In quarries and other types of payload material collection sites, mobile loaders, such as wheel loaders, backhoe loaders, and track type loaders are used to load loose payload material into haul vehicles, such as over the road trucks. Payload information, including the desired type and amount of payload material for each truck needs to be communicated to the quarry personnel who operate the loaders. For instance, this information might be transmitted from a quarry office based computer to a mobile computer on the loader via wireless communication as described in co-owned U.S. Pat. No. 5,848,368. This information enables the loader operator to proceed to the correct pile corresponding to the requested material.
A typical work cycle can begin with the operator first positioning the bucket of the loader at a pile of the requested material. The bucket is then lowered so that the work implement is near the ground surface. The operator then advances into the pile and controls the bucket to raise the work implement through the pile to fill the bucket and lift the material. The operator then tilts or pitches the bucket back to capture the material. The operator then moves the loader to a desired target location, such as an over the road truck, and dumps the captured material from the bucket. The operator then moves the loader back to the pile to start this work cycle over again. In the case of typical over the road trucks, depending upon their size, a full load will typically require between three and six bucket loads to fill the truck with the desired material up to a target load weight.
Many of today's loaders have payload control systems that allow for accurate measurements of the bucket payload. Thus, with each successive bucket, the loader can sum the load weight of the bucket loads to determine an estimated amount of payload already in the truck. Typically, on a final pass of the truck loading cycle, the loader adds less than a full bucket payload to the truck in a process known as tip-off.
There are two approaches to tip-off. One approach is to load the bucket at the pile and use in-vehicle sensors to determine the load in the bucket and tip-off the excess amount at the pile, leaving in the bucket the amount needed at the road truck. This is known as pile tip-off. Another approach is to rack the bucket and partially empty the bucket into the road truck to reach the target road truck capacity, known as truck tip-off.
Because the loader can keep track of how much material, by weight, has been added to the road truck it is important that the loader know what type of tip-off was used. In pile tip-off, the amount remaining in the bucket will be added to the truck load. In truck tip-off, the amount off-loaded will be added to the truck load. In many cases, the final truck payload determines both the sale price of the payload, but may also be used to calculate incentives for the loader operator.
Co-owned U.S. Pat. No. 6,211,471 describes a process that reweighs material in the bucket after the operator performs a partial dump. However, in practice, operators must first pre-set what type of tip-off is being used (pile vs. truck) and then explicitly indicate that they are about to perform a tip-off. This raises several potential issues. If the type of tip-off is incorrect, the load delivered to the truck will be incorrectly calculated, with a potential financial impact. If the operator forgets to indicate a tip-off, the load also may be incorrectly calculated and may require re-weighing or even reloading. In addition, there is a safety concern because the operator must remove his or her hand from the controls to push the tip-off button each time a tip-off is performed. This continuous attention to tip-off setting and the physical motions associated with may, over a period of time, increase operator fatigue.