A new generation of computer-controlled devices is poised to revolutionise material handling operations across the industrial landscape. Intelligent assist devices (IADs) enable a unique collaboration of humans and machines to bring greater levels of productivity, quality, and ergonomic safety to manual operations. Using sophisticated sensors, controls, and proven servo motor technology, IADs allow operators to manipulate and position loads with speed, precision, and ease.
Conventional ergonomic assist equipment is actuated by pressing buttons to control either pneumatic or fixed-speed electric devices. Although these traditional devices have a positive impact on ergonomic safety, they have not been associated with productivity improvements. For applications requiring rapid and accurate movement, they are awkward, slow, and do not take advantage of the natural human ability to coordinate and control motion. In practice, over-travel, bounce, and multiple corrective movements add to cycle time and reduce productivity. The lack of intuitive and responsive control also results in product damage and cumulative trauma injuries. The latter occurs when people force the equipment, or when the frustration of working with unresponsive equipment leads them to put it aside.
In response to these problems, a small group of engineers from the auto industry and academia (including the authors) invented IADs in the mid-1990s. The initial idea was straightforward:
use computer-enabled motion control technology to enhance human capabilities. Today, IADs assist their human partners many ways, including power assist, motion guidance, line-tracking, and semi-automation.
Z-axis lift
An IAD may have only a single axis, several that work independently, or several that work in coordinated motion. IADs may be classified by their axes of motion (see Figure 2). The axes are denoted X and Y (lateral motions), Z (vertical), roll, pitch, and yaw.
An example of a single-axis IAD is the Z-axis electric lifting and balancing unit (see Figure 4). Z-lifts offer a number of key advances over air balancers and hoists, including improved speed, more intuitive control, greater precision, and the ability to program semi-autonomous behaviours.
Two kinds of controls may be offered with Z-lifts: an in-line force sensing handle and a pendant grip. Both devices allow extremely fine control of up/down speed, regardless of payload weight. Proportional control allows smooth and efficient motion, eliminating the need for feathering (rapidly cycling a control button to achieve small motions) that is common to pneumatic and single-speed electric systems.
Some Z-lifts offer another control mode known as ‘float’ or ‘hands-on-payload’ mode, in which no handle or grip is needed. Float mode is an advance over the ‘balance’ operation of some pneumatic lifts, offering two key advantages.
First, the device automatically ‘learns’ the payload weight, so it can balance any load up to its rated capacity, not just one or two preset weights. A second advantage is that the Z-lift can detect and respond to very small operator forces exerted up or down on the payload. As such, the Z-lift requires less operator force and responds without the noticeable delay found with pneumatic balancers. Equally important, Z-lifts allow precise positioning by eliminating impacts caused by the bounce in pneumatic balancers, and the single speed of traditional electric devices.
Some Z-lifts are also programmable. Basic features include up/down motion limits, a gripper interlock, and user profiles that set the sensitivity and speed for individual operators. Some Z-lifts offer a built-in PLC-type logic function that system integrators can use to solve task-specific control issues.
Examples include auxiliary clamp buttons, remote emergency stop, solenoid actuation on the end effector, and proximity sensors interlocked with clamping functions.
Intelligent rail system
While a Z-lift is a good illustration of the functionality that can be packed into a single-axis IAD, an intelligent rail system provides an illustration of how multiple axes can work together (see Figure 1).
Intelligent rail systems address problems associated with traditional overhead cranes and lift assists. While traditional devices can minimise lower back injuries caused by lifting, they can cause injuries to the shoulder, arm, and upper back. Such injuries occur because of the pushing, pulling and twisting forces required to start, stop and redirect the mass of traditional overhead cranes. Additionally, the time required to accelerate and decelerate the overhead mass increases cycle times, especially when precise positioning is required.
An intelligent rail system uses servo-controlled trolleys to power the motion of the overhead crane, so that the operator need only indicate the direction he wishes to move, and the system provides the force to accelerate and decelerate the crane. Either one or two axes can be powered, according to need.
In the case of a cable-suspended load, a sensor detects deviations of the cable from the vertical position and uses this information to control the trolleys. There are no pushbuttons; the IAD moves in response to the operator pushing on the payload. The net effect is that the mass of the overhead structure is masked, eliminating inertia and momentum. The system tracks the operator’s motion, allowing him or her to focus on the positioning task. Not only is starting and stopping much easier for the operator, but, in a two-axis system, it is just as easy to move the load in one direction as another. This is in sharp contrast to conventional bridge crane rail systems where it is more difficult to move the bridge itself than move along the bridge.
In the case of a rigid system such as a manipulator arm, a multi-axis force sensor is used to detect operator intent and apply this information to control the drive units (see Figure 2). The net effect is that the mass of the entire load (including the overhead structure, the manipulator arm, and the payload) is masked from the operator, eliminating the harmful effects of inertia and momentum. Like the Z-lift, intelligent rail systems are programmable. Motion limits can be established for each powered axis, user profiles can be set, and advanced PLC-level functions are available.
Multi-axis IADs, virtual surfaces and semi-autonomy
IADs are capable of a much higher level of functionality using what are known as ‘virtual surfaces’. Virtual surfaces are so named because they are defined in software, but their effects are quite real.
As illustrated in Figure 3, they can be used to guide operator and payload motion while preventing unwanted impacts. Virtual surfaces can improve productivity and ergonomics as well.
By way of analogy, consider the familiar task of drawing a straight line on a piece of paper. While possible to do freehand, the task is done much faster and better with a ruler. Virtual surfaces are like rulers, only multi-dimensional, and most importantly, user-programmable.
An example of a virtual surface application is loading seats in vehicles. As the operator approaches the vehicle, payload motion is guided such that the seats pass through a virtual window aligned with the opening in the side of the vehicle.
This feature automatically adjusts the load to the proper height and prevents damage caused by accidental impact with the painted surfaces or interior trim. The system also provides line tracking, or synchronisation, to keep the virtual window lined up with the moving vehicle.
Multi-axis IADs can also be programmed to perform semi-autonomous functions such as returning to a home or loading position, automatically retrieving a new part, or synchronising with a moving assembly line.
Semi-autonomous operations allow the operator to focus on value-added tasks, while the IAD takes over routine movements.
Multi-axis IADs are ideally suited for the assembly of large components, such as automobile instrument panels, which require both precise handling and secondary assembly operations such as inserting fasteners and connecting wire harnesses. While some elements of such tasks would benefit from the precision and speed of automation, other elements (like connecting wire harnesses) require the dexterity and intelligence of human operators.
Other benefits
Because IADs employ the power of advanced computers, they can provide many ancillary benefits such as:
• Data logging
IADs can log process variables such as the number of cycles, average cycle time, average weight lifted, cumulative weight lifted, and total distance travelled.
• Error-proofing
IADs can be programmed to assist operators by error-proofing tasks. Examples include weighing a case of standard products and indicating if one is not filled, or prohibiting the movement of a part into the storage area designated for another part.
• Preventive and predictive maintenance
IADs have the ability to send email messages to plant maintenance personnel when routine maintenance is required. Additionally, they can notify personnel in the event of fault conditions.
Underlying technology
IAD technology owes a debt to various university and government research programmes in the areas of remote manipulation and haptics – the use of force-feedback to let a person work with a machine in a natural and intuitive manner. Like those disciplines, IAD technology operates on the basis of:
• sensing the intent of the human operator
• processing that intent through sophisticated control algorithms, running on industrially hardened computers
• causing payload motion based on the controller output.
IADs are commercially viable today largely because these three steps have become increasingly cost-effective. Novel and inexpensive human intent sensors have been developed, the cost of embedded computing has dropped dramatically, and increasing levels of automation have led to more cost-effective servo motors.
Safety
Unlike robots, which move according to their own programmed instructions, IADs respond to real-time, human intent. Like any powered machinery, safety is a paramount concern in design, installation, and operation. IADs are subject to a safety standard created in recognition of the unique coexistence of a human and computer-controlled machine in the same work cell. The ASC T15 safety standard for intelligent assist devices, developed by a Robotics Industries Association committee, is expected to become an ANSI standard in the near future. The standard covers dynamic limits, safety circuits, clarity of communication between operator and IAD, and risk assessment procedures.
System integration
Unlike automated systems, IADs generally do not require sophisticated sensors such as vision systems, high levels of precision, or expensive tooling. Instead, IADs leverage human perception and intelligence, capabilities that are difficult or expensive to capture with machines. An additional benefit is strong worker acceptance, because IADs help human workers rather than replace them.
IADs, such as Z-Lifts, can work directly ‘out of the box’, with installation similar to that of a conventional hoist or balancer. To fully exploit the programmable features of an IAD, some degree of set-up is required. Basic features such as setting an interlock weight can generally be accessed using pushbuttons on the IAD itself. More sophisticated features, such as tuning a user profile or logic programming, can be accomplished with easy-to-use graphical interface programmes on a laptop computer.
Physical integration of IADs is quite similar to the integration of conventional assists, although pneumatic supply and logic hoses tend to be replaced by electric power and signal lines. A well-designed IAD will provide power and logic connections for system integrator use, minimising the need for additional electronic enclosures. Also, a well-designed IAD can be installed on existing enclosed-track rail systems, thereby allowing easy retrofitting and simple, familiar installation.
Lasting impact
lADs are powerful tools for productivity, quality and safety. By combining the unmatched human ability to coordinate motion and adapt to changing circumstances, with the strength and precision of industrial machinery, IADs will forever change materials handling.
