path of the laser; the data processing module 6 is connected with the signal receiving module 4 and is used for analyzing and processing the laser signal reflected by the target 1.
It should be noted that the optical path where the laser signal is located refers to the optical path of the laser emitted by the signal emitting module 3 (the emitting optical path 31) and the optical path of the laser reflected by the target 1 (the reflecting optical path 41), that is, the optical path adjusting module 5 is simultaneously disposed on the emitting optical path 31 and the reflecting optical path 41, and adjusts the angle of the emitted laser and the angle of the reflected laser.
The embodiment of the utility model provides an in, signal transmission module 3 and signal reception module 4 are integrated on same laser radar mainboard 2, and to a great extent has simplified the structure of this laser radar device, has reduced current laser radar device's volume, has improved the integrated level, accords with current laser radar's miniaturized development trend. In addition, still be provided with light path adjusting module 5 on laser signal's light path, light path adjusting module 5 is provided with and helps adjusting the laser light path of launching and the laser light path of reflection back, and then has improved the high collimation nature when laser reaches target object 1 and gets into signal reception module 4, has improved the sensitivity and the precision of this laser radar device.
As an alternative implementation, in this embodiment, the signal emitting module 3 may be a Vertical Cavity Surface Emitting Laser (VCSEL) array.
The optical resonant cavity of the vertical cavity surface emitting laser is vertical to the substrate of the laser radar main board 2, laser emission on the surface of the laser radar main board 2 can be realized, and the vertical cavity surface emitting laser has the advantages of low threshold current, no Catastrophic Optical Damage (COD), long service life, stable single-wavelength work, high modulation rate, small divergence angle, low coupling efficiency and the like, and the light beam quality is far higher than that of an Edge Emitting Laser (EEL) and an LED, so that the vertical cavity surface emitting laser has higher application value in the technical fields of high-speed optical communication, laser radar, three-dimensional sensing and imaging and the like.
Therefore, the embodiment of the present invention provides a vertical cavity surface emitting laser array as the signal emitting module 3, which effectively enhances the performance of the signal emitting module 3.
As an alternative, in this embodiment, the signal receiving module 4 may be an Avalanche Photodiode (APD) array.
The Avalanche Photodiode (APD) has the advantages of high sensitivity, small volume, high speed and the like, the response waveband of the avalanche photodiode can reach 900nm-1700nm according to the selection of materials, the peak wavelength is 1550nm, and the avalanche photodiode is suitable for high-speed and high-sensitivity photoelectric detection and is widely applied to the field of long-distance optical communication.
The embodiment of the utility model provides an in adopt avalanche photodiode array as signal receiving module 4, be favorable to reducing the whole volume of laser radar device, realize the miniaturization to help improving this signal receiving module 4's sensitivity and response speed.
As an optional implementation manner, in this embodiment, the signal receiving modules 4 are distributed around the signal transmitting module 3 with the signal transmitting module 3 as a center. Specifically, the signal receiving module 4 may be distributed around the signal transmitting module 3 in a circular ring shape, or may be in a rectangular shape or other shapes, and may be set according to actual requirements. In this embodiment, the signal receiving modules 4 are preferably distributed in a circular ring shape.
The arrangement mode of the signal receiving module 4 and the signal transmitting module 3 is beneficial to enabling the signal receiving module 4 and the signal transmitting module 3 integrated on the same laser radar main board 2 to be compact in structure, the size of the whole laser radar device is reduced to the maximum extent, and miniaturization is achieved; on the other hand, the distribution rule of the laser emission light path 31 and the laser reflection light path 41 is met, and the detection effect of the laser radar is ensured.
Specifically, the laser reflected by the target 1 is easily dispersed and usually deviates from the original laser emitting optical path 31, that is, the reflection optical path 41 is usually distributed on the periphery of the emitting optical path 31, in this embodiment, the signal receiving module 4 is arranged on the periphery of the signal emitting module 3, that is, in order to adapt to the distribution rule of the reflection optical path 41, the reflected laser is received as much as possible, and the detection sensitivity is improved.
As an alternative embodiment, in this embodiment, the optical path adjusting module 5 includes a first lens assembly 51 with a convex surface facing the signal transmitting module 3, and a second lens assembly 52 with a convex surface facing the target 1. The orthographic projection of the first lens assembly 51 on the laser radar main board 2 coincides with the orthographic projection of the signal emitting module 3 on the laser radar main board 2, and the orthographic projection of the second lens assembly 52 on the laser radar main board 2 coincides with the orthographic projection of the signal receiving module 4 on the laser radar main board 2.
That is, the first lens assembly 51 corresponds to the signal emitting module 3 in position, that is, the first lens assembly 51 is disposed on the laser emitting optical path 31. After the signal emitting module 3 emits a laser signal, the laser beam is angle-corrected by the first lens assembly 51 to form parallel light, and then the parallel light is irradiated onto the target object 1. The second lens assembly 52 corresponds to the signal receiving module 4 in position, that is, the second lens assembly 52 is disposed on the laser reflection optical path 41. The laser reflected from the target 1 is collimated into the signal receiving module 4 after being angle-corrected by the second lens assembly 52. Thus, the arrangement of the first lens assembly 51 and the second lens assembly 52 significantly improves the collimation directivity and the luminous efficiency density of the outgoing light, and increases the probability, the optical intensity and the sensitivity of the reflected light entering the signal receiving module 4.
Meanwhile, the interference and noise caused by environment stray light to the detection process are avoided, and the anti-interference capability of the laser radar device is improved.
As an alternative embodiment, in the present embodiment, the first lens assembly 51 is a micro lens array, and the micro lens array is used for shaping the laser light emitted by the signal emitting module 3 into parallel light to be emitted to the target 1. The second lens component 52 is a micro lens array or a fresnel lens, and the micro lens array or the fresnel lens is used for shaping the laser light reflected by the target 1 into parallel light and transmitting the parallel light to the signal receiving module 4.
That is, the first lens assembly 51 and the second lens assembly 52 both use a microlens array, or the first lens assembly 51 uses a microlens array and the second lens assembly 52 uses a fresnel lens. The setting mode is comparatively nimble, can set up according to the actual demand. The micro-lens array has the advantages of low cost, wide application, light and thin Fresnel lens and good light condensation effect.
It should be noted that when the second lens component 52 is a fresnel lens, it means that the peripheral ring structure of the fresnel lens is selected instead of the entire fresnel lens structure. That is, the optical path adjusting module 5 in this embodiment is an entire fresnel lens structure, but the center of the fresnel lens structure does not use a conventional convex lens, but uses a microlens array.
Compared with the traditional laser radar device, the embodiment of the utility model provides a divergent light shaping that the laser radar device launches through the microlens array is the parallel light for the vast majority of light can shine to the target object, and has improved the proportion of the laser that is reflected back by the target object; laser shaping reflected by a target object is transmitted to the signal receiving module in a parallel mode through the micro-lens array or the Fresnel lens, most of laser reflected can be received by the signal receiving module, the utilization rate of the laser is effectively improved, meanwhile, the power of the laser radar device is reduced, and the power consumption is reduced.
As an optional implementation manner, in this embodiment, the wavelength of the laser signal is greater than or equal to 1400 nm. According to the research of human eye physiology and optical structure, the light with the wavelength of more than or equal to 1400nm can not be transmitted into retina, and the human eye can not be damaged even if higher power output is adopted. Therefore, the long-wavelength signal emitting module 3 with the wavelength of more than or equal to 1400nm is used as a laser light source, and the longer detection distance, the higher resolution and the higher safety can be realized.
Specifically, in the present embodiment, the wavelength of the laser signal is preferably 1550 nm. This is because the 1550nm laser is an important light source for free space optical communication (FSO), and can be transmitted in air for a long distance, which is beneficial to eliminate the adverse weather effect and avoid the damage to human eyes.
As an alternative implementation, in this embodiment, the data processing module 6 includes a signal conversion sub-module 61 and a data processing sub-module 62. The signal conversion sub-module 61 is connected to the signal receiving module 4, and is configured to convert the received laser signal reflected by the target 1 into an electrical signal. The data processing submodule 62 is connected to the signal conversion submodule 61, and is configured to process the electrical signal obtained by the signal conversion submodule 61, so as to obtain data such as a distance, a relative speed, and a spatial position relationship between the target object and the laser radar apparatus.
As an optional implementation manner, in this embodiment, the signal conversion sub-module 61 and the data processing sub-module 62 are integrated on the laser radar main board 2 where the signal transmitting module 3 and the signal receiving module 4 are located.
As an optional implementation manner, in this embodiment, the data processing module 6 further includes an image generating module 63 and an output module 64. The image generating module 63 is connected to the data processing module 6, and generates an image signal according to an analysis result of the data processing module 6, where the image signal may be a three-dimensional image or a two-dimensional image. The output module 64 is connected to the image generating module 63, and is configured to output the image signal generated by the image generating module 63 to the terminal 9, where the terminal 9 may be any type of mobile display terminal 9 such as a mobile phone, a tablet computer, and a vehicle-mounted television.
As an optional implementation manner, in this embodiment, the image generation module 63 and the output module 64 are both integrated on the laser radar main board 2 where the signal transmission module 3 and the signal reception module 4 are located.
As an optional implementation manner, in this embodiment, the laser radar apparatus provided in the embodiment of the present invention further includes a control module 7 and a timing module 8. The control module 7 and the time sequence module 8 are both connected with the signal transmitting module 3, the time sequence module 8 is used for generating time sequence pulse signals, and the control module 7 controls the signal transmitting module 3 to generate picosecond-level pulse laser signals according to the time sequence pulse signals and irradiates the target object 1.
As an optional implementation manner, in this embodiment, the control module 7 and the timing module 8 are both integrated on the laser radar main board 2 where the signal transmitting module 3 and the signal receiving module 4 are located.
Example 2
An embodiment of the utility model provides a laser radar system, including the laser radar device and the scanning control device that above-mentioned embodiment 1 provided, scanning control device is connected with the laser radar device. The scanning control device is used for adjusting the deflection direction of the laser radar device. In this embodiment, the scanning control device is preferably a small motor, and the fine adjustment of the deflection direction of the laser radar device is performed by the small motor. Therefore, the laser radar device can emit laser towards different directions, the scanning function is realized, and the road condition and the surrounding environment can be detected and identified on a large scale.
As shown in fig. 3, the scanning control device controls the laser radar device to deflect, so as to scan positions right in front of the vehicle, left in front of the vehicle, right in front of the vehicle, above the vehicle, below the vehicle, and the like, and further realize large-scale detection and identification of road conditions and surrounding environments.
It should be noted that, except for the small motor, other devices capable of achieving fine adjustment of the direction are all suitable for the present invention, which belongs to the protection scope of the present invention.
For a specific structure of the lidar device, please refer to embodiment 1, which is not described herein.
In addition, when the laser radar system is applied specifically, it can be respectively disposed at various positions of a vehicle, an airplane, a ship, an industrial robot, a home service robot, or the like. For example, in fig. 3, a plurality of laser radar systems may be disposed on the vehicle, so as to scan positions right in front of the vehicle, left in front of the vehicle, right in front of the vehicle, above the vehicle, below the vehicle, and so on, and to perform all-around detection and identification on road conditions and objects in the environment in the vehicle driving direction.
It should be noted that, when a plurality of laser radar systems are installed on a vehicle, all-directional detection and identification can be achieved, and at this time, the scanning control device in each laser radar system can drive the laser radar device to further scan, so as to expand the detection range, or the laser radar device may not be driven to scan.
As an optional implementation manner, in this embodiment, a MEMS micro-oscillating mirror is further disposed in the laser radar apparatus, and the MEMS micro-oscillating mirror is disposed on a transmission light path of the laser radar apparatus. Therefore, the laser radar device can realize the scanning function under the action of the MEMS micro-vibrating mirror, and is beneficial to detecting and identifying road conditions and surrounding environments in a large range.
It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications can be made without departing from the scope of the invention.