nonlinearities of the hydraulic servo systems were considered negligible allowing the design of

controllers based on common linear techniques as previously described.


 Performance Specifications

 According to Lau et al. (1988), a robot's performance is measured by its ability to

perform a task. Performance measurements are those general operating characteristics that are

important for determining the robot's suitability for a given task. The performance for

industrial robots is usually specified in terms of accuracy, repeatability, positioning resolution,

and speed. These measurements were also defined by Ranky and Wodzinski (1988), who also

presented very precise methods for determining each of them.

 These performance measurements prove sufficient for industrial robots which operate in

a structured environment. However, in the unpredictable environment found in agricultural

operations, these methods of performance evaluation have little significance. The ultimate

performance measurement is that of determining the robot's suitability for its intended

operation. Because the location of each fruit in the tree is different, the accuracy and

repeatability of the robot were not pertinent. Performance requirements and evaluation

methods for robots which operate in unstructured environments are much more difficult to

assess. Evaluation of the control strategies for the citrus-picking robot made evident the need

for performance criteria for this specific task.