Electric Drives Linear Motion and and Controls Hydraulics Assembly Technologies Pneumatics Service profile Drive & Control How “LOSTPED” Can Help With Sizing and Selecting Linear Motion Systems

What is LOSTPED? Load. The weight or force applied to the system

Orientation. The relative position or direction in which the force is applied

Speed. Speed and acceleration

Travel. The distance or range of motion

Precision. Travel accuracy, LOSTPED is a simple acronym to help specify linear motion components. positioning accuracy, repeatability, accuracy of the Virtually all manufacturing systems is to overlook critical return position at the end of a processes incorporate some application requirements in the stroke type of linear motion. As final system. This can lead to manufacturers become familiar costly redesigns and re-works Environment. The surrounding with the flexibility and simplicity but may also result in an over- conditions in which the system of modular linear motion systems, engineered system that is more will operate these systems—whether one, two costly and less effective than or complete three-axis Cartesian desired. With so many possible Duty Cycle. The amount of robotics systems—are finding solutions, it’s easy to become time it takes to complete a cycle their way into more areas of overwhelmed when tasked with of operation production. designing a linear motion system. How much load will the system A common mistake that engineers need to handle? How fast will and designers make when sizing it need to move. What is the and selecting linear motion most cost-effective design? All of these questions and more questions to ask when determining were considered when Bosch the criteria to size and select a Rexroth’s Linear Motion and linear motion system. Assembly Technologies group developed “LOSTPED”— a LOAD simple acronym that guides the Load refers to the weight or force engineer or designer in gathering applied to the system. All linear the information needed to specify motion systems encounter some the appropriate linear motion Rexroth CKK and CKR Compact modules type of load, such as downward components or modules in any are frequently used in applications forces in material handling given application. requiring side-mounted loads. applications or thrust loads in drilling, pressing or screw driving What Is LOSTPED? solutions move from individual applications. Other applications LOSTPED is an acronym that components to complete linear encounter a constant load, such as stands for Load, Orientation, module or Cartesian systems, a semiconductor wafer-handling Speed, Travel, Precision, the interactions between system application, in which a FOUP Environment and Duty cycle. components — i.e. linear bearing (Front-Opening Unified Pod) Each letter represents one factor guides and ball screw, belt, or is carried from bay to bay for that must be considered when linear motor drives — become drop-off and pick-up. A third sizing and selecting a linear more complex, and designing type is defined by varying loads, motion system. Each factor must the right system becomes more such as a medical dispensing be considered individually as well challenging. The LOSTPED application, where reagent is as in conjunction with the others acronym can help designers avoid deposited in a series of pipettes to ensure the best overall system mistakes by simply reminding one after another, resulting in performance. For example, the them to consider all of the a lighter load at each step. load imposes different demands interrelated factors during system on the bearing system during development and specification. While considering load, it’s also acceleration and deceleration worth taking a look at what type than during constant speed move- How to Use LOSTPED of tool will be at the end of the ments. As more linear motion Below are descriptions of each arm to pick up or carry the load. LOSTPED factor, as well as key Although not specifically related to load, mistakes here can be costly. For example, if a highly sensitive workpiece is picked up in a pick- and-place application, it may be damaged if the wrong type of gripper is used. So although it’s highly unlikely that a designer would forget to consider general system load requirements, he or she may indeed forget to consider certain aspects of those requirements. LOSTPED is a way to ensure completeness.

KEY QUESTIONS TO ASK: • What is the source of the load and Speed and acceleration also affect the selection of a linear motion system. how is it oriented? KEY QUESTIONS TO ASK: best address the speed and • How is the linear module or acceleration needs? actuator oriented? • Is it horizontal, vertical or TRAVEL upside down? Travel refers to the distance • Where is the load oriented relative or range of motion. Not only to the linear module? must the travel distance be • Will the load cause a roll or pitch considered, but also overtravel. moment on the linear module? Allowing some amount of “safety travel,” or additional SPEED space, at the end of the stroke Speed and acceleration also ensures the safety of the system affect the selection of a linear Which linear drive will best address the in case of an emergency stop. speed and acceleration needs? motion system. An applied load creates far different forces on the KEY QUESTIONS TO ASK: system during acceleration and • What is the distance or range • Are there special handling deceleration than it does during of motion? considerations? a constant speed movement. The • How much over travel may be • How much weight or force must type of move profile — trapezoidal required in an emergency stop? be managed? or triangular — must also be • Is the force a downward force, considered, as the acceleration PRECISION lift-off force or side force? required to meet the desired speed Precision is a broad term that is or cycle time will be determined often used to define either travel ORIENTATION by the type of move required. A accuracy (how the system behaves The orientation, or relative position trapezoidal move profile means while moving from point A to or direction in which the force is that the load accelerates quickly, point B), or positioning accuracy applied, is also important but often moves at relatively constant (how closely the system reaches overlooked. Some types of linear speed for a period of time, and the target position). It can also modules or actuators can handle then slows down. A triangular refer to repeatability, or how well higher downward/upward loading move profile means the load the system moves back to the same than side loading because of the accelerates and decelerates quickly, position at the end of each stroke. linear guide system used in the as in point-to-point pick-up and Understanding the difference module design. Other modules, drop-off applications. Speed and between these three terms — travel using different linear guides, acceleration are also critical factors accuracy, positioning accuracy, can handle the same loads in all in determining the appropriate and repeatability — is often directions. The Rexroth Compact linear drive, which is typically a critical to ensuring the system Module CKK, for example, uses a ball screw, a belt, or a linear motor. meets the performance dual Ball Rail System for guidance specifications and that the and is called upon frequently KEY QUESTIONS TO ASK: system is not overcompensating in applications requiring side- • What speed or cycle time must for a high degree of accuracy mounted, or axial, loads. Since be achieved? that may be unnecessary. most high-quality linear motion • Is it a constant speed or suppliers make modules and variable speed? But the main reason to think actuators to handle various • How will the load impact through the precision requirements situations, it’s important to make acceleration and deceleration? is drive-mechanism selection: belt sure that the modules specified can • Is the move profile trapezoidal drive, ball screw, or linear motor. handle the load requirements in or triangular? Each type offers trade-offs between the orientation needed to achieve • Which linear drive will precision, speed, and load-carrying success in the application.