© Magazino

Mobile, Safe Robots

Indus­trial intral­o­gis­tics is an area that is increas­ingly suffering from the shortage of skilled workers, caused by demo­graphic changes. It is often diffi­cult to find personnel to trans­port mate­rials back and forth on a regular basis, espe­cially if they need to work night shifts. Auto­mated guided vehi­cles (AGVs) are not only capable of solving this problem, they can also make trans­port work­flows and, ulti­mately, manu­fac­turing processes as a whole more effi­cient.


To do so, however, they need to bring a lot to the table – they must be intel­li­gent, robust, and maneu­ver­able; they must be able to trans­port high loads; and, of course, they need to guar­antee the safety of everyone in the surrounding area. This also places high demands on the drive tech­nology used in these AGVs.

In order to bridge the gap between auto­mated ware­houses and auto­mated Produc­tion depart­ments, Maga­zino has devel­oped the mobile logis­tics robot SOTO (Fig. 1), which intel­li­gently handles and trans­ports SLCs (small load carriers) in ware­house and produc­tion envi­ron­ments. The special feature of this robot is that it takes SLCs from passive shelves (i.e., shelves without any conveyor elements) as from heights of 400 mm (Fig. 2).

In total, it can trans­port up to 24 SLCs (300 x 200 / 400 x 300 / 600 x 400 mm) with a maximum payload of between 200 and 249 kg. With a trans­port height of 2160 mm and a virtual foot­print of 2500 x 1310 mm, the robot fits through aisles with a width of 1650 mm. It can be deployed by itself or as a fleet in both brown­field and green­field appli­ca­tions. SOTO brings mate­rials directly to the assembly line according to the just-in-time prin­ciple. Its built-in “intel­li­gence” enables it to complete trans­port tasks inde­pen­dently, even complex ones, and react flex­ibly to changes in the surrounding area or changing require­ments. It can completely replace tugger trains or work effec­tively with them. SOTO is typi­cally deployed in auto­mo­tive and elec­tronics produc­tion envi­ron­ments or around injec­tion molding equip­ment, for example.

200-249 kg

payload

24

SLCs

2160 mm

trans­port height

When devel­oping the mobile robots, the experts invested a lot of time in selecting, thor­oughly testing, and comparing poten­tial drive units. The second version of the robot is now avail­able, and it relies on the ArgoDrive driving steering drive from ebm-papst because it was the best at meeting the various appli­ca­tion require­ments (Fig. 3).

ArgoDrive: the driving steering system for AGVs

A flex­ible and robust drive

Ware­house logis­tics areas and produc­tion envi­ron­ments both have one thing in common: Space equals money. When it comes to autonomous robots, this means that they have to navi­gate flex­ibly in tight spaces. This, in turn, calls for drive units which enable the robot to make omni­di­rec­tional move­ments (Fig. 4). With ArgoDrive, each drive unit consists of two brush­less DC motors, trans­mis­sion, the corre­sponding safety sensors, and all the neces­sary connec­tion plugs. Thanks to a super­po­si­tion gear, the two motors contribute to steering, driving, accel­er­a­tion, or braking, depending on what is required at the time. This gives the robot an infi­nite steering angle which enables it to make omni­di­rec­tional move­ments, even from a stationary posi­tion. As a result, the mobile robot can navi­gate safely in tight spaces, move to the exact pick-up and set-down posi­tions, and make adjust­ments on the spot to ensure accu­rate posi­tioning (e.g., when entering the charging station). In addi­tion, the driving steering system ensures that the avail­able space is opti­mally used and that the robot can flex­ibly avoid people or other vehi­cles in tight spaces.

Fig. 2a,b: SOTO can take SLCs from passive shelves …

… and trans­port them just-in-time to the assembly line. (Images | Maga­zino)

Robust­ness was another key require­ment because compo­nents that are installed in a moving envi­ron­ment are always exposed to vibra­tions and other forces. All the neces­sary connecting cables of the drive unit are there­fore perma­nently fixed in place, which prevents annoying prob­lems with the contact points while the robot is in use. Weak contacts are currently the number 1 reason why auto­mated guided vehi­cles fail. 

Compact design

Fig. 3: The ArgoDrive driving steering system from ebm-papst for use in auto­mated guided vehi­cles. In the Light, Stan­dard, and Heavy versions, it can move loads of up to 100 kg, 300 kg, or 500 kg per drive unit. (Image | ebm-papst)

Magnus Eldevik (Fig. 5), Product Marketing Manager at Maga­zino, is delighted with the drive’s compact design: “Because ArgoDrive has such a flat design, we have achieved a low grip­ping height of just 400 mm, ensuring that expen­sive storage space can be used as effi­ciently as possible. Compact drives also mean more space for grip­pers or the payload – and the higher the payload, the more effi­cient the mobile robot ulti­mately is.” The driving steering system is avail­able in different models: Light (up to 100 kg capacity), Stan­dard (up to 300 kg), and Heavy (up to 500 kg). All models have a drive housing measuring 250 x 170 mm (length x width), while the height varies between 103 and 205 mm depending on the model.

Safe inter­ac­tion with others

Safety is para­mount if mobile robots share the space with people and other vehi­cles – it is crucial that the robots reli­ably detect obsta­cles around them. If the protec­tive zone is breached, they must ensure suffi­cient braking power is provided. They must also ensure that the stop command issued by the safety controller is executed reli­ably. In this context, the devel­opers of the mobile robot value the fact that, as stan­dard, ArgoDrive supports various safety func­tions for safe oper­a­tion of auto­mated guided vehi­cles (see tech­nology box). All safety indi­ca­tors that are rele­vant for safety certi­fi­ca­tions, such as MTTFd and B-10 values, are avail­able to ensure compli­ance with the require­ments set out in the AGV stan­dards ISO 13849 and ISO 3691-4.

Because ArgoDrive has such a flat design, we have achieved a low grip­ping height of just 400 mm, ensuring that expen­sive storage space can be used as effi­ciently as possible.

Magnus Eldevik, Product Marketing Manager at Maga­zino

Simple inte­gra­tion

The logis­tics robot SOTO can be easily inte­grated into a wide range of controller systems thanks to stan­dard­ized commu­ni­ca­tion and safety inter­faces such as CANopen, EtherCAT, or Profinet. For the safety controller, the devel­opers at Maga­zino opted for a solu­tion from the company SICK. They also chose an indus­trial PC to control the vehicle. Among other things, this controls the Argo­Drives using the ebm-papst drive controllers. Eldevik comments: “We bene­fited greatly from the excel­lent support provided by ebm-papst here. As beta testers of the drives, we were in regular contact with the manu­fac­turer. Both sides bene­fited greatly from this in-depth and enjoy­able collab­o­ra­tion.”

Fig. 4a,b: An omni­di­rec­tional driving steering system was required …

… to ensure the autonomous robots can navi­gate flex­ibly in tight spaces. (Images | ebm-papst/­Magazino)

Drives for the lifting move­ment and grip­pers

Another reason to choose the drive for this appli­ca­tion was its high degree of effi­ciency, which enables a 5:1 ratio of oper­ating time to charging time (i.e., 8 hours of oper­a­tion with approx. 1.5 hours of charging). A further advan­tage is the green brake func­tion, which signif­i­cantly reduces the energy demand compared to other brake actu­a­tion concepts by lowering the energy consump­tion when the brake is released. Eldevik adds: “Of course, we also found it very useful that ebm-papst offers a wide range of drives which we can use for other things, such as ECI motors for receiving SLCs, i.e., for tipping move­ments in the storage unit. The fact that we can work with different drives from the same manu­fac­turer throughout the mobile robot natu­rally makes the inter­faces much easier for us.” Maga­zino is pleased with the quality of the drives used and the enjoy­able coop­er­a­tion, and can certainly see itself collab­o­rating on other joint projects in the future.

Ruling out colli­sion risks

Safety is a key issue when oper­ating mobile robots and auto­mated guided systems. If the working envi­ron­ment of personnel over­laps with the routes of the AGV, colli­sion risks must be ruled out. ArgoDrive offers several options for this. If the protec­tive zone is breached, for example, the drive system must reli­ably execute the command for a safe stop issued by the safety controller. Above all, a high level of brake power must be avail­able for the drives. Here, the ArgoDrive achieves decel­er­a­tion of up to 2.5 m/s2 using the elec­tric motor brakes, and emer­gency braking is also possible using the addi­tional inte­grated mechan­ical brake. In order to prevent uncon­trolled move­ments, the drive unit also comes to a safe stop if the AGV power supply fails. As a result, the drive supports all typical and neces­sary safety require­ments that apply to ware­houses and produc­tion envi­ron­ments.

For this purpose, the indi­vidual driving steering system is actu­ated by two external controllers. The signals for the steering angle are also designed with redun­dancy and the posi­tion can be queried at any time. The STO func­tion (Safe Torque Off) inte­grated into the controllers ensures a safe stop (PLe). STO and, if neces­sary, the emer­gency stop func­tion of the mechan­ical brake can be trig­gered together. In addi­tion, the drive moni­tors that a defined maximum speed is not exceeded (SLS, Safe Limited Speed) and the vehicle only moves in the permitted direc­tion (SDI, Safe Direc­tion). To ensure this, both motors inte­grated in the ArgoDrive have two inde­pen­dent feed­back systems as stan­dard: The inte­grated hall sensors for commu­ta­tion and the high-reso­lu­tion incre­mental encoder for closed-loop control. By comparing both signals, the elec­tronics can record the speed of the motors while ensuring func­tional safety.

Required fields: Comment, Name & Mail (Mail will not be published). Please also take note of our Privacy protection.