This invention relates generally to the field of systems and devices used to align or provide an indication to the operator of the location of the forks on a forklift relative to the access openings in a pallet or the like, such that the operator knows when the forks are at the correct height for entry into the access openings. More particularly, the invention relates to such systems which utilize visible light means to provide a visual indicator to the forklift operator.
Forklifts or similar load handling equipment are designed to handle pallets and the like by inserting a pair of forks or tines into access openings provided between opposing deck members or the pallet legs for a single deck pallet. The forks are mounted in parallel on a carriage which can be raised or lowered vertically, and usually also tilted slightly, with the forks extending typically a distance four feet forward from the carriage. The front of each fork is tapered or beveled to allow for a small margin of error during the insertion process. Because it is usually desirable to minimize the amount of floor space taken up by stored goods, warehouses are provided with high ceilings and forklifts are designed to raise loads many feet off the ground such that multiple pallets can be stored in a vertical column. Thus, even though the operator is seated on the forklift itself and is therefore a few feet above ground level, the load may need to be deposited onto or retrieved from a stack, rack or shelf many feet above the operator""s head. Because of this, the operator cannot easily determine if the forks are at the optimum height prior to advancing forward to retrieve or deposit the load onto the stack, rack or shelf. Adding to the is problem is the fact that the load itself may block the operator""s line of sight. Thus operators are forced to estimate the correct height of the forks, then slowly advance the forks forward to determine, either by striking the shelf or rack when depositing, or by striking the shelf, rack, pallet or the load itself when retrieving, that the forks are misaligned. This technique can result in damage to the pallets or loads and to the shelves or racks.
There have been attempts made to address the problem of fork misalignment, for instance by providing visual indicators or intelligent alignment systems. For example, Ohntrup et al. in U.S. Pat. No. 3,672,470, issued on Jun. 27, 1972, teaches the use of a photoelectric system wherein a light source and a light sensor is mounted onto the fork. The sensor is designed to detect the difference in reflected light from a solid object versus reflected light from the access openings in the pallet, such that when the latter is detected a visible light indicator is turned on for the operator to indicate that the forks are properly aligned. This system is susceptible to false readings due to ambient light conditions, since strong or weak warehouse illumination may alter the sensitivity of the sensor. Furthermore, Ohntrup et al. teaches mounting the light source and light sensor within or onto the fork itself, which is undesirable in that the light source and light sensor can be easily damaged form routine use of the forklift. An example of a visible light system is taught by Hansen in U.S. Pat. No. 3,854,820, issued Dec. 17, 1974, where a light source capable of producing a collimated beam of light is mounted laterally onto each side of the forklift carriage, with the light beam projected through prisms to produce a fan-shaped or diverging plane of light. As with the Ohntrup et al. device, the exposed mounting of the light source leaves it susceptible to damage. Another drawback to the Hansen device is that the visual indicators are located to the outside of each fork, such that only a small amount if any of the light falls onto the actual pallet to be removed, with most of the light striking the shelving or pallets to either side of the target pallet. Thus the operator is forced to interpret the visual information and must check the visual indicators to both sides of the forks to determine if they are properly aligned. Complicated forklift alignment systems using cameras and microprocessors are shown in U.S. Pat. No. 4,279,328, issued Jul. 21, 1981 to Ahlbom, and in U.S. Pat. No. 5,208,753, issued May 4, 1993 to Acuff.
It is an object of this invention to provide a relatively simple system for assuring proper alignment of forklift forks, where a visible light indicator is provided to the operator, the light indicator being a focused dot or other shape produced by a controlled beam striking an opaque object. It is a further object to provide such a system where the light source is mounted in a manner which makes it less susceptible to accidental damage. It is a further object to provide such a system where the visible light indicator is a visible laser beam which is preferably centrally oriented relative to the forks. It is a further object to provide such a system which incorporates various safety features to minimize or eliminate possible damage to people from inadvertent exposure to the beam from the light source, and in particular a laser beam, by incorporating vibration-responsive, height-responsive and distance-to-load-responsive actuation means. It is a further object to provide such a system which incorporates various safety features to minimize or eliminate possible damage to the system itself, such as from excessively high or low ambient temperatures, by incorporating temperature-responsive actuation means.
The invention is in general an apparatus, device or system for providing a visual indication to a forklift operator of proper vertical alignment of the forks or tines of the forklift relative to the access openings designed to receive the forks of a pallet or like device for supporting a load, which may consist of a single or multiple objects, boxes or the like, even where the proper alignment occurs many feet above the operator""s head. The system comprises in general means to produce a relatively focused or controlled beam of visible light, preferably produced by a laser, where the beam is forwardly directly between the forks in a generally horizontal plane common to the forks themselves, such that the height of the forks is indicated by the height and location of the visible indicator, a dot or the like, produced by the beam when it strikes an object, such as a pallet, shelf or rack, or the load on the pallet, or by it disappearing into the void created by the pallet access opening. By raising or lowering the fork carriage such that the light beam strikes the middle support or a midpoint in the central leg of a single-deck member pallet, or by observing when the light indicator or spot produced by the beam disappears as it is directed into the access opening of the pallet, the operator is provided a visual indication that the forks are properly oriented relative to the pallet. Conversely, if the spot produced by the beam appears on the load, the shelf or the upper or lower portion of the pallet, the operator knows that the forks are improperly aligned and can raise or lower them accordingly before moving forward to insert the forks into the pallet.
The apparatus is mounted onto the carriage to which the forks are mounted in a manner such that the beam is emitted at a height equal to the vertical midpoint of the forks and at some point between the forks, preferably at the lateral midpoint between the forks, whereby the apparatus itself is raised or lowered correspondingly with the forks. The forward extension of the apparatus is minimized such that it does not extend forward beyond the vertical brace stop members, where the combination of the vertical brace stop members and the forks themselves are relatively L-shaped, or beyond the forward side of the carriage where the carriage itself acts as the vertical component limiting load movement in the rearward horizontal direction. Preferably, the apparatus comprises a vertically elongated battery housing containing one or more rechargeable batteries with a laser housing containing the laser producing components affixed to the bottom of the battery housing. Brackets are joined at the upper and lower ends of the battery housing for securing the apparatus by mechanical fasteners to the carriage of the fork lift.
Preferably, the apparatus is equipped with one or more safety features to reduce or prevent danger to personnel and to the beam producing means. The apparatus may comprise vibration-responsive actuation means, whereby the beam producing means is not operational unless the forklift is in motion or vibrations from the forklift motor are sensed. The apparatus may comprise height-responsive actuation means, whereby the beam producing means is not operational unless the apparatus is raised above a predetermined minimal distance from the floor. The apparatus may comprise distance-to-load-responsive actuation means, whereby the beam producing means is not operational unless the apparatus is closer than a predetermined maximum distance from the load, or within a predetermined maximum and minimum distance from the load. The apparatus may comprise temperature-responsive actuation means, whereby the beam producing means is only operational at temperatures below a predetermined maximum temperature, at temperatures above a predetermined minimum temperature, or within the range between the maximum and minimum temperatures.