Mechanical grape harvesters typically use one of two types of picking head: 1) a bow rod shaker; or 2) a trunk shaker. Each has advantages and disadvantages.
Bow rod shakers incorporate loops or "bows" that strike the vine canopy and shake loose the berries. These harvesters are sometimes referred to as canopy or foliage shakers. An example of the interior of a bow rod harvester is shown in Figure 2 of The Wine Group's patent (described further, below):
Such picking heads are used where the cordons are young and might be damaged by a trunk shaker, or where the fruit is further removed from the permanent vine structure.
Trunk shakers, as the name implies, impart vibration to the cordon or upper trunk of the vine. This is typically accomplished with a set of parallel, shaking rails. These picking heads are best suited for more sturdy vines, and for dislodging fruit close to the rigid trunk of the plant.
Why Convert Between Picking Heads?
Because each style of picking head has advantages and disadvantages, and is better suited for use with certain plants depending on age or other characteristics, it makes sense for a fruit producer to have both types of device. This carries with it the associated cost of acquiring both types of machinery, as well as the maintenance and upkeep costs associated with having both. Being able to convert between picking heads on a single device should address some of those costs.
U.S. Patent No. 9,549,502
Enter The Wine Group, Inc., and their patent entitled "Conversion Method of Harvester Picking Head." The patent issued on January 24, 2017, and has one independent claim. In simple terms, the method includes the steps of decoupling the plurality of bow rods used in the bow rod shaker head from both first and second oscillating members, coupling a shaker rail to each of the oscillating members, and replacing the picking head drive element to increase the torque on one of the vertical shafts for use with the trunk shaker configuration.
To get the full details, take a look at the patent here.